Electron-Transfer Barriers and Metal-Ligand Bonding as a Function of Metal Oxidation State. 2. Crystal and Molecular Structures of Tris(2,2′-bipyridine)cobalt(II) Dichloride-2-Water-Ethanol and Tris(2,2′-bipyridine)cobalt(I) Chloride-Water

The structures of tris(2,2′-bipyridine)cobalt(II) dichloride-2-water-ethanol, [Co(C,10H8N2)₃]Cl2.2H₂O.C2H5OH (1), and tris(2,2′-bipyridine)cobalt(I) chloride-water, Co(C10H8N2)₃Cl-H₂O (2), have been determined in order to compare bonding of the high-spin d7 and high-spin d8 configurations and to better understand the electron-transfer reactivity of this couple. Compound 1 crystallizes in the hexagonal crystal system, space group P6522, with a = 13.403 (2) Å, c = 62.566 (10) Å, and Z = 12. The structure refined to a final R value of 0.056. The coordination sphere consists of the six nitrogen atoms of the three bipyridine ligands in an octahedral arrangement about the cobalt with an average Co-N bond length of 2.128 (8) Å. One of the chloride ions is surrounded by twelve C-H-Cl hydrogen bonds involving the H₃ and H₃’ protons on the bipyridine ligands. Compound 2 crystallizes in the orthorhombic crystal system, space group Pna21 with a - 9.713 (6) Å, b = 21.666 (10) Å, c = 13.062 (7) Å, and Z = 4. The structure refined to a final R value of 0.084. The geometry of the coordination sphere of 2 is almost identical with that of 1, with an average Co-N bond length of 2.11 (2) Å. Hydrogen bonding between the H₃ and H₃’ protons on the bipyridine ligand and the chloride ion is also observed in 2. The C-H.Cl hydrogen bonding observed in these complexes and the bond length changes in 1, 2, and tris(2,2′-bipyridine)cobalt(III) are discussed and related to electron-transfer barriers for the series.