Ferromagnetic coupling in hexanuclear gadolinium clusters

The magnetic susceptibilities of hexanuclear gadolinium clusters in the compounds Gd(Gd6ZI12) (Z = Co, Fe, or Mn) and CsGd(Gd6CoI12)2 are reported and subjected to theoretical analysis with the help of density functional theory (DFT) computations. The single-crystal structure of Gd(Gd6CoI12) is reported here as well. We find that the compound with a closed shell of cluster bonding electrons, Gd(Gd6CoI12), exhibits the effects of antiferromagnetic coupling over the entire range of temperatures measured (4-300 K). Clusters with unpaired, delocalized cluster bonding electrons (CBEs) exhibit enhanced susceptibilities consistent with strong ferromagnetic coupling, except at lower temperatures (less than 30 K) where intercluster antiferromagnetic coupling suppresses the susceptibilities. The presence of two unpaired CBEs, as in [Gd6MnI12]3-, yields stronger coupling than when just one unpaired CBE is present, as in [Gd6FeI12]3- or [Gd6CoI12]2-. DFT calculations on model molecular systems, [Gd6CoI12](OPH3)6 and [Gd6CoI12]2(OPH3)10, indicate that the delocalized cluster bonding electrons are highly effective at mediating intracluster ferromagnetic exchange coupling between the Gd atom 4f7 moments and that intercluster coupling is expected to be antiferromagnetic. The DFT calculations were used to calculate the relative energies of various 4f7 spin patterns and form the basis for construction of a simple spin Hamiltonian describing the coupling within the [Gd6CoI12] cluster.     

Heterometallic hexanuclear cluster with an S = 8 spin ground state: MnII[MnII(hfac)2]3[NiII(pao)3]2 (hfac- = hexafluoroacetylacetonate,pao- = pyridine-2-aldoximate)

The heterometallic Mn(II)(4)Ni(II)(2) title compound has been synthesized and characterized by X-ray crystallography. The compound consists of a Ni-Mn-Ni linear moiety, [[Ni-(mu-NO)(3)](2)-Mn], linked by oximate bridges and three Mn(II) hfac terminal units attached by oximate oxygens in a di-mu-oxo fashion, forming a novel heterometallic cluster: Mn[Mn(hfac)(2)](3)[Ni(pao)(3)](2) (1). Magnetic measurements reveal the antiferromagnetic nature of the oximate pathway between Mn(II) and Ni(II) metal ions, which imposes an unusual high-spin ground state (S = 8) for 1.     

The spin coupling in the diiron complex [Fe2(hpdta)(H2O)3Cl

Density functional, multireference configuration interaction, and modified valence configuration interaction calculations are used to investigate the electronic structure and spin coupling of the dinuclear [Fe(2)(hpdta)(H(2)O)(3)Cl] complex (H(5)hpdta = Hydroxypropane-1,3-diamine-N,N,N',N'-tetraacetic acid). The density functional calculations give evidence of both, states with local high-spin iron centres and states with local low-spin iron centres, the relative energy of which strongly depends on the functional. The splitting of states due to the spin coupling between the high-spin iron centres varies by more than a factor of two for different functionals. In an attempt to study to what extent it is possible to undertake configuration interaction calculations on such binuclear compounds, multireference configuration interaction calculations are performed on a [Fe(2)(OH)(5)(H(2)O)(3)(NH(3))(2)Cl] model complex. The results show that, when correlating only the ten iron 3d orbitals and the four valence orbitals of the bridging OH group, the calculated splitting is still by a factor of about 3 smaller than the value for the splitting inferred from magnetic susceptibility measurements. Modified valence configuration interaction calculations are performed to approximately take into account the influence of orbital relaxation effects of all occupied orbitals in the excited configurations. The exchange splitting is significantly increased, but still smaller than the experimental value.     

Ferromagnetic coupling and thermochromism in [Ni(rac-CTH)(mu1,1-N3)2Cu(N3)2], the first end-on azido-bridged bimetallic complex

Reaction of [Ni(rac-CTH)(ClO(4))(2)](rac-CTH = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) with NaN(3) and Cu(NO(3))(2).3H(2)O produces the binuclear complex [Ni(rac-CTH)(mu(1,1)-N(3))(2)Cu(N(3))(2)] 1, which represents the first example of an end-on bridged bimetallic complex; 1 exhibits intramolecular ferromagnetic exchange coupling and thermochromism, this latter being a consequence of the intermolecular interaction at low temperature.     

