Mixed-ligand coordination compounds based on the rigid 4,4′-bis(1-imidazolyl)biphenyl and pyridinedicarboxylate ligands

Abstract The mixed-ligand binuclear complexes [Co 2 (BIBP)(2,6-PDC) 2 (H 2 O) 4 ] ( 1 ), [Ni 2 (BIBP)(2,6-PDC) 2 (H 2 O) 4 ] ( 2 ), and the coordination polymers 1D-{[Zn(BIBP)(2,6-PDC)]·4.5H 2 O} n ( 3 ), 2D-[Ni 2 (BIBP)(2,5-PDC) 2 (H 2 O) 4 ] n ( 4 ), and 3D-{[Ni 2 (BIBP) 3 (2,3-PDC) 2 ]·3.75H 2 O} n ( 5 ) were synthesized in good yields, characterized by IR, thermogravimetry and single X-ray diffraction method (BIBP = 4,4′-bis(1-imidazolyl)biphenyl, 2,6-PDC = 2,6-pyridinedicarboxylate, 2,3-PDC = 2,3-pyridinedicarboxylate, 2,5-PDC = 2,5-pyridinedicarboxylate). Compounds 1 and 2 are binuclear complexes, compound 3 is a 1D polymer, 4 has a 2D laminated structure, and 5 represent a 3D framework. A common motif in the structures, independent of their dimensionality is the bridging action of the neutral BIBP ligand between two metal ions and a metal chelating coordination of the dianionic PDC ligand through the pyridine nitrogen atom and the carboxylate group in 2-position. The comparative single crystal X-ray structure investigations reveal the fine-tuning influence of the carboxylic group positions in the pyridinedicarboxylate (PDC) ligands and the metal nature on the final structure topology and dimensionality. Compounds 1 and 2 are isostructural and represent Co(II) and Ni(II) isomorphs, where the metal ions coordinate two water molecules and the 2,6-PDC ligand in ONO chelate mode, while the bidentate BIBP ligand link the metal ions into a dinuclear complex. In 3 the 2,6-PDC ligand coordinates to the zinc atom in the same ONO chelate mode and two bridging BIBP ligands give a coordination number of five and extend the structure to a 1D polymer with an enantiopure triple-stranded helix motif in a case of spontaneous resolution in the chiral tetragonal space group P 4 3 22. In 4 the 2,5-PDC ligand realises its chelate-bridging function and together with the bridging BIBP ligand form 2D layers with the Ni(II) atoms with hcb (honeycomb or 6,3) topology. In 5 the chelate-bridging 2,3-PDC and BIBP ligands form (4,4)-layers which are interlinked by additional BIBP pillars to a 3D network with two-fold interpenetration of symmetry-related networks.