Two temperature-induced 1D CuII chain enantiomeric pairs showing different magnetic properties and nonlinear optical responses.

ABSTRACT

At different reaction temperatures, using Cu(NO3)2·3H2O to react with enantiomerically pure N-donor ligands (LS/LR), respectively, two pairs of chiral one-dimensional (1D) CuII chain enantiomers formulated as [Cu(µ2-NO3)(NO3)(LS)]n/[Cu(µ2-NO3)(NO3)(LR)]n (S-1-Cu/R-1-Cu, formed at 40 °C with an NO3- group as a sole bridging ligand) and [Cu(µ2-LS)(NO3)2]n/[Cu(µ2-LR)(NO3)2]n (S-2-Cu/R-2-Cu, formed at 25 °C with LS or LR as a bridging ligand) were prepared, where LS/LR = (+)/(-)-4,5-pinenepyridyl-2-pyrazine. Interestingly, such a disparity in bridging ligands leads not only to their distinct structural features but also to their completely different magnetic couplings together with a large difference in their nonlinear optical responses. S-1-Cu with a 1D helical structure shows weak ferromagnetic coupling between CuII ions, while S-2-Cu with a 1D stairway-like structure presents weak antiferromagnetic coupling. In particular, they simultaneously possess both second- and third-harmonic generation (SHG and THG) responses in one molecule with large strength differences. More remarkably, S-1-Cu exhibits a very large THG response (162 × α-SiO2), which is 22.5 times that of S-2-Cu, and the SHG strength of S-1-Cu is more than 3 times that of S-2-Cu. This work demonstrates that reaction temperature has a great impact on the self-assembled structures of coordination polymers and subsequently results in their large performance differences.