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Article

CuII Complexes and Coordination Polymers with Pyridine or Pyrazine Amides and Amino Benzamides—Structures and EPR Patterns

1
Department für Chemie, Institut für Anorganische Chemie, Universität zu Köln, Greinstrasse 6, D-50939 Köln, Germany
2
Department of Chemistry, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
*
Author to whom correspondence should be addressed.
Submission received: 9 November 2020 / Revised: 18 November 2020 / Accepted: 19 November 2020 / Published: 1 December 2020
(This article belongs to the Special Issue Cornerstones in Contemporary Inorganic Chemistry)

Abstract

:
Isonicotine amide, picoline amide, pyrazine 2-amide, 2- and 4-amino benzamides and various CuII salts were used to target CuII complexes of these ligands alongside with 1D and 2D coordination polymers. Under the criterion of obtaining crystalline and single phased materials a number of new compounds were reliably reproduced. Remarkably, for some of these compounds the ideal Cu:ligand ratio of the starting materials turned out to be very different from Cu:ligand ratio in the products. Crystal and molecular structures from single-crystal XRD were obtained for all new compounds; phase purity was checked using powder XRD. We observed exclusively the Oamide and not the NH2amide function binding to CuII. In most of the cases; this occurred in chelates with the second pyridine, pyrazine or aminophenyl N function. µ-O,N ditopic bridging was frequently observed for the N = pyridine, pyrazine or aminophenyl functions, but not exclusively. The geometry around CuII in these compounds was very often axially elongated octahedral or square pyramidal. X-band EPR spectra of powder samples revealed various spectral symmetry patterns ranging from axial over rhombic to inverse axial. Although the EPR spectra cannot be unequivocally correlated to the observed geometry of CuII in the solid state structures, the EPR patterns can help to support assumed structures as shown for the compound [Cu(Ina)2Br2] (Ina = isonicotine amide). As UV-vis absorption spectroscopy and magnetic measurement in the solid can also be roughly correlated to the surrounding of CuII, we suggest the combination of EPR, UV-vis spectroscopy and magnetic measurements to elucidate possible structures of CuII compounds with such ligands.

Graphical Abstract

1. Introduction

Pyridine carboxamides, pyrazine carboxamides and amino-benzamides (Scheme 1) are interesting ditopic ligands for CuII coordination chemistry [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. One reason is their use as versatile building blocks in coordination polymers and MOFs for various applications [1,2,3,8,9,11,12,13,16,20,21,26,27]. Another important reason is the biological relevance of some of the ligands used in this study (Scheme 1) [4,5,6,17,18,24,33]. An interesting general aspect of these ligands is the preference of CuII to the different (offered) donor atoms in the ligands. From the viewpoint of the HSAB principle the N atom of the heteroaromatic cores is softer than the amine function of 4-amino benzamide and both are softer than the O amide function of amides or corresponding carboxylates. From the viewpoint of Cu metalloenzymes the frequent binding of soft ligands such as histidine-N and cysteine-S confirms the tendency of Cu to softer ligands [33]. However, in various Cu enzymes also harder donor functions such as carboxylates were coordinated [34,35]. In metalloenzymes, carboxylate side chains of the peptide are very frequent ligands and were preferably coordinated by hard metal ions, as expected. In contrast to this, carboxamide side chains were less preferred as ligands in metalloenzymes [34,35,36], in agreement with the observation that the carboxamide function coordinates only effectively in chelate ligands as 2-pyridine or 2-pyrazine carboxamides [1,2,3,5,6,15,16,17,18,19,20,22,23,24,25,26,32,37,38,39,40,41].
Herein we report on a study aiming to explore the binding preferences of isonicotinamide (Ina), picolinamide (Pia), pyrazine-2-carboxamide (Pya) and 2- and 4-amino-benzamides (2- and 4-Aba; Scheme 1) towards CuII. We also added the versatile ligand thio-bisacetamide (Tba) to this study, as Tba represents the aliphatic amides and we expected that the ligand will form S^O or S^N chelates. The ligands were reacted with various CuII salts in EtOH without addition of bases to avoid deprotonation of the ligands. The compounds produced were studied in the solid state by single crystal and powder X-ray diffraction, EPR, magnetic measurements and UV-vis absorption spectroscopy. Being aware of the problem that our so-called “combinatorial approach”—which means dissolving metal salts and ligands and crystallising materials out of the mixture—might lead to a plethora of different structures, we aimed to work out reliable procedures for the preparation of defined structures which also allow reproducing the materials. We succeeded in doing so in many cases, and powder X-ray diffraction (PXRD) was used to evaluate the preparation methods and to prove the phase purity of the compounds. This also means that non-crystalline materials and materials which obviously contained mixtures of compounds as could be seen from their colours, which were obtained from further reactions of the seven ligands and the Cu salts, were not further analysed. Interestingly, this comprises all trials using nicotinamide as ligand.
Special focus was also laid on EPR spectroscopy of these solids. Having so many new structures and EPR data in hand we were able to correlate details in the EPR spectra such as spectral symmetry and g values to the local environment of the CuII centres. Magnetic and UV-vis absorption data of selected samples were also recorded.

2. Results and Discussion

2.1. Synthesis of the Cu Complexes

In a first series of experiments CuII salts were reacted with the ligands shown in Scheme 1 in a Cu:ligand ratio of 1:1 in EtOH. Single crystals of 18 compounds were obtained by slow evaporation of the solvent from the reaction mixtures (Table 1). The Cu:ligand ratios were found ranging from 1:1 to 1:4. Coligands to CuII were the anions from the Cu sources: Cl, Br, NO3, BF4, Tfa, EtOH and H2O. ClO4 was not coordinating but found as a counter ion. None of the ligands was found deprotonated in the structures. However, pyrazine-2-carboxamide was converted into pyrazine carboxylate forming the compound [Cu(Pyc)(Tfa)] (11) in neutral aqueous EtOH solution. In HCl acidic solutions isonicotinamide (Ina) was protonated yielding (HIna)2[CuCl4].2H2O (6) and (HIna)[Cu(H2O)Cl3] (7) both containing 4-carboxamidopyridin-1-ium (HIna+) cations. Under similar conditions 4-aminobenzamide was protonated to 4-benzamidyl-ammonium (4-AbaH+) in [Cu(4-HAba)2Cl4] (17). A very interesting finding was that the complex [Cu(Ina)2(NO3)2] (2) could be converted into [Cu(Ina)2Br2] (5) through grinding with KBr. Unfortunately, the obtained crystals of this compound were of poor quality preventing a structure solution. In a previous report of (5) space group P21/c (No. 14) was concluded from 24 reflections by powder XRD and the authors assumed a polymeric structure with a distorted octahedral coordination around CuII [39]. From the new compound [Cu(Ina)4(H2O)2](BF4)2 (1), the crystal structure of the corresponding ClO4 salt was previously reported alongside with the structure of [Cu(Ina)2(H2O)2(NO3)2] (3) [16]. All other crystal structures are new (see Figures S1–S40 and full data in Tables S1–S39 in the Supplementary Materials).
In a further series of experiments, we tried to reproduce the obtained compounds and optimise their yields. Cl and Br turned out to be very strong ligands to CuII compared with the amides and we avoided them in these experiments. Similar observations that Cu–halide bonding dominates the structures of heteroleptic halide pyridine-amide CuII complexes were reported before [3,5,25,26,27,38,40]. Using the same reaction protocol but varying the Cu:ligand ratio, 10 out of these 18 compounds could be reliably reproduced in good to excellent yields and high phase purity as confirmed through elemental analyses and powder XRD (Scheme 2). In turn, this means that the compounds 2, 4, 11, and 14 remained unreproducible.
For some of the compounds such as [Cu(Tba)2](ClO4)2 (18), [Cu(4-Aba)2(EtOH)2](BF4)2 (16), [Cu(Pya)2](BF4)2 (9), and [Cu(2-Aba)2(NO3)2] (13), the optimum Cu:ligand ratio was the same as the stoichiometry of the compound. Remarkably, this is also true for [Cu(Pyc)(Tfa)](12) which was produced from a 1:1 mixture of Cu(Tfa)2∙H2O and pyrazine-amide (Pya).
For other compounds, the optimum ratio lies more to the Cu side with the most remarkable example being [Cu(Ina)4(H2O)2](BF4)2 (1) for which a 2:1 = Cu:ligand ratio was best to observe phase pure material, while a 1:4 ratio prevails in the compound. The most important parameter for the assessment of the synthesis was the phase purity. The second important parameter was the yield. However, it is important to note, that yields were either calculated based on Cu or based on the ligand. For example, for compound (1) a 2:1 ratio in the starting material meant a high yield relative to the ligand (88%) but, of course, a very low yield relative to the starting CuII precursor (22%).
IR spectroscopy allowed revealing some structural features of the compounds (data in the Experimental Section). The presence of BF4, ClO4, and NO3 in the compounds as ligands or as counter anions is easily detectable through their characteristic vibrational modes. On the other hand, the data did not unequivocally allow determining whether these anions are ligands or counter ions. For example, in [Cu(Ina)4(H2O)2](BF4)2 (1) the ν(B–F) vibration is found as a strong band at 1080 cm−1, but as very strong broad resonance at 1050 cm−1 for [Cu(Pya)2](BF4)2 (9). Both structures contain BF4 as counter anion. The complex [Cu(Pia)2(BF4)2] (8) contains two BF4 ligands and the ν(B–F) is found at 1072 cm−1 as a strong band. Furthermore, for [Cu(Ina)2(NO3)2] (2) the ν(NO3) resonance is observed at 1383 cm−1, but is shifted to 1283 cm−1 for [Cu(Pya)(NO3)2] (11) although both contain NO3 ligands. Additionally, for [Cu(Pya)2(H2O)(NO3)](NO3) (10) only one ν(NO3) vibration is found at 1350 cm−1 although one NO3 is coordinated, while the other serves as counter ion.
Quite generally, the coordination to Cu leads to slight blue-shifts of characteristic ligand vibrations. However, there are exceptions like the compounds containing pyrazine 2-amide (Pya). The ν(C=O) resonances for the compounds were found markedly at lower energy compared with those of the uncoordinated ligand. Interestingly, the δ(NH2) resonances of the amide ligands are usually red-shifted upon coordination and suffer from a marked loss of intensity. However, in none of our structures did the NH2amide function act as coordinating (see next paragraph). Thus, IR spectroscopy does not allow the unequivocal assignment of structural details.

