The first hybrid organic-inorganic frameworks based on lanthanide(III) sulfate chains, in situ generated oxalate and organic pillars of 1,4-piperazinediacetic acid

Two series of new three-dimensional (3D) hybrid organic-inorganic frameworks [Ln(2)(H(2)pda)(C2O4) (SO4)(2)(H2O)(2)](n) [I, Ln = Nd (1), Y (2)] and {[Ln(2)(H(2)pda)(C2O4)(SO4)(2)(H2O)(2)] center dot 2H(2)O}n [II, Ln = Pr (3), Ce (4) and Eu (5)] (where H(2)dpa = 1,4-piperazinediacetic acid) have been synthesized by the reactions of H(2)pda, lanthanide oxides and H2SO4 under similar hydrothermal conditions. All compounds are constructed by two-dimensional hybrid organic-inorganic layers, which originate from different lanthanide(III) sulfate chains and in situ generated mu(4)-oxalates, and organic H(2)dpa pillars. The coordination modes of sulfate in I and II are, respectively, eta(4), mu(3)-pentadentate and eta(3),mu(3)-tridentate, resulting in the different inorganic [Ln(SO4)(H2O)]infinity chains that have not been documented so far. In 1, each organic H(2)dpa pillar is connected with two Ln(III) ions in a bis-monodentate fashion, while it is linked to four Ln(III) ions in a bis-bidentate syn-anti mode in II. Meanwhile, each Ln(III) ion in I and II is linked by one and two H2pda ligands, respectively. The observations hint that application of lanthanide(III) sulfate chains and flexible spacer pillars can self-assemble into interesting hybrid organic-inorganic framework solids. Compounds I and 3 are air stable and both the three-dimensional frameworks can be retained below 180 degrees C. The variable-temperature magnetic studies show that the chi(M) values of 1 and 3 increase on the falling temperature, which may be attributed to the depopulation of Stark levels and/or intramolecular antiferromagnetic coupling between the metal centers. (C) 2008 Elsevier Ltd. All rights reserved.