Octahedral Tantalum Bromide Clusters as Catalysts for Light-Driven Hydrogen Evolution.

The development of an efficient hydrogen generation strategy from aqueous protons using sunlight is a current challenge aimed at the production of low-cost, easily accessible, renewable molecular hydrogen. For achieving this goal, non-noble metal containing and highly active catalysts for the hydrogen evolution reaction (HER) are desirable. Octahedral tantalum halide clusters {Ta6(µ-X)12}2+ (X = halogen) represent an emerging class of such HER photocatalysts. In this work, the photocatalytic properties of octahedral aqua tantalum bromide clusters toward HER and in acid and homogeneous aqueous conditions were investigated. The [{Ta6Bri12}Bra2(H2O)a4]·4H2O (i = inner ligand; a = apical ligand) compound is revealed to be an efficient precatalyst in acid (HBr) conditions and with methanol as the sacrificial agent. A response surface methodology (RSM) study was applied for the optimization of the HER conditions, considering the concentrations of both additives (methanol and HBr) as independent variables. An optimal H2 production of 11 mmol·g-1 (TON = 25) was achieved, which displays exceptional catalytic properties compared to regular Ta-based materials. The aqua tantalum bromide clusters assist in the photocatalytic hydrogen generation in agreement with energy-conversion schemes, and plausible active catalytic species and a reaction mechanism were proposed from computational and experimental perspectives.

Noncovalent Dualism in Perylene-Diimide-Based Keggin Anion Complexes: Theoretical and Experimental studies.

We report the synthesis and comprehensive characterization of organic-inorganic hybrid salts formed by bis-cationic N,N'-bis(2-(trimethylammonium)ethylene)perylene-3,4,9,10-tetracarboxylic acid bisimide (PTCD2+) and Keggin-type [XW12O40]n- (X = Si, n = 4; X = P, n = 3) polyoxometalates. (PTCD)3[PW12O40]2·3DMSO·2H2O (2) and (PTCD)2[SiW12O40]·DMSO·2H2O (3) were structurally characterized by single crystal X-ray diffraction. The cations in both structures exhibited infinite chainlike arrangements through π-π interactions, contrasting with the previously reported cation-anion stacking observed in naphthalene diimide derivatives. A detailed theoretical study employing topological analysis of the electron density distribution within the quantum theory of atoms in molecules approach provided further insights into this structural dualism. Atomic force microscopy analyses revealed the formation of self-assembled supramolecular structures on graphite from molecular monolayers (3 nm of thick) to submicrometer aggregates for 2. Hyperspectral Raman spectroscopy imaging revealed that such heterostructures are likely formed by an enhanced π-π interactions. Both complexes demonstrated interesting electrochemical behavior, photoluminescence and X-ray-induced luminescence. Electron spin resonance analysis confirmed charge separation in both compounds, with enhanced efficiency observed in compound 2. Our findings of these perylene-based organic-inorganic hybrid salts offer the potential for their application in optoelectronic devices and functional materials.

Copper- and Silver-Containing Heterometallic Iodobismuthates: Features of Thermochromic Behavior.

Nine heterometallic iodobismuthates with the general formula Cat2{[Bi2M2I10}] (M = Cu(I), Ag(I), Cat = organic cation) were synthesized. According to X-ray diffraction data, their crystal structures consisted of {Bi2I10} units interconnected with Cu(I) or Ag(I) atoms through I-bridging ligands, forming one-dimensional polymers. The compounds are thermally stable up to 200 °C. Optical band gaps (Eg), estimated at room temperature via diffuse reflectance measurements, range from 1.81 to 2.03 eV. Thermally induced changes in optical behavior (thermochromism) for compounds 1-9 were recorded, and general correlations were established. The thermal dependence of Eg appears to be close to linear for all studied compounds.

NMR-Relaxometric Investigation of Mn(II)-Doped Polyoxometalates in Aqueous Solutions.

