(Gd1-xREx)5Si4(RE=Dy, Ho)系列材料磁熵变研究

对 (Gd1-xDyx)5Si4(x=0.1, 0.2, 0.3, 0.35) 和(Gd1-xHox)5Si4(x=0.05, 0.15, 0.25)系列合金的居里温度、磁相变、磁熵变等磁性质进行了研究. 结果发现 该系列合金保持了Gd5Si4的Sm5Ge4正交型晶体结构, 居里温度随着引入的x量的增加而呈近似线性减小趋势;在居里温度附近样品的磁特性符合二级相变规律;通过调节Dy 或Ho的含量调节居里点, 样品中不含贵重元素Ge, 大大降低了成本;在较宽的温度范围和低场下(＜2 T)具有较大的磁熵变值从而使其适合于被制成梯度功能复合材料. 研究表明 (Gd1-xREx)5Si4(RE=Dy, Ho)系列材料有望成为较好的室温低场磁制工质.     

NdSr_（1－x）M_xNiO_4（M＝Ca，Ba）的合成，结构和电学磁学性

用固相法首次合成了ＮｄＳｒ＿（１－ｘ）Ｍ＿ｘＮｉＯ＿４（Ｍ＝Ｃａ：０．０≤１．０；Ｍ＝Ｂａ：０．０≤ｘ≤０．６）系列复合氧化物，并研究了其结构，红外光谱，电学性质和磁学性质。除ＮｄＣａＮｉＯ以正交晶系结晶外，其它试样的结构均属于四方晶系。ＩＲ谱显示随Ｃａ￣（２＋）离子含量的增加，ＮｄＳｒ＿（１－ｘ）Ｍ＿ｘＮｉＯ＿４的Ｎｉ－Ｏ键缩短，Ｃａ￣（２＋）和Ｂａ￣（２＋）引入ＮｄＳｒＮｉＯ＿４以取代Ｓｒ￣（２＋），使试样由金属性导电转变为半导体性导电；随Ｃａ￣（２＋）含量增加，试样的室温电阻率增大。７７～３００Ｋ磁化率与温度关系曲线显示，所有试样的Ｎｉ￣（３＋）都以低自旋状态存在。     

Synthesis, nuclear, and magnetic structures and magnetic properties of [Mn3(OH)2(SO4)2(H2O)2

[Mn(3)(OH)(2)(SO(4))(2)(H(2)O)(2)] and its deuterated analogue were synthesized by a hydrothermal technique and characterized by differential thermal analysis, thermogravimetric analysis, and IR spectroscopy. Its nuclear structure, determined by single-crystal X-ray analysis and Rietveld analysis of neutron powder-diffraction data, consists of a 3D network of chains of edge-sharing Mn(1)O(6), running along the c axis, connected by the apices of Mn(2)O(6) and SO(4) units. It is isostructural to the nickel analogue. Determination of the magnetic structure and measurements of magnetization and heat capacity indicate the coexistence of both magnetic long-range ordering (LRO) and short-range ordering (SRO) below a Néel temperature of 26 K, while the SRO is retained at higher temperatures. The moments of the two independent Mn atoms lie in the bc plane, and that of Mn(1) rotates continuously by 54 degrees towards the c axis on decreasing the temperature from 25 to 1.4 K. While the SRO may be associated with frustration of the moments within a Mn(3) trimer, the LRO is achieved by antiparallel alignment of the four symmetry-related trimers within the magnetic unit cell. A spin-flop field, measured by dc and ac magnetization on a SQUID, is observed at 15 kOe.     

Investigation of Uranium Tris(imido) Complexes: Synthesis,Characterization, and Reduction Chemistry of [U(NDIPP)3(thf)3]

Addition of KC₈ to trivalent [UI₃(thf)₄] in the presence of three equivalents of 2,6‐diisopropylphenylazide (N₃DIPP) results in the formation of the hexavalent uranium tris(imido) complex [U(NDIPP)₃(thf)₃] ( 1 ) through a facile, single‐step synthesis. The X‐ray crystal structure shows an octahedral complex that adopts a facial orientation of the imido substituents. This structural trend is maintained during the single‐electron reduction of 1 to form dimeric [U(NDIPP)₃{K(Et₂O)}]₂ ( 2 ). Variable‐temperature/field magnetization studies of 2 show two independent U^V 5f ¹ centers, with no antiferromagnetic coupling present. Characterization of these complexes was accomplished using single‐crystal X‐ray diffraction, variable‐temperature ¹H NMR spectroscopy, as well as IR and UV/Vis absorption spectroscopic studies.     

