An Exploration of the Structural and Bonding Variability in Mixed‐Ligand Benzimidazole‐2‐thione(bromo)(triarylphosphane)dicopper( I ) Complexes with Diamond‐Shaped Cu 2 (μ‐X) 2 Core Structures

Reaction of copper( I ) bromide with benz‐1,3‐imidazole‐2‐thione (bzimtH 2 ) in the presence of one equivalent of triphenylphosphane (PPh 3 ), tri‐ meta ‐tolylphosphane (tmtp) or tri‐ para ‐tolylphosphane (tptp) in acetonitrile/methanol solvent afforded dinuclear complexes formulated as [CuBr(bzimtH 2 )(PR 3 )] 2 . The new complexes were characterized by IR, UV/Vis, and 1 H NMR spectroscopy, while the crystal structures of [{CuBr(μ 2 ‐S‐bzimtH 2 )(PPh 3 )} 2 ] 0.78 [{Cu(μ 2 ‐Br)(PPh 3 )(bzimtH 2 )} 2 ] 0.22 ( 1 ), [CuBr(μ 2 ‐S‐bzimtH 2 )(tmtp)] 2 ( 2 ) and [CuBr(μ 2 ‐S‐bzimtH 2 )(tptp)] 2 ( 3 ) were determined by single‐crystal X‐ray diffraction methods. In complex 1 , with spectator PPh 3 ligands, the unit cell of the crystal consists of two different half‐molecules, both corresponding to the formula [CuBr(bzimtH 2 )(PPh 3 )] 2 . One of the two molecules (molecule A ) is a symmetrical dicopper( I ) complex in which the exocyclic thione S‐atoms serve as bridges between the Cu I ions. The second one (molecule B ) is disordered and can be resolved into two separate entities, one μ 2 ‐S dicopper( I ) complex, similar to molecule A (molecule B1 ), and another one (molecule B2 ) involving μ 2 ‐Br bridges. In contrast, in complexes 2 and 3 , with spectator tmtp and tptp ligands, only the bzimtH 2 ‐bridged dicopper complexes are formed. Density functional calculations at the B3LYP level of theory provided a satisfactory description of the structural, bonding, electronic and related properties of all dicopper complexes exhibiting the “diamond‐shaped” Cu 2 (μ‐X) 2 (X = S or Br) core structures and account well for their structural preferences. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)