Pressure-tuning vibrational spectra of the heterobimetallic complexes, Ph3MCo(CO)4 (M = Sn, Pb)

Vibrational spectra of two crystalline organometallic complexes of the type, Ph3MCo(CO)4 (Ph = C6H5; M = Sn, Pb), have been recorded at ambient temperature and a range of high pressures up to ∼56 kbar with the aid of diamond-anvil cells (DACs). The IR and Raman data indicate that the SnIV–CoI and PbIV–CoI metal–metal bonded complexes undergo structural transformations at around 33 and 24 kbar, respectively. The pressure dependences of the ν(Sn–Co) and ν(Pb–Co) modes are comparable in the low-pressure phase (about 0.06 cm−1 kbar−1), but are quite different in the high-pressure phase (0.37 and 0.08 cm−1 kbar−1), respectively. The negative pressure dependences of some of the ν(CO) modes suggest that π-backbonding interactions between the Co atom and the CO groups in both compounds are appreciably strengthened with increasing pressure. Possible reasons for the lower phase-transition pressure for the lead (IV) compound are discussed.