The Synthesis and Characterization of a Novel One-Dimensional Bismuth (III) Coordination Polymer as a Precursor for the Production of Bismuth (III) Oxide Nanorods

Abstract

A novel Bi (III) coordination compound, [Bi(HQ)(Cl)₄]_n ((Q = pyridine-4-carbaldehyde thiosemicarbazone), was prepared in this research using a sonochemical technique. SEM, infrared spectroscopy (IR), XRD, and single-crystal X-ray analysis were utilized to analyze the Bi(III) coordination compound. The structure determined using single-crystal X-ray crystallography indicates that the coordination compound is a 1D polymer in solid state and that the coordination number of bismuth (III) ions is six, (BiSCl₅), with one S donor from the organic ligand and five Cl donors from anions. It is equipped with a hemidirectional coordination sphere. It is interesting that the ligand has been protonated in the course of the reaction with a Cl^- ion balancing the charge. This compound’s supramolecular properties are directed and regulated by weak directional intermolecular interactions. Through π–π stacking interactions, the chains interact with one another, forming a 3D framework. Thermolysis of the compound at 170 °C with oleic acid resulted in the formation of pure phase nanosized Bi (III) oxide. SEM technique was used to examine the morphology and size of the bismuth (III) oxide product produced.

1. Introduction

Coordination polymers, a class of solid-state materials characterized by an endless framework structure, are formed when metal ions and organic ligands self-assemble [1,2]. They continue to garner research interest due to their appealing shapes and many prospective applications in catalysis [3], magnetism [4], luminescence [5], drug delivery [6], gas separation [7], absorption [8], etc. It is self-evident that some architectures confer unique characteristics on materials, which are critical for their use [9,10]. However, developing and manufacturing new functional coordination polymers continue to be challenging at the moment.

The coordination sphere distortions in Tl(I), Pb(II), and Bi(III) compounds are of interest because they may be caused by the existence of a lone pair [11,12]. Bi(III) frameworks have garnered considerable attention due to their large ion radius, flexible coordination number, and the possibility of a stereochemically active lone pair of 6s² outer electrons. The stereochemical activity of valence shell electron lone pairs in polymeric and supramolecular substances could be intriguing, since a sudden accumulation of multiple bridging ligands could result in the disappearance of gaps, resulting in a less frequent holodirected configuration [13,14,15,16]. On the other hand, such as Tl(I) and Pb(II), the coordination sphere of Bi(III) is interesting (Scheme 1).

Sonochemistry is a field of study wherein molecules undergo reactions when exposed to high-intensity ultrasound (20 kHz–10 MHz) [17]. Ultrasound causes physical or chemical alterations throughout cavitation, a process that involves the creation, development, and immediate collapsing of bubbles in fluids. Cavitation could produce warm spots with temperatures of approximately 5000 °C, pressures of approximately 500 atm, and a life span of a few microseconds [18]. The high temperatures may accelerate chemical processes, but they can also stimulate the creation of nanoscale structures, most notably via the immediate production of many crystallization nuclei. This method has been extensively used to synthesize nanoscale structures of a variety of chemicals, and recently, many nanoscale materials have been produced with this method [19].

We are primarily interested in the design and synthesis of coordination polymers in this study. We recently published a study on the nanoscale production of different metal–organic coordination polymers [20,21,22]. The coordination characteristics of Bi(III) are investigated using a pyridine-4-carbaldehyde thiosemicarbazone ligand (Scheme 2). Then, we describe a sonochemical technique for producing nanostructures of the coordination compound and its use in the synthesis of nanoscaled Bi(III) oxide particles.

2. Experiment

2.1. Materials

All solvents and reagents used were readily available commercially and were used without additional purification. The IR spectrum was acquired using KBr disks in 400–4000 cm⁻¹ band on a Bruker Vector 22 FTIR spectrometer. Melting points were determined using Electrothermal 9100 equipment and are shown in their unaltered state. The ultrasonic generation was performed in a SONICA-2200 EP ultrasonic bath (frequency of 40 kHz). XPRD experiments were carried out utilizing a Panalytical X’pert diffractometer using monochromatized Cukα radiation. Mercury 2.4 was used to generate modeled XPRD powder shapes based on single-crystal information [23].

The Scherrer method was used to determine the crystallographic diameters of chosen samples. Following coating of Au, samples morphology was examined utilizing a scanning electron microscope (Hitachi, Japan). Data of diffraction for a single crystal of the synthesized coordination polymer were obtained at 298 K using a Bruker D8 VENTURE diffractometer, combined with a Photon II CCD detector and Cu Kα radiation. APEX 3 was used to collect the data, refine cell parameters, and reduce data [24].