2.2. Crystal Structures from Single Crystal XRD

The compounds listed in Table 1 could be obtained as single crystals suitable for single-crystal XRD directly from the reaction mixtures. Amongst the structures we found the 1D coordination polymers 2 (Figure 1), 11 (Figure 2), and 14 (Figure S29, Supplementary) and the 2D coordination polymers 9 (Figure 3), 12 (Figure S23), 15 (Figure S31), and 16 (Figure S34) in which the ditopic ligands isonicotine (Ina), pyrazine 2-amide (Pya), and 4-amino benzamide (4-Aba) bridge between CuII centres. Importantly, Ina, Pya and 4-Aba use the Oamide exclusively and not the NH2amide function for the µ-O,N ditopic bridging with N = pyridine, pyrazine, or aminophenyl functions.
At the same time, Pia, Pya, and 2-Aba form κ2-N,O-chelates with Cu in 8 (Figure S1), 9 (Figure 3), 10 (Figure S18), 11 (Figure 2), and 13 (Figure S26), again exclusively using the Oamide instead of the NH2amide function. Thus, in the Pya-containing compounds 9 and 11 both κ2-N,O chelate binding and µ-O,N ditopic bridging was observed, while for Pia in compound 8, the κ2-N,O chelate binding prevented further µ-O,N ditopic bridging (Figure 4, middle). For compounds containing Ina or 4-Aba no chelate binding is possible and µ-O,N ditopic bridging was observed in some cases but not all. Out of the four compounds containing an 1,4-pyrazine unit three of them, 9, 11, and 12 show µ-N,Npyrazine-bridging, while in 10 one pyrazine N position does not coordinate. In 12 the same pyrazine-2-carboxylate (Pyc) ligand bridges two CuII centres in a µ-N,N fashion, bridges to another CuII using the carboxylate O function (µ-O,O), and shows κ2-N,O chelate binding at the same time, while the Tfa ligand binds terminally (Figure S23).
Nitrate (NO3) ligands are frequently found in terminal binding (2 (Figure 1), 3, 10, 11, 13). However, in compound 11 one of the two NO3 ligands binds in a quasi-κ2-O,O fashion (Figure 2). In 14 both κ2-O,O and terminal binding were observed.
The thio-bisacetamide (Tba) ligand exhibits tridentate N^S^N binding in compound 18 as expected (Figure S39). In (HIna)[Cu(H2O)Cl3] (7) (Figure S13) the pyridine-N protonated HIna+ does not coordinate to CuII. A unique coordination mode is found in (HIna)2[CuCl4] (6) (Figure 4 and Figure S11) with two HIna+ cations occupying the axial positions with the C1=C2 bond of the pyridine ring (Figure 4, left). Although, the Cu⋯C=Ccentroid distance is rather long (3.360(1) Å) we consider this as a bonding contribution.
In the compounds 1, 3, 4, and 7 containing the Ina ligand and 11 which contains the 4-NH3 protonated 4-HAba+ ligand isolated CuII complexes were found. In their structures weak intermolecular forces as hydrogen bridges and π–π stacking are observed. Importantly, such forces were found in all compounds and we cannot neglect their role on the geometry around CuII which is decisive for the physical properties. Nevertheless, these non-covalent forces will not be further discussed, as we wanted to focus on the spectral consequences of the geometry around the Cu centre and not its origin.
The predominant coordination unit around CuII in most of the compounds reported herein is of the frequently observed tetragonally distorted octahedral type (OE in Table 2) [33,37,41,42,43,44,45,46,47,48]. The short equatorial positions are dominated through the N pyridine, pyrazine and aminophenyl functions. Oamide occurs in this plane only in chelates with these N functions, NH2amide–Cu binding was not observed. The CuII–ligand bonds in the equatorial plane lie in the range of 1.93 to 2.08 Å and are comparable with previously reported complexes of these ligands [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,38,39,40,41,42,43,44,45,46]. Remarkably, the shortest Cu–ligand bonds were of the Cu–Oamide type and were found for the chelating Pia, Pya, and 2-Aba ligands, but also for terminating binding of the 4-Aba ligands including the 4-HAba+ cation. The Ina ligand forms exclusively short Cu–N bonds, while the Oamide function does not contribute to the equatorial Cu–ligand bonding. For the compounds containing chlorido ligands, all four equatorial positions were Cl-occupied in (HIna)2[CuCl4] (6) but at the same time the Oamide function coordinates tighter than one of the two chlorido ligands in [Cu(4-Haba)2Cl4] (17). The Cu–Cl distances range from 2.26 to 2.30 Å underlining that Cl is a reasonably strong ligand to CuII.
For the labelling of the structures as OE in Table 2, two axial ligands must be present in a distance elongated to about 10–20% compared to the same ligand in an equatorial position [42]. Further observed cases were square pyramidal structures (Spy in Table 2), two structures containing one long axial and one even longer axial Cu–ligand bond (Spy+1) and the peculiar case of two very long distances to CuII as in (HIna)2[CuCl4] (6) (Figure 4, left) called square planar +2 (SQ+2). In compound 10 (Figure S19) the sixth ligand is not only elongated but also displaced from the ideal position showing an “axial” angle of about 170°. Nevertheless, we assign this to Spy+1. In 14 (Figure S30) the coordination around CuII showed a severely and multiply distorted octahedron (OD).
Non-chelated Oamide binding to CuII was found in the axial (weak) positions only in one compound (2) and no NH2amide coordination, in line with the observation that amide functions in amino acids do not represent an important class of ligands in metalloproteins [34,35,36] and the poor non-biologic coordination chemistry of amides and Cu [33,35,37]. Indeed, searching the CCDC database, gave only the CuII complex [Cu(L)2(OH)2] containing two chelating pyrazine-2,3-dicarboxamide ligands with Cu–NH2amide bonds [49]. Further frequent ligands in the axial positions of our structures were weak ligands as NO3, EtOH, H2O, BF4, and the peculiar SiF62− (Figure 4). Nevertheless, the non-chelating N4pyrazine function of the Pyc ligand (in 12) was found in the axial position. Importantly, the axial non-chelating Oamide (in 2) and N4pyrazine binding (in 12) both represent structures with µ-O,N ditopic bridging. The axial position is occupied by the thio-bisacetamide (Tba) S atoms in compound 18 in line with the preferences of CuII to N over S coordination [33,34,50].

