Conjunction of Chirality and Slow Magnetic Relaxation in the Supramolecular Network Constructed of Crossed Cyano-Bridged Co~Ⅱ-W~Ⅴ Molecular Chains

摘要

The addition of chiral 2,2'-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline) (iPr-Pybox) to a self-assembled Co~(II)-[W~V(CN)_8] magnetic system gives two enantiomorphic cyano-bridged chains, {[Co~(II)((S,S)-iPr-Pybox)(MeOH)]_3[W~v(CN)_8]_2-5.5MeOH-0.5H_2O}_n (1-SS) and {[Co~(II)((R,R)-iPr-Pybox) (MeOH)]_3[W~v(CN)_8]_2·5.SMeOH·0.5H_2O}_n (1-RR). Both compounds crystallize with a structure containing a unique crossed arrangement of one-dimensional chains that form a microporous supramolecular network with large channels (14.9 A X 15.1 A X 15.3 A) filled with methanol. The investigated materials exhibited optical chirality, as confirmed by natural circular dichroism and UV-vis absorption spectra. 1-(SS) and l-(RR) are paramagnets with cyano-mediated Co~(II)-W~v magnetic couplings that lead to a specific spin arrangement with half of the W~v ions coupled ferromagnetically with their Co~(II) neighbors and the other half coupled antiferromag-netically. Significant magnetic anisotropy with the easy axis along the [101] direction was confirmed by single-crystal magnetic studies and can be explained by the single-ion anisotropy of elongated octahedral Co~(II) sites. Below 3 K, the frequency-dependent X"_m(T) signal indicated slow magnetic relaxation characteristic of single-chain magnets.