The asymmetric unit of the solvated title compound, (C7H18N3)4[Bi4Cl16]·2CH3CN, comprises two cations, one half [Bi4Cl16]4−ion and one acetonitrile molecule. OneN,N,N′,N′,N′′,N′′-hexamethylguanidinium ion shows orientational disorder and two sets of N- and C-atom positions were found, with an occupancy ratio of 0.941 (2):0.059 (2). The second cation is not disordered. The C—N bond lengths in the two guanidinium ions range from 1.334 (17) to 1.341 (17) Å, indicating double-bond character and

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... ting towards charge delocalization within the NCN planes. The four BiIIIions are coordinated by six chloride ions in distorted octahedral manner. Two [Bi2Cl8]2−dimers are fused together, forming a centrosymmetric tetranuclear [Bi4Cl16]4−cluster. The bond lengths of bismuth to the terminal chlorides [2.4982 (7)–2.5509 (6) Å] are shorter than those of the double and triply bridging ones [2.7052 (6)–3.0320 (6) Å]. The acetonitrile solvent molecule is disordered over two positions, with an occupancy ratio of 0.818 (4):0.182 (4) for the two orientations. The crystal structure is stabilized by a three-dimensional network of C—H...Cl hydrogen bonds.