Solution behavior of K;5[(Mn(H2O))PW11O39]·7H2O (1), Na3.66(NH4)4.74H3.1[(MnII(H2O))2.75(WO(H2O))0.25(α-B-SbW9O33)2]·27H2O (2), and Na4.6H3.4[(MnII(H2O)3)2(WO2)2(ß-B-TeW9O33)2]·19H2O (3) was studied with NMR-relaxometry and HPLC-ICP-AES (High Performance Liquid Chromatography coupled with Inductively Coupled Plasma Atomic Emission Spectroscopy). According to the data, the [(Mn(H2O))PW11O39]5- Keggin-type anion is the most stable in water among the tested complexes, even in the presence of ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA). Aqueous solutions of 2 and 3 anions are less stable and contain other species resulting from dissociation of Mn2+. Quantum chemical calculations show the change in Mn2+ electronic state between [Mn(H2O)6]2+ and [(Mn(H2O))PW11O39]5-.

Iridium Complexes with BIAN-Type Ligands: Synthesis, Structure and Redox Chemistry.

A series of iridium complexes with bis(diisopropylphenyl)iminoacenaphtene (dpp-bian) ligands, [Ir(cod)(dpp-bian)Cl] (1), [Ir(cod)(NO)(dpp-bian)](BF4)2 (2) and [Ir(cod)(dpp-bian)](BF4) (3), were prepared and characterized by spectroscopic techniques, elemental analysis, X-ray diffraction analysis and cyclic voltammetry (CV). The structures of 1-3 feature a square planar backbone consisting of two C = C π-bonds of 1,5-cyclooctadiene (cod) and two nitrogen atoms of dpp-bian supplemented with a chloride ion (for 1) or a NO group (for 2) to complete a square-pyramidal geometry. In the nitrosyl complex 2, the Ir-N-O group has a bent geometry (the angle is 125°). The CV data for 1 and 3 show two reversible waves between 0 and -1.6 V (vs. Ag/AgCl). Reversible oxidation was also found at E1/2 = 0.60 V for 1. Magnetochemical measurements for 2 in a range from 1.77 to 300 K revealed an increase in the magnetic moment with increasing temperature up to 1.2 µB (at 300 K). Nitrosyl complex 2 is unstable in solution and loses its NO group to yield [Ir(cod)(dpp-bian)](BF4) (3). A paramagnetic complex, [Ir(cod)(dpp-bian)](BF4)2 (4), was also detected in the solution of 2 as a result of its decomposition. The EPR spectrum of 4 in CH2Cl2 is described by the spin Hamiltonian H = gßHS with S = 1/2 and gxx = gyy = 2.393 and gzz = 1.88, which are characteristic of the low-spin 5d7-Ir(II) state. DFT calculations were carried out in order to rationalize the experimental results.

Not So Similar: Different Ways of Nb(V) and Ta(V) Catecholate Complexation.

The reactions between catechol (H2cat) and niobium(V) or tantalum(V) precursors in basic aqueous solutions lead to the formation of catecholate complexes of different natures. The following complexes were isolated and characterized by single-crystal X-ray diffraction (SCXRD): (1) (NH4)3[NbO(cat)3]∙4H2O; (2) K2[Nb(cat)3(Hcat)]·2H2cat·2H2O; (3) Cs3[NbO(cat)3]·H2O; (4) (NH4)4[Ta2O(cat)6]·3H2O; (5) Cs2[Ta(cat)3(Hcat)]·H2cat; (6) Cs4[Ta2O(cat)6]·7H2O. The isolated crystalline products were characterized by elemental analysis, X-ray powder diffraction (XRPD), FTIR, and TGA. The structural features of these complexes, such as {Ta2O} unit geometry, Cs-π interactions, and crystal packing effects, are discussed.

One-Step Interfacial Integration of Graphene Oxide and Organic Chromophores into Multicomponent Nanohybrids with Photoelectric Properties.

