Study Of Spin-Crossover Transition For Complexes Based On Functionalized Bipyridine Ligands

In recently years, the studies of spin-crossover (SCO) are mainly focused on three aspects:(1) Synthesis new class of SCO systems; (2) Understanding the key factors for SCO behavior, for the purpose of control-synthesis; (3) The practical applications of SCO materials. Based on these conditions, this thesis mainly focused on the preparation of mononuclear SCO complexes, construction of 1D and 2D SCO coordination complexes, and the development of new kinds of SCO nano-particles. The merits for study of mononuclear complexes and 1D、2D SCO coordination complexes are the convenience of understanding the structural-functional relationship as well as the enhancement of cooperativity, while the development of nano-particles is aimed at practical applications. The detail contents are as follows:(1) Mononuclear SCO complexes based on diimine ligands. ①.We have obtained four mononu-clear complexes:Fe(4,5-dmpi)3(C104-)2, Fe(4,5-dmpi)3(BF4-)2, Fe(4,5-dmpi)3(PF6-)2 and Fe(4,5-dmpi)3(SbF6-)2, and have investigated their magnetic properties. Results revealed that:the influence of the counter anions on the transition temperature are follows the order SbF6->BF4->PF6->ClO4-. ②.Combined with ligands NCX-, we have obtained two mononuclear complexes Fe(4,5-dmpi)2(SCN)2 and Fe(4,5-dmpi)2(SeCN)2, the former one is in HS state while the latter display complete SCO transition; ③. We also obtained a mononuclear complexe [Fe (4,4’-dmbpy)3(C104) (SCN)]·3H2O, which display complete SCO transition between 350-220 K with a thermal hysteresis of 7 K.(2) Mononuclear SCO complexes based on H2Bpz2-diimine system. We have employed ligand 4,4’-dabpy and combined it with ligands HbBpz2, CN- and p-aba, respectively, we have obtained ①. A HS state complex [Fe(H2Bpz2)2(4,4’-dabpy)]CH3OH, the spin state of it has been induced from paramagnetic behavior to crossover situation through protonation of one amino group of 4,4’-dabpy. ②.We have obtained a mononuclear complexe [Fe(4,4’-dabpy)2(CN)2]H2O CH3OH, the SCO properties of it was tuned by lattice solvents; ③.We also have obtained a tetra-nuclear complex [Fe4O2(p-aba)7(4,4’-dabpy)2](p-aba)-(C2HSOH)2 (CH3CN)2.(3) 1D and 2D SCO coordination complexes. We have employed the bridging ligands 4,4’-bipy, 4,4’-dps and 1,3-dpp, respectively. And have ①obtained 1D coordination complexes{Fe(4,4’-bipy)2 (H2O)2}(4,4’-bipy) and [Fe(NCS)2(4,4’-dps)2]2(2,5-DCP), for the investigation of the influences of ligand field and guest molecules on the structure and SCO properties. ②We have synthesized and characterized two 2D porous coordination polymers [Fe(1,3-dpp)2(NCX)2], X= S and Se, which featured 2-fold interpenetration and ligand field-dependent SCO properties.(4) Fe-1,2,4-triazole SCO system. We have synthesized a series halogen atoms substituent 1,2, 4-triazole related Schiff base ligands. The magnetic investigation of the related 1D FeⅡ-coordination polymers revealed that the electronegative halogen atoms induce an increase in the π acceptor character of these ligands and cooperative character between the 1D polymers, which result in the increase of the ligand field strength, and induce the occurrence of SCO at higher temperatures consequently.(5) Similar-Liposomal self-assembly SCO vesicular nanosphere. We have synthesized a series of hydrophobic alkyl-2,2’-bpy ligands (dpbdc, dbbdc, debdc, dhbdc, dhebdc, dobdc, dnbdc, ddbdc and dcbdc), and combined with the hydrophilic Fe(bpz)2 to constructe SCO complexes ([Fe(H2Bpz2)2 (dp bdc)], [Fe(H2Bpz2)2(dbbdc)], [Fe(H2Bpz2)2(debdc)], [Fe(H2Bpz2)2(dhbdc)], [Fe(H2Bpz2)2(dhebdc)], [Fe(H2Bpz2)2(dobdc)], [Fe(H2Bpz2)2(dnbdc)], [Fe(H2Bpz2)2(ddbdc)] and [Fe(H2Bpz2)2(dcbdc)]). These complexes formed vesicular nanosphere in hot water (60 ℃), through a similar-liposomal self-assembly process. Results revealed that the hydrophilic alkyl tails play a dominant role in driving the self-assembly nanosphere as well as determining the final size. In addition, this vesicular nanosphere self-assembly improved the spin-transition temperatures when compared with the bulk materials. We believe that this strategy will offer new aspects on future developments of novel forms of nanoparticles for application-oriented purposes.