Ferromagnetic coupling in the three-dimensional malonato-bridged gadoliniumIII complex [Gd2(mal)3(H2O)6] (H2mal = malonic acid)

The novel gadolinium(III) complex of formula [Gd(2)(mal)(3)(H(2)O)(6)] (1) (H(2)mal = 1,3-propanedioic acid) has been prepared and characterized by X-ray diffraction analysis. Crystal data for 1: monoclinic, space group I2/a, a = 11.1064(10) A, b = 12.2524(10) A, c =13.6098(2) A, beta = 92.925(10) degrees, U = 1849.5(3) A(3), Z = 4. Compound 1 is a three-dimensional network made up of malonate-bridged gadolinium(III) ions where the malonate exhibits two bridging modes, eta(5)-bidentate + unidentate and eta(3):eta(3) + bis(unidentate). The gadolinium atom is nine-coordinate with three water molecules and six malonate oxygen atoms from three malonate ligands forming a distorted monocapped square antiprism. The shortest metal-metal separations are 4.2763(3) A [through the oxo-carboxylate bridge] and 6.541(3) A [through the carboxylate in the anti-syn coordination mode]. The value of the angle at the oxo-carboxylate atom is 116.8(2) degrees. Variable-temperature magnetic susceptibility measurements reveal the occurrence of a significant ferromagnetic interaction through the oxo-carboxylate pathway (J = +0.048(1) cm(-1), H = -JS(Gd(1)) x S(Gd(1a))).     

Transmission of spin—spin coupling constants through different paths in bicyclo(2,2,1)heptane: their calculation using inner projections of the polarization propagator

Inner projections of the polarization propagator are used to calculate components of the Fermi contact interaction between protons attached to the bridgehead carbon atoms of bicyclo(2,2,1)Heptane. Four- and five-bond paths and throuh-space interaction are considered. Reasonable path additivity and agreement with experimental data are found at the INDO level.     

Antiferromagnetic coupling in a six-coordinate high spin cobalt(II)-semiquinonato complex

The 3,5-di-tert-butyl-catecholato and 9,10-phenanthrenecatecholato adducts of the cobalt-tetraazamacrocycle complex Co(Me(4)cyclam)(2+) (Me(4)cyclam = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) were synthesized and oxidized. The oxidation reaction products were isolated in the solid state as hexafluorophosphate derivatives. Both these complexes can be formulated as 1:1 cobalt(II)-semiquinonato complexes, that is, Co(Me(4)cyclam)(DBSQ)PF(6) (1) and Co(Me(4)cyclam)(PhSQ)PF(6) (2), in the temperature range 4-300 K, in striking contrast with the charge distribution found in similar adducts formed by related tetraazamacrocycles. The synthesis strategy and the structural, spectroscopic, and magnetic properties are reported and discussed. The crystallographic data for 2 are as follows: monoclinic, space group P2(1)/a, nomicron. 14, a = 14.087(4) A, b = 15.873(4) A, c = 14.263 (7) A, alpha = 89.91(3) degrees, beta = 107.34(2) degrees, gamma = 90.08(2) degrees, Z = 4. Both these complexes are characterized by triplet electronic ground states arising from the antiferromagnetic coupling between the high-spin d(7) metal ion and the radical ligand.     

Synthesis,crystal structure,magnetic properties and electrochemical behavior of the mixed valence compound [CuI(CN)3CuII(dipn)]

A mixed-valence cyano-bridged Cu^II/Cu^I complex, 1, has been prepared. Complex 1 was fully characterized spectroscopically (UV-Vis and IR), and its structure was determined by X-ray crystallography. The magnetic property was measured in the temperature range 2–300?K. Electrochemical studies of 1 reveal a one-electron oxidation-reduction process associated with the Cu(II)/Cu(I) couple.     

Ferromagnetic coupling between low- and high-spin iron(III) ions in the tetranuclear complex fac-[[FeIII[HB(pz)3](CN)2(mu-CN)]3FeIII(H2O)3]* 6H2O ([HB(pz)3]- = hydrotris(1-pyrazolyl)borate)

