Structural preferences of quadruply bonded bimetallic complexes. A DFT study of the chelated (alpha) and bridged (beta) isomers in Mo2Cl4(H2P(CH2)(n) PH2)(2) (n=1, 2)

摘要

The structure of the quadruply bonded Mo2Cl4(H2P(CH2)(2)PH2)(2) (n = 1, 2) bimetallic complexes, with two chelating (alpha isomer) or two bridging (beta isomer) diphosphine ligands, is studied by means of DFT calculations with the B3LYP functional. For each complex (1-alpha, 1-beta and 2-alpha, 2-beta, for n = 1 and 2, respectively), full geometry optimization is performed for both the lowest singlet (delta(2)) and triplet ((3)delta delta*) states. The chelated or isomers (1-alpha and 2-alpha) adopt an essentially eclipsed conformation in both the singlet and the triplet states. The 1-beta complex is found to be staggered in the triplet state. Three structures are optimized for the 2-beta isomer with a chair (2-beta(c)), a twist (2-beta(t)) or a boat (2-beta(b)) conformation of the Mo-P-C-C-P-Mo six-membered rings. The 2-beta(c) and 2-beta(t) complexes adopt a twisted conformation in both the singlet and the triplet states while the 2-beta(b) complex is eclipsed in the singlet state. A singlet ground state is found for all these complexes, the P isomer being more stable than the or isomer by 17.1 and 7.0 kcal mol(-t) for n = 1 and n = 2, respectively. These geometrical and energetic results are discussed with respect to available experimental data. (C) 2000 Elsevier Science S.A. All rights reserved. [References: 51]