Synthesis and Structure of Zinc(II) and Cobalt(II) Coordination Polymers Involving the Elongated 2',3',5',6' Tetramethylterphenyl-4, 4''-dicarboxylate Ligand

Abstract The elongated linker 2',3',5',6'-tetramethylterphenyl-4,4''-dicarboxylic acid (H2L) was employed in the synthesis of zinc(II) and cobalt(II) coordination polymers with single or mixed bridging ligands. Seven compounds, that include the solvate H2L·2DMSO (1·2DMSO), the 1D coordination polymer [Zn(L)(DMF)2]n (2), the two 2D coordination polymers {[Zn(L)(DEF)]2·2DEF}n (3) and {[Co(L)(DEF)]2·2DEF}n (4), and the three mixed ligand 3D coordination polymers {[Zn2(L)2(BIBP)]·2DEF}n (5), {[Co2(L)2(BIBP)]·2DEF}n (6) and {[Zn3(L)3(BIPY)1.5]·4DMF·1.5H2O}n (7), (where DMSO is dimethylsulfoxide, DMF is dimethylformamide, DEF is diethylformamide, BIBP stands for 4,4′-bis(1-imidazolyl)biphenyl, and BIPY for 4,4'-bipyridine) have been synthesized and characterized by IR spectroscopy, thermogravimetry, and single-crystal X-ray diffraction. In 2 the zinc atom adopts a tetrahedral O4 environment due to the monodentate coordination of two DMF molecules and two deprotonated bridging L2- ligands. The latter connect the zinc atoms in a zigzag-like chain. In the coordination polymers 3 to 7 the secondary building unit (SBU) is the paddle-wheel moiety {M2(O2C-)4(N/O)2}. The metal atoms are five coordinated with distorted square pyramidal coordination geometry by oxygen atoms from carboxylate groups of four different L2- linkers, and one axial DEF-O atom in 3 and 4, BIBP-imidazolyl-N atom in 5 and 6 or BIPY-N atom in 7. Furthermore, the L2- ligands link the SBUs to a (4,4) 2D sql net. In 5-7 these sql nets are additionally linked by BIBP or BIPY ligands as pillars to provide pillared-layer 3D and three-fold interpenetrated frameworks. Remarkably, the BIBP pillar yields bsn (beta-Sn) topology, the BIPY pillar pcu (α-Po) topology.