Structural diversity of the lanthanide oxalates: Condensation of neodymium oxygen polyhedra under hydrothermal conditions

New neodymium hydroxo-oxalate and oxalate [Nd-6(H2O)(6)(C2O4)(7)(OH)(4)]center dot 4H(2)O (1) and [Nd-2(H2O)(4) (C2O4)(3)]center dot 2H(2)O (2) were synthesized by hydrothermal reaction at 150 degrees C between neodymium nitrate and oxalic acid solutions at pH = 10-11 obtained by adding various monoamines. The structures were determined from single-crystal X-ray diffraction data. The two compounds crystallize in the monoclinic system with space group P2(1)/c and a = 17.4384 (11), b = 8.1717 (5), c = 12.9929 (7), beta = 94.66 (1)degrees, V = 1845.38 (19) angstrom(3), Z = 2 for 1 and a = 9.8249 (2) angstrom, b = 8.2487 (2) angstrom, c = 10.1911 (3) angstrom, beta = 99.09 (1), V = 815.53 (4) angstrom(3), Z = 2 for 2. Full matrix least-squares refinement yielded R-1 = 0.0365 and 0.0267 for 6033 and 3382 independent reflections for 1 and 2 respectively. In 2, the three-dimensional neodymium-oxalate arrangement results from dimeric units of edge shared NdO9 polyhedra connected through oxalate ions acting as bis-bidentate. In 1, the neodymium atoms are connected through mu(2)-OH and mu(3)-OH ions to form a hexanuclear inorganic core [Nd-6(OH)(4)(H2O)(6)] with an unprecedently reported geometry leading to a hexanuclear polyhedra block. The blocks are connected through an O-O bridge involving two oxygen atoms of two oxalate ions to build a centipede-like ribbon. The ribbons are further connected through oxalate ions to form a three dimensional neodymium oxalate arrangement. In 1, oxalates adopt four distinct bridging modes of coordination, mu(2), mu(3), mu(4) and mu(5). (C) 2013 Elsevier B.V. All rights reserved.