Crystal structures of seven gold(III) complexes of the form LAuX ₃ (L = substituted pyridine, X = Cl or Br)

The structures of seven gold(III) halide derivatives of general formula L Au X 3 ( L = methylpyridines or dimethylpyridines, X = Cl or Br) are presented: trichlorido(2-methylpyridine)gold(III), [AuCl 3 (C 6 H 7 N)], 1 (as two polymorphs 1a and 1b ); tribromido(2-methylpyridine)gold(III), [AuBr 3 (C 6 H 7 N)], 2 ; tribromido(3-methylpyridine)gold(III), [AuBr 3 (C 6 H 7 N)], 3 ; tribromido(2,4-dimethylpyridine)gold(III), [AuBr 3 (C 7 H 9 N)], 4 ; trichlorido(3,5-dimethylpyridine)gold(III), [AuCl 3 (C 7 H 9 N)], 5 ; tribromido(3,5-dimethylpyridine)gold(III), [AuBr 3 (C 7 H 9 N)], 6 , and trichlorido(2,6-dimethylpyridine)gold(III), [AuCl 3 (C 7 H 9 N)], 7 . Additionally, the structure of 8 , the 1:1 adduct of 2 and 6 , [AuBr 3 (C 6 H 7 N)]·[AuBr 3 (C 7 H 9 N)], 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 L Au X 3 involving simple pyridines (taken from the Cambridge Structural Database) are compared with those of 1 – 8 .