SYNTHESIS, CRYSTAL-STRUCTURE, AND THERMAL-BEHAVIOR OF ORGANICALLY TEMPLATED 3-DIMENSIONAL TUNNEL STRUCTURES BASED ON ALPHA-KEGGIN PHOSPHODODECAMOLYBDATE AND DIAZINES

Three salts of diazonium cation (C4H5N2+) encapsulated alpha-Keggin ph osphododecamolybdate, (pyridazinium)(3)[PMo12O40]. 1/2H(2)O (i), (pyri midinium)(3)[PMO12O40]. 3H(2)O (2), and (pyrazinium)(3)[PMo12O40]. 3H( 2)O (3) have been synthesized at room temperature and atmospheric pres sure in an organic-aqueous medium. Compounds 1-3 crystallize in the tr igonal space group R3. Crystal data for compound 1 is as follows: a = 17.704(6) Angstrom, c = 22.918(3) Angstrom, V = 6221(3) Angstrom(3), Z = 6, R = 0.028 for 3703 observed reflection with I > 3 sigma(I); for compound 2, a = 19.002(1) Angstrom, c = 21.524(1) Angstrom, V = 6745(1 ) Angstrom(3), Z = 6 and R = 0.043 for 2143 observed reflections with I > 2 sigma(I); for compound 3, a = 17.820(2) Angstrom, c = 24.369(2) Angstrom, V= 6701(1) Angstrom(3), Z = 6, and R = 0.047 for 3699 observ ed reflections with I > 3 sigma(1). These compounds contain the Keggin clusters arranged in a three-dimensional tunnel structure where the o rganic templates are sandwiched by two polyanions. Although the three salts are isostructural, the arrangement of organic cations and water molecules relative to the polyanion framework shows some significant d ifferences that have been analyzed by means of ab initio calculations. Differences in the thermal behavior of the three compounds have also been explained on the basis of the different crystal arrangements.