CO, cationic and dicationic complexes are common. RNC ligands are typically terminal, but bridging RNC ligands are common. Bridging isocyanides are always bent. General trends can be appreciated by inspection of the homoleptic complexes of the first row transition metals. Homoleptic complexes IR spectroscopy The νC≡N band in isocyanides is intense in the range of 2165–2110 cm−1. The value of νC≡N is diagnostic of the electronic character of the complex. In complexes where RNC is primarily a sigma donor ligand, νC≡N shifts to higher energies vs free isocyanide. Thus, for , νC≡N = 2152, 2120 cm−l. In contrast, for the electron-rich species Fe2(CNEt)9, νC≡N = 2060, 1920, 1701, 1652 cm−l. See also Cyanometalate - coordination compounds containing cyanide ligands (coordinating via C) Transition metal nitrile complexes - coordination compounds containing nitrile ligands, which are isomers of isonitriles References Coordination complexes Isocyanides