Conformation-controlled assembly of coordination polymers with 1,2-bis(3-pyridylcarboxamide)benzene: Structures and properties

Abstract

Self-assembly of 1,2-bis(3-pyridylcarboxylamide)benzene (H 2bpb) with sulfate salts gave rise to three new coordination polymers, [Ni 2(H 2bpb) 2(H 2O) 2(CH 3OH) 2(SO 4) 2] n · nCH 3OH 1, [Co 2(H 2bpb) 2(CH 3OH) 2(DMF) 2(SO 4) 2] n · 0.5 nH 2O 2 (DMF = N, N′-dimethylformamide) and [Zn 2(H 2bpb) 2(CH 3OH) 2(DMF) 2(SO 4) 2] n · 0.5 nH 2O 3. They all crystallize in a monoclinic space group C2/ c, with two crystallographically distinct metal nodes being surrounded by slightly distorted octahedra. There is a homologous chair-like unit with bridging ligand H 2bpb as the back and bis(monodentate) sulfate anion as the seat in their crystal structures. Through the recognition of strong π⋯π stacking interactions between benzene rings, those chains formed by the unlimited extension of the chair-like units stack up to produce 1-D channels along c axis where lattice molecules and terminal ligands are accommodated. Interestingly, the trans,trans,syn achiral conformation with C s symmetry of H 2bpb which is further enforced by sulfate-bridged coordination and intramolecular hydrogen bonding in the chair-like units, controls over the assembling architectures. Further investigation on the thermal and fluorescent properties of complexes 1– 3 shows that the homologous chair-like units in all complexes are stable enough until to 320 °C and that the fluorescence nature of H 2bpb is not sensitive to its conformations.