Structural, electronic and magnetic properties of metal–metal bonded dinuclear rhenium complexes bridged by organocyanide acceptor ligands

Abstract

The syntheses, spectroscopic properties, redox chemistry, and solid-state structures of products obtained from the reaction of Re₂Cl₄(dppm)₂ (dppm = bis(diphenylphosphino) methane) with the polycyano acceptors TCNQ (7,7,8,8-tetracyanoquinodimethanido) and DM-DCNQI (2,5-dimethyl-N,N′-dicyanoquinonediimine) are described. The compounds [Re₂Cl₄(dppm)₂]₂(μ-TCNQ), 1, and [Re₂Cl₄(dppm)₂]₂(μ-DM-DCNQI), 2, have been prepared by reaction of two equivalents of Re₂Cl₄(dppm)₂ with TCNQ and DMDCNQI, respectively, in THF or CH₂Cl₂. A single-crystal X-ray crystallographic study of [Re₂Cl₄(dppm)₂]₂(μ-TCNQ)·10THF revealed the presence of a trans-μ₂ bidentate mode for the bridging TCNQ ligand that joins two Re₂Cl₄(dppm)₂ molecules through equatorial positions. In a similar fashion, the compound [Re₂Cl₄(dppm)₂]₂(μ-DM-DCNQI)·10THF consists of two Re₂ units coordinated to the two nitrile positions of the DM-DCNQI ligand. The electronic properties of both compounds are unusual in that they exhibit intense, broad absorptions that span the near-IR region and extend into the mid-IR. The electrochemistry of the compounds consists of numerous oxidation and reduction processes in the range of +2.0 to −2.0 V as determined by cyclic voltammetry. Both 1 and 2 exhibit temperature independent paramagnetism (TIP) with large χ_TIP values of 7.29 × 10⁻³ and 6.23 × 10⁻³ emu mol⁻¹, respectively.