Four novel coordination polymers of transition metals built using a semi rigid oxygen donor ligand: Crystal structures, novel topology and emission studies

摘要

Four new coordination polymers namely, [Cd_3(L_1) _2(DMA)_4]_n (1), [Mn(HL_1)(H _2O)_3]n (2), [Mn(H_2L _2)]_n (3) and {[Co_2(HL_2)(L _2)]·(Et_4N)·(1.5H_2O)}_n (4) have been synthesized with semi-rigid ether bridged tricarboxylic acid ligands H_3L_1 and H_3L_2 [H _3L_1 = 5-(4-carboxy-phenoxy)-isophthalic acid and H _3L_2 = 5-(2-carboxy-phenoxy)-isophthalic acid] with various transition metal ions using hydro(solvo)thermal techniques. All the coordination polymers have been structurally characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and X-ray single crystallography. Single crystal X-ray studies show that these coordination polymers contain homometallic clusters varying from dimeric to trimeric units except 2 which is a linear monomeric. On reacting para-isomer of the ligand H_3L_1 with metal ions, 2D and 3D supramolecular structures have been obtained while with the ortho-isomer H _3L_2 dimeric 2D and 3D framework were obtained. Topological analysis reveals that 1 and 3 are binodal (3,6)-connected kgd net, 2 is also a binodal (3,3)-connected honey-comb type hcb net, while 4 shows unprecedented (3,3,6)-connected pkb5 topological trinodal-network. Interestingly, 3 and 4 exhibits unusual coordination modes involving one of carbonyl O atom of an acid functional group. Moreover, in 4 ethereal O atom is also coordinated to one of the metal center. All complexes show high thermal stability, thus losing coordinated and lattice solvent molecules in the range, ～100-200 °C. Upon excitation at 325 nm, compounds 1-4 exhibit solid-state luminescences at room temperature.