The Nature of the M≡E Bond: Theoretical Investigation of the Molecules [(RO) 3 M≡E] (M = Mo, W; E = N, P, As, Sb, Bi; R = H, Me) and [(Me 3 CO) 3 Mo≡P]

The electronic and molecular structures of the metal‐pnicogen complexes [(RO) 3 M≡E] (M = Mo, W; E = N, P, As, Sb, Bi; R = H, Me) and [(Me 3 CO) 3 M≡P] have been investigated at the DFT level using the exchange correlation functionals B3LYP and BP86. The nature of the M≡E interactions was analyzed with charge and energy decomposition methods. The bonding analyses show that the metal‐pnicogen bonds are genuine triple bonds containing a σ‐ and a degenerate π‐bond. The M−E σ‐bonds are always polarized towards the pnicogen atom E, particularly for the nitrogen complexes. The M−N π‐bonds are also polarized towards nitrogen, while the π‐bonds of the heavier pnicogens P−Bi show a small polarization towards the metal atom. The M−E σ‐bonds at the pnicogen E are sp n ‐hybridized; the p character is always > 80% of the total AO contribution. The hybridization of the metal atoms in the nitrido complexes is approximately sd 2 and that in the heavier homologues, approximately sd. The ratio of the energy contributions of the σ‐ and π‐orbitals to the covalent bonding in [(HO) 3 M≡E] is about 50:50 for all pnicogen atoms E. The metal−nitrido bonds in [(HO) 3 M≡N] are more covalent than electrostatic. The covalent character becomes smaller when the pnicogen atom becomes heavier with the trend N >> P > As > Sb > Bi. The [(HO) 3 M≡E] tungsten complexes have stronger bonds that are slightly less covalent than the molybdenum complexes, the π‐bonding contribution in the former species is slightly larger than in the latter. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)