The novel mononuclear PPh4-fac-[FeIII[HB(pz)3](CN)3]*H2O (1) [PPh4+= tetraphenylphosphonium cation; (HB(pz)3)- = hydrotris(1-pyrazolyl)borate] and tetranuclear fac-[[FeIII[HB(pz)3](CN)2(mu-CN)]3FeIII(H2O)3]*6H2O (2) have been prepared and characterized by X-ray diffraction analysis. Crystal data for compound 1: monoclinic, space group P21/c, a = 9.575(3) A, b = 21.984(4) A, c = 16.863(3) A, beta = 100.34(2) degrees, U = 3486(1) A3, Z = 4. Crystal data for compound 2: orthorhombic, space group Pnam, a = 14.084(3) A, b = 14.799(4) A, c = 25.725(5) A, U = 5362(2) A3, Z = 4. Compound 1 is a low-spin iron(III) compound with three cyanide ligands in fac arrangement and a tridentate pyrazolylborate ligand building a distorted octahedral environment around the iron atom. Compound 2 is the first example of a molecular species containing three peripheral low-spin iron(III) ions linked to a central high-spin iron(III) cation by single cyanide bridges, the anion of 1 acting as a monodentate ligand in 2. Variable-temperature magnetic susceptibility measurements of 2 reveal the occurrence of a significant ferromagnetic coupling between the three peripheral low-spin iron(III) centers and the central high-spin iron(III) ion cations leading to a low-lying nonet spin state.     

A hexanuclear manganese(III) complex constructed from triangular-shaped [Mn3O] units with azide bridge

On the basis of triangular-shaped secondary building units, a hexanuclear manganese(III) complex, [Mn^III₆O₂(sao)₆(N₃)₂(H₂O)₈]·2.5H₂O (1) (H₂sao = salicylaldoxime), was synthesized and structurally characterized. The structure of 1 consists of two triangular-shaped [Mn₃O] connected with end-to-end (EE) azide group. Magnetic data analysis shows that antiferromagnetic couplings dominated in the complex.     

Interacting networks and spin polarization in (Dy,Ca)MnO3

Solid solutions of Dy_1−xCa_xMnO₃ (0.00⩽x⩽0.60) were prepared by solid state reaction of oxides and carbonates. Sintered bodies were obtained by firing between 1250 and 1450 °C. All compositions, including DyMnO₃, crystallize in a perovskite structure of O′-type orthorhombic symmetry and space group Pbnm. Increase of Ca²⁺ content leads to a monotonic decrease of the orthorhombicity factor b/a. Electrical measurements show a semiconducting behavior for all compositions. The room temperature conductivity increases with Ca content, attaining relatively high values at x=0.60 and a correlative very low value of the activation energy. Thermally-activated small-polaron hopping mechanism controls the conductivity. Antiferromagnetic interactions between Dy spins are observed at T_N=9.5 K. DyMnO₃ behaves as a metamagnetic-like system, with no remanent magnetization at zero field. ZFC/FC cycles and the thermal evolution of the remanent magnetization of the Dy_1−xCa_xMnO₃ solid solution show the presence of two interacting magnetic networks: a Dy sublattice, with a Curie–Weiss thermal dependence above T_N, aligned antiparallel to the ferromagnetically ordered (T_c=80 K) Mn network. The local field at a given site depends on the exchange interaction J between these two sublattices, leading to a spin reversal when the magnetic moment of the dysprosium network is larger than the one produced by the ferromagnetic Mn sublattice.     

MnII[MnII(CN)4]—A Magnetic Interpenetrating Three-Dimensional Diamondlike Solid

Three-dimensional extended diamondlike networks containing four-coordinate metal centers can be constructed from [Mn^II(CN)₄]²⁻ building blocks. Besides the title compound, which was prepared and its magnetic properties studied in detail, other novel magnetic solids might be able to be synthesized.     

Ferromagnetic intermolecular interaction in the galvinoxyl radical: Cooperation of spin polarization and charge-transfer interaction

The orbital energies and the intermolecular overlap integrals of the galvinoxyl radical are calculated. It is found that the ferromagnetic intermolecular interaction in galvinoxyl can be qualitatively interpreted by a combined effect of spin polarization within the radical and charge-transfer interaction between the radicals.     

四氮杂环十二烷铒配合物的合成及其晶体结构

氮气保护下, 在无水乙腈中合成了1, 4, 7, 10-四氮杂环十二烷(Cyclen)与稀土铒的配合物并得到浅红色棱柱状晶体。元素分析结果表明该配合物的组成为Er(Cyclen)(CF3SO3)3(CH3CN)。用X射线衍射方法研究了其单晶结构。晶体属单斜晶系, P21/a空间群。晶胞参数为a=1.7335(4), b=1.8027(4),c=0.8772(3)nm, β=97.64(3)°, V=2.7171(2)nm^3, Z=4。其中铒为八配位,形成四方反棱柱型配位多面体。     

Structural study of the thermal and photochemical spin states in the spin crossover complex [Fe(phen)2(NCSe)2