Synthesis, crystal structures, and properties of oxovanadium(IV)-lanthanide(III) heteronuclear complexes

A new series of oxovanadium(IV)-lanthanide(III) heteronuclear complexes [Yb(H2O)8]2[(VO)2(TTHA)](3)21 H2O (1), {[Ho(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)} 8.5 H2O (2), {[Gd(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)}8.5 H2O (3), {[Eu(H2O)7][(VO)2(TTHA)](1.5)} 10.5 H2O (4), and [Pr2(H2O)6(SO4)2][(VO)2(TTHA)] (5) (H6TTHA=triethylenetetraaminehexaacetic acid) were prepared by using the bulky flexible organic acid H(6)TTHA as structure-directing agent. X-ray crystallographic studies reveal that they contain the same [(VO)2(TTHA)]2- unit as building block, but the Ln3+ ion lies in different coordination environments. Although the lanthanide ions always exhibit similar chemical behavior, the structures of the complexes are not homologous. Compound 1 is composed of a [Yb(H2O)8]3+ ion and a [(VO)2(TTHA)]2- ion. Compounds 2 and 3 are isomorphous; both contain a trinuclear [Ln(H2O)7(VO)2(TTHA)]+ (Ln=Ho for 2 and Gd for 3) ion and a [(VO)2(TTHA)]2- ion. Compound 4 is an extended one-dimensional chain, in which each Eu3+ ion links two [(VO)2(TTHA)]2- ions. For 5, the structure is further assembled into a three-dimensional network with an interesting framework topology comprising V2Pr2 and V4Pr2 heterometallic lattices. Moreover, 4 and 5 are the first oxovanadium(IV)-lanthanide(III) coordination polymers and thus enlarge the realm of 3d-4f complexes. The IR, UV/Vis, and EPR spectra and the magnetic properties of the heterometallic complexes were studied. Notably, 2 shows unusual ferromagnetic interactions between the VO2+ and Ho3+ ions.     

Front Cover: Water-Solvation-Dependent Spin Transitions in Cobalt(II)-Octacyanidometallate Complexes (Eur. J. Inorg. Chem. 30/2023)

The spin-crossover (SCO) and charge-transfer (CT) phenomena, the switching processes between two distinguishable magnetic states, are promising for developing materials capable of sophisticated memory and sensing functionalities. The majority of SCO systems are based on iron(II) complexes. However, cobalt(II)-2,2′:6′,2′′-terpyridine (terpy) systems emerge as a promising alternative. In this work, new complex salts [Co^II(terpy)₂]₂[Mo^IV(CN)₈] ⋅ 15H₂O, Co₂Mo (H₂O), and [Co^II(terpy)₂]₃[W^V(CN)₈]₂ ⋅ 12H₂O, Co₃W₂ (H₂O) were synthesized and physiochemically characterized. Structural studies for both compounds revealed [Co(terpy)₂]²⁺ layers pillared by octacyanidometallate anions and completed with water molecules between them. Magnetic studies confirmed that the (de)solvated phases of both complexes exhibit partial SCO on the cobalt(II) centers: Co^II−LS (S_Co(II)-LS=¹/₂)↔Co^II−HS (S_Co(II)-HS=³/₂). Moreover, handling dehydrated samples in a high-humidity environment leads to partial recovery of previous magnetic properties via humidity-induced SCO for Co₂Mo : Co^II−HS→Co^II−LS, and the new phenomenon of isothermal humidity-activated charge-transfer-induced spin transition, which we define here as HACTIST, for Co₃W₂ : Co^II−HS⋅⋅⋅W^V (S_Co(II)-HS=³/₂ and S_W(V)=¹/₂)→Co^III−LS⋅⋅⋅W^IV (S_W(IV)=0 and S_Co(III)-LS=0). These comprehensive studies shed light on the water-solvation-dependent spin transitions in Co(II)-octacyanidometallate(IV/V) complexes.     

