Bridge-Dependent Donor-Metal-Acceptor-Metal-Donor (D–M–A–M–D) Systems: From Charge Transfer to Electron Transfer in Dioxolene-Ge-Diimine Complexes

Abstract

Synthesis and structural characterization of a family of germanium-dioxolene complexes with ditopic N-donor ligands (L¹-L⁵) (L¹=1,2-bis(pyridin-2-ylmethylene)hydrazine L²=1,6-bis-(pyridin-2-yl)-2,5-diaza-1,5-hexadiene, L³=N,N-bis(pyridin-2-ylmethylene)-1,4-benzenediamine, L⁴=N,N-bis(pyridin-2-ylmethylene)-(biphenyl)-4,4-diamine, L⁵=2,2’-azopyridine) is reported. The reaction of germanium bis-catecholate with bridging ligands L¹ – L⁴, differing by the nature of the linker between pyridine sites gives rise to dinuclear digermanium complexes (36Cat₂Ge)₂L¹⁻⁴ (36Cat=dianion of 3,6-di-tert-butylcatechol) 1–4 of DMAMD type (donor-metal-acceptor-metal-donor) with a charge transfer in the UV-Vis region. In opposite, the interaction of the 36Cat₂Ge with 2,2’-azopyridine (L⁵) results in the two-electron transfer from the donor 36Cat²⁻ ligands to the azopyridine bridge forming stable open-shell complex 5 [(36SQ)(36CatGe)]₂(L⁵)²⁻ (36SQ=radical-anionic semiquinonate ligand). Molecular structures of compounds 3 and 5 were determined by single crystal X-ray diffraction analysis. Electronic structures of complexes 1–5 were studied by means of DFT calculations.