Crystal structures of five halido gold complexes involving piperidine or pyrrolidine as ligands or (protonated) as cations.

In bromido-(pyrrolidine-κ)gold(I) bis-(pyrrolidine-κ)gold(I) bromide, [AuBr(pyr)]·[Au(pyr)]Br (pyr = pyrrolidine, CHN), , alternating [AuBr(pyr)] mol-ecules and [Au(pyr)] cations are connected by aurophilic contacts to form infinite chains of residues parallel to the axis. The chains are cross-linked by three N-H⋯Br hydrogen bonds and an Au⋯Br contact to form a layer structure parallel to the plane. Tri-chlorido-(piperidine-κ)gold(III), [AuCl(pip)] (pip = piperidine, CHN), , consists of mol-ecules with the expected square-planar coordination at the gold atom, which are connected by an N-H⋯Cl hydrogen bond and an Au⋯Cl contact to form a layer structure parallel to the plane. The structures of bis-(piperidinium) tetra-chlorido-aurate(III) chloride, (pipH)[AuCl]Cl, , and bis-(pyrrolidinium) tetra-bromido-aurate(III) bromide, (pyrH)[AuBr]Br, , are closely related but not isotypic. Compound crystallizes in space group ; the Au and two Br atoms of the anion lie in the mirror plane , , 0, whereas the bromide ions occupy special positions 0, 0.5, 0 and 0, 0.5, 0.25, with site symmetry 2/. The NH group forms a hydrogen bond to one bromide ion, and also a three-centre hydrogen bond to the other bromide atom and to a metal-bonded Br atom. The packing involves chains of hydrogen-bonded pyrrolidinium and bromide ions parallel to the axis, combined with a layer structure of [AuBr] and bromide anions, parallel to the plane and involving Au⋯Br and Br⋯Br contacts. Compound , however, crystallizes pseudosymmetrically in space group 2; two chlorine atoms of the anion lie on the twofold axis 0.5, 0.5, , and there are two independent cations. The packing is closely similar to that of , but there are no N-H⋯Cl hydrogen bonds to metal-bonded chlorines. The contact distances Au⋯Cl are appreciably longer than their Au⋯Br counterparts in , whereas the Cl⋯Cl contact is much shorter than Br⋯Br in . Tri-bromido-(piperidine-κ)gold(III) crystallizes as its di-chloro-methane solvate, [AuBr(pip)]·CHCl, . It too displays a square-planar coordination at the gold atom. The packing involves hydrogen bonds N-H⋯Br, stacking of neighbouring AuBr units by Au⋯Br contacts, and a short Br⋯Br contact; these combine to form a layer structure parallel to the plane.