PHASE AND STRUCTURAL STUDY OF CLATHRATE FORMATION IN THE [ZN (MEPY)2(NCS)2]-MEPY SYSTEM (MEPY = 4-METHYLPYRIDINE)

A phase diagram of the [Zn(MePy)2(NCS)2]-MePy binary system has been s tudied by DTA and solubility methods. Two compounds melting incongruen tly (at 63 and 57-degrees-C) have been discovered in the system. They have been obtained as separate phases with crystals of different shape (needles and octahedra). Their composition has been determined by ana lytical methods and verified by X-ray structural analysis: [Zn(MePy)4( NCS)2] . 0.67 MePy.xH2O, where x depends on the synthesis conditions, and [Zn(MePy)4(NCS)2].MePy, respectively. The preliminary X-ray study of the first compound (at -100-degrees-C) has shown it to be isostruct ural with The known clathrates of the common formula [M(MePy)4(NCS)2] . 0.67MePy.xH2O, where M = Cu, Mn, Mg and x = 0 - 0.33. The unit cell parameters are as follows: a = 27.20(1), c = 11.202(4) angstrom, space group R3BAR, Z = 9. The X-ray study of [Zn(MePy)4(NCS)2].MePy (at -50 -degrees-C) has shown at to be analogous to the 'organic zeolite' beta -phase with the guest MePy molecules located in the channels formed by molecular packing of the [Zn(MePy)4(NCS)2] host. The cell is tetragon al, the space group I4(1)/a, a = 16.845(6), c = 23.496(7) angstrom, V = 6667(4) angstrom3, Z = 8, D(calc.) = 1.289 g cm-3, R = 0.074. The zi nc cation is surrounded by a slightly irregular octahedron of six nitr ogen atoms of the MePy and NCS ligands. The crystallisation field of t he host [Zn(MePy)4(NCS)2] complex in the temperature range concerned i s absent in the phase diagram. It suggests contact stabilization of th e [Zn(MePy)4(NCS)2] molecule by the guest in the clathrates.