2.3. X-Band EPR Spectroscopy and Magnetic Measurements

X-Band EPR spectra of the microcrystalline materials were recorded at 298 and 110 K, Figure 5 and Figure 6 show representative examples, Table 3 lists essential parameters.
EPR spectra of axial, rhombic and isotropic geometry were observed and, having full structural information from XRD, will be correlated to the local environment of the CuII centres in the following.
EPR spectra of axial symmetry with g > g (Group I in Table 3, Figure 5 (left)) were observed for most of the tetragonally elongated octahedral species (OE) and square pyramidal systems with an extra-long distance to a sixth ligand (SPy+1) in line with previous reports [24,41,42,43,44,45,46,47,48,49,50,51,52]. Cu hyper fine structure (HFS, coupling to the 63Cu (69.17%) and 65Cu (30.83%) nuclei both with I = 3/2 [53]) was only observed in one case, [Cu(Ina)4(H2O)2](BF4)2 (Figure 5 (left)), on the parallel g component (A = 180 G). The prevailing absence of HFS is in line with spectra of related species in the solid (see Table 3) [15,16,17,18,20,24]. The g anisotropy (Δg) in this group of complexes lies above values of 0.2 while the averaged g values (gav) vary from 2.12 to 2.20. Exceptions are (HIna)2[CuCl4]·2H2O (6) and [Cu(H–Aba)2Cl4] (17) for which a rhombic spectrum was observed (Figure 5 (middle) and Figure S43). On the other hand, the Δg values lie in the same range as for compounds of group I.
Rhombic spectra were recorded for [Cu(Pya)2](BF4)2 (9), [Cu(4-Aba)2(EtOH)2](ClO4)2 (15) and [Cu(4-Aba)2(EtOH)2](BF4)2 (16) (group IV) when measured at 110 K (group II). Remarkably, the spectra of the two latter compounds are axial at 298 K and for [Cu(4-Aba)2(EtOH)2](ClO4)2 (15) a gradual transition between the rhombic and axial spectrum was observed between 110 and 298 K (Figure 6). The Δg values for this group of complexes lie markedly below 0.2 and their gav values range from 2.1 to 2.17. A detailed inspection of the metrics around CuII showed very similar geometries for [Cu(4-Aba)2(EtOH)2](ClO4)2 (15) at 150 K and [Cu(4-Aba)2(EtOH)2](BF4)2 (16) at 298 K. We therefore concluded that in this group either very tiny changes in geometry and with this a change of the character of the electronic ground state from the predominant {dx2-y2}1 (axial) to a {dz2}1 electronic ground state (rhombic or inverse axial) [42,47,48,54,55] were decisive and axial or rhombic spectra were observed. Importantly, this group is defined by a rather low g anisotropy Δg.
An isotropic broad spectrum with g values around 2.15 was observed for [Cu(Pyc)(Tfa)](12) containing a square pyramidally coordinated CuII (group III). An isotropic spectrum was also found for the structurally ill-defined [Cu(Ina)2Br2] (5). Our findings for 5 are in line with the reported spectrum and g values for this compound by Atac et al. [22], while for the [Cu(Ina)2Cl2] derivative this group reports a rhombic spectrum. From our EPR results we conclude a square pyramidal coordination for CuII in [Cu(Ina)2Br2] (5).
A rather uncommon inverse axial EPR spectrum was observed for [Cu2(Aba)2(H2O)3(NO3)3](NO3) (14). This type of symmetry is frequently observed for either axially compressed octahedral structures, {dz2}1 ground states, or both, in contrast to the predominant {dx2-y2}1 and axially elongated octahedral coordination [38,48,54,55]. However, this structure represents several marked distortions from octahedral geometry, but not a compression. So, we can conclude a {dz2}1 electronic ground state for the two CuII centres in this compound.
We selected the samples [Cu(Ina)2(NO3)2] (2), [Cu(Pya)(NO3)2] (11), [Cu(Pyc)(Tfa)](12), and [Cu(4-Aba)2(EtOH)2](ClO4)2 (15) for T-dependent magnetic measurements (Figure 7). 2 and 11 are 1D structures, while 12 and 15 represent 2D coordination polymers. Above 150 K a linear Curie-Weiss dependence is observed, in line with isolated CuII centres. At lower T, slight deviations were observed and the χ−1 graph tails down to zero, indicative for small anti-ferromagnetic coupling between the Cu centres in the solids. The shortest Cu⋯Cu contacts are 7.083 (1) Å (2), 5.822 (1) Å (11), 5.118 (2) and 7.079 (2) Å (12), and 8.463 (3) Å (15) and thus far too long for a super-exchange magnetic coupling. We assume that the alignment of the CuII centres in the 1D and 2D lattices is responsible for this effect. The magnetic moments (Table 4) are markedly below the spin-only value of 1.73 and positive Curie-Weiss constants are in line with this assumption. In contrast to this, for [Cu(Ina)2Br2] a µB of 1.90 has been reported alongside with [Cu(Ina)Cl2] and [Cu(Ina)(NCS)2] with 1.80 and 1.60 µB, respectively [39]. Higher values were due to spin-orbit coupling which is caused through heavy atoms such as Br or Cl. For our compounds only light N, O, or F atoms bind to CuII [3,5,10,15,19,52,56].

2.4. Absorption Spectroscopy in the Solid and in Solution

All microcrystalline materials show colours corresponding to absorptions in the visible region. UV-vis absorption spectroscopy on selected samples (Table 5) reveals low-wavelengths absorptions ranging from 640 to 780 nm (15,600 to 12,820 cm−1) which were assigned to the typical CuII d9 system. Comparison of the three Pya-containing species reveals that the highest absorption energy is recorded for [Cu(Pya)2](BF4)2 (9) with a tetrahedrally elongated (OE) structure, followed by [Cu(Pya)2(H2O)(NO3)](NO3) (10) having an SPy+1 configuration with the sixth ligand markedly elongated, while [Cu(Pya)(NO3)2] (11) exhibits a maximum red-shifted by 2810 cm−1 in line with its square pyramidal (SPy) coordination. The long-wavelength absorption observed for [Cu(Pyc)(Tfa)](12) is rather high in energy in view of the only five coordinating atoms. This is probably due to the Tfa ligand with a very short Cu–O distance indicative for its binding strength. For [Cu(Ina)2Br2] we found approximately the same absorption maximum as reported [22] in keeping with the assumption that we have obtained the same structure.
A view of a collection of similar structures (Table 5) confirmed that the absorption energy increased with increasing coordination number for very similar O and N coordinating pyridine-amides. For the unknown structures [Cu(clof)2(Et2nia)2] [18] and [Cu(meclof)2(Et2nia)2] [24], elongated octahedral coordination can be reasonably assumed from the UV-vis data, while the structure of [Cu(clof)2(Ina)2] probably represents a square pyramid.

3. Experimental Section

3.1. Methods and Instrumentation

1H and 13C NMR spectra were recorded in DMSO-d6 using a Bruker Avance II 300 spectrometer (Bruker, Rheinhausen, Germany). Elemental analyses were carried out using a HEKAtech CHNS EuroEA 3000 Analyzer (Hekatech, Wegberg, Germany). IR spectra were recorded using KBr or polyethylene pellets using an IFS/66v/S or an Alpha-T spectrometers (Bruker, Rheinhausen, Germany). UV-vis absorption spectra were measured on transparent KBr pellets using a Shimadzu UV-3600 photo spectrometer (Shimadzu Europe, Duisburg, Germany). EPR spectra were recorded in the X-band on a Bruker System ELEXSYS 500E equipped with a Bruker Variable Temperature Unit ER 4131VT (500 to 100 K) (Bruker, Rheinhausen, Germany). The g values were calibrated using a dpph sample. The magnetic measurements were carried out on finely ground samples using a MPMS XL7 (Quantum Design, Darmstadt, Germany) instrument measuring from 2 to 300 K at a magnetic field of 1 T.

3.2. Single Crystal Structure Determination

The measurements were performed at 293(2) K or 110(2) K using graphite monochromatised Mo-Kα radiation (λ = 0.71073 Å) on an IPDS II instrument (STOE & Cie., Darmstadt, Germany). The structures were solved by dual space methods using ShelXT-2015 [57] and refined by full-matrix least-squares techniques against F2 (SHELXL-2017/1) [58,59]. The numerical absorption corrections (X-RED V1.31; STOE & Cie, 2005, Darmstadt, Germany) were performed after optimising the crystal shapes using the X-SHAPE V1.06 (STOE & Cie, 1999, Darmstadt, Germany) [60,61]. The non-hydrogen atoms were refined with anisotropic displacement parameters. H atoms were included by using appropriate riding models. More details on the crystal structures is provided in the Supplementary Materials. CCDC 1058949–1058951, 1058953–1058957, 1058960–1058963, and 2025467–2025471 contain the full crystallographic data. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ UK. Fax: +44-1223-336-033; Email: [email protected].

3.3. Powder X-ray Diffraction (PXRD)

Data collection was carried out with a Huber G670 diffractometer (Huber, Rimsting, Germany) equipped with a Ge(111) monochromator using Cu-Kα1 radiation with λ = 1.5405 Å and an image plate detector. The samples were measured as flat samples between two almost X-ray transparent foils. The foil gives rise to two broad reflections at 2θ ≈ 21.5° and 2θ ≈ 23.7°. PXRD data were visualised with the WinXPOW software package (STOE & Cie., 2012, Darmstadt, Germany) [62], which was also used to calculate line diagrams based on single crystal data. Gnuplot4.6 was used for the visualisation of PXRD patterns [63].

3.4. Syntheses

3.4.1. General

Picolinamide and nicotinamide were synthesised from their (commercially available) carboxylic acids (details in the Supplementary Materials), all other chemicals were used as supplied. Water-free reactions were carried out under inert gas conditions and performed using Schlenk techniques. Solvents were dried using an MBRAUN MB SPS-800 (MBRAUN, Garching, Germany) solvent purification system.

