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

Self-assembly of 1,2-bis(3-pyridylcarboxylamide)benzene (H2bpb) with sulfate salts gave rise to three new coordination polymers, [Ni2(H2bpb)2(H2O)2(CH3OH)2(SO4)2]n · nCH3OH 1, [Co2(H2bpb)2(CH3OH)2(DMF)2(SO4)2]n · 0.5nH2O 2 (DMF = N,N′-dimethylformamide) and [Zn2(H2bpb)2(CH3OH)2(DMF)2(SO4)2]n · 0.5nH2O 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 H2bpb 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 Cs symmetry of H2bpb 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 H2bpb is not sensitive to its conformations.