A one-step protocol for interfacial self-assembly of graphene oxide (GO), glutamine-substituted perylene diimide (PDI-glu), 10,12-pentacosadiynoic acid (PCDA), and zinc acetate into three- and four-component hybrid nanofilms through hydrogen and coordination bonding was developed. The hybrids deposited onto solid supports were studied after polymerization of PCDA by UV-vis absorption, fluorescence, and Raman spectroscopies, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results of spectroscopic studies suggest that the hybrids assembled through H-bonds can maintain the light-induced Förster energy transfer from the PDI-glu chromophore to the conjugated polymer and then to GO leading to fluorescence quenching. In the hybrids assembled through coordination bonding with zinc clusters, the energy transfer proceeds from PDI-glu to the PDA polymer, whereas the transfer from PDA to GO is quenched completely. Another important characteristic of these ultrathin hybrids is their stability with respect to photobleaching of chromophores due to the acceptor properties of GO. The as-assembled hybrid nanofilms were integrated with conventional photovoltaic planar architectures to study their photoelectric properties. The zinc-containing hybrids integrated with a hole transport layer exhibited photovoltaic properties. The cell with the integrated four-component hybrid comprising both PDI-glu and PDA showed a photocurrent/dark current ratio almost an order higher than that of the three-component hybrid assembled with PDA only. The supramolecular method based on the interfacial self-assembly can be extended to a wide variety of organic chromophores and polymerizable surfactants for integrating them into multicomponent functional GO-based nanohybrids with targeted properties for organic electronics.

Niobium and Tantalum Halocyanide Clusters: The Complete Family.

Synthetic procedures providing straightforward access to the whole family of Nb and Ta halide clusters with terminal cyanide ligands have been developed. Corresponding [M6X12(CN)12]4- (M = Nb, Ta; X = Cl, Br) can be accessed by ligand-exchange procedures from K4Nb6X18 (X = Cl, Br) and Bu4NCN, (Et4N)2[Ta6Cl18] and Bu4NCN and from [Ta6Br12(H2O)4Br2]·4H2O and KCN in moderate to high yields (50-80%). The products were isolated as Bu4N salts. The compounds were investigated both experimentally and by quantum chemistry, revealing correlations between structural, electrochemical, electrostatic, electronic, and topological features as a function of type of metal, halide, and charge.

Sterically Hindered Tellurium(IV) Catecholate as a Lewis Acid.

Sterically hindered tellurium catecholate Te(Cat36)2 (Cat36 = 3,6-di-tert-butyl-catecholate) was synthesized with the reaction of amorphous Te with 3,6-di-tert-butyl-o-benzoquinone. Adducts of Te(Cat36)2 with various O- and N-donors were isolated and characterized by means of single-crystal X-ray diffraction along with IR, UV-vis, and NMR (1H, 13C, and 125Te) spectroscopies. In the crystal structure of the adduct with 2,2'-bipyridine (bipy), the unprecedented µ-κ2N,N':κ2N,N'-bridging coordination mode of bipy was observed. Various intermolecular interactions Te...O, Te...N, and Te...C in adducts were analyzed using density functional theory calculations and quantum theory of atoms in molecules analysis. The estimated strength for appropriate short contacts varies from 0.9 to 5.3 kcal/mol, and they are attractive and purely non-covalent.

Coordination of Pt(IV) by {P8W48} Macrocyclic Inorganic Cavitand: Structural, Solution, and Electrochemical Studies.

Hydrothermal reaction of a macrocyclic inorganic POM cavitand Li17(NH4)21H2[P8W48O184] with [Pt(H2O)2(OH)4] results in coordination of up to six {Pt(H2O)x(OH)4-x} fragments to the internal surface of the polyoxoanion. The product was isolated as K22(NH4)9H3[{Pt(OH)3(H2O)}6P8W48O184]·79H2O (1) and characterized by multiple techniques in the solid state (SCXRD, XRPD, XPS, FTIR, and TGA) and in solution (NMR, ESI-MS, and HPLC-ICP-AES). Electrochemical properties were studied both in solution and as components of the paste electrode. The complex shows electrocatalytic activity in water oxidation.

Heteroleptic Pd(II) and Pt(II) Complexes with Redox-Active Ligands: Synthesis, Structure, and Multimodal Anticancer Mechanism.

