Bond angles in transition-metal tricarbonyl compounds: A test of the theory of hybrid bond orbitals.

The theory of hybrid bond orbitals is used to calculate equations giving the value of the bond angle OC-M-CO in relation to the bond number of the metal-carbonyl bond for tricarbonyl groups in which the transition-metal atom is enneacovalent or octacovalent and the group has approximate trigonal symmetry. For cobalt and iron and their congeners the average experimental values lie within about 1 degrees of the theoretical values for enneacovalence, which are 101.9 degrees for Co(CO)(3) and 94.5 degrees for Fe(CO)(3). This agreement provides strong support for the theory. For Mn(CO)(3) and Cr(CO)(3) the experimental values indicate the average covalence to be about 8.4 and 7.7, respectively, in agreement with considerations based on the electroneutrality principle.