Inorganics, Volume 5, Issue 3 (September 2017) – 22 articles

Assembled complexes, [Fe(NCX)₂(bpanth)₂]_n (X = S, Se, BH₃; bpanth = 9,10-bis(4-pyridyl)anthracene), were synthesized. The iron for the three complexes was in temperature-independent high spin state by ⁵⁷Fe Mössbauer spectroscopy and magnetic susceptibility measurement. X-ray structural analysis revealed the interpenetrated structure of [Fe(NCS)₂(bpanth)₂]_n. In the local structure around the iron atom, the coordinated pyridine planes were shown to be a parallel type, which is in accordance with the results investigated by density functional theory (DFT) calculation. This complex (X = S) has CH–π interactions between the H atom of coordinated pyridine and the neighboring anthracene of the other 2D grid. It was suggested that the interpenetrated structure was supported by the stabilization of CH–π interaction, and this intermolecular interaction forced the relatively unstable parallel structure. That is, the unstable local structure is compensated by the stabilization due to intermolecular interaction, which controlled the spin state as high spin state. Full article

Selective manipulation of spin states in iron(II) complexes by thermal or photonic energy is a desirable goal in the context of developing molecular functional materials. As dynamic spin-state equilibration in isolated iron(II) complexes typically limits the lifetime of a given spin state to nanoseconds, synthetic strategies need to be developed that aim at inhibited relaxation. Herein we show that modulation of the reaction coordinate through careful selection of the ligand can indeed massively slow down dynamic exchange. Detailed structural analysis of [FeL]²⁺ and [ZnL]²⁺ (L: tris(1-methyl-2-{[pyridin-2-yl]-methylene}hydrazinyl)phosphane sulfide) with crystallographic and computational methods clearly reveals a unique trigonal-directing effect of the extended-tripod ligand L during spin crossover, which superimposes the ubiquitous [FeN₆] breathing with trigonal torsion, akin to the archetypal Bailar twist. As a consequence of the diverging reaction coordinates in [FeL]²⁺ and in the tren-derived complex [Fe(tren)py₃]²⁺, their thermal barriers differ massively, although the spin crossover energies are close to identical. As is shown by time-resolved transient spectroscopy and dynamic ¹H-NMR line broadening, reference systems deriving from tren (tris-(2-aminoethyl)amine), which greatly lack such trigonal torsion, harbor very rapid spin-state exchange. Full article

A pioneering research on a self-assembly of the magneto-anisotropic module [Re(CN)₇]³⁻ with the Mn(III) complexes involving Salen type (N,N′-ethylenebis(salicylideneiminate)) Schiff base (SB) ligands was performed using the known [Mn(^3MeOSalen)(H₂O)₂]₂(ClO₄)₂·H₂O (1) and the firstly synthesized [Mn₂(^5MeSalen)₂OAc]PF₆ (2). In the case of 1, a slow diffusion of the component solutions led to the ionic compound Ph₄P[Mn(^3MeOSalen)(H₂O)₂]₂[Re(CN)₇]·6H₂O (3). The direct mixing of the same solutions has resulted in the microcrystalline nearly insoluble solid [Mn(^3MeOSalen)(H₂O))₄Re(CN)₇]ClO₄·1.5MeCN·6.5H₂O, which is likely to comprise the pentanuclear clusters [(Mn^III(SB)(H₂O))₄Re(CN)₇]⁺. The use of 2 resulted in a 2D-network assembly of octanuclear clusters, [{(Mn(^5MeSalen))₆(H₂O)₂Re(CN)₇}₂Re(CN)₇]Cl₂(PF₆)·H₂O (4), incorporating one Re-center in a pentagonal bipyramid coordination environment, while another has strongly distorted capped trigonal prism as a coordination polyhedron. The latter was observed for the first time for Re(IV) complexes. A synthetic challenge to obtain the 0D assemblies with Re:Mn ≥ 3 has yielded a hexanuclear complex [Mn(^5MeSalen)H₂O(i-PrOH)][(Mn(^5MeSalen))₅H₂O(i-PrOH)₂Re(CN)₇](PF₆)₂(OAc)·2i-PrOH (5) being 1D chain via a bridging phenoxyl group. Owing to a low solubility of the final product, an addition of a bulk anion Ph₄B⁻ to the MeCN/MeOH solution of [Re(CN)₇]³⁻and 1 in ratio 1:6 resulted in rhenium-free matter [Mn(^3MeOSalen)(H₂O)₂][Mn(^3MeOSalen)(H₂O)MeCN](Ph₄B)₂·5MeCN (6). Full article

