Effects of solvents and Lewis bases on the pentacyanocobaltate(II) anion

Abstract

The e.s.r. spectra of [Co(CN)₅]^3– in the presence of various bases are very similar, showing small effects due to weak interactions. With pyridine and diethylamine, hyperfine coupling to N (11.5 and 11.25 G) suggests a stronger interaction. With triphenylphosphine the unpaired electron density in the metal 3d_z² orbital is reduced to only 39% whilst that in a p orbital on phosphours is in excess of 46%. This substantial delocalisation is associated with a considerable ‘flattening’ of the phosphine ligand. In the presence of triphenylarsine and tirphenylstibine, complete reduction of the base takes place. The quadrupole coupling constant, Q′, for [Co(CN)₅]^3– is –2.5 × 10^–4 cm^–1, from which it is deduced that the orbital coefficient β₂² for the d_xy orbital is 0.85.