Slow Magnetic Relaxation,Antiferromagnetic Ordering,and Metamagnetism in MnII(H2dapsc)-FeIII(CN)6 Chain Complex with Highly Anisotropic Fe-CN-Mn Spin Coupling

Reactions of [Mn(H₂dapsc)Cl₂] ⋅ H₂O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K₃[Fe(CN)₆] and (PPh₄)₃[Fe(CN)₆] lead to the formation of the chain polymeric complex {[Mn(H₂dapsc)][Fe(CN)₆][K(H₂O)_3.5]}_n ⋅ 1.5n H₂O ( 1 ) and the discrete pentanuclear complex {[Mn(H₂dapsc)]₃[Fe(CN)₆]₂(H₂O)₂} ⋅ 4 CH₃OH ⋅ 3.4 H₂O ( 2 ), respectively. In the crystal structure of 1 the high-spin [Mn^II(H₂dapsc)]²⁺ cations and low-spin hexacyanoferrate(III) anions are assembled into alternating heterometallic cyano-bridged chains. The K⁺ ions are located between the chains and are coordinated by oxygen atoms of the H₂dapsc ligand and water molecules. The magnetic structure of 1 is built from ferrimagnetic chains, which are antiferromagnetically coupled. The complex exhibits metamagnetism and frequency-dependent ac magnetic susceptibility, indicating single-chain magnetic behavior with a Mydosh-parameter φ=0.12 and an effective energy barrier (U_eff/k_B) of 36.0 K with τ₀=2.34×10⁻¹¹ s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [Fe^III(CN)₆]³⁻ and [Mn^II(H₂dapsc)]²⁺ units resulting from orbital degeneracy and unquenched orbital momentum of [Fe^III(CN)₆]³⁻ complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.     

Density functional study of magnetic exchange of dinuclear manganese complexes with the heteropoly-molyanion:[Mn~(II)_2(X~(n )Mo_9O_(33))_2]~(2(n-10)-) (X=P~V, As~V, Se~VI)

The magnetic exchange interactions between the dimanganese(II)-substituted complexes and the het-eropolymolyanion, [MnII2(Xn Mo9O33)2]2(n-10)-(X = PV(I), AsV(II) and SeVI(III)), are investigated by using density functional theory combined with broken-symmetry approach (DFT-BS) method. The calculated magnetic exchange coupling constant (J) of complex II is in reasonable agreement with the responding experimental value and the negative J values indicate that antiferromagnetic exchange interactions exist in these complexes. Furthermore, the influence of the central heteroatom on the exchange cou-pling within the dimanganese core unit is studied from standpoints of geometry, spin density and fron-tier orbitals. It demonstrates that the change of the heteroatom X via PV-AsV-SeVI elongates the dis-tances of Mn1···Mn2 and shortens the distances of Ob···Ob, and reduces the effectiveness of the super-exchange pathways, consequently, decreasing the magnitude of the antiferromagnetic coupling constant, J, of these species.     

Structural and magnetic studies of the tris(cyclopentadienyl)manganese(II) "paddle-wheel" anions [Cp(3-n)(MeCp)(n)Mn](-) (n=0-3, MeCp=C(5)H(4)CH(3), Cp=C(5)H(5))

The ion-contact complexes [{(eta(5)-Cp)(2)Mn(eta(2):eta(5)-Cp)K}(3)]x0.5 THF (1x0.5 THF) and [{(eta(2)-Cp)(2)(eta(2);eta(5)-MeCp)MnK(thf)}]x2 THF (2x2 THF) and ion-separated complexes [Mg(thf)(6)][(eta(2)-Cp)(3)Mn](2) (3), [Mg(thf)(6)][(eta(2)-Cp)(eta(2)-MeCp)(2)Mn)](2)x0.5 THF (4x0.5 THF), [Mg(thf)(6)][(eta(2)-MeCp)(3)Mn)](2)x0.5 THF (5x0.5 THF) and [Li([12]crown-4)](5)[(eta-Cp)(3)Mn](5) (6) (Cp=C(5)H(5), CpMe=C(5)H(4)CH(3)), have been prepared and structurally characterised. The effects of varying the Cp and CpMe ligands in complexes 1-5 have been probed by variable-temperature magnetic susceptibility measurements and EPR spectroscopic studies.     