3.4.2. Synthesis of the CuII Compounds—General Method

The following compounds were synthesised through dissolving suitable CuII salts in EtOH, heating these solutions to 70 °C and then slowly adding the ligands to the mixture. Upon standing and slow evaporation of the solvent at ambient temperatures in the fume hood, the materials were obtained in yields from 39 to 75% referring to the CuII starting material and from 30 to 90% referring to the ligand.
[Cu(Ina)4(H2O)2](BF4)2 (1). From 0.690 g (2 mmol) Cu(BF4)2.6H2O and 0.122 g (1 mmol) Ina. Yield: 0.624 g (0.82 mmol, 41% referred to Cu and 82% to Ina) blue plates. Elemental analysis calculated for C24H28B2Cu1F8N8O6 (761.69): C 37.85, H 3.71, N 14.71; found: C 37.83, H 3.70, N 14.71%. IR (KBr pellet): 3421 s; 3292 m, νas(NH2); 3196 s, νs(NH2); 3072 sh, ν(pyr–H); 1678 s, ν(C=O); 1606 s, δ(NH2); 1554 s, 1549 s, ν(C=C), ν(C=N); 1425 sh, ν(C–C); 1415 s, ν(C–N); 1080 s, ν(B–F); 639 s, δ(N–C=O) cm−1. PXRD is available in the Supplementary Materials.
[Cu(Ina)2(NO3)2] (2). From 0.481 g (2 mmol) Cu(NO3)2.3H2O and 0.122 g (1 mmol) Ina. Yield: 0.337 g (0.78 mmol, 39% referred to Cu and 78% to Ina), blue plates. Elemental analysis calculated for C12H12Cu1N6O8 (431.81): C 33.38, H 2.80, N 19.46; found: C 33.36, H 2.81, N 19.44%. IR (PE pellet): 3426 s, 3311 m, νas(NH2); 3181 s, νs(NH2); 3082 m, ν(pyr–H); 1705 s, ν(C=O); 1623 s, δ(NH2); 1614 s, 1546 s, ν(C=C), ν(C=N); 1424 s, ν(C–C); 1381 s, ν(C–N); 1383 s, ν(NO3); 1118 m, ν(CN); 484 s, δ(N–C=O) cm−1.
[Cu(Ina)2(H2O)2(NO3)2] (3). From 0.482 g (2 mmol) Cu(NO3)2.3H2O and 0.144 g (1 mmol) Ina. Yield: 0.383 g (0.82 mmol, 41% referred to Cu and 82% to Ina), blue blocks. Elemental analysis calculated for C12H16Cu1N6O10 (467.84): C 30.81, H 3.45, N 17.96; found: C 30.83, H 3.46, N 17.94%. The compound was previously reported and obtained from a 1:2 mixture of Cu:ligand [16].
[Cu(Pia)2(BF4)2] (8). From 0.690 g (2 mmol) Cu(BF4)2.6H2O and 0.122 g (1 mmol) Pia. Yield: 0.385 g (0.8 mmol, 40% referred to Cu and 80% to Pia) light blue plates. Elemental analysis calculated for C12H12B2Cu1F8N4O2 (481.41): C 29.94, H 2.51, N 11.64; found: C 29.89, H 2.50, N 11.63%. IR (KBr pellet): 3415 m, 3247 m, 3024 m, ν(NH2); 1666 s, ν(C=O); 1560 s, 1444 s, ν(C=C), ν(C=N); 1311 w, ν(C=N); 1072 s, ν(B–F); 906 sh, ν(C–N) ring; 767 m, δ(C–N) ring; 656 m, δ(N–C=O) cm−1. PXRD is available in the Supplementary Materials.
[Cu(Pya)2](BF4)2 (9). From 0.345 g (1 mmol) Cu(BF4)2.6H2O and 0.123 g (1 mmol) Pya. Yield: 0.208 g (0.43 mmol, 43% referred to Cu and 86% to Pya) light blue plates. Elemental analysis calculated for C10H10B2Cu1F8N6O2 (483.38): C 24.85, H 2.09, N 17.39; found: C 24.88, H 2.10, N 17.36%. IR (KBr pellet): 3400 m, 3276 s, νas(N–H); 3239 s, νs(N–H); 1697 s, ν(C=O); 1619 m, ν(NH2); 1578 m, 1542 w, 1496 m, ν(C=C), ν(N=C); 1414 m; 1459 m, amide; 1212 w, δ(CH); 1182 m, ν14(ring); 1108-985 vs, ν(B–F); 871 m, γ(CH); 780 m, δ(OH)+ν1(ring); 666 w, ω(NH2); 602 m, δ(N–C=O); 456 m, ν16(ring) cm−1; δ(NH2) and δ(CH) were probably obscured. PXRD is available in the Supplementary Materials.
[Cu(Pya)2(H2O)(NO3)](NO3) (10). From 0.482 g (2 mmol) Cu(NO3)2.3H2O and 0.123 g (1 mmol) Pya. Yield: 0.406 g (0.9 mmol, 45% referred to Cu and 90% to Pya) blue plates. Elemental analysis calculated for C10H12Cu1N8O9 (451.80): C 26.58, H 2.68, N 24.80; found: C 26.51, H 2.66, N 24.75%. IR (KBr pellet): 3600–2975 m, ν(O–H) H2O; 3339 m, νas(N–H); 3150 s, νs(N–H); 1681 s, ν(C=O); 1605 s, ν(NH2); 1567 m, 1530 w, 1492 m, ν(C=C), ν(N=C); 1449 s, 1397 m, amide; 1350 s, ν(NO3); 1199 w, δ(CH); 1175 m, ν14(ring); 1081 m, δ(NH2); 1058 s, δ(CH); 1022 sh, ν12(ring); 882 m, γ(CH); 803 m, δ(OH)+ν1(ring); 690 w, ω(NH2); 641–561 m, δ(N–C=O); 467 m, ν16(ring) cm−1. PXRD is available in the Supplementary Materials.
[Cu(Pya)(NO3)2] (11). From 0.241 g (1 mmol) Cu(NO3)2.3H2O and 0.123 g (1 mmol) Pya. Yield: 0.233 g (0.245 mmol, 75% referred to Cu and Pya) blue plates. Elemental analysis calculated for C5H5Cu1N5O7 (310.67): C 19.33, H 1.62, N 22.54; found: C 19.31, H 1.64, N 22.51%. IR (KBr pellet): 3386 m, 3287 s, νas(N–H); 3090 s, νs(N–H); 1693 s, ν(C=O); 1630 m, ν(NH2); 1599 m, 1543 w, ν(C=C), ν(N=C); 1310 s, amide; 1212 w, δ(CH); 1488 s, 1421 s, 1282 s, ν(NO3); 1116 m, ν14 ring; 1077 m, δ(NH2); 1058 s, δ(CH); 1021 s, ν12 ring; 871 m, γ(CH); 803 m, δ(OH)+ν1(ring); 689 m, ω(NH2); 483 w, δ(N–C=O) cm−1.
[Cu(Pyc)(Tfa)](12). From 0.308 g (1 mmol) Cu(Tfa)2.H2O and 0.123 g (1 mmol) Pya. Yield: 0.263 g (0.88 mmol, 88% referred to Cu and Pya) blue blocks. Elemental analysis calculated for C7H3Cu1F3N2O4 (299.65): C 28.06, H 1.01, N 9.35; found: C 28.08, H 1.04, N 9.33%. IR (KBr pellet): 3236 s, ν(ring–H); 1696 vs, ν(C=O) of Tfa; 1728 s ν(C=O) of Pyc; 1587 m, 1520 m, 1440 m, ν(C=C), ν(N=C); 1207–1138 s, ν(C–F); 1065 w, δ(CH); 1047 m, ν12(ring); 867 sh; γ(CH); 779 sh, δ(OH)+ν1(ring); 468 m, ν16(ring) cm−1; Not observed (obscured): νas(N–H), νs(N–H), ν(NH2), amide, δ(CH), δ(NH2), ω(NH2), and δ(N–C=O). FIR (KBr pellet): 614 m, ring; 580 m, ν1(Cu–O); 516 m, ν2(Cu–O); 475 m, ring; 420 m, ν3(Cu–O); 317 m, ν1(Cu–N11); 291 s, ν2(Cu–N12) cm−1. PXRD is available in the Supplementary Materials.
[Cu(2-Aba)2(NO3)2] (13). From 0.241 g (1 mmol) Cu(NO3)2.3H2O and 0.136 g (1 mmol) 2-Aba. Yield: 0.202 g (0.44 mmol, 44% referred to Cu and 88% to 2-Aba) green plates. Elemental analysis calculated for C14H16Cu1N6O8 (459.86): C 36.57, H 3.51, N 18.28; found: C 36.55, H 3.54, N 18.30%. PXRD is available in the Supplementary Materials.
(Cu2(4-Aba)2(NO3)3(H2O)3)(NO3) (14). From 0.241 g (1 mmol) Cu(NO3)2.3H2O and 0.136 g (1 mmol) 4-Aba, Yield: 0.295 g (0.42 mmol, 84% referred to Cu and 4-Aba) green needles. Elemental analysis calculated for C14H22Cu2N6O8 (701.46): C 23.97, H 3.16, N 15.97; found: C 23.98, H 3.13, N 15.97%.
[Cu(4-Aba)2(EtOH)2](ClO4)2 (15). From 0.370 g (1 mmol) Cu(ClO4)2.6H2O and 0.408 g (3 mmol) 4-Aba.Yield: 0.564 g (0.90 mmol, 90% referred to Cu and 30% to 4-Aba) green blocks. Elemental analysis calculated for C18H28Cl2Cu1N4O12 (626.88): C 34.49, H 4.50, N 8.94; found: C 34.48, H 4.52, N 8.93%. IR (KBr pellet): 3441 s, ν(O–H) EtOH; 3362 ms; 3292 s, νas(N–H); 3252 m, νs(N–H); 3058 m, ν(aryl–H); 1650 s, 1611 s, ν(C=O), δ(NH2); 1550 s, ν(C=C) ring; 1450 s, δs,as(CH2,CH3) EtOH; 1197-992 vs, ν(C–O) EtOH; 1046 s, 620 m, ClO4 cm−1; δ(N–C=O) probably obscured. PXRD is available in the Supplementary Materials.
[Cu(4-Aba)2(EtOH)2](BF4)2 (16). From 0.345 g (1 mmol) Cu(BF4)2.6H2O and 0.408 g (3 mmol) 4-Aba. Yield: 0.553 g (0.92 mmol, 92% referred to Cu and 31% to 4-Aba) green blocks. Elemental analysis calculated for C18H28B2Cu1F8N4O4 (601.60): C 35.94, H 4.69, N 9.31; found: C 35.93, H 4.66, N 9.33%. IR (KBr pellet): 3450 s, ν(O–H) EtOH; 3379 m, 3319 s, νas(N–H); 3277 s, νs(N–H); 3175 m, ν(aryl–H); 1652 s, 1610 s, ν(C=O), δ(NH2); 1555 s, ν(C=C) ring; 1453 s, δs,as(CH2,CH3) EtOH; 1199-911 s, ν(C–O) EtOH, ν(B–F) cm−1. PXRD is available in the Supplementary Materials.
[Cu(4-HAba)2Cl4] (17). From 0.370 g (1 mmol) Cu(ClO4)2.6H2O and 0.136 g (1 mmol) 4-Aba and 5 mL concentrated aqueous HCl. Yield: 0.206 g (0.43 mmol, 43% referred to Cu and 86% to 4-Aba) brown platelets. Elemental analysis calculated for C14H18Cl4Cu1N4O2 (479.67): C 35.06, H 3.78, N 11.68; found: C 35.03, H 3.77, N 11.67%. IR (KBr pellet): 3378 s, νas(N–H); 3001-2650 s, νs(N–H); 2580–2560 m, ν(N–H) amine; 1650 s, 1611 m, ν(C=O), δ(NH2); 1550 m, ν(C=C) ring; 579 m, δ(N–C=O) cm−1. FIR (KBr pellet): 547 m, ν1(Cu–O); 473 m, ring; 380 m, ν2(Cu–O); 318 m, ν1(Cu–Cl); 278 m, ν2(Cu–Cl) cm−1; ν(aryl–H) probably obscured.
[Cu(Tba)2](ClO4)2 (18). From 0.370 g (1 mmol) Cu(ClO4)2.6H2O and 0.272 g (2 mmol) Tba Yield: 0.508 g (0.91 mmol, 91% referred to Cu and Tba) brown platelets. Elemental analysis calculated for C8H16Cl2Cu1N4O12S2 (558.80): C 17.20, H 2.89, N 10.03; found: C 17.23, H 2.88, N 10.03%. IR (KBr pellet): 3428 s, νas(N–H); 3329 s, νs(N–H); 2975 s, 2927 w, ν(C–H); 1653 s, 1600 m, ν(C=O), ν(NH2); 1388 m, ν(C–N); 1086 vs, 580 s, ClO4; 575 m, δ(N–C=O); 623 m, ν(S–C) cm−1.