We solved the structure using direct processes with SHELXS and anisotropically adjusted all F² data utilizing a complete matrix weighted least-squares technique with w = 1/[σ²(F_o)² + (0.035P)²] weight, where p = (F_o² + 2F_c²)/3. Mercury 2.4 was used to create molecular displays.

Table 1. Coordination compounds crystallographic data and structural refinements.

Chemical Formula	C7H9BiCl4N4S
Mr	532.02
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	298(2)
a, b, c (Å)	11.3205 (4), 7.4736 (3), 17.8244 (6)
β(°)	97.9430(10)°
V(Å3)	1493.56(9)
Z	4
Crystal size (mm3)	0.200 × 0.100 × 0.030
Theta range for data collection	3.943 to 72.090°
Max. and min. transmission	0.7535, 0.2404
Rint	0.0574
Absorption coefficient mm−1	30.948
R,wR2 [I > 2σ(I)]	0.0838, 0.2181
R, wR2 (all data)	0.0856, 0.2247
No. of reflections	8804
No. of parameters	155
No. of restraints	0
Absorption correction	Multi-scan (Bruker SADABS)
Δ›max, Δ›min (e Å−3)	5.003, −4.488
Goodness-of-fit on F2	1.060

contains the crystallographic data and arranging modification for the produced coordination polymer, whereas

Table 2. Selected lengths and angles of bond for [Bi(HQ)(Cl)₄]_n.

Bi(1)-Cl(3)	2.542(3)	Cl(3)-Bi(1)-Cl(4)	89.73(11)
Bi(1)-Cl(4)	2.620(2)	Cl(3)-Bi(1)-Cl(2)	88.27(14)
Bi(1)-Cl(2)	2.714(4)	Cl(4)-Bi(1)-Cl(2)	91.25(12)
Bi(1)-Cl(1)	2.769(4)	Cl(3)-Bi(1)-Cl(1)	97.02(14)
Bi(1)-S(1)	2.841(3)	Cl(4)-Bi(1)-Cl(1)	170.90(12)
Bi(1)-Cl(1)#1	2.861(3)	Cl(2)-Bi(1)-Cl(1)	95.03(16)
N(1)-H(1A)	0.86	Cl(3)-Bi(1)-S(1)	89.60(12)
Cl(1)-Bi(1)-S(1)	80.60(15)	Cl(4)-Bi(1)-S(1)	93.41(9)
Cl(3)-Bi(1)-Cl(1)#1	173.81(14)	Cl(2)-Bi(1)-S(1)	174.87(13)
Cl(4)-Bi(1)-Cl(1)#1	85.71(12)	Cl(2)-Bi(1)-Cl(1)#1	87.64(17)
S(1)-Bi(1)-Cl(1)#1	94.85(14)	Cl(1)-Bi(1)-Cl(1)#1	87.97(5)
Bi(1)-Cl(1)-Bi(1)#2	147.3(2)

Symmetry transformations used to generate equivalent atoms: #1 −x + 2,y + 1/2, −z + 1/2 #2 −x + 2, y − 1/2, −z + 1/2.

contains the specified lengths and angles of the bond. The details about crystal structure of [Bi(HQ)(Cl)₄]_n is provided in Supplementary Materials.

2.2. Isolated Single Crystal of [Bi(HQ)(Cl)₄]_n Synthesis

We obtained single crystals of [Bi(HQ)(Cl)₄]_n by combining bismuth(III) chloride (2 mmol) and the Q ligand (2 mmol) in the main arm of a branching tube. CH₃OH was supplied with care to completely fill both arms. After sealing the tube, the arm that contains the ligands was immersed in a 60 °C oil bath; however, the other arm was stored at room temperature. After seven days of isolating and filtering the crystals inside the cooler arm, it was washed using acetone and ether and allowed to dry naturally (Figure 1) (yield: 52%).

FTIR (KBr) = (632, 801, 1088, 1491, 1605, 1636, 2901, 3441) cm⁻¹.

2.3. Synthesis of the Compound [Bi(HQ)(Cl)₄]_n in Bulk Form

We put 0.18 g of synthesized ligand and 0.315 g of bismuth (III) chloride into a small bottle, added approximately 20 mL of methanol, and stirred it for at least 60 min with a magnet to produce sedimentation. If sediment does not form, it is better to stop the system as a reflux system (for a minimum of 3h) to allow sediment to develop. Sediment formation occurred simultaneously in the examined system. The sediment was then screened and the FTIR spectra were analyzed (Yield: 49%). The following are the major peaks in its infrared spectrum:

FTIR (KBr) = (630, 878, 1108, 1492, 1594, 2941, 3262, 3422) cm⁻¹.