Syntheses,Crystal Structures and Magnetic Properties of Cobalt(Ⅱ) and Manganese(Ⅱ) Coordination Polymers Constructed from 5-(Pyridin-4-yl)Isophthalate Ligands

Two coordination polymers, namely {[Co(L)(H2O)]·H2O}n(1) and [Mn(L)(phen)]n(2, H2L = 5-(pyridin-4-yl)isophthalic acid, phen = 1,10-phenanthroline), have been hydrothermally synthesized and characterized by elemental analysis, IR, TG, magnetic properties, and single-crystal X-ray diffraction. 1 belongs to the triclinic system, space group P1 with a = 7.2188(7), b = 10.0835(8), c = 10.2069(7) ?, α = 113.713(7), β = 99.490(7), γ = 104.516(8)o, V = 628.24(9) ?3, C13H11NCoO6, Mr = 336.16, Z = 2, Dc = 1.777 Mg/m3, μ(MoKα) = 1.395 mm–1, F(000) = 342, S = 1.041, the final R = 0.0381 and wR = 0.0819 for 3744 observed reflections(I 2σ(I)) and R = 0.0448 and wR = 0.0874 for all data. 2 belongs to the monoclinic system, space group P2/c with a = 12.9185(3), b = 10.4343(2), c = 31.7650(6)?, β = 101.282(2)o, V = 4199.08(13)?3, C50H30N6Mn2O8, Mr = 952.68, Z = 4, Dc = 1.507 Mg/m3, μ(MoKα) = 5.447 mm–1, F(000) = 1944, S = 1.128, the final R = 0.1003 and wR = 0.1052 for 8247 observed reflections(I 2σ(I)) and R = 0.2595 and wR = 0.2625 for all data. Single-crystal X-ray diffraction studies show that compound 1 features a 2D sheet structure based on a dicobalt(II) subunit, which is further extended into a 3D metal-organic supramolecular framework by O–H···O hydrogen bond. Compound 2 also possesses a 2D sheet, which is held together into a 3D supramolecular architecture via C–H···O hydrogen bond and π-π stacking interactions. Magnetic studies for compound 2 show antiferromagnetic coupling between the adjacent metal centers, with J = –11.8 cm–1 and g = 2.12 for 2.     

不同工艺和原料对Mn_(1.2)Fe_(0.8)P_(0.48)Si_(0.52)化合物磁热效应的影响

用不同的工艺和原料制备了3个名义成分相同的Mn1.2Fe0.8P0.48S i0.52化合物。X射线衍射结果表明,3个化合物均为Fe2P型六角结构(空间群为P-62m),并且存在少量的(Fe,Mn)3S i相。通过磁性测量发现,3个样品的居里温度有所不同,但是都在室温附近(270~290 K)。以Fe2P为原料制备的化合物具有较大的磁熵变,在1.5 T的磁场变化下其最大磁熵变为13.6 J.(kg.K)-1。以行星样品球磨机制备的化合物具有较小的热滞,最小热滞为6.7 K。这些表明不同的制备工艺和原料对化合物的居里温度、热滞和磁熵变都具有一定的影响。同时低成本的原料、简单的制备工艺、较小的热滞和较大的磁熵变使得Mn1.2Fe0.8P0.48S i0.52化合物成为一种理想的室温磁致冷候选材料。     

Synthesis, crystal structure, and magnetic properties of a cobalt(II) complex with (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol

A novel bridging ligand, (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol (I), and its cobalt(II) complex, [Co(I)₂(NCS)₂]_n (II), were prepared. The structures of ligand I and complex II were determined by single crystal X-ray analysis. Magnetic susceptibility measurements were performed for cobalt (II) complex II. Compound I crystallised in orthorhombic space group Pbca with a = 7.6585(14) Å, b = 12.209(2) Å, c = 23.207(4) Å, V= 2170.0(7) ų and Z=8. Complex II crystallised in monoclinic space group P2₁/n with a = 13.223(8) Å, b = 16.959(10) Å, c = 13.948(8) Å, β = 115.395(10)°, V= 2826(3) ų and Z = 4. Each cobalt(II) ion is surrounded by two NCS^? anions and four pyridyl moieties from two bridging ligands. Each bridging ligand connects two neighbouring Co(II) ions to form a 2-dimensional structure. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K revealed that magnetic interactions between the cobalt ions are weak.     