3.4.3. Further Syntheses

[Cu(Ina)2(H2O)3(SiF6)].H2O (4). Amounts of 173 mg (0.5 mmol) Cu(BF4)2.6H2O and 62 mg (0.5 mmol) Ina were each dissolved in 15 mL EtOH, stirred at 70 °C for 30 min and then the two solutions were combined. Standing for about 2 weeks in a glass beaker while letting the solvent evaporate allowed collecting blue needles. Yield: 0.104 g (0.2 mmol, 40% referred to Cu and 80% to Ina). Elemental analysis calculated for C12H20Cu1F6N4O6Si1 (521.94): C 27.61, H 3.86, N 10.73; found: C 27.63, H 3.86, N 10.74%. IR (KBr pellet): 3695-3270 m, ν(O–H) H2O; 3423 s, 3316 s, νas(N–H); 3181 s, νs(N–H); 3079 m, ν(pyr–H); 1705 s, ν(C=O); 1626 m, δ(NH2); 1612 s, 1552 s, ν(C=C), ν(C=N); 1421 s, ν(C–C); 1388 s, ν(C–N); 740 s, SiF62−; 490 s, δ(N–C=O) cm−1. FIR (KBr pellet) 286 m, ν(Cu–N); 255 m, ν(Cu–N); 186 m, ν(Cu–F) cm−1.
[Cu(Ina)2Br2] (5) was synthesised by dissolving 216 mg (0.5 mmol) [Cu(Ina)2(NO3)2] (2) and 71 mg (0.6 mmol) KBr each in 30 mL of EtOH at 70 °C. Mixing of the two solutions produced a green precipitate which was filtered off and dissolved in 20 mL of water. Slow evaporation gave 58 mg (0.125 mmol, 25%) green needles after about 3 weeks. Elemental analysis calculated for C12H12Cu1Br2N4O2 (467.61): C 30.82, H 2.59, N 11.98; found: C 30.83, H 2.56, N 11.94%. IR (KBr pellet): 3402 s, 3248 m, νas(NH2); 3186 s, νs(NH2); 3067 m, ν(pyr–H); 1714 s, ν(C=O); 1661 s, δ(NH2); 1609 s, 1556 m, ν(C=C), ν(C=N); 1416 s, ν(C–C); 1118 w, ν(CN); 546 s, δ(N–C=O) cm−1. Qualitatively, the compound can also be prepared by grinding [Cu(Ina)2(NO3)2] (2) with KBr in a mortar. The compound was previously reported [39] but no details as to the Cu:ligand ratio were provided.
(HIna)2[CuCl4].2H2O (6). Amounts of 85.5 mg (0.5 mmol) CuCl2.2H2O and 61 mg (0.5 mmol) Ina were dissolved in EtOH and 1.3 mL concentrated HCl were added. The mixture was heated up to 70 °C and then left for slow evaporation of the solvent at ambient temperatures in the fume hood. After about 20 days, 126 mg (0.26 mmol, 52%) of blue plates were obtained. Elemental analysis calculated for C12H18Cl4Cu1N4O4 (487.64): C 29.56, H 3.72, N 11.49; found: C 29.55, H 3.70, N 11.50%.
(HIna)[Cu(H2O)Cl3] (7). Amounts of 85.5 mg (0.5 mmol) CuCl2.2H2O and 61 mg (0.5 mmol) Ina were suspended in 12 mL H2O in a Teflon container and 3.5 mg (0.01 mmol) Gd2O3 and 1.3 mL concentrated HCl were added. The container was heated in an autoclave for 2 days at 140 °C. After cooling and opening the reaction mixture was immersed in a glass beaker. After 4 weeks evaporation, 53 mg (0.17 mmol, 34%) of light blue platelets were obtained. Elemental analysis calculated for C6H9Cl3Cu1N2O2 (311.05): C 23.17, H 2.92, N 9.01; found: C 23.13, H 2.96, N 9.00%. Remark: the role of Gd2O3 as catalyst was checked by a blind reaction without Gd2O3. The reaction occurred very slowly and only traces of the target product were obtained.

