Electronic transfer between ligands in the tris(2,2′-bipyridine) complexes consisting of monoanion radicals

Zero-valent tris(2,2'-bipyridine) aluminium ([Al(bpy)3]) is formulated as tris(2,2'-bipyridine (1-)) aluminium(III): each bipyridine ligand traps an electron. The ground-state doublet (2E) is more stabilized than the ground-state quartet (4A1) by a contribution of vacant aluminium 3d(pi) orbitals. The filled ruthenium 4d(pi) orbitals also take part in the spin pairing in the ground state of [Ru(bpy)3]-, a ruthenium(II) complex of three bipyridine monoanions. Both 2E and 4A1 ground states of a system of three monoanions have a common spatial wavefunction but differ only in their spin function and thus they are inert for Jahn-Teller distortion and preferential solvation. The bipyridine monoanion complexes obtained by one- and two-electron reduction of the trisbipyridine metal complexes are in the accidentally degenerate ground states consisting of 2A2, 2E and 1A1, 1E; 3E, 3A2, respectively, which can be admixed by Jahn-Teller distortion and/or preferential solvation. The nonlinear solute-solvent interaction results in the preferential solvation around one of three ligands which stabilizes each trapped electron localized on a single ligand much more than anticipated for the Jahn-Teller distortion mechanism.