A mixed valence zinc dithiolene system with spectator metal and reactor ligands

Neutral complexes of zinc with N,N'-diisopropylpiperazine-2,3-dithione ( Pr₂Dt⁰) and N,N'-dimethylpiperazine-2,3-dithione (Me₂Dt⁰) with chloride or maleonitriledithiolate (mnt^2-) as coligands have been synthesized and characterized. The molecular structures of these zinc complexes have been determined using single crystal X-ray diffractometry. Complexes recrystallize in monoclinic P type systems with zinc adopting a distorted tetrahedral geometry. Two zinc complexes with mixed-valent dithiolene ligands exhibit ligand-to-ligand charge transfer bands. Optimized geometries, molecular vibrations and electronic structures of charge-transfer complexes were calculated using density functional theory (B3LYP/6-311G+(d,p) level). Redox orbitals are shown to be almost exclusively ligand in nature, with a HOMO based heavily on the electron-rich maleonitriledithiolate ligand, and a LUMO comprised mostly of the electron-deficient dithione ligand. Charge transfer is thus believed to proceed from dithiolate HOMO to dithione LUMO, showing ligand-to-ligand redox interplay across a d¹⁰ metal.