Bis(4-picoline-κN)gold(I) dibromidoaurate(I) and bis(4-picoline-κN)gold(I) dichloridoaurate(I): space-group ambiguity?

Bis(4-picoline-κN)gold(I) dibromidoaurate(I), [Au(C6H7N)2][AuBr2], (I), crystallizes in the monoclinic space group P21/n, with two half cations and one general anion in the asymmetric unit. The cations, located on centres of inversion, assemble to form chains parallel to the a axis, but there are no significant contacts between the cations. Cohesion is provided by flanking anions, which are connected to the cations by short Au···Au contacts and C-H···Br hydrogen bonds, and to each other by Br···Br contacts. The corresponding chloride derivative, [Au(C6H7N)2][AuCl2], (II), is isotypic. A previous structure determination of (II), reported in the space group P1 with very similar axis lengths to those of (I) [Lin et al. (2008). Inorg. Chem. 47, 2543-2551], might be identical to the structure presented here, except that its γ angle of 88.79 (7)° seems to rule out a monoclinic cell. No phase transformation of (II) could be detected on the basis of data sets recorded at 100, 200 and 295 K.