The C–O stretching vibrations and force constants of phosphine- and arsine-substituted cobalt carbonyl complexes [LCo(CO)3]2 and [LCo(CO)3]2Hg complexes

Abstract

The i.r. spectra of [LCo(CO)₃]₂ and [{LCo(CO)₃}₂Hg] complexes (L = R₃P, R₃= Et₃,Buⁿ₃, and PhEt₂; L = R₃As, R₃= Et₃,Buⁿ₃, PhEt₂, Ph₂H, and Ph₂Me) have been investigated in the 1800–2050 and 3800–4100 cm^–1 regions and absorption bands due to ν(CO) fundamental and binary combination vibrations are identified and assigned. The frequencies of the former are used to calculate force constants on a non-rigorous model, and these in turn are used to calculate the frequencies of the fundamental ν(CO) vibrations of molecules containing one ¹³CO ligand. Some of the weak absorption bands which lie between 1850 and 2050 cm^–1 may then be attributed to these ‘isotopic molecules whilst others are assigned to the formally i.r.-inactive vibrations of ‘normal’ molecules. The implications of the non-rigorous force constants are discussed.