4. Conclusions

New CuII complexes and coordination polymers of isonicotineamide (Ina) and picolinamide (Pia), pyrazine 2-amide (Pya), 2- and 4-amino benzamides (2-Aba and 4-Aba) ligands were synthesised from various CuII sources. Under the criterion of crystallinity and phase purity we were able to reliably reproduce many of the materials in reasonable yields. Crystal and molecular structures from single-crystal XRD were obtained for all new compounds; phase purity was checked using powder XRD. For the optimisation of the reaction protocols, the Cu:ligand stoichiometry of the starting materials was varied and we observed marked deviations of the Cu:ligand ratio in products compared with the starting materials. For three compounds containing the pyridine amides Ina and Pia, high Cu loadings of 2:1 were necessary to obtain phase pure compounds with Cu:ligand ratios of 1:4 and 1:2. In contrast to this, for the amino benzamide 4-Aba the optimum ratio of starting materials was 1:3 or 1:2 to obtain compounds with a Cu:ligand ratio of 1:2. In the structures, we exclusively observed Oamide and not NH2amide binding to CuII, in most of the cases supported by chelating of the second N binding function (pyridine, pyrazine, or aminophenyl) on the ligands. The ditopic ligands Ina, Pya, and 4-Aba frequently bridge µ-O,N between CuII centres forming 1D or 2D coordination polymers. Again, no NH2amide binding occurred. However, the same ligands were also found in terminal non-bridging modes. Nitrate, NO3, is often competing with amide ligand binding and might be one important reason for the saturation of CuII preventing the µ-O,N bridging and formation of polymers. The coordination surrounding CuII in these structures is dominated by the ubiquitous axial elongated octahedral geometry (OE). The second important coordination polyhedron is the square pyramid (SPy). The occurrence of these two polyhedra cannot be correlated with the polymeric or non-polymeric character of the compounds. The strong pyridine, pyrazine, or aminophenyl-N functions dominate the equatorial binding plane. Oamide occurs in this plane only in chelates with these N functions. Non-chelated Oamide binding to CuII was found in the axial (weak) position as expected, alongside with other weak ligands such as NO3, EtOH, H2O, BF4, and the peculiar SiF62−. X-band EPR spectra of powder samples revealed various spectral symmetry patterns ranging from axial over rhombic to inverse axial. Although the EPR spectra cannot be unequivocally correlated to the observed geometry of CuII in the solid state structures, the EPR patterns can help to support assumed structures as shown for the compound [Cu(Ina)2Br2] (Ina = isonicotine amide). As UV-vis absorption spectroscopy and magnetic measurements in the solid can also be reasonably correlated with the surrounding of CuII, we suggest the combination of EPR, UV-vis spectroscopy, and magnetic measurements to elucidate or support possible structures of CuII compounds with such ligands if no unequivocal structural information is available.
As we can reliably reproduce some of the presented materials here, we will study the biological properties, for example, the antiproliferative activity of selected compounds, in the near future.

Supplementary Materials

The following are available online at https://0-www-mdpi-com.brum.beds.ac.uk/2304-6740/8/12/65/s1, Figures S1–S40 showing crystal and molecular structures and powder XRD patterns of [Cu(Pia)2(BF4)2] (8), [Cu(Ina)2(NO3)2] (2), [Cu(Ina)4(H2O)2](BF4)2 (1), [Cu(Ina)2(H2O)3(SiF6)]·H2O (4), (HIna)2[CuCl4]∙2H2O (6), (HIna)[Cu(H2O)Cl3] (7), [Cu(Pya)2](BF4)2 (9), [Cu(Pya)2(H2O)(NO3)](NO3) (10), [Cu(Pya)(NO3)2] (11), [Cu(Pyc)(Tfa)](12), [Cu(2-Aba)2(NO3)2] (13), [Cu2(4-Aba)2(H2O)3(NO3)3](NO3) (14), [Cu(4-Aba)2(EtOH)2](ClO4)2 (15), [Cu(4-Aba)2(EtOH)2](BF4)2 (6), [Cu(4-AbaH)2Cl4] (17), and [Cu(Tba)2](ClO4)2 (18) and Figures S41–S48 showing X-Band EPR spectra of [Cu(Ina)2(H2O)2(NO3)2] (2), [Cu(Tba)2](ClO4)2 (18), [Cu(Pya)2(H2O)(NO3)](NO3) (10), [Cu(Ina)2(H2O)3(SiF6)]∙H2O (4), [Cu(Pya)(NO3)2] (11), [Cu(Pia)2](BF4)2 (8), (HIna)2[CuCl4].2H2O (6), [Cu(Pyc)(Tfa)](12), and [Cu(Ina)2Br2] (5), together with Supplementary Tables S1–S39 containing crystal structure and refinement data of all compounds.

Author Contributions

I.W. and N.N.A.T.W. carried out the syntheses; S.S. and I.P. collected XRD data, solved the structures and provided figures and tables; K.B., K.S. and A.K. measured and analysed EPR spectra; G.M. and A.K. designed and supervised the project and provided the equipment; A.K. wrote the draft; G.M. and A.K. revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

General funding is gratefully acknowledged to the University of Cologne. A.K. acknowledges the German Academic Exchange Service (DAAD)—KD_0001052598-2 for a short-time guest lectureship and the Shiraz University, Iran, for support.

Acknowledgments

We thank Horst Schumacher, Department of Chemistry of the University of Cologne, for the PXRD measurements.

Conflicts of Interest

The authors declare no conflict of interest.

