3,4-Lutidinium salts with the diiodidoaurate(I) anion: structure of [(3,4-lut) 2 H] + ·[AuI 2 ] - and of two polymorphs of [(3,4-lut) 2 H + ] 2 ·[AuI 2 ] - ·I .

Reactions between potassium tetraiodidoaurate(III) and pyridine (py, C5 H5 N) or 3,4-lutidine (3,4-dimethylpyridine, 3,4-lut, C7 H9 N) were tested as possible sources of azaaromatic complexes of gold(III) iodide, but all identifiable products contained gold(I). The previously known structure dipyridinegold(I) diiodidoaurate(I), [Au(py)2 ]+ ·[AuI2 ]- , (3) [Adams et al. (1982). Z. Anorg. Allg. Chem. 485, 81-91], was redetermined at 100 K. The reactions with 3,4-lutidine gave three different types of crystal in small quantities. 3,4-Dimethylpyridine-3,4-dimethylpyridinium diiodidoaurate(I), [(3,4-lut)2 H]+ ·[AuI2 ]- , (1), consists of an [AuI2 ]- anion on a general position and two [(3,4-lut)2 H]+ cations across twofold axes. Bis(3,4-dimethylpyridine-3,4-dimethylpyridinium) diiodidoaurate(I) iodide, [(3,4-lut)2 H+ ]2 ·[AuI2 ]- ·I- , (2), crystallizes as two polymorphs, each forming pseudosymmetric inversion twins, in the space groups P21 and Pc (but resembling P21 /m and P2/c), respectively. These are essentially identical layer structures differing only in their stacking patterns and thus might be regarded as polytypes.