A supramolecular double sulfate salt with a lamellar type: crystal structure and thermal behavior

The synthesis of a series of supramolecular double sulfate salts using transition metals and the aromatic amine α-methylbenzylamine afforded an unexpected hybrid lamellar structure type. (C8H12N)2[M(H2O)4(SO4)2]·2H2O (M = Fe to Zn) crystallizes with a monoclinic structure (S.G. P21/n), with a significant interlamellar distance of more than 16 Å. While comparable to common clay materials, the crystal structure is actually supramolecular; in particular, the mineral layer is built from hydrogen bonds only. The interlayer space is filled with aromatic amines that form chains through C-H···π interactions. The thermal study of all metal compounds revealed good stability of the filled compounds up to 200 °C. The dehydration proceeds differently according to the metal incorporated into the structure. In particular, the stepped release of water drastically modifies the interlayer space, which is able to vary from 14.8 to 18.8 Å, in an opposite way for the Zn-related compound compared to other metals.