2.4. Synthesis of the [Bi(HQ)(Cl)₄]_n Nanostructure

The nanostructure of [Bi(HQ)(Cl)₄]_n was produced by placing 10 mL of a 0.1 M solution of bismuth(III) chloride in water in a dense ultrasonic probe and dropwise adding 10 mL of a solution containing 0.1 M of Q ligand in methanol/water. The precipitates obtained were screened, washed, and left to dry in the air (yield: 43%).

FTIR (KBr) = (793, 815, 1107, 1493, 1607, 2982, 3228, 3380) cm⁻¹.

3. Results and Discussion

The combination of bismuth(III) chloride with pyridine-4-carbaldehyde thiosemicarbazone resulted in the formation of [Bi(HQ)(Cl)₄]_n, a novel 1-dimensional coordination molecule. The nanostructure of the chemical was evaluated using the ultrasonic method in an aqueous solution. The branched-tube method was used to produce appropriate single crystals of the prepared chemical for X-ray crystallography. Scheme 3 illustrates two distinct ways for producing [Bi(HQ)(Cl)₄]_n materials.

The FTIR spectrum of the compound is shown in Figure 2 in its nano, bulk, and crystalline forms. Comparing these spectra reveals their resemblance, with the matching major peaks overlapping significantly.

The bands of absorption with variable strengths in a range of 1400–1600 cm⁻¹ in FTIR spectra of these chemicals are ascribed to the vibrations of the ligand pyridine ring, which is linked to the C=N and C=C bonds. Peaks associated with imine C=N are observed as crisp bands in the range of 1600 cm⁻¹ that have moved to shorter waves as a result of the ligand’s coordination to the metal and the development of a compound with minimal displacement.

The tensile N-H peaks in the compound’s vibrational spectra are located at 3235 cm⁻¹ and show the existence of the ligand’s N-H group when coupled to the central metal, as well as the presence of the ligand in the neutral structure during the compound’s synthesis. For all three compounds, the associated band of the creation of a new C=N bond is not seen, indicating that the L ligand contributed to the coordination of the metallic ion in the form of ketones. The C=S group in the compound is detected with a little displacement in the vicinity of 1700 cm⁻¹, indicating that it is coordinated to the metal.

The N-N group is detected in the 1052 cm⁻¹ region, and this adsorption band is moved to lower wavenumbers in the spectra of all three compounds than in the ligand spectrum, indicating that the nitrogen atom of azomethine is not coordinated to the metallic ion.

The findings of the study reveal that when ligand tautomerization occurs, the ligand takes part in the forming of compounds in enol form, and the absorption band of N-N is removed, C-N and N-N are shifted to high numbers, and a new C=N bond is formed in the wavenumber 1400–1600 cm⁻¹. Furthermore, the existence of the N-N band in the spectra of compounds shows that the ligand is not tautomerized in the solid form and that the ligand is in coordination with the metallic ion in the ketonic form. As can be observed, there is an excellent match in all regions between the nanomaterial, crystal, and manufactured bulk [11].

The produced nanoscale coordination polymer’s surface morphology was studied using SEM. SEM analysis demonstrates that the produced nanoparticles are of varying sizes and shapes (Figure 3).

The generated XPRD pattern of [Bi(HQ)(Cl)₄]_n is shown in Figure 4 in contrast to an experimental XRD pattern of a nanostructure. Acceptable matches by minor changes in 2θ were observed between the experimental and simulated XPRD patterns. It demonstrates that the production of nanoparticles through sonochemistry is equivalent to that produced via crystallography. The extension of the peaks shows that the particles are nanoscale in size.

In Figure 5, X-ray diffraction analysis reveals that the produced coordination product in solid is a 1D coordination polymer with the ligand monodentately linked to the bismuth metal through the S atom. This compound has a Z value of 4 and is formed in a monoclinic crystal lattice. It is a member of the space group P2₁/c.

The unit cell is shown in Figure 6. The structural units are connected through symmetric components such as screw axes of 2₁, glide planes, and symmetry centers. The screw axes 2₁ are parallel to axis b, and the two glide planes are perpendicular to axis b, as shown in Figure 7. The symmetry centers at the middle of a unit cell serve as a link between these units.

A kind of bismuth with an asymmetric coordination sphere is found in this structure. Every bismuth central metal in this combination is connected to a sulfur atom of Q ligands and five chlorine atoms, two of which are linked to other units that repeat and three of which are free. As a result of the BiSCl₅ pattern, bismuth has a coordination number of six. Communication between structural units in the produced coordination polymer occurs through a single Bi-Cl bond that is in the bridge mode, resulting in the creation of the polymeric structure.