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Scheme 1. Protoligands (ligand precursor prior to deprotonation) with abbreviations used in this study. In red: acidic protons.
Scheme 1. Protoligands (ligand precursor prior to deprotonation) with abbreviations used in this study. In red: acidic protons.
Inorganics 08 00065 sch001
Scheme 2. Results of reproduction and optimisation reactions with yields and purities decreasing along the colour series: Inorganics 08 00065 i001 Inorganics 08 00065 i002 Inorganics 08 00065 i003 Inorganics 08 00065 i004. Yields were defined relative to the ligands (for details, see Experimental Section).
Scheme 2. Results of reproduction and optimisation reactions with yields and purities decreasing along the colour series: Inorganics 08 00065 i001 Inorganics 08 00065 i002 Inorganics 08 00065 i003 Inorganics 08 00065 i004. Yields were defined relative to the ligands (for details, see Experimental Section).
Inorganics 08 00065 sch002
Figure 1. ORTEP representation (50% probability level) of the molecular entity within the structure of   1 [Cu(Ina)2(NO3)2] (2) (left); packing along the c axis in the crystal (right); H atoms were omitted for clarity.
Figure 1. ORTEP representation (50% probability level) of the molecular entity within the structure of   1 [Cu(Ina)2(NO3)2] (2) (left); packing along the c axis in the crystal (right); H atoms were omitted for clarity.
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Figure 2. ORTEP representation (50% probability level) of the molecular entity within the structure of   1 [Cu(Pya)(NO3)2] (11) (left); packing along the b axis in the crystal (right); H atoms were omitted for clarity.
Figure 2. ORTEP representation (50% probability level) of the molecular entity within the structure of   1 [Cu(Pya)(NO3)2] (11) (left); packing along the b axis in the crystal (right); H atoms were omitted for clarity.
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Figure 3. ORTEP representation (50% probability level) of the molecular entity within the structure of   2 [Cu(Pya)2](BF4)2 (9) (left); packing along the a axis in the crystal (right); H atoms were omitted for clarity.
Figure 3. ORTEP representation (50% probability level) of the molecular entity within the structure of   2 [Cu(Pya)2](BF4)2 (9) (left); packing along the a axis in the crystal (right); H atoms were omitted for clarity.
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Figure 4. ORTEP representation (50% probability level) of the molecular entities within the structures of (HIna)2[CuCl4] 2H2O (6) (left) of [Cu(Pia)2(BF4)2] (8) (middle) and [Cu(Ina)2(H2O)3(SiF6)]·H2O (4) (right); H atoms were omitted for clarity.
Figure 4. ORTEP representation (50% probability level) of the molecular entities within the structures of (HIna)2[CuCl4] 2H2O (6) (left) of [Cu(Pia)2(BF4)2] (8) (middle) and [Cu(Ina)2(H2O)3(SiF6)]·H2O (4) (right); H atoms were omitted for clarity.
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Figure 5. X-band EPR spectra of microcrystalline samples of [Cu(Ina)4(H2O)2](BF4)2 (1) (left, frequency = 9.455063 GHz, simulation in red with parameters in Table 3), (Cu(H-Aba)2Cl4) (17) (middle, frequency = 9.454244 GHz, simulation in red), and [Cu2(Aba)2(H2O)3(NO3)3](NO3) (14) (right, frequency = 9.448669 GHz, simulation in red), all measured at 298 K.
Figure 5. X-band EPR spectra of microcrystalline samples of [Cu(Ina)4(H2O)2](BF4)2 (1) (left, frequency = 9.455063 GHz, simulation in red with parameters in Table 3), (Cu(H-Aba)2Cl4) (17) (middle, frequency = 9.454244 GHz, simulation in red), and [Cu2(Aba)2(H2O)3(NO3)3](NO3) (14) (right, frequency = 9.448669 GHz, simulation in red), all measured at 298 K.
Inorganics 08 00065 g005
Figure 6. X-band EPR spectra of a microcrystalline sample of [Cu(4-Aba)2(EtOH)2](ClO4)2 (15) at 110 K (frequency = 9.459916 GHz) and 295 K (frequency = 9.448669 GHz) both with simulations in red (left) and at temperatures ranging from 130 to 270 K (right).
Figure 6. X-band EPR spectra of a microcrystalline sample of [Cu(4-Aba)2(EtOH)2](ClO4)2 (15) at 110 K (frequency = 9.459916 GHz) and 295 K (frequency = 9.448669 GHz) both with simulations in red (left) and at temperatures ranging from 130 to 270 K (right).
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Figure 7. Thermal dependence of χ and χ−1 of selected CuII compounds.
Figure 7. Thermal dependence of χ and χ−1 of selected CuII compounds.
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Table 1. Overview over the obtained crystalline compounds and structures.
Table 1. Overview over the obtained crystalline compounds and structures.
LigandCuII PrecursorCompoundFormula (Weight)Space Group
InaCu(BF4)2∙6H2O[Cu(Ina)4(H2O)2](BF4)2 (1)C24H28B2Cu1F8N8O6 (761.69)C2/c (No. 15) d
InaCu(NO3)2∙3H2O 1 [Cu(Ina)2(NO3)2] (2)C12H12Cu1N6O8 (431.81)P212121 (No. 19)
InaCu(NO3)2∙3H2O[Cu(Ina)2(H2O)2(NO3)2] (3)C12H16Cu1N6O10 (467.84)P21/c (No. 14) e
InaCu(BF4)2∙6H2O[Cu(Ina)2(H2O)3(SiF6)]·H2O (4)C12H20Cu1F6N4O6Si1 (521.94)P-1 (No. 2)
Ina[Cu(Ina)2(NO3)2][Cu(Ina)2Br2] (5)C12H12Br2Cu1N4O2 (467.61)P21 (No. 4) f
HIna+ aCuCl2∙2H2O(HIna)2[CuCl4]∙2H2O (6)C12H18Cl4CuN4O4 (487.64)P-1 (No. 2)
HIna+ aCuCl2∙2H2O(HIna)[Cu(H2O)Cl3] (7)C6H9Cl3Cu1N2O2 (311.05)P-1 (No. 2)
PiaCu(BF4)2∙6H2O[Cu(Pia)2(BF4)2] (8)C12H12B2Cu1F8N4O2 (481.41)P-1 (No. 2)
PyaCu(BF4)2∙6H2O 2 [Cu(Pya)2](BF4)2 (9)C10H10B2Cu1F8N6O2 (483.38)P21/c (No. 14)
PyaCu(NO3)2∙3H2O[Cu(Pya)2(H2O)(NO3)](NO3) (10)C10H12Cu1N8O9 (451.80)P-1 (No. 2)
PyaCu(NO3)2∙3H2O 1 [Cu(Pya)(NO3)2] (11)C5H5Cu1N5O7 (310.67)C2/c (No. 15)
Pyc− bCu(Tfa)2∙H2O 2 [Cu(Pyc)(Tfa)] (12)C7H3Cu1F3N2O4 (299.65)P212121 (No. 19)
2-AbaCu(NO3)2∙3H2O[Cu(2-Aba)2(NO3)2] (13)C14H16Cu1N6O8 (459.86)P21/n (No. 14) g
4-AbaCu(NO3)2∙3H2O 1 [Cu2(4-Aba)2(H2O)3(NO3)3](NO3) (14)C14H22Cu2N8O17 (701.46)C2/c (No. 15) h
4-AbaCu(ClO4)2∙6H2O 2 [Cu(4-Aba)2(EtOH)2](ClO4)2 (15)C18H28Cl2Cu1N4O12 (626.88)P21/c (No. 14)
4-AbaCu(BF4)2∙6H2O 2 [Cu(4-Aba)2(EtOH)2](BF4)2 (16)C18H28B2Cu1F8N4O4 (601.60)P21/c (No. 14)
4-HAba+ cCu(ClO4)2∙6H2O + HCl[Cu(4-HAba)2Cl4] (17)C14H18Cl4Cu1N4O2 (479.67)P21/c (No. 14)
TbaCu(ClO4)2∙6H2O[Cu(Tba)2](ClO4)2 (18)C8H16Cl2Cu1N4O12S2 (558.80)C2/m (No. 12)
a HIna+ = 4-carboxamidopyridin-1-ium. b Pyc = pyrazine-2-carboxylate. Tfa = trifluoroacetate. c 4-AbaH+ = 4-benzamidyl ammonium. d The ClO4-salt was reported in C2/c previously, [16]. e Reported previously, [16]. f No valid structure refinement possible; previous assignment from powder XRD = P21/c (No. 14), from [22]. g A refinement in the standard space group P21/c was not successful. h The structure could not be fully refined: The nitrate anions around the N2 (coordinating) and N3 (non-coordinating) atoms show systematic disorder due to symmetric alternation. For the coordinating N2-nitrate there are two possible symmetric identical positions to bridge between the two Cu1 ions, both with an occupation of 0.5. This leads to two nitrate anions in very close proximity in the cell, but must be understood as alternating motif in consecutive cells. The non-coordinating nitrate N3 atom shows similar disorder (for details, see Tables S30 and S31).
Table 2. Selected binding parameters (distances in Å, angles in °) around the CuII centres.
Table 2. Selected binding parameters (distances in Å, angles in °) around the CuII centres.
ComplexGeometry aT (K)Cu–L1 bCu–L2Cu–L3Cu–L4Cu–L5Cu–L6
L1–Cu–L2L2–Cu–L3L3–Cu–L4L1–Cu–L5L1–Cu–L6L1–Cu–L3L5–Cu–L6
[Cu(Ina)4(H2O)2](BF4)2 (1)OE298(2)2.024(3)
N21
2.045(4)
N11
=N11=N212.392(5)
O1
2.645(5)
O2
91.7(1)°88.9(2)°91.7(1)°86.5(1)°93.4(1)°173.0(1)°180°
1 [Cu(Ina)2(NO3)2] (2)SPy+1298(2)1.987(5)
O31
1.994(5)
N21
2.002(5)
N11
2.004(4)
O41
2.314(4)
O11
-
90.1(2)°87.7(2)°89.1(2)°78.9(2)°-165.5(2)°-
[Cu(Ina)2(H2O)2(NO3)2] (3) cOE296(2)1.984(1)
O2
1.992(1)
N1
2.507(1)
O3
90.0(1)°90.0(1)° 95.6(1)°84.4(1)°180°180°
