Structural systematics of rare earth complexes. XVI. (Maximally) hydrated rare earth(III) bromides

Room-temperature single-crystal X-ray structure determinations carried out on rare earth bromides crystallized from water at room temperature define three series of hydrates LnBr(3).nH(2)O. For Ln = La, Ce, a heptahydrate phase (n = 7) is defined, triclinic , a approximate to 8.6, b approximate to 9.4, c approximate to 8.3 Angstrom, alpha approximate to 108, beta approximate to 99, gamma approximate to 72 degrees, isomorphous with the array described for the 'early' (Ln = La-Pr) rare earth chlorides, being binuclear [(H2O)(7)Ln(mu-Br)(2)Ln(OH2)(7)] Br-4, Z = 1 dimer; conventional R on \F\ were 0.051, 0.042 for 2323, 3451 independent 'observed' (I > 3 sigma(I)) diffractometer reflections respectively. For Ln = Pr(-)Dy, a hexahydrate phase is defined, monoclinic P 2/n, a approximate to 10.0, b approximate to 6.8, c approximate to 8.2 Angstrom, beta approximate to 93.5 degrees, Z = 2 f.u., isomorphous with the array defined for the heavier (Ln = Nd, Lu, Y) rare earth chlorides, being [(H2O)(6)LnBr(2)] Br, with R 0.029, 0.034 for N-o 1590, 1388 respectively. For Ln = Ho(-)Lu, Y, an octahydrate is defined for the first time, monoclinic P 2(1)/n, a approximate to 8.1, b approximate to 16.0, c approximate to 10.1 Angstrom, beta approximate to 94.0 degrees, Z = 4 f.u., a new array of the form [Ln(OH2)(8)] Br-3 emerging, with R 0.061, 0.048, 0.042 for N-o 1191, 2402, 1674 respectively, the metal environment being square antiprismatic.