Synthesis, structure and spectroscopy of clathrate inclusion compounds of cobalt(II), cadmium(II) and zinc(II) trans-4-styrylpyridine nitrates as host with trans-4-styrylpyridine as guest (2:1)

New clathrate inclusion compounds with the general formula, MA(3)X(2) . 1/2G (M = Co(II)( 1), Cd(II)(2), and Zn(II)(3), X = NO3- and A and G = trans-4-styrylpyridine), differing from the usual Werner clathrates, MA(4)X(2) . 2G, have been prepared and characterized by elemental and thermal analyses, IR and electronic spectroscopy and X-ray crystallography. Two representative compounds [Co(stpy)(3)(NO3)(2)] . 1/2stpy (1) and [Cd(stpy)(3)(NO3)(2)] . 1/2 stpy (2) are investigated by single crystal X-ray diffraction. Compound (1) crystallizes in the triclinic space group P (1) over right arrow with a = 10.966(2), b = 12.802(4), c = 16.063(5) Angstrom alpha = 83.38(3), beta = 71.30(2), gamma = 76.88(3) degrees, Z = 2. The structure is made up of discrete molecules of [Co(stpy)(3)(NO3)(2)]. The central Co(II) is surrounded by three stpy nitrogen atoms and four oxygen atoms of two asymmetrically coordinated bidentate nitrate ligands. One of the oxygens is semicoordinated leading to a distorted octahedral geometry for Co(II). Compound (2) crystallizes in the monoclinic space group P2(1)/n with a = 15.597(3), b = 18.313(5), c = 16.188(3) Angstrom beta = 115.998(14)degrees and Z = 4. The structure consists of neutral molecules of [Cd(stpy)(3)(NO3)(2)]. The geometry around Cd(II) is best described as pentagonal bipyramid with four oxygen atoms from symmetrical bidentate nitrate groups and one stpy nitrogen atom in the equatorial positions. Two other nitrogen atoms from stpy ligands occupy the axial positions. The guest stpy molecules are trapped in the centrosymmetrical cavities in lattices of both 1 and 2. Compound 3 is found to be isomorphous with 2. A large splitting of the symmetric and asymmetric NO2 stretching vibrations reveals the presence of bidentate nitrate ligands. Thermogravimetric and DTA studies on the Cd(II) compound, show it to be a thermally stable inclusion compound.