Study On Bistable Molecular Magnets Based On Tetrazine Radical Bridge

Significant progress including both the anisotropic energy barrier and blocking temperature have been achieved after nearly thirty years of development in the field of single-molecule magnets.A key underpinning of research on the construction of high-performance SMMs is the opportunity to maximize uniaxial maximized magnetic anisotropy through modulating the coordination geometry as well as the spin-orbit coupling of the target molecules.Research of SMMs in recent years indicate that strong exchange couplings mediated by the radical bridges can effectively suppress the QTM and increase the relaxation times,for which tetrazine-based ligands have attracted considerable attentions due to the ease of satisfying the requirement for convenient syhthesis and stable redox isomers.Here in we report the synthesis and magnetic studies of a series of binuclear,tetranuclear and polynuclear complexes through self-assembly between the different metal species and pre-designed tetrazine-based bis-tridentate bridging ligands.The details are as follows:Self-assembly of Co(Ⅱ)salts and the tetrazine bridging ligands in the absence of other coligands afforded four polynuclear Co(Ⅱ)complexes:{[Co2(LBpy-o1)2][BPh4]2}.5CH3CN(1),{[Co2(LBpy-O1)2][ClO4]2}.5DMF(2),{Co4(LBpy-O3)2(LBpy-O2)2[ClO4]6}-4CH3CN(3)and {[Co2(LPhen-O1)2][BPh4]2}·5CH3CN(4).Single-crystal X-ray diffraction studies revealed that the tetrazine ligands has been catalyzed in situ as open-cyclic LBpy-O1,Lphen-O1,LBpy-O2 ligands or five-membered rings(LBpy-O3).Similar reactions in the presence of terpyridine coligands led to complexes{[Fe2(L4N-Bpy)(Tpy)2][CF3SO3]4}·3DMF(5),[Co2(LBpy-O3)(Bpp)2][C1O4]4(6)and[Co2(LBpy-O3)(Tpy)2](CF3SO3)4(7),among which the tetrazine units of 5 did not undergo the ring-opening process.No spin transition was observed for 5.Further attempts through the reaction between the open-cyclic dinuclear Co(Ⅱ)units and tricyanoferric building blocks towards the electron transfer materials afforded another two polynuclear Fe-Co complexes:{[(Tp)Fe(CN)3]9[Co6(LBpy-O3)3][CF3SO3]2}·13CH3CN(8)and {[(Tp*)Fe(CN)3]4[CO2(LBpy-O3)]}.4CH3CN(9).No electron transfer behavior was observed for both the complexes.