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Heterogeneous dinuclear rhodium(II) coordination polymer, [Rh2(p-BDC)2]n (p-BDC = 1,4-benzenedicarboxylate), which formed self-assembly infinite two-dimentional slit sheets structure was performed as hydrogen production catalyst for photochemical reduction of water under visible light irradiation in the presence of a multicomponent system containing Ru(bpy)32+, MV2+, and EDTA–2Na.

The synthesis and characterization of a Keggin-type mono-rhenium(V)- substituted polyoxotungstate are described. The dimethylammonium salt [Me2NH2]4[PW11ReVO40] was obtained as analytically pure homogeneous black-purple crystals by reacting mono-lacunary Keggin polyoxotungstate with [ReIVCl6]2- in water, followed by crystallization from acetone at ca. 5 °C. Single-crystal X-ray structural analysis of [PW11ReVO40]4- revealed a monomeric structure with overall Td symmetry. Characterization of [Me2NH2]4[PW11ReVO40] was also accomplished by elemental analysis, magnetic susceptibility, TG/DTA, FTIR, UV-vis, diffuse reflectance (DR) UV-vis, and solution 31P-NMR spectroscopy. Furthermore, [PW11ReVO40]4- and the Dawson-type dirhenium(V)-oxido-bridged polyoxotungstate [O{ReV(OH)(α2-P2W17O61)}2]14- were supported onto anatase TiO2 surface by the precipitation methods using CsCl and Pt(NH3)4Cl2. With these materials, hydrogen evolution from water in the presence of EDTA·2Na (ethylenediamine tetraacetic acid disodium salt) under visible light irradiation (≥400 nm) was achieved.

In this study, we investigated the photochemical production of hydrogen from water using bio-inspired heterogeneous microporous porphyrin coordination lattices (PCLs), [Ru2(MTCPP)BF4] (M = H2 (PCL-1), Zn (PCL-2); TCPP = Tetrakis(4-carboxyphenyl)porphyrin), under visible (380 nm <) and UV (320 nm <) light irradiations. In the presence of Na2EDTA (as a sacrificial donor) and MV2+ (methyl-vilologen; as a electron relay), PCLs exhibits photocatalytic activity for hydrogen evolution; the maximum amounts of turnover numbers (TONs) of PCL-1 and PCL-2 at 24 h irradiation were 20.8 and 29.9, respectively. In the catalytic reactions, the relation between PCLs and MV2+ was similar to the relation between a [cytochrome c3 hydrogenase] pair and lysine residues in enzymatic reactions. By using the hydrogen production rate and the MV+ (methyl-vilologen radical-cation) concentration, kinetic parameters such as affinities between MV+ and PCLs, maximum reaction rate, and total efficiency of the reaction are introduced using the Michaelis-Menten equation. These parameters indicated that PCLs are good artificial enzyme model catalysts. The stability of the PCLs after the catalytic reactions was confirmed by X-ray photoelectron spectroscopy and Fourier transform-infrared spectra. These results indicated that the frameworks of PCLs are stable for this catalytic reaction.

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The electronic configurations and the nature of chemical bonds of the classical lantern-type dinuclear rhodium(II) tetraacetato complexes [Rh2(CH3COO)4(L)2] (L = H2O, free) have been carefully investigated with broken symmetry (BS) Hartree–Fock (HF), BS density functional theory (DFT), and BS hybrid DFT (HDFT) methods. Several electronic configurations have been proposed for the ground states of the [Rh2(RCOO)4(H2O)2] complexes. In this study, we concluded that those different electronic configurations originate from the position of the axial H2Os, and not along the Rh–Rh length. The BS(U)B3LYP calculation indicates that the stability of the σ and δ orbitals changed when the Rh–OH2 length was 2.35 Å. The natural orbital (NO) analyses and chemical indices clearly indicate that there is a σ-type single bond between the Rh ions, and that the axial H2Os does not affect the overlap.

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