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

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(C₆H_7N)], 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. [ABSTRACT FROM AUTHOR]