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 [CoL₂]ⁿ⁺ species

Abstract

The nature of bonding in a series of complexes [CoL₂]ⁿ⁺ [L = the tripodal ligand tris(2-pyridyl)methane or 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 ab 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 Coⁱ–N ≈ Coⁱⁱ–N > Coⁱⁱⁱ–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 d⁸ cobalt(I)–ligand formulation rather than as d⁷ cobalt(II)–ligand radical.