Crystal structures of trans-di-bromido-bis-(4-picoline)gold(III) tetra-bromido-aurate(III) nitro-methane monosolvate, bis-(2-picolinium) tetra-bromido-aurate(III) bromide, and five salts of the type picolinium or lutidinium tetra-halogenidoaurate(III).

2-Picolinium tetra-chlorido-aurate(III), (C₆H₈N)[AuCl₄] or (2-PicH)[AuCl₄], 1, and 2-picolinium tetra-bromido-aurate(III), (C₆H₈N)[AuBr₄] or (2-PicH)[AuBr₄], 2, both crystallize in the space group P1 with Z = 4, but are not isotypic. Bis(2-picolinium) tetra-bromido-aurate(III) bromide, (C₆H₈N)₂[AuBr₄]Br or (2-PicH)₂[AuBr₄]Br, 3, crystallizes in the space group P1 with Z = 2. All atoms of 1-3 lie on general positions. 3-Picolinium tetra-bromido-aurate(III), (C₆H₈N)[AuCl₄] or (3-PicH)[AuBr₄], 4, crystallizes in the space group P2₁/c with Z = 4; the two independent anions each display inversion symmetry. trans-Di-bromido-bis-(4-picoline)gold(III) tetra-bromido-aurate(III) nitro-methane mono-sol-vate, [AuBr₂(C₆H₇N)₂](AuBr₄]·CH₃NO₂ or [(4-Pic)₂AuBr₂](AuBr₄]·CH₃NO₂, 5, and 4-picolinium tetra-bromido-aurate(III), (C₆H₈N)[AuBr₄] or (4-PicH)[AuBr₄], 6, both crystallize in the space group P1 with Z = 2; both involve two independent anions with inversion symmetry. 2,4-Lutidinium tetra-bromido-aurate(III), (C₇H₁₀N)[AuBr₄] or (2,4-LutH)[AuBr₄], 7, crystallizes in the space group P2₁2₁2₁ with Z = 4. All the gold(III) species show the expected square-planar geometry. The main inter-est centres on the packing patterns. In 1, hydrogen bonds, Cl⋯Cl contacts, axial Au⋯Cl contacts ('coinage bonds') and Cl⋯π contacts combine to form layers parallel to (101). In 2, similar contacts (but involving Br) link the residues to form corrugated layers parallel to the ac plane. In 3, classical hydrogen bonds, Br⋯Br contacts and a coinage bond, all involving the free bromide ion, combine to produce rings of composition Au₂Br₄, which are then linked by another Br⋯Br contact, to form chains of residues parallel to [011]. In 4, hydrogen bonds and a Br⋯Br contact generate chains of residues parallel to [101], which are in turn linked by a Br⋯π contact. In 5, Br⋯Br contacts and coinage bonds link the anions and cations to form a corrugated layer structure parallel to the ac plane, involving six-membered Au₂Br₄ and ten-membered Au₄Br₆ rings. A similar combination of contacts in 6 leads to a layer structure parallel to the ab plane, also involving a pattern of six- and ten-membered rings topologically analogous to that of 5. However, the angles in the rings of the two layers differ appreciably, and 6 also contains a short Br⋯π contact. In 7, a hydrogen bond combines with a coinage bond to produce a ribbon of residues parallel to the a axis. Three further, longer and perhaps borderline, Br⋯Br and Br⋯Cg contacts link the ribbons to form a three-dimensional pattern.