A series of novel N-heterocyclic carbene coinage metal complexes containing a naphthalimide (NI) chromophore has been prepared and fully characterized. Two types of molecules are described those where the NI unit is directly attached to the carbene unit with the general formulae [(L¹)–M–X], M = Cu, X = Cl (1a); M = Ag, X = I (1b) and M = Au, X = Cl, (1c). While in the second family, a π-extended carbene ligand precursor L²–H⁺I⁻ (3) was prepared where the NI unit is distant from the imidazole unit via a phenyl-alkyne bridge. Only two N-heterocyclic carbene metal complexes were prepared [(L²)–M–Cl], M = Cu (2a) and M = Au (2c). The related silver carbene compound could not be isolated. The molecular structure of the carbene complex 1c was determined and confirmed the formation of the target compound. Interestingly, the structure shows the presence of an aurophilic interaction Au···Au at 3.407 Å between two individual molecules. The photophysical properties of the compounds were investigated in solution at room temperature. Preliminary results suggested that all compounds are luminescent and act as blue emitters (420–451 nm). These transition emissions can be attributed to the intraligand origin of the NI chromphore. Moreover, the carbene complexes featuring L² ligand with π-extended system were found to be more luminescent. Full article

It is of utmost importance to optimise and stabilise hydrogen storage capacity during multiple cycles of hydrogen release and uptake to realise a hydrogen-based energy system. Here, the direct solvent-based synthesis of magnesium hydride, MgH₂, from dibutyl magnesium, MgBu₂, in four different carbon aerogels with different porosities, i.e., pore sizes, 15 < D_avg < 26 nm, surface area 800 < S_BET < 2100 m²/g, and total pore volume, 1.3 < V_tot < 2.5 cm³/g, is investigated. Three independent infiltrations of MgBu₂, each with three individual hydrogenations, are conducted for each scaffold. The volumetric and gravimetric loading of MgH₂ is in the range 17 to 20 vol % and 24 to 40 wt %, which is only slightly larger as compared to the first infiltration assigned to the large difference in molar volume of MgH₂ and MgBu₂. Despite the rigorous infiltration and sample preparation techniques, particular issues are highlighted relating to the presence of unwanted gaseous by-products, Mg/MgH₂ containment within the scaffold, and the purity of the carbon aerogel scaffold. The results presented provide a research path for future researchers to improve the nanoconfinement process for hydrogen storage applications. Full article

Synthesis of platinum(II) conjugate with acetylated betulinic acid tris(hydroxymethyl)aminomethane ester (BATRIS) is presented (BATRISPt). HR-ESI-MS and multinuclear NMR spectroscopy, as well as elemental analysis were used for characterization of BATRISPt. Cytotoxicity (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), crystal violet (CV), and sulforhodamine B (SRB) assays) of BA, BATRIS, BATRISPt, and cisplatin were assessed on seven different tumor cell lines: melanoma B16, colon HCT116 and DLD-1, adenocarcinoma HeLa, breast MCF-7, and anaplastic thyroid tumor 8505C and SW1736; as well as normal MRC-5 fibroblasts. Furthermore, the effect of the mentioned compounds on the apoptosis (Annexin V/PI assay) and autophagy induction (acridine orange (AO) assay) as well as caspase 3, 8, and 9 activation were investigated on the selected B16 melanoma cell line. BATRISPt showed lower activity than BA, BATRIS, or cisplatin. All tested compounds triggered apoptosis in B16 cells. Induction of autophagy was observed in B16 cells exposed only to BATRIS. On the other hand, new conjugate activates caspases 8 and 9 in B16 cells with higher impact than BATRIS or cisplatin alone. Full article

