An Experimental and Theoretical (DFT) Investigation of the Coordination Mode of 2,4‐Dithiouracil (2,4‐dtucH 2 ) in Copper( I ) Complexes with1,2‐Bis(diphenylphosphanyl)benzene (dppbz): The Crystal Structures of [Cu(μ‐Br)(dppbz)] 2 and [CuBr(dppbz)(2,4‐dtucH 2 )]

Novel copper( I ) mixed‐ligand complexes containing 1,2‐bis(diphenylphosphanyl)benzene (dppbz) and 2,4‐dithiouracil (2,4‐dtucH 2 ) ligands have been synthesised by addition of the thione ligand to the dinuclear [Cu(μ‐X)(dppbz)] 2 intermediate in acetonitrile/methanol or acetone solution. The molecular structures of both the precursor [Cu(μ‐Br)(dppbz)] 2 and the [CuBr(dppbz)(2,4‐dtucH 2 )] complexes were established by single‐crystal X‐ray diffraction. Interestingly, the structure of the thione‐free dimer involves two diphosphane‐chelated Cu I centres bridged by two bromide ligands, thus forming a non‐planar Cu 2 Br 2 core. The structure of [CuBr(dppbz)(2,4‐dtucH 2 )] corresponds to a four‐coordinate Cu I centre in a tetrahedral coordination environment with the heterocyclic dithione ligand being coordinated to the metal centre in a unidentate fashion through its exocyclic sulfur donor atom. The structural, bonding and electronic properties of the model complexes [Cu(μ‐X)(dppbz)] 2 and [CuX(dppbz)(2,4‐dtucH 2 )] (X = Cl, Br, or I) are adequately described by DFT/B3LYP computational techniques. All model dinuclear [Cu(μ‐X)(dppbz)] 2 complexes exhibit π‐type MOs delocalised over the entire four‐membered Cu(μ‐X) 2 Cu ring, thereby accounting for the near equivalency of the Cu–X bonds. Moreover, the [Cu(μ‐X)(dppbz)] 2 dimers possess a σ‐type MO corresponding to weak Cu ··· Cu bonding interactions, which further stabilize the Cu(μ‐X) 2 Cu ring. According to our calculations, the interaction energies of the 2,4‐dtucH 2 ligand with the Cu I centre are predicted to be about 13–16 kcal mol –1 . The coordination of the 2,4‐dtucH 2 ligand is further stabilized by an X ··· H–N hydrogen bond that is perpendicular to the plane of the dppbz ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)