Monday, June 3, 2019

Single Molecule Magnets and Single Chain Magnets Analysis

Single Molecule Magnets and Single Chain Magnets AnalysisThe social organisations and magnetized propertiesmolecular nanomagnetsphenolic oxime complexesGUAN ShengyangTable of Contents (Jump to)1 Introduction1.1 Research undercoat1.2 Introduction to nanomagnets1.2.1 Single iota magnet1.2.2 Single Chain magnet (magnetic nanowires)1.3 Structure of phenolic oxime and complexes2 Researches2.1 Iron complex2.2 Manganese complexes2.3 decomposable containing cobalt and sodium ions2.4 Complex containing lanthanide3 Conclusion4 BibliographyAbstractThe basic concepts needed to understand and model whizchain magnets will also be reviewed.1 Introduction1.1 Research backgroundThe researches on molecular nanomagnets began from 1990s, when the primary single molecule magnet (SMM) Mn12O12(O2CPh)16(H2O)4 was researched by Christougroup of University of Florida. GS1This mixed-valent manganese complex was found to have an brachydactylic high spin ground state of S=10GS2 and highest blocking temp erature (below which temperature could the nanomagnets show magnetic properties) in its family (Mn12O12(O2CR)16(H2O)4, R = various). A large number of SMMs have been report since then. TheseGS3 kind of complexes display the classical property of magnetization hysteresisGS4 and quantum properties of quantum tunnelling of the magnetization (QTM). These initial discoveries provide a molecular approach to nano-scale magnetism.Following investigation of single molecule magnets (SMMs) and single chain magnets (SCMs) explorers their capability applications in high-density information storageGS5, quantum computingGS6, magnetic refrigeration GS7and so on. However, to date, nanomagnets discovered have rattling low blocking temperature (TB). So it is very important to choose appropriate chelate ligands and corresponding metal centres to construct a proper complex with properties to improve blocking temperature (TB) for practical application.Phenolic oxime is a family of compounds with gener ic structure shown in Figure 1. The phenolate and oxime function groups could form intramolecular hydrogen bonding with its neighbour. These hydrogen bonding resulting in strong coordination effect on metal ions. Such property makes phenolic oxime a good extractant for copperGS8 in mining industry. Detailed discussion of the phenolic oxime complex structure will be introduced in SECTION 1.3 .Figure 1 general structure of phenolic oximeIn this review, knowledge of nanomagnets will be introduced firstly to provide an overview of this field. Then the structure and magnetic properties of compounds with phenolic oxime ligand will be introduced. New techniques applied in implication will also be included. It is hoped that this review could be used to respect the potential of phenolic oxime ligand in high performance nanomagnets.1.2 Introduction to nanomagnets1.2.1 Single molecule magnetIt is helpful to describe the basic theory of SMM with an example. The first single molecule magnet (S MM) Mn12O12(O2CCH3 )16(H2O) 4 4H2O2CH3CO2HGS9 was determined to have an S=10 ground spin state, which is contri howevered by the antiferromagnetic interactions between 4 MnIV ions and 8 MnIII ionsGS10. However, not wish normal size magnet, SMM shows slow magnetic relaxation below a characteristic blocking temperature. This phenomenon is explained by the exist of an energy barrier in reorientation process of magnetic moment. Sessoli confirmed there exists a relatively large zero-field dissever in this molecule by high-field EPR experiments with a CO2 far-infrared laser. This axial zero-field splitting leads to a splitting of the S=10 state into 21 levels -10 , -9 , -8, -7, -6 , -50, 1, 2, 38, 9, 10. Each level is characterized by a spin projection quantum number ms, corresponding potential energy ..(1)Daxial zero-field splitting parameter. In Mn12O12(O2CCH3 )16(H2O) 4 4H2O2CH3CO2H D=-0.5cm-1Figure 2 Figure 1. PovRay representation of the core ofMn12O12(O2CCH3 )16(H2O) 4 4H2 O2CH3CO2H, showing the relative positions of the MnIV ions (shaded circles), MnIII ions (solid circles), and 3-O2 connect (open circlesGS11).Figure 3 Plot of potential energy of different spin state versus magnetization directionFrom Figure 3, it could be known that the splitting of potential energy levels resulting in a potential energy barrier in the process of changing the magnetic moment. For the example SMM, this barrier equals to E(ms=0)-E(ms=10)=100D. Due to the subtle value of D, this barrier could be easily crossed in room temperature. If sample SMM is magnetized at 1.5K, the magnetic relaxation time becomes too farsighted to measure. When fitted into Arrhenius relationship.