Reticular three-dimensional 3d-4f frameworks constructed through substituted imidazole-dicarboxylate: syntheses, luminescence and magnetic properties study

A family of heteronuclear metal organic frameworks (MOFs) using lanthanide and transition metal ion based on a rigid ligand of substituted imidazoledicarboxylic acid, namely, {[Ln(2)Zn(2) (mu(3)-Hmimda)(2) (mu(3)-mimda)(2)center dot 4H(2)O](n)center dot mn H2O}, Ln = Nd, m = 2 (1), Ln = Ho, m = 3 (2), Ln = Er, m = 2 (3), Ln = Yb, m = 3 (4), [Tb2Co2(mu(3)-Hmimda)(2) (mu(3)-mimda)(2)center dot 4H(2)O](n)center dot 2nH(2)O} (5) and [Dy2Co2 (mu(3)-Hmimda)(2) (mu(3)-mimda)(2)center dot 4H(2)O](n)center dot nH(2)O} (6), (H(3)mimda = 1H-2-methyl-4,5-imidazole-dicarboxylic acid), have been developed and characterized. All the complexes (except for a little disparity for 1) are isostructural, and all crystallize in the monoclinic system. They possess an extended reticular-like porous structure constructed from corrugated 2D layers. Direct current (dc) magnetic susceptibility measurements for 1-5 indicated depopulation of the Stark components at low temperature and/or possible weak anti-ferromagnetic interactions within heteronuclear MOFs. Alternating current (ac) susceptibility studies reveal that the Dy(III)-Co(II) complex exhibits both possible ferromagnetic couplings and frequency-dependent out-of-phase signals, behaviour of single-ion magnet nature. Fluorescence properties of series complexes both in near-infrared (NIR) and visible regions have been comparatively studied.