Metal carbonyl complexes

This chapter discusses metal carbonyl complexes, one of the most important classes of organometallic compounds. Carbon monoxide (CO) binds firmly to blood haemoglobin and renders it unavailable for oxygen transport. Metal carbonyls, in particular the volatile compounds, are therefore highly toxic; nickel tetracarbonyl Ni(CO)4 is a very potent carcinogen. The structures of metal carbonyls can be explained using the 18-electron rule. This is fulfilled if Cr, Fe, and Ni bind six, five, and four CO ligands, respectively, to give monomeric compounds. The carbonyls of Mn and Co form metal–metal bonded dimers to attain an 18 VE configuration. The chapter then looks at metal carbonyl anions, metal carbonyl hydrides, metal carbonyl halides, and metal carbonyl clusters.