A Series of Heterometallic Three-Dimensional Frameworks Constructed from Imidazole-Dicarboxylate: Structures, Luminescence, and Magnetic Properties

The combination of lanthanide and zinc nitrates reaction with a rigid 1-H-2-methyl-4,5-imidazole-dicarboxylic acid yields a new, zinc complex of Zn-(Hmimda)(2)center dot 2H(2)O (1) and a family of heteronuclear polymers, namely, {[Ln(2)Zn(2)(mu(3)-Hmimda)(2) (mu(3)-mimda)(2)center dot 4H(2)O]center dot mH(2)O}(n), Ln = Sm, m = 2(2), Ln = Eu, m = 3 (3), Ln = Gd, m = 2 (4), Ln = Tb, m = 3 (5), Ln = Dy, m = 3 (6) (H(3)mimda = 1H-2-methyl-4,5-imidazole-dicarboxylic acid). Structural analysis shows that complexes 2-6 are isostructural and all crystallize in the monoclinic system, except for a slight disparity for 2. They have an extended nonporous structure constructed from tetraheteronuclear edifices with new framework topology, in which the Ln(III)-Zn square tetranuclear complexes act as the second building unit, which are further interconnected by the Hmimda to afford a two-dimensional corrugated layer. Both compounds 5 and 6 exhibit characteristic fluorescence in the visible region. The variable temperature magnetic investigations indicate that the magnetic interactions are mainly ascribed to depopulation of the Stark levels or possible antiferromagnetic couplings. The Dy(III)-Zn(II) compound exhibits possible ferromagnetic couplings and slow magnetic relaxation behavior of a single-molecule magnet nature.