Crystal structures of three 4-methyl-piperidinium salts (one as three polymorphs) with tetrahalogenidoaurate(III), halide and (in one case) di-chloro-iodate(I) counter-anions.

The structures of three 4-methyl-pyridinium tetra-halogenidoaurate(III) halides, one also including a di-chloro-iodate(I) anion, are presented. Bis(4-methyl-piperidinium) tetra-bromido-aurate(III) bromide, (4-Me-pipH)[AuBr]Br, , crystallizes in space group 2/ with = 4. The gold atom lies on the inversion centre 0.75, 0.75, 0.5 and the bromide ion on the twofold axis 0.5, , 0.25. Bis(4-methyl-piperidinium) tetra-chlorido-aurate(III) chloride, (4-Me-pipH)[AuCl]Cl, , was obtained as three polymorphs, none of which is isotypic to . Polymorph crystallizes in space group 2/ with = 4; all atoms lie on general positions. Polymorph crystallizes in space group 2/ with = 8; two chloride ions lie on the twofold axes 0, , 1/4 and 0.5, , 0.25. Polymorph crystallizes in space group 1 with = 10; all atoms lie on general positions. Hexa-kis-(4-methyl-piperidinium) tetra-kis-{tetra-chlorido-aurate(III)} di-chloro-iodate(I) chloride, (4-Me-pipH)AuClCl, , crystallizes in space group 1 with = 1; two gold atoms occupy inversion centres, as do the iodine atom and one chloride. This is the first time that we have observed the chlorinating agent PhICl to be 'non-innocent'. The main inter-est centres on the crystal packings, which involve hydrogen, halogen and coinage bonds, and display prominent substructures, one type involving the cations and the halides, and the other type involving the anions. A common feature in the packing of compounds and is a chain consisting of cations linked by halide ions. In , the chains are flanked by tetra-bromido-aurate ions short Br⋯Br contacts. The anions form zigzag chains Br⋯Br⋯Br groupings. In polymorph , chains of cations and chloride ions connect to chains of tetra-chlorido-aurate ions to form a layer structure. In polymorph , cation/chloride chains connect with chains of tetra-chlorido-aurate and chloride anions to form a layer structure; approximately linear Au⋯Cl⋯Au groupings are a striking feature (these are also seen in and ). The asymmetric unit of polymorph is an ensemble 27 Å long. Cation/chloride chains are linked by tetra-chlorido-aurates to form one-dimensional polymers. The tetra-chlorido-aurate and chloride ions associate to form a layer structure. In the packing of compound the chloride/tetra-chlorido-aurate substructure is dominant. Two tetra-chlorido-aurate ions associate with the free chloride to form a layer structure; the layers are linked in the third dimension the third tetra-chloro-aurate and the di-chloro-iodate ions. There is no independent cation/chloride substructure; the cations may be considered as being inter-spersed in the spaces of the anionic substructure, forming hydrogen bonds (some multicentred) to chlorine atoms of the anions. A brief database survey of other structures involving aryl- or alkyl-ammonium cations, tetra-halogenidoaurates and halides is presented, including packing diagrams of selected examples.