Construction of coordination polymers from semirigid ditopic 2,2´-Biimidazole derivatives : synthesis, crystal structures and characterization

Eight coordination polymers (CPs), {[Ag(L1)]ClO4}n (1), {[Ag(L2)1.5]ClO4·C2H3N}n (2a), {[Ag(L2)]ClO4}n (2b), [Zn(L1)Cl2]n (3), {[Zn(L2)Cl2]·CHCl3}n (4), {[Cu(L1)2Cl]Cl·H2O}n (5), [Cu2(L2)(μ-Cl)2]n (6), and [Cu4(L2)(μ-Cl)4]n (7) were synthesized via self-assembly of corresponding metal ions and biimidazole based ditopic ligands, 1,1′-bis(pyridin-3-ylmethyl)-2,2′-biimidazole L1 and 1,1′-bis(pyridin-4-ylmethyl)-2,2′-biimidazole L2. These ligands possess conformational flexibility and two pairs of coordination sites: pyridine nitrogen (NPy) atoms and imidazole nitrogen (NIm) atoms. Depending on the metal center in CPs, the biimidazole compounds act as tetra- (1, 7), tri- (2a), or bidentate (2a, 2b, 3-6) ligands binding to the metal either via NPy or NIm, or both. All these CPs were structurally fully characterized with single crystal X-ray structure, mass spectrometry, and NMR spectroscopy. The solid state photophysical properties and thermal stabilities of the CPs were also briefly studied in the solid state.