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

Abstract

Four new coordination polymers namely, [Cd3(L1)2(DMA)4]n (1), [Mn(HL1)(H2O)3]n (2), [Mn(H2L2)]n (3) and {[Co2(HL2)(L2)]·(Et4N)·(1.5H2O)}n (4) have been synthesized with semi-rigid ether bridged tricarboxylic acid ligands H3L1 and H3L2 [H3L1=5-(4-carboxy-phenoxy)-isophthalic acid and H3L2=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 H3L1 with metal ions, 2D and 3D supramolecular structures have been obtained while with the ortho-isomer H3L2 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 325nm, compounds 1–4 exhibit solid-state luminescences at room temperature.