Mixed-ligand cobalt, nickel and zinc coordination polymers based on flexible 1,4-bis((1H-imidazol-1-yl)methyl)benzene and rigid carboxylate linkers

Abstract

The mixed-ligand coordination polymers {[Zn(BIX)2.5](NO3)2·5.5H2O}n (1), {[Co(BIX)(HBTC)](BIX)0.5·H2O}n (4), [Ni(BIX)2(BDC)(H2O)]n (5), [Zn(BIX)(PDC)]n (6), [Ni(BIX)(PDC)(H2O)]n (7) and [Zn(BIX)0.5(HIDC)]n (8) were synthesized, structurally characterized and compared to the known coordination polymers {[Co(BIX)3](NO3)2·4H2O}n (2) and {[Zn2(BIX)(BTC)(OH)]·H2O}n (3) to determine the mutual influence of an anionic carboxyl ligand and a neutral N-donor ligand (BIX=1,4-bis((1H-imidazol-1-yl)methyl)-benzene; H3BTC=1,2,3-benzene-tricarboxylic acid; H2BDC=1,3-benzene-dicarboxylic acid (isophthalic acid); H2PDC=3,4-pyridine-dicarboxylic acid; H3IDC=4,5-imidazole-dicarboxylic acid). Compound 1 is a 1D ladder-like structure with two bridging and one terminal (dangling) BIX ligand. Neighboring ladders mutually entangle with the dangling BIX ligand being threaded through {Zn4(BIX)4} openings from adjacent strands. Compound 2 shows a 3D pcu-network with octahedrally coordinated cobalt ions bridged by three crystallographically different inversion-symmetric BIX ligands. The overall structure motifs in the mixed-ligand compounds are 1D metal-carboxylate chain-structures, bridged by neutral BIX ligands to form either 1D ladder-like strands (4), 2D networks (3, 5 with square lattice, 4,4 or sql topology, 7, 8 with honeycomb, 6,3 or hcb topology) or 3D frameworks (6 with diamond, 6,6 or dia topology). Noteworthy, compound 4 forms a 1D tubular structure of stacked {Co2(BIX)2} metallacycles that are threaded with uncoordinated BIX ligands like a rotaxane. A tetrahedral asymmetric Zn atom is formed in the crystals of 6 with spontaneous resolution as only one Zn configuration assembles into the 3D chiral framework of each single crystal.