[Cu(Ina)2(H2O)3(SiF6)]·H2O (4)OE298(2)1.969(2)
O1
1.986(2)
O2
1.999(2)
N21
2.026(2)
N11
2.409(2)
F1
2.513(2)
O4
90.1(1)°89.6(1)°88.2(1)°88.2(1)°84.9(1)°180°170.9(1)°
(HIna)2[CuCl4]∙2H2O (6)SP+2298(2)2.263(1)
Cl1
2.270(1)
Cl2
=Cl1=Cl23.360(1) = (py)=L5
(HIna)[Cu(H2O)Cl3] (7) cSPy298(2)1.980(4)
O1
2.251(1)
Cl2
2.268(1)
Cl1
2.279(1)
Cl3
2.923(1)
Cl2′
-
87.4(1)°93.2(1)°92.6(1)°--172.5(1)°-
[Cu(Pia)2(BF4)2] (8)OE150(2)1.935(3)
O1
1.958(4)
N1
=O1=N12.589(3)
F4
=F4
83.3(2)°96.6(1)°83 (2)°89.7(1)°90.3(1)°180°180°
2 [Cu(Pya)2](BF4)2 (9)OE298(2)1.957(2)
O11
1.984(3)
N12
=O11=N122.447(3)
N11
=N11
82.2(1)°97.7(1)°82.2(1)°85.5(1)°94.4(1)°180°180°
[Cu(Pya)2(H2O)(NO3)](NO3) (10)Spy+1298(2)1.935(4)
O11
1.938(4)
O21
1.984(4)
N21
1.989(4)
N11
2.234(4)
O5
2.818(4)
O43
82.7(1)°97.6(1)°82.7(1)°94.3(2)°89.7(1)°172.1(1)°169.8(1)°
1 [Cu(Pya)(NO3)2] (11)SPy298(2)1.953(2)
O11
1.979(2)
O31
1.998(2)
N12
2.004(2)
N11
2.238(2)
O21
2.572(3)
O33
81.6(1)°89.3(1)°92.3(1)°91.0(1)°93.6(1)°169.2(1)°136.9(1)°
2 [Cu(Pyc)(Tfa)] (12) dSPy298(2)1.942(5)
O1
1.944(7)
O11
1.997(6)
O12
2.065(8)
N11
2.272(8)
N12
-
88.8(2)°97.6(2)°92.7(3)°96.5(3)°-171.3(2)°-
[Cu(2-Aba)2(NO3)2] (13)OE298(2)1.976(3)
O1
2.010(4)
N1
=O1=N12.506(5)
O3
=O3
87.3(2)°92.7(2)°87.3(2)°92.8(1)°87.1(1)°180°180°
1 [Cu2(4-Aba)2(H2O)3(NO3)3](NO3) (14) eOD298(2)1.942(4)
O11
1.969(4)
O21
2.016(4)
N11
2.034(5)
O21
2.262(4)
O32
2.35(1)
O23
89.1(2)°88.2(2)°93.3(2)°82.9(2)°95.2(3)°176.0(2)°143.1(3)°
2 [Cu(4-Aba)2(EtOH)2](ClO4)2 (15) OE150(2)1.951(2)
O11
2.077(4)
N11
=N11=O112.529(2)
O21
=O21
87.8(1)°92.1(1)°87.8(1)°94.4(1)°85.5(1)°180°180°
2 [Cu(4-Aba)2(EtOH)2](BF4)2 (16)OE298(2)1.951(2)
O11
2.062(3)
N11
=O11=N112.545(2)
O1
=O1
87.9(1)°92.1(1)°87.9(1)°87.3(1)°92.6(1)°180°180°
[Cu(4-HAba)2Cl4] (17) fOE298(2)1.957(6)
O1
2.313(3)
Cl1
=O1=Cl2.867(2)
Cl2
=Cl2
89.6(2)°90.4(2)°89.6(2)°98.2(2)°81.8(2)°180°180°
[Cu(Tba)2](ClO4)2 (18)OE298(2)1.976(2)
O11
=O11=O11=O112.625(1)
S11
=S11
90.9(1)°89.1(1)°90.9(1)°81.5(1)°98.4(1)°180°180°
a OE = tetrahedrally elongated octahedral, OD = otherwise distorted octahedral, SPy = square pyramidal, b L1 is defined by the shortest Cu–ligand bond, L2 to L4 lie in the equatorial plane, L5 and L6 in the elongated axial positions. c Data from [16]. d Pyc = pyrazine-2-carboxylate. e Two species with slightly different bonding parameters. f 4-AbaH+ = 4-benzamidyl ammonium.
Table 3. Selected X-band EPR data of CuII compounds.a
Table 3. Selected X-band EPR data of CuII compounds.a
CompoundT (K)gavg/g1g2g/g3ΔgSpectral Geom.CuII Geom.
Group I
[Cu(Ina)2(NO3)2] (2)2982.1432.280 2.0740.206axialSPy+1
[Cu(Ina)4(H2O)2](BF4)2 (1) b2982.1182.260 2.0480.212axialOE
(HIna)2[CuCl4].2H2O (6)2982.1322.2662.0822.0470.219rhombicSP+2
[Cu(Ina)2(H2O)3(SiF6)]·H2O (4)2982.1542.326 2.0680.258axialOE
[Cu(Ina)2(H2O)2(NO3)2] (3)2982.1562.297 2.0850.212axialOE
[Cu(4-HAba)2Cl4] (17)2982.1752.2862.1692.0660.219rhombicOE
[Cu(Pya)(NO3)2] (11)2982.1792.372 2.0830.289axialSPy
[Cu(Pya)2(H2O)(NO3)](NO3) (10)2982.1832.400 2.0750.325axialSPy+1
similar compounds
[Cu(CCl3COO)2(MNA)2]∙2H2O c2982.1432.280 2.0750.205axialOE
[Cu(Ina)2(µ-N,S-SCN)2] d2982.202.27 2.070.200axialOE
[Cu(meclof)2(2-pyca)2] e2982.1422.290 2.0680.222axialOE
[Cu(clof)2(4-pymeth)2(H2O)] 2H2O f2982.1282.271 2.0540.217axialSPy
[Cu(clof)2(Et2nia)2] f2982.1322.289 2.0530.236axialg
[Cu(clof)2(Ina)2] f2982.1532.285 2.0870.198axialg
[Cu(tolf)2(Et2nia)2)(H2O)2] h2982.1302.294 2.0480.246axialOE
[Cu(tolf)2(Nia)2] h2982.1572.319 2.0760.243axialg
Group II
[Cu(Pya)2](BF4)2 (9)2982.1402.2042.1392.0780.126rhombicOE
[Cu(4-Aba)2(EtOH)2](ClO4)2 (15)1102.1372.2312.1232.0590.172rhombicOE
[Cu(4-Aba)2(EtOH)2](ClO4)2 (15)2982.1112.200 2.0660.133axialOE
[Cu(4-Aba)2(EtOH)2](BF4)2 (16)1102.1392.2202.1402.0580.162rhombicOE
[Cu(4-Aba)2(EtOH)2](BF4)2 (16)2982.1102.196 2.0680.131axialOE
[Cu(TBA)2](ClO4)2 (18)2982.1302.228 2.0800.147axialOE
similar compounds
[Cu2(Ina)2(µ-1,1-N3)2(µ-1,3-N3)2] d2982.172.22 2.070.150axialSPy+1
[Cu(Ina)2(µ-1,1-N3)2(µ-O,O-SO4)]∙2H2O d2982.172.242.182.090.150rhombicSPy
Group III
[Cu(Pyc)(Tfa)] (12)2982.138 2.138 0isotropicSPy
[Cu(Ina)2Br2] (5)2982.111 2.111 0isotropicSPy i
Group IV
[Cu2(Aba)2(H2O)3(NO3)3](NO3) (14)2982.1412.190 2.0500.112inv. axialOD
a Measured at 298 K or 110 K on microcrystalline powders; gav = averaged g value = (g + 2g)/3 or (g1 + g2 + g3)/3; Δg = gg or g1g3. OE = tetragonal elongated octahedral, OD = otherwise distorted octahedral, SPy = square pyramidal. b An HFS A of 180 G was observed. c From [20]; MNA = N-methylnicotinamide; an HFS A of 165 G is observed. d From [15]. e From [18]; meclof = meclofenamate; 2-pyca = 2-pyridylcarbinol. f From [24]; clof = 2-(4-chlorophenoxy)-2-methylpropionic acid; 4-pymeth = 4-pyridylmethanol, Et2nia = N,N-diethylnicotinamide, an HFS A of 165 G is observed for [Cu(clof)2(Et2nia)2]. g No structure reported. h From [17], tolf = tolfenamic (N-(2-methyl-3-chlorophenyl)anthranilic) acid. i No unequivocal structure from XRD (see text); previous assignment OE from powder XRD and IR, [22].
Table 4. Magnetic moments and Curie-Weiss constants of selected CuII compounds.a
Table 4. Magnetic moments and Curie-Weiss constants of selected CuII compounds.a
CompoundμB θCW (K)EPR SymmetrySymmetry Around CuII
[Cu(Ina)2(NO3)2] (2)1.5036.9axialSPy + 1
[Cu(Pya)(NO3)2] (11)1.656.55isotropicSPy
[Cu(Pyc)(Tfa)] (12)1.5648.3isotropicSPy
[Cu(Aba)2(EtOH)2](ClO4)2 (15)1.5242.8axialOE
a Magnetic moments in Bohr magnetons µB and Curie-Weiss constants θCW in K.
Table 5. UV-vis absorption maxima of selected copper complexes.a.
Table 5. UV-vis absorption maxima of selected copper complexes.a.
Compoundλ (nm/cm−1) of d-d BandsColour of the CrystalsSymmetry Around CuII b
[Cu(Pya)2](BF4)2 (9)613/16,310blueOE
[Cu(Pya)2(H2O)(NO3)](NO3) (10)640/15,630blueSPy + 1
[Cu(Pya)(NO3)2] (11)780/12,820blueSPy
[Cu(Pyc)(Tfa)] (12)664/15,060turquoiseSPy
[Cu(Ina)2Br2] (5)691/14,470dark green- b
similar compounds
[Cu(tolf)2(Et2nia)2)(H2O)2] c614/16,290blueOE
[Cu(meclof)2(2-pyca)2] d615/16,260blueOE
[Cu(meclof)2(Et2nia)2] d605/16,530blue- e
[Cu(clof)2(4-pymeth)2(H2O)] 2H2O f620/16,130blueSPy
[Cu(clof)2(Ina)2] f660/15,150blue- e
[Cu(clof)2(Et2nia)2] f603/16,580violet- e
a Measured as KBr pellets. b OE = tetrahedrally elongated octahedral, SPy = square pyramidal. b No unequivocal structure from XRD (see text); previous assignment OE from powder XRD and IR, [22], reported absorption at 675 nm/14,800 cm−1. c From [17], tolf = tolfenamic (N-(2-methyl-3-chlorophenyl)anthranilic) acid. d From [18]; meclof = meclofenamate; 2-pyca = 2-pyridylcarbinol, Et2nia = N,N-diethylnicotinamide. e No structure reported. f From [24]; clof = 2-(4-chlorophenoxy)-2-methylpropionic acid; 4-pymeth = 4-pyridylmethanol.
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Wackerbarth, I.; Widhyadnyani, N.N.A.T.; Schmitz, S.; Stirnat, K.; Butsch, K.; Pantenburg, I.; Meyer, G.; Klein, A. CuII Complexes and Coordination Polymers with Pyridine or Pyrazine Amides and Amino Benzamides—Structures and EPR Patterns. Inorganics 2020, 8, 65. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics8120065

AMA Style

Wackerbarth I, Widhyadnyani NNAT, Schmitz S, Stirnat K, Butsch K, Pantenburg I, Meyer G, Klein A. CuII Complexes and Coordination Polymers with Pyridine or Pyrazine Amides and Amino Benzamides—Structures and EPR Patterns. Inorganics. 2020; 8(12):65. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics8120065

Chicago/Turabian Style

Wackerbarth, Ines, Ni Nyoman Agnes Tri Widhyadnyani, Simon Schmitz, Kathrin Stirnat, Katharina Butsch, Ingo Pantenburg, Gerd Meyer, and Axel Klein. 2020. "CuII Complexes and Coordination Polymers with Pyridine or Pyrazine Amides and Amino Benzamides—Structures and EPR Patterns" Inorganics 8, no. 12: 65. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics8120065

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