[MPy4(NCO)(2)]center dot 2Py clathrates (M = M(II) = Mn, Fe, Co, Ni, Cu, Zn, Cd; Py = pyridine)

The title compounds form an isostructural series and are isomorphic with ot her [MPy4X2].2Py clathrates (XRD, KM4 diffractometer, cell parameters and s pace group Ccca from 17-80 reflections). In the clathrate [NiPy4(NCO)(2)].2 Py studied in detail (XRD, CAD-4 diffractometer, lambda CuKalpha, omega/2 t heta scan mode, theta(max) = 78 degrees, 990 strong reflections, 104 parame ters, R = 0.053), the host molecule has 222 symmetry, and the twofold axes run along the coordination bonds. The trans-octahedral environment of nicke l consists of sir nitrogen atoms of four pyridine and two isocyanate ligand s. The coordination polyhedron is slightly distorted due to changes in the bond lengths. The molecule has a propeller conformation. The guest molecule s lie in the cavities of the crystal structure in conformity with the van d er Waals type of packing. The host complex [NiPy4(NCO)(2)] (XRD, CAD-4 diff ractometer; 4615 strong reflections, 560 parameters, R = 0.037) crystallize s in the triclinic crystal system (space group P1) with two independent asy mmetric molecules in the unit cell. The molecular structure is analogous to that in the clathrate phase, but the coordination angles are severely dist orted; one of the molecules acquires a distorted propeller conformation, an d the other; a centrosymmetric conformation, which is less favorable. While being structurally identical, the [MPy4(NCO)(2)].2Py clathrates differ hea vily in the properties. The first four complexes dissociate to host complex es, and their thermal stability changes in the sequence Mn< Fe< Co< Ni: the Cu and Zn clathrates decompose in one step to dipyridine complexes with de composition of host complexes. Decomposition of rite Cd clathrate follows o ne of these patterns depending on conditions. The results air compared with those for other known systems. Synthetic procedures are given.