(2)The magnetic anisotropy of the SMM is caused by the structure of the eight MnIII ions. Each MnIII ion with in octahedral crystal shows JahnTeller distortion. These distortionGS12 together with spin-orbital interaction give rise to the easy axis type of magnetoanisotropy.To conclude, a typical SMM consists of an inner magnetic core with a surrounding shell of organic ligands. The desired SMM requires well isolated system which introduce high spin ground state (S) with a high magnetic anisotropy of the easy-axis (Ising) type. The difficulty is high spin ground state often requests for several nucleuses, but the magnetic orientation of each nuclei tends to obey Maximum Entropy Models. In this way, the highest magnetoanisotropy of a molecule couldnt be achieved easily. Some researches show that replacing magnetic core with lanthanideGS13 ions or using single nuclearity spincluster GS14could avoid this problem. Their approaches will be discussed in SECTION Single Chain magnet (magnetic nanowires)While clusters of SMM can be considered as zero dimensional material, it is possible that one dimensional materials such as nanowires exhibit slow magnetic relaxation and hysteresis effects which are not associated with cubic (3D) order. At 1963, GlauberGS15 predicted one dimen sion Ising model (easy axial) would show magnetization relaxation under low temperature. Due to insufficient knowledge in this field of study and stringent conditions required in the synthesis procedure, chemist wasnt be able to find any evidences to support or against the prediction, until Gatteschi et al successfully synthesis Co(hfac)2(NITPhOMeGS16) in 2001.Figure 4 Structure of NITPhOMe=4-methoxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxideFigure 5 Drawing of unit cell ofCo(hfac)2(NITPhOMe)2. Large dark spheres represent the metal ions. Hydrogen, fluorine, and to the highest degree of the methyl carbon atoms have been omitted for clarityThe structure of the SCM consists of Co(hfac)2 and radicals arranged in helices alternately( Figure 5). In this one dimensional structure, the magnetic core (octahedral cobalt(II) centres) has overall S=1/2 and shows easy axis of magnetization in the chain directionSG17. Detailed analysis of spectrums could be found in Caneschis report in 2001.To conclude, three essential conditions are need for design SCMs 1) the ratio of the interaction and interactions is very large. 2) the material must behave as a 1D Ising ferro- or ferrimagnet. This requires the grammatical construction block or the core of the chain have large ground state spin. 3) the interchain interactions should be minimized to avoid the magnetism of the material be associated with three-dimensional (3D) order. This final condition also apply for SMMs.1.3 Structure of phenolic oxime and complexesMetal complexes with a planar, electronically delocalized structure have proven particularly attractive for ontogeny of cooperative electronic properties because of the strong moleculemolecule interactions that can arise from -stacking of the planar units2 Researches2.1 3d nanomagnetMany 3d nanomagnets have been synthesized and researched on since the first SMM was discovered.f hexanuclear MnIII SMMs based on the complex MnIII6O2(sao)6(O2CH)2(EtOH)4(saoH2=sali cylaldoximeGS18)9-12Spin Switching via Targeted Structural Distortion2.2 Iron complexVariation of alkyl groups on the ligand fromt-octyl ton-propyl enabled electronic closing off of the complexes in the crystal structures of M(L1)2contrasting with -stacking interactions for M(L2)2(M = Ni, Cu). This was evidenced by a one-dimensional antiferromagnetic chain for Cu(L2)2but ideal paramagnetic behaviour for Cu(L1)2down to 1.8 K.2.3 Complex containing cobalt and sodium ions2.4 Complex containing lanthanideAlthough many magnetic transition metal complexes have been synthesised, the temperature required for transition metal complex to exhibit magnetization relaxation (i.e. blocking temperature) is too low. Hence lanthanide metals were introduced to the complex to increase the blocking temperature.4 BibliographyGS1R. Sessoli, H.-L. Tsai, A.R. Schake, S. Wang,J.B. Vincent, K. Folting, D. Gatteschi, G. Christou,and D.N. Hendrickson, J. Am. Chem. Soc. 115(1993) p. 1804.Sessoli, R. Tsai, H.-L. Schake, A.R. Wang, S. Vincent, J.B. Folting, K. Gatteschi, D. Christou, G. Hendrickson, D.N.J. Am. Chem. Soc.1993, 115, 1804-1816.GS2-GS3Resonant magnetization tunnelling in the half-integer-spin single-molecule magnet PPh4Mn12O12(O2CEt)16(H2O)4Spin Tweaking of a High-Spin Molecule An Mn25Single-Molecule Magnet with autonomic nervous system=61/2 Ground StateNew Routes to Polymetallic Clusters Fluoride-Based Tri-, Deca-, and Hexaicosametallic MnIIIClusters and their Magnetic PropertiesMolecular Cube of ReIIand MnIIThat Exhibits Single-Molecule MagnetismSyntheses, structures and single-molecule magnetic behaviors of two dicubane Mn4complexesGS4Macroscopic Measurement of Resonant Magnetization Tunneling in High-Spin Molecules

No comments:

Post a Comment