Crystal structures of tri-chlorido-(4-methyl-piperidine)gold(III) and two polymorphs of tri-bromido(4-methyl-piperidine)-gold(III)

Abstract

Tri-chlorido-(4-methyl-piperidine)-gold(III), [AuCl₃(C₆H₁₃N)], 1, crystallizes in Pbca with Z = 8. Tri-bromido-(4-methyl-piperidine)-gold(III), [AuBr₃(C₆H₁₃N)], 2, crystallizes as two polymorphs, 2a in Pnma with Z = 4 (imposed mirror symmetry) and 2b, which is isotypic to 1. The Au-N bonds trans to Cl are somewhat shorter than those trans to Br, and the Au-Cl bonds trans to N are longer than those cis to N, whereas the Au-Br bonds trans to N are slightly shorter than the cis bonds. The methyl and AuX ₃ groups (X = halogen) occupy equatorial positions at the six-membered ring. The packing of all three structures involves chains of mol-ecules with offset stacking of the AuX ₃ moieties associated with short Au⋯X contacts; for 1 and 2b these are reinforced by N-H⋯X hydrogen bonds, whereas for 2a there are no classical hydrogen bonds and the chains are inter-connected by Br⋯Br contacts.

Keywords: crystal structure; gold; hydrogen bonds; methyl­piperidine; polymorph.