The molecule lacks a symmetry center, and the bismuth–chlorine bonds are not identical in length. Additionally, the angles around the core metal atom are not identical in the coordination cortex; the angles formed by the ligand and the central metal are according to what is shown in Table 2. The HQ Ligand is covalently linked to the core metal through the S of thiosemicarbazide and functions as a monodentate ligand in the polymer shape. In solid form, this chemical is a 1D coordination compound. Figure 8 illustrates the compound’s polymeric structure. This is comparable with other bismuth coordination compounds reported in the literature [22,25,26]. As a reported structure in reference [22], the coordination sphere of Bi(III) with seven coordination numbers was reported to be hemidirected with an asymmetrical shape.

It is interesting that the ligand has been protonated in the course of the reaction and that a Cl ion balances the charge. The pyridine nitrogen N1 was protonated during the reaction to balance the charges. This leads to a lower theoretical yield since the Cl atom is provided by one of the starting materials (BiCl₃).

In coordination polymers, in addition to coordination covalent strong bonds that cause the polymer to expand in a 1D step, weak interactions such as hydrogen and aromatic interactions cause self-accumulation of 1D chains and transform the structure into a 3D supermolecule via intermolecular interactions.

Without considering weak interactions, the composition has the structure of a 1D coordination polymer. By examining weak interactions, it is possible to detect the existence of seven hydrogen bonds in this structure, which transforms into a three-dimensional structure shown in Figure 9. Additionally,

Table 3. The crystal structure of [Bi(HQ)(Cl)₄]_n reveals a number of noncovalent interactions.

D-H...A	d(D-H)	d(H...A)	d(D...A)	<(DHA)
N1—H1A···Cl2 i	0.86	2.25	3.103 (5)	170.2
N3—H3A···Cl2 ii	0.86	2.36	3.205 (5)	169.5
N4—H4A···Cl3 iii	0.86	2.61	3.247 (5)	131.9
N4—H4A···Cl4 iv	0.86	2.95	2.452 (5)	119.1
N4—H4B···Cl4	0.86	2.34	3.195 (5)	170.0
C5—H5A···Cl3 v	0.93	2.91	3.661 (5)	138.9
C6—H6A···Cl4 ii	0.93	2.89	3.720 (5)	149.8

Symmetry code(s): (i) x−1, −y + 1/2, z + 1/2; (ii) x, −y + 1/2, z + 1/2; (iii) −x + 1, y + 1/2, −z + 1/2; (iv) −x + 1, y − 1/2, −z + 1/2; (v) −x + 1, −y, −z + 1.

shows H bonds.

Bi₂O₃ nanorods were produced via thermolysis of 1 at 170 °C with oleic acid as a surfactant. The powder XRD patterns (Figure 10) match the standard pattern of the Bi₂O₃ tetragonal structure (JCPDS card file No. 76-1730), which confirms the formation of bismuth oxide. The average size of the particles was estimated by the Scherrer formula as 24 nm.

Moreover, SEM images of the residue obtained from the thermolysis of 1 at 180 °C using oleic acid as the surfactant show that the Bi₂O₃ oxide NPs have a rod shape whose diameter is around 40–60 nm (Figure 11), comparable with reported in the literature [27,28,29].

Figure 12 displays the XPS spectra of Bi₂O₃ nano oxide. Two asymmetric peaks centered at 158.7 eV and 163.9 eV are due to the transitions of 4f_7/2 and 4f_5/2, respectively, and are attributed to Bi³⁺ ions in Bi₂O₃, crystal, which indicates that Bi³⁺ exists in the product in the form of bismuth oxide which is close to the reported values for crystalline Bi₂O₃ [30,31]. The O1 s spectrum for Bi₂O₃ indicates a peak at 531.1 eV, which is close to the value of 530.9 eV reported in the literature [32].

4. Conclusions

In this study, a new bismuth (II) coordination polymer [Bi(HQ)(Cl)₄]_n nanostructure was produced using ultrasonic, and its crystal structure was examined. The novel coordination compound was structurally characterized using spectrophotometry, single-crystal crystallography, and SEM. In solid state, the compound’s structure resulted in a 1D coordination polymer. The coordination number of Bi (III) ions was found to be six by using one sulfur atom from the organic ligand and five Cl atoms from anions. It is interesting that the ligand was protonated in the course of the reaction and that a Cl ion balanced the charge. The complete system exhibited a 3D structure due to numerous weak interactions. Moreover, the calcination of compound 1 by thermolysis of 1 at 170 °C using oleic acid occurred as the surfactant yielded uniform Bi₂O₃ nanorods.