Design,Assembly And Physical Properties Of Multifunctional Molecule-based Magnetic Materials

Recently,advanced multifunctional molecule-based magnetic materials have been an emerging trend in the field of materials science and synthetic chemistry.Combining two or more different physical properties in molecule-based magnets is prerequisite to observe magnetoelectric coupling effect,magnetic circular dichroism,electrically controlled magnetic moment behaviours in functional complexes,which not only has significant theoretical values but a wide and potential prospect.Various bifunctional systems coupling single-molecule magnets(SMMs)or spin-crossover(SCO)properties with luminescence,conductivity,chirality have been reported.Such properties can simply coexist in the same crystal lattice,even cross-or synergetic effects have also been observed,which are of great significance for practical device applications.Based on this,a series of multifunctional single molecule magnets and spin-crossover complexes have been designed and synthesized and the coexist or synergetic effects of multiple properties were investigated.More details are as follows:1.Supported by bulky chiral macrocycles,two air-stable mononuclear macrocyclic DyⅢ enantiomers Dy-S and Dy-R with terminal fluoride ligands were prepared.Single crystal structures show that two fluoride ligands are negatively charged and axially coordinated to DyⅢ ions with very short Dy-F distances and six electroneutral nitrogen atoms in the equatorial plane,weakly coordinated to DyⅢ ions,indicated by the long average Dy-N distance.At the same time,two complexes both display a hula-loop coordination geometries around DyⅢ ions,contributing to a typical zero-field SMM behaviour.Notably,a rather slow rate of magnetic relaxation appears in the low temperature regime,indicated frequency-dependent out-of-phase(ac)magnetic susceptibilities peaks.Ab initio calculations reveal that they possess strong axiality in the ground KDs and the magnetic relaxation pathways most probably go through the first-excited KDs.2.Two new dimeric dysprosium(Ⅲ)complexes Dy-SCN and Dy-NO3 have been assembled using multidentate ligand,hmpd.The use of different coordination anions for two complexes results in distinct coordination symmetries of metal sites.The Dy centers in complexes Dy-SCN and Dy-NO3 display capped octahedron and triangular dodecahedron coordination symmetries,respectively.Consequently,two compounds exhibit distinct magnetic properties.Complex Dy-SCN displays a typical zero-field SMM behavior while under dc field of 1100 Oe,only slow magnetic relaxation behavior is observed for complex Dy-NO3.Different coordination anions of two complexes lead to two distinct magnetic interactions,namely ferromagnetic and antiferromagnetic for Dy-SCN and Dy-NO3,respectively.Ab initio calculations reveal that these interactions may result from strong intramolecular dipolar couplings that are ferromagnetic for DySCN while antiferromagnetic for Dy-NO3,while exchange couplings are antiferromagnetic in both cases.Two complexes exhibit characteristic narrow bands of DyⅢ ions with relatively strong residual emission bands of organic ligands,which most likely due to unreasonable energy gaps between the triplet state of the ligand and the accepted level of DyⅢ ions and the presence of high-energy O-H oscillators.3.A series of highly thermally stable lanthanide compounds,[Ln(hfac)3(TPE-tz)](Ln-TPE-tz,Ln=Sm,Eu,Gd,Dy,Er,Yb)have been isolated by the reaction of the aggregation-induced emission(AIE)-active organic ligand with Ln(Ⅲ)β-diketonate precursor,Ln(hfac)3·2H2O.Due to different energy gaps between the triplet state of ligands and the accepted level of Ln(Ⅲ)ions,Eu-TPE-tz exhibit remarkably enhanced luminescence intensity upon aggregation,i.e.the typical AIE behavior,while Dy-TPEtz display weak characteristic emission bands of Dy(Ⅲ)ions.Crystalline aggregates of Dy(hfac)3(TPE-tz)exhibit effective piezochromism in emission colour with a shift of ca.20 nm at emission maximum.Magnetic studies showed that Dy-TPE-tz is a fieldinduced SMM.4.Two novel fluorescent SCO complexes bpp-TPE-Fe and bpp-TPA-Fe have been synthetized using AIE-active ligands bpp-TPE and bpp-TPA,respectively.These complexes show typical AIE behaviors in solution and strong emissions in the solid state.In addition,due to the D-A structure of bpp-TPA-Fe,this complex exhibits bright full-color emissions in 11 solvents with different polarity.Importantly,both complexes display synergetic effect between the spin-state switch and luminescent properties.Temperature-dependent absorption spectra indicate that the modulation mechanism probably derives from energy transfer between fluorescent ligand and FeⅡ ions in low spin state.