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)2·2H2O (1) and a family of heteronuclear polymers, namely, {[Ln2Zn2­(μ3-Hmimda)2 (μ3-mimda)2·4H2O]·mH2O}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) (H3mimda = 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.