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, LnIIIH[O3P(CH2)nPO3](n = 1-3)

A series of lanthanide and yttrium propylenediphosphonates has been prepared hydrothermally (210 degrees C, 4 days) by action of propylenediphosphonic acid on the metal chlorides. The crystal structure of the gadolinium. compound (GdH)-H-III[O3P(CH2)(3)PO3] has been determined ab initio from X-ray powder diffraction data and refined by the Rietveld method. The compound crystallizes in the monoclinic space group C2/m (no. 12) with a = 8.2141(3) Angstrom, b = 18.9644(8) Angstrom, c = 5.2622(2) Angstrom, beta = 111.999(2)degrees 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 consists of inorganic Gd-P-O sheets joined by organic groups with an interlayer spacing of 9.58 Angstrom. The entire series of the lanthanide elements and yttrium give isotypic structures. Attempts with ethylenediphosphonic acid and gadolinium led to the analogous compound (GaH)-H-III[O3P(CH2)(2)PO3] which crystallizes in the monoclinic space group P2(1)/c (no. 14) with cell parameters 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 distance 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 interlamellar 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, beta = 111.433(2)degrees, Z = 4, and final agreement factors R-p = 0.092, R-wp = 0.121, Bragg R = 0.059, R-F = 0.035 and chi(2) = 1.98).