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 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 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.