Theoretical Studies on theRedox-Stimulated Isomerizationin Electrochromic Osmium Sulfoxide Complexes.

Redox-stimulatedintramolecular isomerization of the DMSO ligandin [Os(bpy)2(DMSO)2]2+(bpy = 2,2′-bipyridine;DMSO = dimethyl sulfoxide) was explored theoretically for better understandingthe electrochromic properties of osmium sulfoxide complexes. It isfound that the HOMO–LUMO gap is decreased because the electrontransfer amount from DMSO1 ligand to Os center using Os–S1linkage is larger than that using Os–O1linkage, which makes the absorption of such electrochromic Os(II)sulfoxide complexes red-shifted. Moreover, it is observed that Os–Olinkage is preferred by the “hard” Os(III) metal andthe “soft” Os(I) metal prefers Os–S linkage,compared with Os(II). Intrinsic reaction pathway calculation resultsdemonstrate that Os–S1→ Os–O1isomerization is favored by Os(II) oxidation, while Os–O1→ Os–S1isomerization is much easierto be triggered by reduction of Os(III) or Os(II). In addition, DMSO2linkage isomerization becomes much harder to proceed attributed tothe increased bond-strength between DMSO2 and Os center upon Os(II)–O1→ Os(II)–S1rearrangement, whichmakes only one DMSO ligand isomerized observed experimentally. [ABSTRACT FROM AUTHOR]