A series of heteroleptic square-planar Pt and Pd complexes with bis(diisopropylphenyl) iminoacenaphtene (dpp-Bian) and Cl, 1,3-dithia-2-thione-4,5-dithiolate (dmit), or 1,3-dithia-2-thione-4,5-diselenolate (dsit) ligands have been prepared and characterized by spectroscopic techniques, elemental analysis, X-ray diffraction analysis, and cyclic voltammetry (CV). The intermolecular noncovalent interactions in the crystal structures were assessed by density functional theory (DFT) calculations. The anticancer activity of Pd complexes in breast cancer cell lines was limited by their solubility. Pd(dpp-Bian) complexes with dmit and dsit ligands as well as an uncoordinated dpp-Bian ligand were devoid of cytotoxicity, while the [Pd(dpp-Bian)Cl2] complex was cytotoxic. On the contrary, all Pt(dpp-Bian) complexes demonstrated anticancer activity in a low micromolar concentration range, which was 8-20 times higher than the activity of cisplatin, and up to 2.5-fold selectivity toward cancer cells over healthy fibroblasts. The presence of a redox-active dpp-Bian ligand in Pt and Pd complexes resulted in the induction of reactive oxygen species (ROS) in cancer cells. In addition, these complexes were able to intercalate into DNA, indicating the dual mechanism of action.

Proton Affinity in the Chemistry of Beta-Octamolybdate: HPLC-ICP-AES, NMR and Structural Studies.

The affinity of [ß-Mo8O26]4- toward different proton sources has been studied in various conditions. The proposed sites for proton coordination were highlighted with single crystal X-ray diffraction (SCXRD) analysis of (Bu4N)3[ß-{Ag(py-NH2)Mo8O26]}] (1) and from analysis of reported structures. Structural rearrangement of [ß-Mo8O26]4- as a direct response to protonation was studied in solution with 95Mo NMR and HPLC-ICP-AES techniques. A new type of proton transfer reaction between (Bu4N)4[ß-Mo8O26] and (Bu4N)4H2[V10O28] in DMSO results in both polyoxometalates transformation into [V2Mo4O19]4-, which was confirmed by the 95Mo, 51V NMR and HPLC-ICP-AES techniques. The same type of reaction with [H4SiW12O40] in DMSO leads to metal redistribution with formation of [W2Mo4O19]2-.

One-Dimensional Iodoantimonate(III) and Iodobismuthate(III) Supramolecular Hybrids with Diiodine: Structural Features, Stability and Optical Properties.

Two isostructural pairs of supramolecular iodoantimonate(III) and iodobismuthate(III) complexes with I2 units "trapped" in solid state via halogen bonding-Cat3[[M2I9](I2)} (Cat = tetramethylammonium and 1-methylpyridinium, M = Sb(III) and Bi(III)) were prepared. For all compounds, values of optical band gaps were determined, together with thermal stability; the complexes were additionally characterized by Raman spectroscopy.

Supramolecular Diiodine-Bromostannate(IV) Complexes: Narrow Bandgap Semiconductors.

Three supramolecular bromostannates(IV) with "trapped" diiodine molecules, Cat2{[SnBr6](I2)} (Cat = Me4N+ (1), 1-MePy+ (2) and 4-MePyH (3)), were synthesized. In all cases, I2 linkers are connected with bromide ligands via halogen···halogen non-covalent interactions. Articles 1-3 were studied using Raman spectroscopy, thermogravimetric analysis, and diffuse reflectance spectroscopy. The latter indicates that 1-3 are narrow band gap semiconductors.

Trapping of Ag+ into a Perfect Six-Coordinated Environment: Structural Analysis, Quantum Chemical Calculations and Electrochemistry.

