Reaction products between gold(III) bromide and tetramethylthiourea: dibromobis(tetramethylthiourea)gold(III) dibromoaurate(I) and bromo(tetramethylthiourea)gold(I). Synthesis, crystal and molecular structure, and infrared spectra

Abstract

The compounds dibromobis(tetramethylthiourea)gold(III) dibromoaurate(I), [Au(tmtu)₂Br₂][AuBr₂], and bromo(tetramethylthiourea)gold(I), [Au(tmtu)Br] were prepared and characterized by means of X-ray diffraction. The crystals of [Au(tmtu)₂Br₂][AuBr₂] are triclinic, space group P, (C_i¹, no. 2) with a= 8.223(1), b= 9.987(1), c= 8.078(1)Å, α= 105.74(1), β= 117.20(1), γ= 84.35(1)°, and Z= 2; the crystals of [Au(tmtu)Br] are monoclinic, space group P2₁/c, (C_2h⁵, no. 14) with a= 6.999(1), b= 19.898(1), c= 8.044(1)Å, β= 115.75(1)°, and Z= 4. The structures were solved by the heavy-atom method, and least-squares refinement of structural parameters led to a conventional R factor of 0.034 (R′= 0.034) for 1 677 and R= 0.028 (R′= 0.029) for 1 271 independent reflections for [Au(tmtu)₂Br₂][AuBr₂] and [Au(tmtu)Br] respectively. The compound [Au(tmtu)₂Br₂][AuBr₂] is ionic. The structure consists of centrosymmetric units in which the two gold atoms are four- and two-co-ordinated, respectively. The ligand is trans-co-ordinated to the gold (III) of the cationic part of the compound, together with two bromine atoms forming a square-planar geometry; the anionic part is formed by linearly co-ordinate dibromoaurate(I). The structure of [Au(tmtu)Br] consists of two-co-ordinated gold(I) units. Each tetramethylthiourea is bonded by the sulphur atom. Infrared bands are diagnostic of the co-ordination environments around the metal atoms.