N-donor ligand mediated assembly of divalent zinc and cadmium coordination polymers based on 2,3,2′,3′-thiaphthalic acid: structures and properties

A series of five metal–organic frameworks, namely, {[Cd2(tdpa)(H2O)3]·H2O}n (1), {[Cd2(tdpa)(bpe)(H2O)3]}n (2), {[Cd2(tdpa)(bix)]}n (3), {[Cd2(tdpa)(bpg)(H2O)4]·3H2O}n (4) and {[Zn4(tdpa)2(bpy)2(H2O)11]·4H2O}n (5) have been hydro(solvo)thermally synthesized through the reaction of 2,3,2′,3′- thiaphthalic acid (H4tdpa) with divalent zinc and cadmium salts in the presence of ancillary nitrogen ligands (bpy = 4,4′-bipyridine, bpg = meso-α,β-bi(4-pyridyl) glycol, bpe = 1,2-di(pyridin-4-yl)ethane and bix = 1,4-bis((1H-imidazol-1-yl)methyl)benzene) and structurally characterized by elemental analysis, IR and X-ray diffraction. In complexes 1, 2 and 3, rod-shaped {Cd12Cd22C6O10}n Cd-chain secondary building units (SBUs) have been formed. For 1, such rod-shaped SBUs are linked together through tdpa4− itself to form a metal–organic layer. For 2 and 3, such metal–organic SBUs are further associated together by bpe or bix ligands in four orientations to form a robust 3D metal–organic network, respectively. In compound 4, a 3D Cd–tdpa metal–organic network is accomplished through tdpa4− anion ligands, and further stabilized by bpg. In complex 5, zinc atoms are bridged by tdpa4− anion ligands and bpy to form infinite Zn–tdpa chains. Luminescence and thermal analysis of these complexes have also been investigated.