Crystal structures of four gold(I) complexes [AuL 2]+[AuX 2]− and a by-product (L·LH+)[AuBr2]− (L = substituted pyridine, X = Cl or Br)

Abstract

Bis(2-methylpyridine)gold(I) dibromidoaurate(I), [Au(C6H7N)2][AuBr2], (1), crystallizes in space group C2/c with Z = 4. Both gold atoms lie on twofold axes and are connected by an aurophilic contact. A second aurophilic contact leads to infinite chains of alternating cations and anions parallel to the b axis, and the residues are further connected by a short H...Au contact and a borderline Br...Br contact. Bis(3-methylpyridine)gold(I) dibromidoaurate(I), [Au(C6H7N)2][AuBr2], (2), crystallizes in space group C2/m with Z = 2. Both gold atoms lie on special positions with symmetry 2/m and are connected by an aurophilic contact; all other atoms except for one methyl hydrogen lie in mirror planes. The extended structure is closely analogous to that of 1, although the structures are formally not isotypic. Bis(3,5-dimethylpyridine)gold(I) dichloridoaurate(I), [Au(C7H9N)2][AuCl2], (3) crystallizes in space group P\overline{1} with Z = 2. The cation lies on a general position, and there are two independent anions in which the gold atoms lie on inversion centres. The cation and one anion associate via three short H...Cl contacts to form a ribbon structure parallel to the b axis; aurophilic contacts link adjacent ribbons. Bis(3,5-dimethylpyridine)gold(I) dibromidoaurate(I), [Au(C7H9N)2][AuBr2], (4) is isotypic to 3. Attempts to make similar compounds involving 2-bromopyridine led instead to 2-bromopyridinium dibromidoaurate(I)–2-bromopyridine (1/1), (C5H5BrN)[AuBr2]·C5H4BrN, (5), which crystallizes in space group P\overline{1} with Z = 2; all atoms lie on general positions. The 2-bromopyridinium cation is linked to the 2-bromopyridine molecule by an N—H...N hydrogen bond. Two formula units aggregate to form inversion-symmetric dimers involving Br...Br, Au...Br and H...Br contacts.