Constructing a Series of Azide-Bridged CuII Magnetic Low-Dimensional Coordination Polymers by using Pybox Ligands

Four azide-copper coordination polymers, [Cu2L1(N3)4]n, [Cu2L2(N3)4]n, [Cu2L3R(N3)4]n, and [Cu2L3S(N3)4]n, were synthesized by using pybox [pyridine-2,6-bis(oxazolines)] as coligands {L1: 2,6-bis(4,5-dihydrooxazol-2-yl)pyridine; L2: 2,6-bis(5,6-dihydro-4H-1,3-oxazin-2-yl)pyridine; L3R or 3S: 2,6-bis[(R or S)-4-benzyl-4,5-dihydrooxazol-2-yl]pyridine}. Compounds 1 and 2 possess similar 1D infinite azide-copper hexagonal tapes with three types of N3 bridges (two single end-on N3 bridges and one double end-on N3 bridge). Compounds 3R and 3S possess an azide-copper 2D honeycomb layer with two types of N3 bridges (a single end-to-end N3 bridge and a double end-on N3 bridge). The chirality of these enantiopure layered structures is controlled by the addition of the chiral pybox ligand in the synthesis, which is very rare for the reported azide-copper coordination polymers. The double end-on N3 bridge transfers mainly ferromagnetic exchange coupling interactions in these four compounds. Owing to the steric hindrance of the pybox ligands, the interchain and interlayer separations are broadened, which weakens the magnetic interactions between them. Thus, no long-range ferromagnetic ordering was observed above 1.8 K. A magnetostructural correlation was also discussed in detail.