Vladimir S. Mironov

Room-temperature magnetic anisotropy of lanthanide complexes: A model study for various coordination polyhedra

The dependence of the room-temperature magnetic anisotropy Δχ of lanthanide complexes on the type of the coordination polyhedron and on the nature of the lanthanide ion is quantitatively analyzed in terms of a model approach based on numerical calculations. The aim of this study is to establish general regularities in the variation of the sign and magnitude of the magnetic anisotropy of lanthanide complexes at room-temperature and to estimate its maximal value. Except for some special cases, the variation of the sign of the magnetic anisotropy over the series of isostructural lanthanide complexes is found to obey a general sign rule, according to which Ce(III), Pr(III), Nd(III), Sm(III), Tb(III), Dy(III), and Ho(III) complexes have one sign of Δχ and Eu(III), Er(III), Tm(III), and Yb(III) complexes have the opposite sign. Depending on the specific coordination polyhedron, a maximal magnetic anisotropy is observed for Tb(III), Dy(III), or Tm(III) complexes, and its absolute value can reach 50 000×10−6 cm3 ...

On the magnetic anisotropy of lanthanide-containing metallomesogens

A general theoretical model of the origin of the magnetic anisotropy in paramagnetic metal-containing liquid crystals is developed. General relations between the molecular magnetic anisotropy of mesogenic lanthanide complexes and the macroscopic magnetic anisotropy of these liquid crystals in the mesophase are obtained. The net magnetic anisotropy of a real metallomesogen is shown to be the result of a complex interplay between the molecular magnetic anisotropy, orientation of the long molecular axis, and disorder effects. The sign of the magnetic anisotropy Δχ depends not only on the anisotropy of the tensor of molecular magnetic susceptibility, but also on the orientation of the long molecular axis of rodlike lanthanide complexes with respect to the principal magnetic axes of the molecular tensor of magnetic susceptibility. The influence of micro- and macroscopic disorder in real liquid crystals is discussed. Numerical parametric calculations were used to rationalize the variation of the magnitude and s...

Influence of crystal-field perturbations on the room-temperature magnetic anisotropy of lanthanide complexes

The room-temperature magnetic susceptibility anisotropy of eight-coordinate lanthanide ions was modelled numerically for polyhedra resulting from distortions of the regular cube to a tetragonal prism, antiprism, and dodecahedron. Our aim is to illustrate how the magnitude and sign of the room-temperature magnetic anisotropy can be related to the shape of the coordination polyhedron and to estimate its maximum value. Tb(III), Dy(III), and Tm(III) ions are found to have the largest values of the magnetic anisotropy in all coordination polyhedra. These results are helpful to rationalize the orientational behavior of lanthanide-containing liquid crystals in an external magnetic field.

Origin of Dissimilar Single-Molecule Magnet Behavior of Three MnII2MoIII Complexes Based on [MoIII(CN)7]4– Heptacyanomolybdate: Interplay of MoIII–CN–MnII Anisotropic Exchange Interactions

The origin of contrasting single-molecule magnet (SMM) behavior of three MnII2MoIII complexes based on [MoIII(CN)7]4– heptacyanomolybdate is analyzed; only the apical Mn2Mo isomer exhibits SMM properties with Ueff = 40.5 cm(-1) and TB = 3.2 K, while the two equatorial isomers are simple paramagnets [Qian, K.; J. Am. Chem. Soc. 2013, 135, 13302]. A microscopic theory of anisotropic spin coupling between orbitally degenerate [MoIII(CN)7](4-) complexes (pentagonal bipyramid) and bound MnII ions is developed. It is shown that the [MoIII(CN)7](4-) complex has a unique property of uniaxial anisotropic spin coupling in the apical and equatorial MoIII-CN-MnII pairs, H̑eff = -Jxy(SMoxSMnx + SMoySMny) - JzSMozSMnz, regardless of their actual low symmetry. The difference in the SMM behavior originates from a different ratio between the anisotropic exchange parameters Jz and Jxy for the apical and equatorial Mo-CN-Mn groups. In the apical Mn2Mo isomer, an Ising-type anisotropic spin coupling (Jz = -34, Jxy = -11 cm(-1)) produces a double-well potential of spin states resulting in SMM behavior. Exchange anisotropy of an xy-type (|Jz| < |Jxy|) in the equatorial Mn2Mo isomers results in a single-well potential with no SMM properties. The prospects of anisotropic uniaxial spin coupling in engineering of high Ueff and TB values are discussed.