The spin-crossover (SCO) phenomenon between a high-spin and a low-spin state has attracted much attention in the field of materials science. Among the various kinds of SCO complexes, the triazole-bridged iron(II) polymeric chain system, [Fe(II)(R-trz)₃]X₂·xH₂O (where trz is triazole and X is the anion), exhibiting the SCO phenomenon with thermal hysteresis around room temperature, has been extensively studied from the viewpoint of molecular memory and molecular devices. In connection with this system, we have controlled the SCO phenomenon according to the characteristic properties of counter ions. In the case of X being C_nH_2n+1SO₃⁻, the spin transition temperature (T_1/2) increases with increasing the length (n) of the alkyl chain of the counter ion and saturates above n = 5, which is attributed to the increase in the intermolecular interaction of the alkyl chains of C_nH_2n+1SO₃⁻, called the fastener effect. The hysteresis width of T_1/2 decreases with increasing n, showing the even-odd, also known as parity, effect. In the cases where X is toluenesulfonate (tos: CH₃C₆H₄SO₃⁻) and aminobenzenesulfonate (abs: NH₂C₆H₄SO₃⁻), T_1/2 and its hysteresis width vary drastically with the structural isomerism (ortho-, metha-, and para-substitution) of counter ions, which implies the possibility of photoinduced spin transition by means of the photoisomerization of counter ions. From this strategy, we have synthesized [Fe(II)(NH₂-trz)₃](SP150)₂·2H₂O (SP150 = N-alkylsulfonated spiropyran) and investigated the SCO phenomenon. Moreover, we have developed [Fe(II)(R-trz)₃]@Nafion films exhibiting spin transition around room temperature, where the Nafion membrane behaves as a counter anion as well as a transparent substrate, and investigated the photogenerated high-spin state below 35 K. The lifetime of the photogenerated high-spin state strongly depends on the intensity of irradiated light. Full article

In a series of Hofmann-like spin crossover complexes, two new compounds, {Fe(3-F-4-Methyl-py)₂[Au(CN)₂]₂} (1) and {Fe(3-Methyl-py)₂[Au(CN)₂]₂} (2) (py = pyridine) are described. The series maintains a uniform 2-dimentional (2-D) layer structure of {Fe[Au(CN)₂]₂}. The layers are combined with another layer by strong aurophilic interactions, which results in a bilayer structure. Both coordination compounds 1 and 2 at 293 K crystallize in the centrosymmetric space groups P2₁/c. The asymmetric unit contains two pyridine derivative ligands, one type of Fe²⁺, and two types of crystallographically distinct [Au(CN)₂]⁻ units. Compound 1 undergoes a complete two-step spin transition. On the other hand, 2 maintains the characteristic of the high-spin state. The present compounds and other closely related bilayer compounds are compared and discussed in terms of the cooperativity and critical temperature. The bilayer structure is able to be further linked by substituent-substituent contact resulting in 3-dimentional (3-D) network cooperativity. Full article

To develop a new spin-crossover functional material, a magnetic hybrid compound [Fe(qsal)₂][Ni(mnt)₂] was designed and synthesized (Hqsal = N-(8-quinolyl)salicylaldimine, mnt = maleonitriledithiolate). The temperature dependence of magnetic susceptibility suggested the coexistence of the high-spin (HS) Fe(III) cation and π-radical anion at room temperature and a magnetic transition below 100 K. The thermal variation of crystal structures revealed that strong π-stacking interaction between the π-ligand in the [Fe(qsal)₂] cation and [Ni(mnt)₂] anion induced the distortion of an Fe(III) coordination structure and the suppression of a dimerization of the [Ni(mnt)₂] anion. Transfer integral calculations indicated that the magnetic transition below 100 K originated from a spin-singlet formation transformation in the [Ni(mnt)₂] dimer. The magnetic relaxation of Mössbauer spectra and large thermal variation of a g-value in electron paramagnetic resonance spectra below the magnetic transition temperature implied the existence of a magnetic correlation between d-spin and π-spin. Full article

