Polar potassium rare earth nitrates K 2 [RE(NO 3 ) 5 (H 2 O) 2 ] (RE = La, Ce, Pr and Nd). I. Crystal growth and crystal structures

• Published in: Journal of applied crystallography 2000-04, Vol.33 (2), p.372-379
• Main Authors: Held, P., Hellwig, H., Rühle, S., Bohatý, L.
• Format: Article
• Language: English
• ISSN: 0021-8898
• DOI: 10.1107/S0021889800000868

Using a standard evaporation technique at 311 K, large single crystals of the polar orthorhombic potassium rare earth nitrates K 2 RE(NO 3 ) 5 .2H 2 O, where RE = La, Ce, Pr or Nd, of optical quality and dimensions up to 5 × 5 × 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 Fdd 2; Z = 8; La compound: a = 11.2814 (6), b = 21.480 (1), c = 12.2589 (4) Å, R = 0.94%; Ce compound: a = 11.263 (3), b = 21.404 (3), c = 12.230 (4) Å, R = 1.92%; Pr compound: a = 11.213 (2), b = 21.392 (4), c = 12.204 (2) Å, R = 1.58%; Nd compound: a = 11.197 (1), b = 21.378 (1), c = 12.195 (1) Å, R = 1.55%]. The main structural feature is the diaquapentanitratolanthanide(III) group, [RE(NO 3 ) 5 (H 2 O) 2 ] 2− , as stated earlier by Eriksson, Larsson, Niinistö & 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 [REO 12 ] is a distorted icosahedron; its geometry is discussed using a simple hard-sphere model.