Two unique lanthanide–organic frameworks based on 1H-2-methyl-4,5-imidazole-dicarboxylate and oxalate: Crystal structure, luminescence and magnetic properties

Abstract

The reactions in mixtures of water–ethanol between lanthanide salts and nitrogen N-hetrocyclic carboxylic acid, in the presence of ammonium oxalate, result in two interesting lanthanide–organic coordination polymers, formulated as, {[Sm4(Hmimda)4(μ4-C2O4)2·6H2O]·8H2O}i (1), [Eu4(Hmimda)4(μ4-C2O4)2·6H2O]·4H2O}n (2), (H3mimda=1H-2-methyl-4, 5-imidazole-dicarboxylic acid). The polymers 1 and 2 are isostructural, and are both built from zig-zag 1D chains constructed from Ln-Hmimda moieties bridged by oxalate, as the secondary building unit (SBU). The Hmimda ligand further is interconnected the 1D chains to form the 3D framework. Variable-temperature magnetic susceptibility measurements indicate that the μ4-k4 O bridging fashion of oxalate results in the possible antiferromagnetic interactions occurring between the adjacent lanthanide(III) centers. The photo-luminescent and thermalgravimetric analyses of the polymers were also determined.