Four Fe(III) spin-crossover (SCO) compounds, [Fe(HL1)₂](HCl₄TPA) (1-Cl), [Fe(HL1)₂](HBr₄TPA) (1-Br), [Fe(HL2)₂](HCl₄TPA) (2-Cl), and [Fe(HL2)₂](HBr₄TPA) (2-Br) (HL1 = 4-chloro-2-nitro-6-(1-(2-(pyridine-2-yl)hydrazono)ethyl)phenolate; HL2 = 4-bromo-2-nitro-6-(1-(2-(pyridine-2-yl)hydrazono)ethyl)phenolate; HCl₄TPA = 2,3,5,6-tetrachloro-4-carboxybenzoate; and HBr₄TPA = 2,3,5,6-tetrabromo-4-carboxybenzoate), were synthesized to investigate the halogen substituent change effect in salicylaldehyde 2-pyridyl hydrazone-type ligands and dicarboxylic acids in SCO complexes to the spin-transition temperature. Crystal structure analyses showed that these compounds were isostructural. In addition, a one-dimensional hydrogen–bonded column was formed by the dicarboxylic acid anion and weak hydrogen bonds between the Fe(III) complexes. From Mössbauer spectroscopy and magnetic property measurements, these compounds were confirmed to exhibit gradual SCO. The spin-transition temperature can be shifted by changing the halogen substituent in the salicylaldehyde 2-pyridyl hydrazone-type ligands and dicarboxylic acids without changing the molecular arrangement in the crystal packing. Full article

Spin-crossover (SCO) behavior of a series of [Fe(X-pybox)₂](ClO₄)₂ was investigated, where X-pybox stands for 4-X-substituted 2,6-bis(oxazolin-2-yl)pyridine with X = H, Cl, Ph, CH₃O, and CH₃S. We confirmed that the mother compound [Fe(H-pybox)₂](ClO₄)₂ underwent SCO above room temperature. After X was introduced, the SCO temperatures (T_1/2) were modulated as 310, 230, and 330 K for X = Cl, Ph, and CH₃S, respectively. The CH₃O derivative possessed the high-spin state down to 2 K. Crystallographic analysis for X = H, Cl, CH₃O, and CH₃S was successful, being consistent with the results of the magnetic study. Distorted coordination structures stabilize the HS (high-spin) state, and the highest degree of the coordination structure distortion is found in the CH₃O derivative. A plot of T_1/2 against the Hammett substituent constant σ_p showed a positive relation. Solution susceptometry was also performed to remove intermolecular interaction and rigid crystal lattice effects, and the T_1/2’s were determined as 260, 270, 240, 170, and 210 K for X = H, Cl, Ph, CH₃O, and CH₃S, respectively, in acetone. The substituent effect on T_1/2 became very distinct, and it is clarified that electron-donating groups stabilize the HS state. Full article

The structural and magnetic properties of a range of new iron(III) bis-tridentate Schiff base complexes are described with emphasis on how intermolecular structural interactions influence spin states and spin crossover (SCO) in these d⁵ materials. Three pairs of complexes were investigated. The first pair are the neutral, heteroleptic complexes [Fe(3-OMe-SalEen)(thsa)] 1 and [Fe(3-MeOSalEen)(3-EtOthsa)] 2, where 3-R-HSalEen = (E)-2-(((2-(ethylamino)ethyl)imino)methyl)-6-R-phenol and 3-R-H₂thsa = thiosemicarbazone-3-R-salicylaldimine. They display spin transitions above room temperature. However, 2 shows incomplete and gradual change, while SCO in 1 is complete and more abrupt. Lower cooperativity in 2 is ascribed to the lack of π–π interactions, compared to 1. The second pair, cationic species [Fe(3-EtOSalEen)₂]NO₃ 3 and [Fe(3-EtOSalEen)₂]Cl 4 differ only in the counter-anion. They show partial SCO above room temperature with 3 displaying a sharp transition at 343 K. Weak hydrogen bonds from cation to Cl⁻ probably lead to weaker cooperativity in 4. The last pair, CsH₂O[Fe(3-MeO-thsa)₂] 5 and Cs(H₂O)₂[Fe(5-NO₂-thsa)₂] 6, are anionic homoleptic chelates that have different substituents on the salicylaldiminate rings of thsa²⁻. The Cs cations bond to O atoms of water and the ligands, in unusual ways thus forming attractive 1D and 3D networks in 5 and 6, respectively, and 5 remains HS (high spin) at all temperatures while 6 remains LS (low spin). Comparisons are made to other literature examples of Cs salts of [Fe(5-R-thsa)₂]⁻ (R = H and Br). Full article

