Hybrid open frameworks (MIL-n). Part 6 - Hydrothermal synthesis and X-ray powder ab initio structure determination of MIL-11, a series of lanthanide organodiphosphonates with three-dimensional networks, Ln(III)H[O3P(CH2)(n)PO3](n = 1-3)

A series of lanthanide and yttrium propylenediphosphonates has been prepare d hydrothermally (210 degrees C, 4 days) by action of propylenediphosphonic acid on the metal chlorides. The crystal structure of the gadolinium. comp ound (GdH)-H-III[O3P(CH2)(3)PO3] has been determined ab initio from X-ray p owder diffraction data and refined by the Rietveld method. The compound cry stallizes in the monoclinic space group C2/m (no. 12) with a = 8.2141(3) An gstrom, b = 18.9644(8) Angstrom, c = 5.2622(2) Angstrom, beta = 111.999(2)d egrees and Z = 4. The final agreement factors are R-p = 0.113, R-wp = 0.142 , Bragg R = 0.050, R-F = 0.034 and chi(2) = 1.91. In the three-dimensional structure, the gadolinium atoms are eight-coordinated. The framework consis ts of inorganic Gd-P-O sheets joined by organic groups with an interlayer s pacing of 9.58 Angstrom. The entire series of the lanthanide elements and y ttrium give isotypic structures. Attempts with ethylenediphosphonic acid an d gadolinium led to the analogous compound (GaH)-H-III[O3P(CH2)(2)PO3] whic h crystallizes in the monoclinic space group P2(1)/c (no. 14) with cell par ameters a = 5.2918(9), b = 15.975(3), c = 8.338(1) Angstrom, beta = 111.491 (6)degrees, Z = 4(final agreement factors R-p = 0.078, R-wp = 0.105; Bragg R = 0.034, R-F = 0.026 and chi(2) = 1.50), and with an interlamellar distan ce of d = 7.99 Angstrom. Moreover, the action of methylenediphosphonic acid on La, Ce, Pr and Nd chloride led to a similar structure with a shorter in terlamellar distance, d = 7.03 Angstrom for (PrH)-H-III[O3P(CH2)PO3] (space group C2/m, with a = 8.3271(4), b = 14.0645(7), c = 5.3489(3) Angstrom, be ta = 111.433(2)degrees, Z = 4, and final agreement factors R-p = 0.092, R-w p = 0.121, Bragg R = 0.059, R-F = 0.035 and chi(2) = 1.98).