Structural systematics of rare earth complexes. XIII - ('Maximally') hydrated (heavy) rare earth nitrates

Room-temperature single-crystal X-ray structure determinations are known for a number of 'maximally hydrated' nitrates of, in particular, the lighter lanthanoid elements; in all cases, all nitrates coordinate as O,O'-bidentate ligands so that the series may be represented at the outset as Ln(O2NO)(3).x H2O. Two distinct triclinic <P(1)over bar> hexahydrate phases of similar cell dimensions are recognized, the most distinctive distinguishing feature being that in the La, Ce phase the 11-coordinate Ln is surrounded by three O,O'-bidentate nitrate and five O-unidentate water molecule ligands; the domain of the other, with four coordinated water molecules, extends from Ln = Pr to Ln = Dy (inclusive of Y). At local ambience, we have crystallized heavier members of the series as pentahydrates, isomorphous with the previously characterized Ln = Eu example, also containing a molecule of the form [Ln(O2NO)(3)(OH2)(4)] (with a molecule of water of crystallization), but a different stereoisomer to that found in the Ln = Pr(-)Dy array. Structure determinations are recorded for Ln = Dy, Er, Yb, conventional R on \F\ 0.042, 0.034, 0.029 for N-o = 3858, 3980, 3935 independent 'observed' (I > 3 sigma(I)) diffractometer reflections. For Ln = Lu a new tetrahydrate phase is described, monoclinic P2(1)/n, a 7.379(7), b 10.364(5), c 14.26(1) Angstrom, beta 96.09(7)degrees, Z = 4, R 0.048 for N-o 2324, together with a new triclinic <P(1)over bar> trihydrate, a 12.591(4), b 12.144(3), c 7.355(2) Angstrom, alpha 80.22(2), beta 77.68(3), gamma 62.30(2)degrees, Z = 4, R 0.051 for N-o 4552. In both of the latter, Lu is nine-coordinate, with three bidentate nitrate groups and three coordinated water molecules; remarkably, the two independent molecules of the asymmetric unit in the triclinic phase are distinct isomers, one having the water molecules fac, derivative of the 10-coordinate array of the Pr(-)Yb series with quasi-3 symmetry, while the other, like that in the monoclinic phase, is mer.