Six new coordination compounds based on rigid 5-(3-carboxy-phenyl)-pyridine-2-carboxylic acid: synthesis, structural variations and properties

Abstract

Six new coordination compounds Ni(cppca)(H₂O)₄·2H₂O (1), Co(cppca)(H₂O)₄·2H₂O (2), {Cd₂(cppca)₂(H₂O)₅}_n (3), {[Cd₃(cppca)₂(H₂P₂O₇)(H₂O)₆]·2H₂O}_n (4), {Cu(Hcppca)₂}_n (5) and {[Mn₇(cppca)₆(Hcppca)₂(H₂O)₁₀]·2H₂O}_n (6) have been obtained by reactions of the corresponding metal salts and the rigid ligand 5-(3-carboxy-phenyl)-pyridine-2-carboxylic acid (H₂cppca) under solvothermal conditions. All the compounds were fully characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, thermal analysis and powder X-ray diffraction. The single-crystal X-ray analyses showed that compounds 1–6 have rich structural chemistry ranging from mononuclear (1 and 2), one-dimensional (3 and 4), two-dimensional (5) to three-dimensional (6) structures. Moreover, the framework of compound 6 may be simplified into a 3-nodal net with Schlafli symbol {4²·6}{4²·8²·10²}{4³·6²·8·10⁴}₂, which shows an unprecedented (3,4,5)-connected topology net. The fluorescent properties of compounds 3 and 4 were investigated in the solid state and in various solvent emulsions, which indicated that compounds 3 and 4 are both highly sensitive fluorescent probes for the acetone molecules. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic interactions between metal centers in compounds 1, 2, 5 and 6.