Crystal structures and properties of four coordination polymers based on a new asymmetric ligand: Tuning structure/dimensionality by various organic solvents

Abstract

An asymmetric ligand, 4,4′-([2,3′-bipyridine]-4,6-diyl)dibenzoic acid (H2L) was successfully used to construct four new coordination polymers, namely [M(HL)2]n (M = Cd(1), Co(2), Zn(3)) and [Ni(L)(H2O)2]n·H2O (4), which were solvothermally synthesized and structurally characterized. In coordination polymers 1–4, two ligands bridge two metal centres through carboxylate oxygen atoms and pyridyl nitrogen atoms to form a rhombic grid motif. Amongst, each rhombic grid connects to adjacent ones through the metal nodes to construct spirolike 1D chain of 1–3 with the partially deprotonated 2-connected HL− ligands, whereas, the completely deprotonated 3- connected L2− ligands make rhombic grids construct 2D network of 4. The various structure/dimensionality of 1–4 essentially originates from the types of organic solvents, because dipolar DMF solvent results in complete deprotonated L2− in 4, conversely, polar NMP and MeCN only cause partial deprotonation of ligand in 1–3. Interestingly, an enhanced luminescence appears in 1 and 3, compared to H2L ligand, while 2 and 4 reveal antiferromagnetic behaviors. Moreover, the sensing experiments indicate that 1 and 3 possess luminescent quenching effects on sensing nitrobenzene. This work provides a promising approach to design and construct new coordination polymers with tunable structure/dimensionality by using different organic solvents.