Synthesis, Structure, and Magnetic Properties of 1D {[MnIII(CN)6][MnII(dapsc)]}n Coordination Polymers: Origin of Unconventional Single-Chain Magnet Behavior

Two one-dimensional cyano-bridged coordination polymers, namely, {[MnII(dapsc)][MnIII(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O) (I) and {[MnII(dapsc)][MnIII(CN)6][K(H2O)2(MeOH)2]}n (II), based on alternating high-spin MnII(dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of Ueff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII-CN-MnII spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [MnIII(CN)6]3-. The prospects of [MnIII(CN)6]3- complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.

A New Approach to the Synthesis of Spirophosphoranes on the Basis of Spontaneous Rearrangement of O,O′-Bis(2-Iminophenyl) Arylphosphonites

Abstract O,O-bis(2-benzylideneaminophenyl) arylphosphonites undergo a spontaneous rearrangement into spirophosphoranes, 1-aryl-6,7-diphenyl-3,4:9,10-dibenzo-2,11-dioxa-5,8-diaza-1-phosphatricyclo[6.3.0.01,5]undeca-3,9-dienes. GRAPHICAL ABSTRACT

Reactions of 2-(2-Arylidenaminoaryloxy)Areno-1,3,2-Dioxaphosphole with Trifluoropyruvic and Mesoxalic Ethyl Esters. Synthesis of Cage Phosphoranes with the P–C and P–N Bonds

GRAPHICAL ABSTRACT Abstract Reaction of 2-(2-arylidenaminoaryloxy)areno-1,3,2-dioxaphosphole with trifluoropruvic and mesoxalic ethyl esters gives tricyclic cage phosphoranes with the P–C and Р–N bonds. The structure of one isolated diastereoisomer was established by XRD.

Synthesis and Some Properties of 2-(5-Methyl-2-Phenyl-2H-1,2,3-Diazaphosphol-4-yl)-4H-Benzo[d]-1,3,2-Dioxaphosphorin-4-One

Abstract 2-(5-Methyl-2-phenyl-2Н-1,2,3-diazaphosphol-4-yl)-4H-benzo[d]-1,3,2-dioxaphosphorin-4-one 1 readily reacts with hexafluoroacetone, mesoxalic acid diethyl ester, trifluoropyruvic acid ethyl ester and chloral to give 2-(5-methyl-2-phenyl-2H-1,2,3-dizaphosphole-4-yl)-derivatives of 1,3,2- and 1,4,2-dioxaphosphepines. GRAPHICAL ABSTRACT

First-order Phase Transition in UO2: The Interplay of the 5f2–5f2 Superexchange Interaction and Jahn–Teller Effect

The competition of the superexchange interaction and the cooperative Jahn–Teller (JT) effect in the first-order magnetic and structural phase transition in UO2 is analyzed. The effective spin Hamiltonian of the superexchange interaction between the neighboring U4+ ions in the cubic crystal lattice of UO2 is calculated for the first time in terms of a specially adapted kinetic exchange model. The 5f2–5f2 superexchange interaction is shown to be essentially non-Heisenberg: the effective spin Hamiltonian is anisotropic and contains large biquadratic terms, which formally correspond to a quadrupole–quadrupole interaction. The strength of the JT effect in UO2 is estimated from the calculations of the linear vibronic coupling constants between the local eg, t2g(1) and t2g(2) JT modes and the Γ5 ground state of U4+ performed in terms of a semiempirical crystal field model for 5f electrons. Despite the Γ5⊗eg and Γ5⊗t2g(2) parameters are found to be much larger than Γ5⊗t2g(1), the actual lattice distortion in UO2 is of a pure t2g(1) character. Our results indicate that the superexchange interaction is the major driving force of the phase transition in UO2, which causes the magnetic and orbital ordering and suppresses the cooperative JT effect.

A new hybrid molecular metal assembling a BEDT-TTF conducting network and the magnetic chain anion [Mn2Cl5(H2O)5]−∞: α-(BEDT-TTF)2[Mn2Cl5(H2O)5]

The synthesis, X-ray crystal and electronic band structures as well as magnetotransport and magnetic properties of the α-(BEDT-TTF)2[Mn2Cl5(H2O)5] radical cation salt with a new type of magnetic polymeric complex anion, [Mn2Cl5(H2O)5]−∞, are reported. The crystal structure is characterized by radical cation layers alternating with layers of the polymeric 1-D chain anions constructed from MnCl3(H2O)3 and MnCl4(H2O)2 octahedra connected to each other via the apical Cl atoms. The calculated electronic band structure suggests that the salt should be a stable 2-D metal and the conductivity measurements show that it exhibits metallic behavior down to 0.4 K. Shubnikov-de Haas oscillations, observed at B > 10 T, are characterized by two fundamental frequencies, corresponding to cross-sections of the Fermi surface, in agreement with the electronic band structure calculations. Magnetic measurements reveal antiferromagnetic correlations in the anion network.