Stabilization of cobalt(I) by the tripodal ligands tris(2-pyridyl)methane and tris(2-pyridyl)phosphine. Structural, spectroscopic and ab initio studies of the [CoL(2)](n+) species

The nature of bonding in a series of complexes [CoL(2)](n+) [L = the tripodal ligand tris(2-pyridyl)methane dr tris(2-pyridyl)phosphine, n = 1-3] has been investigated by single-crystal X-ray diffraction; X-ray absorption and electronic spectroscopy and density functional theory hb initio calculations. The structural Studies reveal that the cobalt ions each exist in a distorted octahedral geometry defined by six N-donor atoms; the cations are all centrosymmetric. In both series of complexes the bond lengths Co-I-N approximate to Co-II-N > Co-III-N. Data from the various studies indicate that the 'cobalt(I)' state of the complex [Co{X(C5H4N-2)(3)}(2)](+) (X = CH or P) is better described by the d(8) cobalt(I)-ligand formulation rather than as d(7) cobalt(II)-ligand radical.