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.