Two new dinuclear iron(II) complexes (1·PF₆ and 1·AsF₆) of the general formula [Fe^II₂(L2^C3)₂](X)₄·nH₂O·mMeCN (X = PF₆, n = m = 1.5 for 1·PF₆ and X = AsF₆, n = 3, m = 1 for 1·AsF₆) have been prepared and structurally characterized, where L2^C3 is a bis-1,2,3-triazolimine type Schiff-base ligand, 1,1′-[propane-1,3-diylbis(1H-1,2,3-triazole-1,4-diyl)]bis{N-[2-(pyridin-2-yl)ethyl]methanimine}. Single crystal X-ray structure analyses revealed that 1·PF₆ and 1·AsF₆ are isostructural. The complex-cation [Fe^II₂(L2^C3)₂]⁴⁺ of both has the same dinuclear double helicate architecture, in which each iron(II) center has an N6 octahedral coordination environment. Neighboring helicates are connected by intermolecular π–π interactions to give a chiral one-dimensional (1D) structure, and cationic 1D chains with the opposite chirality exist in the crystal lattice to give a heterochiral crystal. Magnetic and differential scanning calorimetry (DSC) studies were performed only for 1·AsF₆, since the thermal stability in a high-temperature spin crossover (SCO) region of 1·PF₆ is poorer than that of 1·AsF₆. 1·AsF₆ shows an unsymmetrical hysteretic SCO between the low-spin–low-spin (LS–LS) and high-spin–high-spin (HS–HS) states at above room temperature. The critical temperatures of warming (T_c↑) and cooling (T_c↓) modes in the abrupt spin transition area are 485 and 401 K, respectively, indicating the occurrence of 84 K-wide thermal hysteresis in the first thermal cycle. Full article

[Fe(dppOH)₂]²⁺ (dppOH = 2,6-di(pyrazol-1-yl)-4-(hydroxymethyl)pyridine) is known to show spin crossover (SCO) behavior and light-induced excited spin state transitions (LIESST). Here, we show that the SCO properties of the [Fe(dppOH)₂]²⁺ complex can be altered by a crystal engineering approach employing counter anion exchange with polyoxometalate (POM) anions. Using this strategy, two new composite materials (TBA)[Fe(dppOH)₂][PMo₁₂O₄₀] (1) and [Fe(dppOH)₂]₃[PMo₁₂O₄₀]₂ (2) (TBA = tetra-n-butylammonium) have been isolated and studied by single crystal X-ray diffraction and magnetic susceptibility measurements. 1 was found to be in a high spin state at 300 K and showed no spin crossover behavior due to a dense packing structure induced by hydrogen bonding between the hydroxyl group of the dppOH ligands and the POM anions. Conversely, 2 contains two crystallographically unique Fe centers, where one is in the low spin state whilst the other is locked in a high spin state in a manner analogous to 1. As a result, 2 was found to show partial spin crossover behavior around 230 K with a decrease in the χ_mT value of 1.9 emu·mol⁻¹·K. This simple approach could therefore provide a useful method to aid in the design of next generation spin crossover materials. Full article

Metal organic complexes consisting of transition metal centers linked by organic ligands, may show bistability which enables the system to be observed in two different electronic states depending on external condition. One of the spectacular examples of molecular bistability is the spin-crossover phenomena. Spin-Crossover (SCO) describes the phenomena in which the transition metal ion in the complex under the influence of external stimuli may show a crossover between a low-spin and high-spin state. For applications in memory devices, it is desirable to make the SCO phenomena cooperative, which may happen with associated hysteresis effect. In this respect, compounds with extended solid state structures containing metal ions connected by organic spacer linkers like linear polymers, coordination network solids are preferred candidates over isolated molecules or molecular assemblies. The microscopic understanding, design and control of mechanism driving cooperativity, however, are challenging. In this review we discuss the recent theoretical progress in this direction. Full article