Synthesis,Magnetic Properties,and STM Spectroscopy of Cobalt(II) Cubanes [CoII4(Cl)4(HL)4]

Reaction of cobalt(II) chloride hexahydrate with N‐substituted diethanolamines H₂L^2–4 ( 3 ) in the presence of LiH in anhydrous THF leads under anaerobic conditions to the formation of three isostructural tetranuclear cobalt(II) complexes [Co^II₄(Cl)₄(HL^2–4)₄] ( 4 ) with a [Co₄(μ₃‐O)₄]⁴⁺ cubane core. According to X‐ray structural analyses, the complexes 4 a , c crystallize in the tetragonal space group I4₁/a, whereas for complex 4 b the tetragonal space group P$\bar 4$ was found. In the solid state the orientation of the cubane cores and the formation of a 3D framework were controlled by the ligand substituents of the cobalt(II) cubanes 4 . This also allowed detailed magnetic investigations on single crystals. The analysis of the SQUID magnetic susceptibility data for 4 a gave intramolecular ferromagnetic couplings of the cobalt(II) ions (J₁≈20.4 K, J₂≈7.6 K), resulting in an S=6 ground‐state multiplet. The anisotropy was found to be of the easy‐axis type (D=?1.55 K) with a resulting anisotropy barrier of Δ≈55.8 K. Two‐dimensional electron‐gas (2DEG) Hall magnetization measurements revealed that complex 4 a is a single‐molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep‐rate dependencies below a blocking temperature of about 4.4 K. The hysteresis loops collapse at zero field owing to fast quantum tunneling of the magnetization (QTM). The structural and electronic properties of cobalt(II) cubane 4 a , deposited on a highly oriented pyrolytic graphite (HOPG) surface, were investigated by means of STM and current imaging tunneling spectroscopy (CITS) at RT and standard atmospheric pressure. In CITS measurements the rather large contrast found at the expected locations of the metal centers of the molecules indicated the presence of a strongly localized LUMO.     

Acetonitrile-facilitated reductive dimerization of TCNE to octacyanobutanediide, [C4(CN)8]2-, by Iron(II) chloride

The redox properties of MCl2 (M=Mn, Fe, Co) acetonitrile solvates were electrochemically and spectroscopically characterized. The three voltammogram waves at 0.86, 0.48, and 0.21 V versus SCE for FeCl(2) dissolved in MeCN are assigned as one-electron reduction potentials for [Fe(II)Cl(x)(NCMe)4-x]2-x (1相似文献   

Poly(phenylene sulfide) magnetic composites. I. Relations of percolation between rheology,electrical, and magnetic properties

Poly(phenylene sulfide)/ferrosoferric oxide composites (PPS/Fe₃O₄) with various loading levels were prepared by melt compounding. The microstructure of composites was investigated using SEM and XRD. The rheological, electrical and magnetic properties were characterized respectively by the parallel plate rheometer, high resistance meter, and magnetometer. The results reveal that the Fe₃O₄ particles are well dispersed in the PPS matrix due to their nice affinity, which results in a weak strain overshoot at large amplitude oscillatory level. Both the rheological and the electrical responses of the composites show a typical percolation behavior. But the rheological percolation presents lower threshold (< 40 wt %) than that of electrical percolation (～ 50 wt %), which is attributed to the difference structure of the percolation network. The magnetic response, however, shows good linear relation with Fe₃O₄ loadings, indicating that the physical percolation has little influence on the magnetic properties. This is mainly due to the yielded long‐range magnetic interactions among Fe₃O₄ particles in the applied field, which are far stronger than those nonmagnetic physical interactions accounting for percolation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 233–243, 2008