Structure and internal rotation in quadruply bonded α-Mo 2Cl 4(P–P) 2 complexes: a density functional theory study of the cis-Mo 2Cl 4(PH 3) 4 complex

Abstract

The cis-Mo 2Cl 4(PH 3) 4 complex is used as a model for the α-isomer of the Mo 2Cl 4(P–P) 2 complexes where P–P is a diphosphine ligand. Density functional theory calculations with the B3LYP functional are performed for the lowest singlet (δ 2) and triplet ( 3 δδ ∗) states. The eclipsed C 2h conformation is found to be the most stable structure for both these electronic states, the singlet state being the electronic ground state. The singlet–triplet energy difference, which gives a measure of the δ-bond energy, is equal to 10.9 kcal/mol (spin-projected broken-symmetry calculations). A rotational barrier around the Mo–Mo bond of about 27 kcal/mol is found for both electronic states, the singlet state remaining the electronic ground state whatever the value of the internal rotational angle.