Polar potassium rare earth nitrates K-2[RE(NO3)(5)(H2O)(2)] (RE = La, Ce, Pr and Nd). I. Crystal growth and crystal structures

摘要

Using a standard evaporation technique at 311 K, large single crystals of the polar orthorhombic potassium rare earth nitrates K2RE(NO3)(5).2H(2)O, where RE = La, Ce, Pr or Nd, of optical quality and dimensions up to 5 x 5 x 4 cm, were grown from aqueous solutions containing a stoichiometric ratio of potassium and rare earth ions (K:RE = 2:1) and a surplus of nitric acid. Detailed structural and crystal chemical analyses of all four isomorphic compounds based on single-crystal X-ray diffraction data were carried out [space group Fdd2; Z = 8; La compound: a = 11.2814 (6), b = 21.480 (1), c = 12.2589 (4) Angstrom, R = 0.94%; Ce compound: a = 11.263 (3), b = 21.404 (3), c 12.230 (4) Angstrom, R = 1.92%; Pr compound: a = 11.213 (2), b = 21.392 (4), c = 12.204 (2) Angstrom, R = 1.58%; Nd compound: a = 11.197 (1). b = 21.378 (1), c = 12.195 (1) Angstrom, R = 1.55%]. The main structural feature is the diaquapentanitratolanthanide(III) group, [RE(NO3)(5)(H2O)(2)](2-), as stated earlier by Eriksson, Larsson, Niinisto & Valkonen [Acta Chem. Scand. Ser. A, (1980), 34, 567-572] for the La compound. The rare earth atoms are surrounded by 12 O atoms, two of which belong to water molecules, the remaining ten belonging to five bidentate nitrate groups. The coordination polyhedron [REO12] is a distorted icosahedron; its geometry is discussed using a simple hard-sphere model. (C) 2000 International Union of Crystallography Printed in Great Britain - all rights reserved. [References: 24]