Crystal structures of four gold(I) complexes [AuL2]+[AuX2]− and a by-product (L·LH+)[AuBr2]− (L = substituted pyridine, X = Cl or Br)

Abstract

In the four main structures, the anions and cations are connected by aurophilic contacts, hydrogen bonds C—H⋯halogen and (in two cases) C—H⋯Au contacts. In the by-product without pyridinic N coordination a N—H⋯N bond dominates the packing pattern supported by Br⋯Br, H⋯Br, and Au⋯Br contacts.

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

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

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.