title: Electronic Structure of Rh(2)(&mgr;-CO)(CO)(2)(H(2)PCH(2)PH(2))(2). An Example of a Non-A-Frame Structure.
abstract: Calculations based on density functional theory (DFT) and Hartree-Fock configuration interaction (HF-CI) methodology have been carried out to investigate the rhodium-rhodium coupling in Rh(2)(CO)(2)(dppm)(2), 1 (dppm = Ph(2)PCH(2)PPh(2)) and in Rh(2)(&mgr;-CO)(CO)(2)(dppm)(2), 2. DFT geometries, obtained with the Dgauss program, are in good agreement with those determined from X-ray, but HF geometries, calculated using the same basis sets, yield bond distances systematically too long. Calculations indicate that the rhodium atoms in 1 are linked by a single bond. The insertion of a semibridging carbonyl between the two metal atoms leads to a shortening of the rhodium-rhodium distance and also to a noticeable weakening of the metal-metal interaction. Both effects, and also the stabilization of the HOMO of 2, are related to an observed change from square planar to tetrahedral of the ligand environment of the Rh atom proximal to the inserted CO. Both MO analysis and bond characterization from the topology of the charge density confirm the existence of a bonding interaction between the semibridging carbonyl and the distal rhodium atom. The electronic structures of the dicationic complex [Rh(2)(CO)(3)(dppm)(2)](2+) and of the A-frame-like, isoelectronic system Rh(2)Br(2)(&mgr;-CO) (dppm)(2) are also discussed. The electron deformation density is derived from 2 by means of several methodological approaches, namely, HF, HF-CI, DFT, and DFT + gradient corrections. The HF deformation density obtained in the plane containing the metals and the three CO ligands is discussed, as well as the "correlation density" obtained from the difference maps DFT - HF and CI - HF.
authors.affiliation: Departament de Química, Universitat Rovira i Virgili, Pç Imperial Tàrraco 1, 43005 Tarragona, Spain, Laboratoire de Chimie Quantique, UPR 139 du CNRS, Université Louis Pasteur, F-67000 Strasbourg, France, and Applications Scientifiques du Calcul Intensif (ASCI), UPR 9029 du CNRS, Orsay, France.
authors.forename: Carles
authors.initials: C
authors.lastname: Bo
authors.forename: Miquel
authors.initials: M
authors.lastname: Costas
authors.forename: Josep M.
authors.initials: JM
authors.lastname: Poblet
authors.forename: Marie-Mad.
authors.initials: MM
authors.lastname: Rohmer
authors.forename: Marc
authors.initials: M
authors.lastname: Benard