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

Abstract

Two series of new three-dimensional (3D) hybrid organic–inorganic frameworks [Ln 2(H 2pda)(C 2O 4)(SO 4) 2(H 2O) 2] n [I, Ln = Nd ( 1), Y ( 2)] and {[Ln 2(H 2pda)(C 2O 4)(SO 4) 2(H 2O) 2] · 2H 2O} n [II, Ln = Pr ( 3), Ce ( 4) and Eu ( 5)] (where H 2dpa = 1,4-piperazinediacetic acid) have been synthesized by the reactions of H 2pda, lanthanide oxides and H 2SO 4 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 μ 4-oxalates, and organic H 2dpa pillars. The coordination modes of sulfate in I and II are, respectively, η 4,μ 3-pentadentate and η 3,μ 3-tridentate, resulting in the different inorganic [Ln(SO 4)(H 2O)]∞ chains that have not been documented so far. In I, each organic H 2dpa 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 1 and 3 are air stable and both the three-dimensional frameworks can be retained below 180 °C. The variable-temperature magnetic studies show that the χ 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.