Crystal structures of seven gold(III) complexes of the form LAuX3 (L = substituted pyridine, X = Cl or Br)

Abstract

The structures of seven gold(III) halide derivatives of general formula LAuX3 (L = methylpyridines or dimethylpyridines, X = Cl or Br) are presented: trichlorido(2-methylpyridine)gold(III), [AuCl3(C6H7N)], 1 (as two polymorphs 1a and 1b); tribromido(2-methylpyridine)gold(III), [AuBr3(C6H7N)], 2; tribromido(3-methylpyridine)gold(III), [AuBr3(C6H7N)], 3; tribromido(2,4-dimethylpyridine)gold(III), [AuBr3(C7H9N)], 4; trichlorido(3,5-dimethylpyridine)gold(III), [AuCl3(C7H9N)], 5; tribromido(3,5-dimethylpyridine)gold(III), [AuBr3(C7H9N)], 6, and trichlorido(2,6-dimethylpyridine)gold(III), [AuCl3(C7H9N)], 7. Additionally, the structure of 8, the 1:1 adduct of 2 and 6, [AuBr3(C6H7N)]·[AuBr3(C7H9N)], is included. All the structures crystallize solvent-free, and all have Z′ = 1 except for 5 and 7, which display crystallographic twofold rotation symmetry, and 4, which has Z′ = 2. 1a and 2 are isotypic. The coordination geometry at the gold(III) atoms is, as expected, square-planar. Four of the crystals (1a, 1b, 2 and 8) were non-merohedral twins, and these structures were refined using the ‘HKLF 5’ method. The largest interplanar angles between the pyridine ring and the coordination plane are observed for those structures with a 2-methyl substituent of the pyridine ring. The Au—N bonds are consistently longer trans to Br (average 2.059 Å) than trans to Cl (average 2.036 Å). In the crystal packing, a frequent feature is the offset-stacked and approximately rectangular dimeric moiety (Au—X)2, with antiparallel Au—X bonds linked by Au...X contacts at the vacant positions axial to the coordination plane. The dimers are connected by further secondary interactions (Au...X or X...X contacts, `weak' C—H...X hydrogen bonds) to form chain, double chain (`ladder') or layer structures, and in several cases linked again in the third dimension. Only 1b and 7 contain no offset dimers; these structures instead involve C—H...Cl hydrogen bonds combined with Cl...Cl contacts (1b) or Cl...π contacts (7). The packing patterns of seven further complexes LAuX3 involving simple pyridines (taken from the Cambridge Structural Database) are compared with those of 1–8.

Keywords

• crystal structure
• gold
• pyridine
• polymorphs
• twinning
• halogen bonds
• coinage bonds