Structural studies of halide hexaalkylguanidinium salts

Crystal structure of the series of three hexaalkylguanidinium halides (hexa-n-propylguanidinium tri-n-propylguanidinium diiodide (1), hexa-n-butylguanidinium bromide (2) and hexa-n-pentylguanidinium bromide (3) has been revealed and reported for the first time. Investigated hexalkylguanidinium derivatives belong to the group of compounds which find application as phase transfer catalysts, however due to their different structural features related to the length of the aliphatic substituent and the size of the halide anion, they might be potentially useful also for crystal engineering. Compound 1 represents a first example of a crystalline alkylguanidinium salt containing two chemically distinct cations. Performed analysis allowed for detailed description of the geometry of cationic species within 1−3 and enabled its comparison with structurally-similar systems. Investigated compounds showed essential differences in the supramolecular architecture of ions in their crystals. Adjacent tri-n-propylguanidinium cations and the iodide anions in the crystal network of 1 were interacting via the N−H···I− and C−H···I− hydrogen bonds. In the case of both bromides (2 and 3), no hydrogen bonds have been identified.