which is the most effective hydrogen evolution catalyst (HEC) among rhodium complexes developed to date. Artificial photosynthesis (AP) systems with [2(H 2 O) 2 ] or [3(H 2 O) 2 ], [Ir(ppy) 2 (bpy)](PF 6 ), and TEA showed highly efficient hydrogen evolution activities; the turnover numbers (TON) of hydrogen evolution per Rh by the AP systems with [2(H 2 O) 2 ] and [3(H 2 O) 2 ] after 12 h of photoirradiation were 3334 and 3138, respectively. Experimental analyses and density functional theory (DFT) calculations afforded valuable insight into the hydrogen evolution mechanism of paddlewheel-type dirhodium complexes; (i) hydrogen evolution activities of the AP systems with [2(H 2 O) 2 ] and [3(H 2 O) 2 ] were slightly lower than that of the AP system with [1(H 2 O) 2 ] despite one-electron reduction potentials of [2(H 2 O) 2 ] and [3(H 2 O) 2 ] lie on the anode side than that of [1(H 2 O) 2 ], and (ii) two different pathways exist during the early stages in the photochemical hydrogen evolution by [2(H 2 O) 2 ] and [3(H 2 O) 2 ]. Moreover, the relative free-energy diagrams estimated by DFT calculations clarified the energy profiles of the mechanism including the rate-determining steps of the hydrogen evolution by [1(H 2 O) 2 ]À [3(H 2 O) 2 ]. ns. The laser pulse, the flash lamp, and the gate of the ICCD was synchronized using a digital pulse generator (DG535, Stanford Research Systems).

The one-dimensional coordination polymer [Rh2(HA)4]n (1G; HA = hexanoate) exhibits a drastic vapochromic color change from green to red upon exposure to pyridine (py) vapor. Heating the red discrete complex...

A novel heteroleptic paddlewheel-type dirhodium (Rh2) complex [Rh2(O2CCH3)3(PABC)] (1; PABC = para-aminobenzenecarboxylate), which has an amino group as a potential donor site for coordination with the metal ion, was synthesized and characterized by 1H NMR, ESI-TOF-MS, infrared spectra, and elemental analysis. The slow evaporation of N,N-dimethylformamide (DMF)-dissolved 1 produces the purple-colored crystalline polymeric species [Rh2(O2CCH3)3 (PABC)(DMF)]n (1P). Single-crystal and powder X-ray diffraction analyses, as well as thermo-gravimetric analysis, clarified that 1P formed a one-dimensional polymeric structure, in which the two axial sites of the Rh2 ion in 1P are coordinated by a DMF molecule and an amino group of the PABC ligand of the neighboring molecule 1, by coordination-induced self-assembly (polymerization) with an Rh-amino bond. The reversible structural change (self-assembly and disassembly transformations) between the discrete species [Rh2(O2CCH3)3(PABC)(DMF)2] (1D; green solution) and the polymeric species 1P (purple solid) was accompanied by a color change, which easily occurred by the dissolution and evaporation procedures with DMF.

The Cover Feature shows the catalytic proton reduction to hydrogen molecule by paddlewheel‐type dirhodium tetracarboxylate complex. In their Full Paper, Yusuke Kataoka et al. reported that the dirhodium complexes with electron withdrawing carboxylate ligands served as highly efficient hydrogen evolution catalysts for the photochemical water reduction reactions when coupled with cyclometalated iridium complex and triethylamine. Combination of experimental analyses and density functional theory (DFT) calculations indicated that two different reaction pathways exist during the early stages in the photochemical hydrogen evolution catalyzed by dirhodium complexes. Moreover, the relative free‐energy diagrams estimated by DFT calculations clarified the energy profiles of the mechanism including the rate‐determining steps of hydrogen evolution catalyzed by dirhodium complexes. More information can be found in the Full Paper by Yusuke Kataoka et al. on page 6218 in Issue 24, 2019 (DOI: 10.1002/cctc.201901534).