Structure of the hydrated potassium hexamolybdate complex of hexaoxacyclooctadecane (18-crown-6)

Abstract

(C 12H2406)2 . K2M06019. H20, orthorhombic, P2~2121, a = 11.678 (3), b = 11.361 (3), c = 35.84 (1) A, U = 4755 (2)/~3, Z = 4, D x = 2 . 1 0 1 M g m -3, g = 1.77 mm -1 (for Mo Ka). A Mo6029 anion is located between two crown-complex cations forming a sandwich structure. The sandwich structures connect with each other through a water molecule. The water molecule is strongly linked to two K + cations by an ion-dipole interaction. Introduction. The merits of crown complexes in the structural study of polyanions have been described in a preceding paper (Nagano, 1979). Following the structural study of (C12H240~) 2. K2MoO 4. 5H20, in which the MoO~anion is a precursor of polymolybate anions, a series of 18-crown-6 complexes of X2Mo6019 (X = Na, K, Rb and NH4) have been prepared and (CI2H2406)2.K2Mo6019. H20 has been subjected to Xray study. A yellow precipitate was obtained from an aqueous solution of 18-crown-6 and K2MoO 4 heated on a steam-bath for one hour (pH = 1.0; 18-crown6 : K2MoO 4 = 1 : 3). Repeated recrystallization of the precipitate from CH3CN gave lemon-yellow crystals. The intensities of the reflections were measured from a crystal of dimensions 0.35 x 0.40 x 0.40 mm with a Rigaku automatic four-circle diffractometer (graphite monochromator, Mo Ka radiation). The to-scan method was used because of the long c axis. Three reference reflections were measured every 50 reflections; no significant changes were observed over the period of data collection. Intensities of reflections from crystals of polymolybdate salts with a large organic ion as a counter cation are generally weak. The intensities of 3112 independent reflections [20 3a(IFol )] were adopted for the structure determination. The structure was solved by the heavy-atom method and refined by the block-diagonal least-squares technique for non-hydrogen atoms. Anisotropic temperature factors were used for all non-hydrogen atoms. The H atoms of 18-crown-6 molecules were included in the refinement in their idealized positions ( C H = 1.00 A, H C H = 109.47 °, B = 5.0 /~2). The atomic scattering factors and corrections for anomalous dispersion were taken from International Tables for X-ray Crystallography (1974). The function minimized was ~ w(IFol -IFcl) 2, where w = 0.7 for IFol 50.0 and w = 1.0 otherwise. The R value (R = Y wllFol IFcll/~ wlFol) was 0.045. The atomic coordinates are listed in Table 1. The sandwich structure of (CI2H2406)2.K2Mo6019 is shown in Fig. 1. A view of the crystal structure along the b axis is shown in Fig. 2.* * Lists of structure factors, anisotropic thermal parameters and H-atom coordinates have been deposited with the British Library Lending Division as Supplementary Publication No. SUP 34515 (27 pp.). Copies may be obtained through The Executive Secretary, International Union of Crystallography, 5 Abbey Square, Chester CH 1 2HU, England. la0~,,-60~ v~0132la-c,~-6(2) Fig. 1. The sandwich structure of (CI2H2406)2.K2Mo6OIg. The vibration ellipsoids are drawn at the 30% probability level (Johnson, 1965). Aq I is related to Aq by the symmetry of the twofold screw axis parallel to the c axis.