Wechselwirkungen von Hetero-π-Systemen mit Zentralmetallatomen in niedrigen Oxydationsstufen. ESR-Untersuchungen zur Struktur und Bindung an Niedrig-spin-d5-(S = 1/2)-Tris(benzil-bis-N-phenylimin)vanadium(0) und Bis(benzil-bis-N-phenylimin)cobalt(0)

Interaction of Hetero-π-Systems with Central Metal Atoms in Low Oxidation States. ESR Investigations on Structure and Bonding in Low Spin d⁵-(S = 1/2)-Tris(benzil-bis-N-phenylimine)vanadium(0) and Bis(benzil-bis-N-phenylimine)cobalt(0) ESR investigations on V(N??N)₃ and Co(N??N)₂(N??N: Benzil-bis-N-phenylimine) are reported. The ESR parameters — g, A^V — indicate trigonal coordination geometry (D₃) for V(N??N)₃ disturbed by a small lower-symmetric ligand-field component. Interpretation of these parameters in terms of a ligand-field model for a low-spin d⁵ electronic configuration shows the electronic ground state to be ²A₁ and yields a large value for the trigonal field splitting parameter K. The ESR spectrum of Co(N??N)₂ could be obtained at 4.2 K only. Its rhombic symmetry and the absence of hyperfine interactions with the nuclei ⁵⁹Co and ¹⁴N is consistent with a rhombically distorted, compressed tetrahedral symmetry (D₂) for Co(N??N)₂. The spin-Hamiltonian parameters are discussed in terms of the metal-ligand bond character and the electronic spectrum.