A theoretical investigation of the ring-opening polymerization (ROP) mechanism of rac-lactide (LA) with an yttrium complex featuring a N-heterocyclic carbine (NHC) tethered moiety is reported. It was found that the carbonyl of lactide is attacked by N(SiMe₃)₂ group rather than NHC species at the chain initiation step. The polymerization selectivity was further investigated via two consecutive insertions of lactide monomer molecules. The insertion of the second monomer in different assembly modes indicated that the steric interactions between the last enchained monomer unit and the incoming monomer together with the repulsion between the incoming monomer and the ligand framework are the primary factors determining the stereoselectivity. The interaction energy between the monomer and the metal center could also play an important role in the stereocontrol. Full article

An aspect of nanochemistry that has attracted significant attention is the formation of nanoarchitectures from the self-assembly of metal complexes, based on the design of compounds having cooperative functionalities. This technique is currently seen as important within the field of nanomaterials. In the present review, we describe the methods that allow tuning of the intermolecular interactions between spin crossover (SCO) complexes in various media. These approaches include the use of lipophilic derivatives, lipids, and diblock copolypeptide amphiphiles. The resulting supramolecular assemblies can enhance the solubility of various SCO complexes in both organic and aqueous media. In addition, amphiphilic modifications of coordination systems can result in metastable structures and dynamic structural transformations leading to unique solution properties, including spin state switching. The supramolecular chemistry of metal complexes is unprecedented in its scope and potential applications, and it is hoped that the studies presented herein will promote further investigation of dynamic supramolecular devices. Full article

Treatment of the known half-sandwich complexes of the type [(η⁶-C₆H₆)RuCl₂(P(OR)₃)] (R = Me or Ph) with SnCl₂ yielded three new half-sandwich ruthenium complexes (C1–C3): [(η⁶-C₆H₆)RuCl(SnCl₃)(P(OMe)₃)] (C1), [(η⁶-C₆H₆)RuCl(SnCl₃)(P(OPh)₃)] (C2) and the bis-stannyl complex [(η⁶-C₆H₆)Ru(SnCl₃)₂(P(OMe)₃)] (C3) by facile insertion of SnCl₂ into the Ru–Cl bonds. Treatment of the known complexes [(η⁶-C₆H₆)RuCl(SnCl₃)(PPh₃)] and [(η⁶-C₆H₆)RuCl₂(PPh₃)] with 4-dimethylaminopyridine (DAMP) and ammonium tetrafluoroborate afforded the complex salts: [(η⁶-C₆H₆)Ru(SnCl₃)(PPh₃)(DAMP)]⁺BF₄⁻ (C4) and [(η⁶-C₆H₆)RuCl(PPh₃)(DAMP)]⁺BF₄⁻ (C5) respectively. Complexes C1–C5 have been fully characterized by spectroscopic means (IR, UV–vis, multinuclear NMR, ESI–MS) and their thermal behaviour elucidated by thermal gravimetric analysis (TGA). Structural characterization by single crystal X-ray crystallography of the novel complex C2 and [(η⁶-C₆H₆)RuCl₂(P(OPh)₃)], the latter having escaped elucidation by this method, is also reported. Finally, the cytotoxicity of the complexes was determined on the A2780 (human ovarian cancer), A2780cisR (human ovarian cis-platin-resistant cancer), and the HEK293 (human embryonic kidney) cell lines and discussed, and an attempt is made to elucidate the effect of the stannyl ligand on cytotoxicity. Full article

We present a systematic study on the adsorption properties of molecular oxygen on Pt, Ni and PtNi clusters previously deposited on MgO(100) by means of density functional theory calculations. We map the different adsorption sites for a variety of cluster geometries, including icosahedra, decahedra, truncated octahedra and cuboctahedra, in the size range between 25–58 atoms. The average adsorption energy depends on the chemical composition, varying from 2 eV for pure Ni, 1.07 for pure Pt and 1.09 for a Pt ${}_{shell}$ Ni ${}_{core}$ nanoalloy. To correlate the adsorption map to the adsorption properties, we opt for a geometrical descriptor based on the metallic coordination up to the second coordination shell. We find an almost linear relationship between the second coordination shell and adsorption energy, with low coordination sites, such as those located at the (111)/(111) and (111)/(100) cluster edges-displaying adsorption energies above 1 eV, while higher coordination sites such as (111) cluster facets have an interaction of 0.4 eV or lower. The inclusion of van der Waals corrections leads to an overall increase of the O ${}_2$ adsorption energy without an alteration of the general adsorption trends. Full article

