Spectroscopic studies on matrix-isolated metal carbonyls. Part II. Infrared spectra and structures of Pd(CO)4, Pd(CO)3, Pd(CO)2, and PdCO

Abstract

The co-condensation of palladium atoms with carbon monoxide in inert matrices at low temperatures leads to the formation of binary palladium carbonyls. This paper describes the characterisation of these using i.r. spectroscopy, and with the aid of C¹⁸O isotope enrichment, the four most prominent species are shown to be Pd(CO)₄T_d, Pd(CO)₃D_3h, Pd(CO)₂D_∞h, and PdCO. Diffusion studies indicate that the lower carbonyls readily react with excess CO to yield Pd(CO)₄, and that this species is stable in a xenon matrix up to ca. 80 K. The appropriate principal and interaction carbonyl force constants are evaluated for all four species, and an estimate is also obtained for the palladium–carbon stretching force constant in Pd(CO)₄