Self-assembly of (Bu4N)4[ß-Mo8O26], AgNO3, and 2-bis[(2,6-diisopropylphenyl)-imino]acenaphthene (dpp-bian) in DMF solution resulted in the (Bu4N)2[ß-{Ag(dpp-bian)}2Mo8O26] (1) complex. The complex was characterized by single crystal X-ray diffraction (SCXRD), X-ray powder diffraction (XRPD), diffuse reflectance (DR), infrared spectroscopy (IR), and elemental analysis. Comprehensive SCXRD studies of the crystal structure show the presence of Ag+ in an uncommon coordination environment without a clear preference for Ag-N over Ag-O bonding. Quantum chemical calculations were performed to qualify the nature of the Ag-N/Ag-O interactions and to assign the electronic transitions observed in the UV-Vis absorption spectra. The electrochemical behavior of the complex combines POM and redox ligand signatures. Complex 1 demonstrates catalytic activity in the electrochemical reduction of CO2.

Selenium(IV) Polybromide Complexes: Structural Diversity Driven by Halogen and Chalcogen Bonding.

Reactions between bromoselenate(IV)-containing solutions, dibromine and salts of pyridinium-family organic cations resulted in structurally diverse, bromine-rich polybromine-bromoselenates(IV): (4-MePyH)5[Se2Br9][SeBr6](Br3)2 (1), (2-MePyH)2{[SeBr6](Br2)} (2), (PyH)2{[SeBr5]Br(Br2)2} (3), (1-MePy)2{[SeBr6](Br2)} (4). The compounds feature halogen and (in the case of 3) chalcogen bonding in solid state, resulting in formation of supramolecular architectures of different dimensionality. DFT calculations allowed estimation of the energies of non-covalent interactions in 1-4; additionally, characterization by Raman spectroscopy was performed.

Zn(II) and Co(II) 3D Coordination Polymers Based on 2-Iodoterephtalic Acid and 1,2-bis(4-pyridyl)ethane: Structures and Sorption Properties.

Metal-organic frameworks [M2(2-I-bdc)2bpe] (M = Zn(II) (1), Co(II) (2), 2-I-bdc = 2-iodoterephtalic acid, and bpe = 1,2-bis(4-pyridyl)ethane) were prepared and characterized by X-ray diffractometry. Both compounds retain their 3D structure after the removal of guest DMF molecules. Selectivity of sorption of different organic substrates from the gas phase was investigated for both complexes.

Oxochloroselenate(IV) with Incorporated {Cl2 }: The Case of Strong Cl⋠⋠⋠Cl Halogen Bonding.

Reaction of SeO2 , tetramethylammonium (TMA) chloride, aqueous HCl and Cl2 yields oxochloroselenate with incorporated Cl2 units, TMA3 {[Se2 O2 Cl7 ](Cl2 )}. The main feature of this compound is the strong (up to 3.5 kcal mol-1 , according to DFT calculations) Cl⋅⋅⋅Cl bonding, which is also detected by Raman spectroscopy.

Paramagnetic Rhenium Iodide Cluster with N-Heterocyclic Carbene.

triangulo-Trirhenium nonaiodide Re3I9 reacts with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) to produce the novel 13-electron paramagnetic cluster Re3I8(IMes)2, which was characterized by means of X-ray diffraction analysis, ESR spectroscopy, magnetometry, and quantum chemistry.

Unexpected Polymorphism in Bromoantimonate(III) Complexes and Its Effect on Optical Properties.

Reactions of [SbBr6]3- containing HBr solutions with bromide salts of 1,1'-(1,2-ethanediyl)bis(pyridine) (PyC22+) or 1,1'-(1,2-ethanediyl)bis(3,5-dimethylpyridine) (3,5-MePyC22+) initially result in the formation of the deep orange complexes Cat[SbBr5] (1 and 2), featuring unusual Sb···Br interactions in the solid state. In the mother liquor, 1 transforms into discrete binuclear (C2Py)2[Sb2Br10], which demonstrates polymorphism (triclinic 3 and monoclinic 4), while 2 transforms into polymeric (3,5-MePy){[SbBr4]} (5). DFT calculations reveal that the system of noncovalent Sb···Br contacts may be responsible for the appearance of the observed optical properties (unusual deep orange coloring).