• Forster, Paul M.
• Johnstone, Erik V.
• Sørensen, Lasse Kragh
• Todorova, Tanya K.
• Poineau, Frederic
• Galván, Ignacio Fdez
• Czerwinski, Kenneth R.
• Sattelberger, Alfred P.
• Lindh, Roland

Abstract

<p>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.</p>

Topics

• impedance spectroscopy
• molybdenum
• x-ray diffraction
• theory
• space group
• rhenium
• Technetium