title: Molecular and Electronic Structure of Re2Br4(PMe3)4.
abstract: The dinuclear rhenium(II) complex Re2Br4(PMe3)4 was prepared from the reduction of [Re2Br8](2-) with (n-Bu4N)BH4 in the presence of PMe3 in propanol. The complex was characterized by single-crystal X-ray diffraction (SCXRD) and UV-visible spectroscopy. It crystallizes in the monoclinic C2/c space group and is isostructural with its molybdenum and technetium analogues. The Re-Re distance (2.2521(3) Å) is slightly longer than the one in Re2Cl4(PMe3)4 (2.247(1) Å). The molecular and electronic structure of Re2X4(PMe3)4 (X = Cl, Br) were studied by multiconfigurational quantum chemical methods. The computed ground-state geometry is in excellent agreement with the experimental structure determined by SCXRD. The calculated total bond order (2.75) is consistent with the presence of an electron-rich triple bond and is similar to the one found for Re2Cl4(PMe3)4. The electronic absorption spectrum of Re2Br4(PMe3)4 was recorded in benzene and shows a series of low-intensity bands in the range 10 000-26 000 cm(-1). The absorption bands were assigned based on calculations of the excitation energies with the multireference wave functions followed by second-order perturbation theory using the CASSCF/CASPT2 method. Calculations predict that the lowest energy band corresponds to the δ* → σ* transition, while the next higher energy bands were attributed to the δ* → π*, δ → σ*, and δ → π* transitions.
authors.affiliation: Department of Chemistry, University of Nevada Las Vegas , Las Vegas, Nevada 89154, United States.
authors.forename: Erik V
authors.initials: EV
authors.lastname: Johnstone
authors.affiliation: Department of Chemistry, University of Nevada Las Vegas , Las Vegas, Nevada 89154, United States.
authors.forename: Frederic
authors.initials: F
authors.lastname: Poineau
authors.affiliation: Laboratoire de Chimie des Processus Biologiques, UMR 8229 CNRS, UPMC-Paris 6, Collège de France , 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France.
authors.forename: Tanya K
authors.initials: TK
authors.lastname: Todorova
authors.affiliation: Department of Chemistry, University of Nevada Las Vegas , Las Vegas, Nevada 89154, United States.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Forster
authors.forename: Lasse K
authors.initials: LK
authors.lastname: Sørensen
authors.forename: Ignacio
authors.initials: I
authors.lastname: Fdez Galván
authors.forename: Roland
authors.initials: R
authors.lastname: Lindh
authors.affiliation: Department of Chemistry, University of Nevada Las Vegas , Las Vegas, Nevada 89154, United States.
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Czerwinski
authors.affiliation: Department of Chemistry, University of Nevada Las Vegas , Las Vegas, Nevada 89154, United States.|Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Alfred P
authors.initials: AP
authors.lastname: Sattelberger