Crystal structures of <i>trans</i> -dibromidobis(4-picoline)gold(III) tetrabromidoaurate(III) nitromethane monosolvate, bis(2-picolinium) tetrabromidoaurate(III) bromide, and five salts of the type picolinium or lutidinium tetrahalogenidoaurate(III)

2-Picolinium tetra-chlorido-aurate(III), (C₆H₈N)[AuCl₄] or (2-PicH)[AuCl₄], <b>1</b>, and 2-picolinium tetra-bromido-aurate(III), (C₆H₈N)[AuBr₄] or (2-PicH)[AuBr₄], <b>2</b>, both crystallize in the space group <i>P</i>1 with <i>Z</i> = 4, but are not isotypic. Bis(2-picolinium) tetra-bromido-aurate(III) bromide, (C₆H₈N)₂[AuBr₄]Br or (2-PicH)₂[AuBr₄]Br, <b>3</b>, crystallizes in the space group <i>P</i>1 with <i>Z</i> = 2. All atoms of <b>1</b>-<b>3</b> lie on general positions. 3-Picolinium tetra-bromido-aurate(III), (C₆H₈N)[AuCl₄] or (3-PicH)[AuBr₄], <b>4</b>, crystallizes in the space group <i>P</i>2₁/<i>c</i> with <i>Z</i> = 4; the two independent anions each display inversion symmetry. <i>trans</i>-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, <b>5</b>, and 4-picolinium tetra-bromido-aurate(III), (C₆H₈N)[AuBr₄] or (4-PicH)[AuBr₄], <b>6</b>, both crystallize in the space group <i>P</i>1 with <i>Z</i> = 2; both involve two independent anions with inversion symmetry. 2,4-Lutidinium tetra-bromido-aurate(III), (C₇H₁₀N)[AuBr₄] or (2,4-LutH)[AuBr₄], <b>7</b>, crystallizes in the space group <i>P</i>2₁2₁2₁ with <i>Z</i> = 4. All the gold(III) species show the expected square-planar geometry. The main inter-est centres on the packing patterns. In <b>1</b>, hydrogen bonds, Cl⋯Cl contacts, axial Au⋯Cl contacts ('coinage bonds') and Cl⋯π contacts combine to form layers parallel to (101). In <b>2</b>, similar contacts (but involving Br) link the residues to form corrugated layers parallel to the <i>ac</i> plane. In <b>3</b>, 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 <b>4</b>, 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 <b>5</b>, Br⋯Br contacts and coinage bonds link the anions and cations to form a corrugated layer structure parallel to the <i>ac</i> plane, involving six-membered Au₂Br₄ and ten-membered Au₄Br₆ rings. A similar combination of contacts in <b>6</b> leads to a layer structure parallel to the <i>ab</i> plane, also involving a pattern of six- and ten-membered rings topologically analogous to that of <b>5</b>. However, the angles in the rings of the two layers differ appreciably, and <b>6</b> also contains a short Br⋯π contact. In <b>7</b>, a hydrogen bond combines with a coinage bond to produce a ribbon of residues parallel to the <i>a</i> axis. Three further, longer and perhaps borderline, Br⋯Br and Br⋯<i>Cg</i> contacts link the ribbons to form a three-dimensional pattern.