Syntheses, Structures, and Photoluminescent and Magnetic Studies of Metal−Organic Frameworks Assembled with 5-Sulfosalicylic Acid and 1,4-Bis(imidazol-1-ylmethyl)-benzene

Four novel interesting coordination polymers, [Cd3(bix)3(SSA)2(H2O)4]n (1), [Co(bix)2(HSSA)(H2O)·H2O]n (2), [Ni(bix)2(HSSA)(H2O)·H2O]n (3) and [Mn(bix)2·(HSSA)·2H2O]n (4) (bix = 1,4-bis(imidazol-1-ylmethyl)-benzene; H3SSA = 5-sulfosalicylic acid), have been synthesized under hydrothermal conditions and structurally characterized. Polymer 1 features a two-dimensional (2D) infinite layer framework built from tri-cadmium clusters, which is further stacked along the c-axis via strong
interlayer hydrogen-bond interactions to form a three-dimensional (3D) network. Both polymers 2 and 3 exhibit one-dimensional
(1D) double-stranded chains, which are connected by strong hydrogen-bond interactions along the c-axis to result in 2D layers; in
addition, the layers are further stacked along the b-axis by π−π interactions. Polymer 4 also possesses 1D double-stranded chains.
It is noteworthy that ligand HSSA in compound 4 is not coordinated to the metal ions but only acts as an anion moiety to compensate
the charge balance. The fluorescent properties for these compounds were investigated and the mechanisms were validated by density
functional theory (DFT) calculations on the experimental geometries. In addition, 4 is nearly paramagnetic, whereas weak ferromagnetic
interactions between M(II) (M = Co, Ni) ions have been found in 2 and 3.