The first structural data for [Fe(phen)(2)(NCSe)(2)] (obtained using the extraction method of sample preparation) in its high-spin, low-spin and LIESST induced metastable high-spin states have been recorded using synchrotron radiation single crystal diffraction. The space group for all of the spin states was found to be Pbcn. On cooling from the high-spin state (HS-1) at 292 K through the spin crossover at about 235 K to the low-spin state at 100 K (LS-1) the iron coordination environment changed to a more regular octahedral geometry and the Fe-N bond lengths decreased by 0.216 and 0.196 A (Fe-N(phen)) and 0.147 A (Fe-N(CSe)). When the low-spin state was illuminated with visible light at about 26 K, the structure of this LIESST induced metastable high-spin state (HS-2) was very similar to that of HS-1 with regards to the Fe-phen bond lengths, but there were some differences in the bond lengths in the Fe-NCSe unit between HS-1 and HS-2. When HS-2 was warmed in the dark to 50 K, the resultant low-spin state (LS-2) had an essentially identical structure to LS-1. In all spin states, all of the shortest intermolecular contacts (in terms of van der Waals radii) involved the NCSe ligand, which may be important in describing the cooperativity in the solid state. The quality of the samples was confirmed by magnetic susceptibility and IR measurements.     

Structure and Magnetic Ordering of the Anomalous Layered (2D) Ferrimagnet [NEt4]2MnII3(CN)8 and 3D Bridged‐Layered Antiferromagnet [NEt4]MnII3(CN)7 Prussian Blue Analogues

The reaction of Mn^II and [NEt₄]CN leads to the isolation of solvated [NEt₄]Mn₃(CN)₇ ( 1 ) and [NEt₄]₂Mn₃(CN)₈ ( 2 ), which have hexagonal unit cells [ 1 : R$\bar 3$ m, a=8.0738(1), c=29.086(1) Å; 2 : P$\bar 3$ m1, a=7.9992(3), c=14.014(1) Å] rather than the face centered cubic lattice that is typical of Prussian blue structured materials. The formula units of both 1 and 2 are composed of one low‐ and two high‐spin Mn^II ions. Each low‐spin, octahedral [Mn^II(CN)₆]^4? bonds to six high‐spin tetrahedral Mn^II ions through the N atoms, and each of the tetrahedral Mn^II ions are bound to three low‐spin octahedral [Mn^II(CN)₆]^4? moieties. For 2 , the fourth cyanide on the tetrahedral Mn^II site is C bound and is terminal. In contrast, it is orientationally disordered and bridges two tetrahedral Mn^II centers for 1 forming an extended 3D network structure. The layers of octahedra are separated by 14.01 Å (c axis) for 2 , and 9.70 Å (c/3) for 1 . The [NEt₄]⁺ cations and solvent are disordered and reside between the layers. Both 1 and 2 possess antiferromagnetic superexchange coupling between each low‐spin (S=1/2) octahedral Mn^II site and two high‐spin (S=5/2) tetrahedral Mn^II sites within a layer. Analogue 2 orders as a ferrimagnet at 27(±1) K with a coercive field and remanent magnetization of 1140 Oe and 22 800 emuOe mol^?1, respectively, and the magnetization approaches saturation of 49 800 emuOe mol^?1 at 90 000 Oe. In contrast, the bonding via bridging cyanides between the ferrimagnetic layers leads to antiferromagnetic coupling, and 3D structured 1 has a different magnetic behavior to 2 . Thus, 1 is a Prussian blue analogue with an antiferromagnetic ground state [T_c=27 K from d(χT)/dT].     

Crystal structure and fluorescence spectrum of the complex [Eu(III)(TTA)3(phen)]

The title complex Eu(III)(TTA)₃(phen) (where TTA = thenoyltrifluoroacetone monoanion; phen = 1,10-phenanthroline) has been synthesized in mixed solvents of acetone and ethanol (1:1 volume ratio) and its crystal structure has been determined by X-ray diffraction. The complex crystals are triclinic, space group P 1 (# 2) with cell dimensions of a = 1.32.41 (2) nm, b = 1.5278(4) nm, c = 0.9755(3) nm, α = 92.49 (2)°, β = 102.57(2)°, γ = 91.62(2)°, V = 1.9268(8) nm³, Z = 2, μ (Mo Ka)= 18.77 cm^?1, D_x=1.720 g/cm³. The coordination geometry of Eu atom is a distorted square antiprism, and the encapsulated structure that can meet the structural requirement of the typical europium luminescent sensor. The fluorescence spectrum suggests that the complex is a strong photoluminescent material.