CONTACT STABILIZATION OF HOST COMPLEX MOLECULES DURING CLATHRATE FORMATION: THE PYRIDINE-ZINC NITRATE AND THE PYRIDINE-CADMIUM NITRATE SYSTEMS

Clathrate formation ranges of the phase diagrams of two binary systems Py-Zn(NO3)2 and Py-Cd(NO3)2 (Py = pyridine) were studied. A clathrate of composition [MPy4(NO3)2]·2Py (M = Zn, Cd) was observed in each of the systems. The space group Ccca (orthorhombic system) and the parameters of the unit cells of both clathrates were determined by X-ray analysis of their single crystals. The data obtained show them to be isostructural with the clathrate [NiPy4(NO3)2]·2Py whose structure is known and suggest the actual presence of the host molecules trans-[MPy4(NO3)2] (M = Zn,Cd) inside the clathrate phases. Host complexes do not form as separate compounds but can only arise in clathrate phases due to contact stabilization by the guest molecules. Both Zn- and Cd-clathrates are of constant composition and melt incongruently at 62.3(6) and 106.0(5)°C, respectively, yielding the complexes [ZnPy3(NO3)2] and [CdPy3(NO3)2], these melting congruently at 131.4(5) and 169.5(5)°C, respectively. During thermal decomp...