Extraction constants (K_ex & K_ex±) for the extraction of silver picrate (AgPic) by benzo-18-crown-6 ether (B18C6) into 1,2-dichloroethane (DCE) were determined at 298 K and various ionic strength (I)-values of a water phase with or without excess HNO₃. Here the symbols, K_ex and K_ex±, were defined as [AgLPic]_DCE/P and [AgL⁺]_DCE[Pic⁻]_DCE/P with P = [Ag⁺][L]_DCE[Pic⁻] and L = B18C6, respectively; [ ]_DCE refers to the concentration of the corresponding species in the DCE phase at equilibrium. Simultaneously, K_D,Pic (= [Pic⁻]_DCE/[Pic⁻]) and K_1,DCE (= K_ex/K_ex±) values for given I and I_DCE values were determined, where the symbol I_DCE shows I of the DCE phase. Also, equilibrium potential differences (Δφ_eq) based on the Pic⁻ transfer at the water/DCE interface were obtained from the analysis of the K_D,Pic [= K_D,Pic^S exp{−(F/RT) Δφ_eq}] values; the symbol K_D,Pic^S shows K_D,Pic at Δφ_eq = 0 V. On the basis of these results, I dependences of logK_ex and logK_ex± and I_DCE ones of logK_1,DCE and logK_ex± were examined. Extraction experiments of AgClO₄ and AgNO₃ by B18C6 into DCE were done for comparison. The logK_ex±-versus-Δφ_eq plot for the above Ag(I) extraction systems with Pic⁻, ClO₄⁻, and NO₃⁻ gave a good positive correlation. Full article

We assess the feasibility of efficiently calculating accurate thermodynamic properties of (SiO₂)_n·(H₂O)_m nanoclusters, using classical interatomic forcefields (FFs). Specifically, we use a recently parameterized FF for hydroxylated bulk silica systems (FFSiOH) to calculate zero-point energies and thermal contributions to vibrational internal energy and entropy, in order to estimate the free energy correction to the internal electronic energy of these nanoclusters. The performance of FFSiOH is then benchmarked against the results of corresponding calculations using density functional theory (DFT) calculations employing the B3LYP functional. Results are reported first for a set of (SiO₂)_n·(H₂O)_m clusters with n = 4, 8 and 16, each possessing three different degrees of hydroxylation (R = m/n): 0.0, 0.25 and 0.5. Secondly, we consider five distinct hydroxylated nanocluster isomers with the same (SiO₂)₁₆·(H₂O)₄ composition. Finally, the free energies for the progressive hydroxylation of three nanoclusters with R = 0–0.5 are also calculated. Our results demonstrate that, in all cases, the use of FFSiOH can provide estimates of thermodynamic properties with an accuracy close to that of DFT calculations, and at a fraction of the computational cost. Full article

Amongst many strategies for renewable energy conversion, light-driven water splitting to produce clean H₂ represents a promising approach and has attracted increasing attention in recent years. Owing to the multi-electron/multi-proton transfer nature of water splitting, low-cost and competent catalysts are needed. Along the rapid development of metal–organic frameworks (MOFs) during the last two decades or so, MOFs have been recognized as an interesting group of catalysts or catalyst supports for photocatalytic water splitting. The modular synthesis, intrinsically high surface area, tunable porosity, and diverse metal nodes and organic struts of MOFs render them excellent catalyst candidates for photocatalytic water splitting. To date, the application of MOFs and their derivatives as photocatalysts for water splitting has become a burgeoning field. Herein, we showcase several representative MOF-based photocatalytic systems for both H₂ and O₂ evolution reactions (HER, OER). The design principle of each catalytic system is specifically discussed. The current challenges and opportunities of utilizing MOFs for photocatalytic water splitting are discussed in the end. Full article