The M–M, M–H, and M–CO bonding interactions existing in the group 7 transition metal carbonyl complexes [M(CO)] and [M(μ-H)(CO)] (M = Mn, Tc, Re) have been theoretically studied under the perspective of the Quantum Theory of Atoms in Molecules (QTAIM). Several local and integral topological properties of the electron density involved in these interactions, as well as the source function (SF) and the electron localization function, have been computed. The results confirm that the metal atoms in the binuclear [M(CO)] complexes are connected through a localized M–M bond that implicates little electron density (it increases from M = Mn to Tc and Re). On the other hand, such a bonding has not been found in the trinuclear [M(μ-H)(CO)] complexes, which, instead, contain a 6c–6e bonding interaction delocalized over their six-membered M(μ-H) ring, as revealed by the non-negligible non-bonding delocalization indexes. The existence of significant CO to M π-back-donation, slightly higher in the trinuclear clusters than in the binuclear complexes, is indicated by the M···O delocalization indexes and SF calculations.

This work has been supported by MINECO-FEDER projects (MAT2013-40950-R and CTQ2013-40619-P) and Gobierno del Principado de Asturias grants (GRUPIN14-060 and GRUPIN14-009).

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