Spin Polarization Mechanism Research Articles

Theoretical design of magnetic wires from acene and nanocorone derivatives.

Theoretical calculations on a series of molecular models based on amino derivatives of linear and cycled acenes acting as organic linkers between two copper(ii) ions have shown a wire-like magnetic behaviour, so that the intermetallic magnetic communication does not vanish when the linker becomes larger due to its polyradical nature. Hence, these models can be considered as molecular magnetic wires, which can be used as active components for molecular spintronics, where the information transport is based on spin carriers instead of the more conventional charge transport. The nature of the spin ground state along these two series of models is governed by the topology of the organic linker, in agreement with the spin polarization mechanism, allowing a wide diversity in the design of molecular spintronic circuits. Different approaches to search for the more stable spin configuration have been tested, the most efficient being the one that allows generating a guess function that agrees with the spin polarization mechanism.

Inhomogeneous nuclear spin polarization induced by helicity-modulated optical excitation of fluorine-bound electron spins in ZnSe

Optically-induced nuclear spin polarization in a fluorine-doped ZnSe epilayer is studied by time-resolved Kerr rotation using resonant excitation of donor-bound excitons. Excitation with helicity-modulated laser pulses results in a transverse nuclear spin polarization, which is detected as a change of the Larmor precession frequency of the donor-bound electron spins. The frequency shift in dependence on the transverse magnetic field exhibits a pronounced dispersion-like shape with resonances at the fields of nuclear magnetic resonance of the constituent zinc and selenium isotopes. It is studied as a function of external parameters, particularly of constant and radio frequency external magnetic fields. The width of the resonance and its shape indicate a strong spatial inhomogeneity of the nuclear spin polarization in the vicinity of a fluorine donor. A mechanism of optically-induced nuclear spin polarization is suggested based on the concept of resonant nuclear spin cooling driven by the inhomogeneous Knight field of the donor-bound electron.

Symmetry, distorted band structure, and spin-orbit coupling of group-III metal-monochalcogenide monolayers

The electronic structure of (group-III) metal-monochalcogenide monolayers exhibits many unusual features. Some, such as the unusually distorted upper valence band dispersion we describe as a 'caldera', are primarily the result of purely orbital interactions. Others, including spin splitting and wavefunction spin-mixing, are directly driven by spin-orbit coupling. We employ elementary group theory to explain the origins of these properties, and use a tight-binding model to calculate the phenomena enabled by them, such as band-edge carrier effective g-factors, optical absorption spectrum, conduction electron spin orientation, and a relaxation-induced upper valence band population inversion and spin polarization mechanism.

Spin propagation through the C–C and C–H bonds

The signs of spin density on the carbon atoms and protons attached to them in nitroxides (nitroxyl radicals) with fixed geometry strictly alternate demonstrating unambiguously that spin propagation along the carbon chains of saturated C–C bonds occurs by a mechanism of spin polarization. Spin densities, both calculated and measured by NMR spectroscopy, exhibit convincing agreement both in signs and magnitudes.

Chemical disorder as an engineering tool for spin polarization inMn3Ga-based Heusler systems

Our study highlights spin-polarization mechanisms in metals, by focusing on the mobilities of conducting electrons with different spins instead of their quantities. Here, we engineer electron mobility by applying chemical disorder induced by non-stoichiometric variations. As a practical example, we discuss the scheme that establishes such variations in tetragonal Mn3Ga Heusler material. We justify this approach using first-principles calculations of the spin-projected conductivity components based on the Kubo-Greenwood formalism. It follows that, in majority of the cases, even a small substitution of some other transition element instead of Mn may lead to a substantial increase in spin-polarization along the tetragonal axis.

Dicopper(II) metallacyclophanes as multifunctional magnetic devices: a joint experimental and computational study.

Metallosupramolecular complexes constitute an important advance in the emerging fields of molecular spintronics and quantum computation and a useful platform in the development of active components of spintronic circuits and quantum computers for applications in information processing and storage. The external control of chemical reactivity (electro- and photochemical) and physical properties (electronic and magnetic) in metallosupramolecular complexes is a current challenge in supramolecular coordination chemistry, which lies at the interface of several other supramolecular disciplines, including electro-, photo-, and magnetochemistry. The specific control of current flow or spin delocalization through a molecular assembly in response to one or many input signals leads to the concept of developing a molecule-based spintronics that can be viewed as a potential alternative to the classical molecule-based electronics. A great variety of factors can influence over these electronically or magnetically coupled, metallosupramolecular complexes in a reversible manner, electronic or photonic external stimuli being the most promising ones. The response ability of the metal centers and/or the organic bridging ligands to the application of an electric field or light irradiation, together with the geometrical features that allow the precise positioning in space of substituent groups, make these metal-organic systems particularly suitable to build highly integrated molecular spintronic circuits. In this Account, we describe the chemistry and physics of dinuclear copper(II) metallacyclophanes with oxamato-containing dinucleating ligands featuring redox- and photoactive aromatic spacers. Our recent works on dicopper(II) metallacyclophanes and earlier ones on related organic cyclophanes are now compared in a critical manner. Special focus is placed on the ligand design as well as in the combination of experimental and computational methods to demonstrate the multifunctionality nature of these metallosupramolecular complexes. This new class of oxamato-based dicopper(II) metallacyclophanes affords an excellent synthetic and theoretical set of models for both chemical and physical fundamental studies on redox- and photo-triggered, long-distance electron exchange phenomena, which are two major topics in molecular magnetism and molecular electronics. Apart from their use as ground tests for the fundamental research on the relative importance of the spin delocalization and spin polarization mechanisms of the electron exchange interaction through extended π-conjugated aromatic ligands in polymetallic complexes, oxamato-based dicopper(II) metallacyclophanes possessing spin-containing electro- and chromophores at the metal and/or the ligand counterparts emerge as potentially active (magnetic and electronic) molecular components to build a metal-based spintronic circuit. They are thus unique examples of multifunctional magnetic complexes to get single-molecule spintronic devices by controlling and allowing the spin communication, when serving as molecular magnetic couplers and wires, or by exhibiting bistable spin behavior, when acting as molecular magnetic rectifiers and switches. Oxamato-based dicopper(II) metallacyclophanes also emerge as potential candidates for the study of coherent electron transport through single molecules, both experimentally and theoretically. The results presented herein, which are a first step in the metallosupramolecular approach to molecular spintronics, intend to attract the attention of physicists and materials scientists with a large expertice in the manipulation and measurement of single-molecule electron transport properties, as well as in the processing and addressing of molecules on different supports.

Enhancing the ferromagnetic coupling in extended phloroglucinol complexes by increasing the metal SOMO-ligand overlap: synthesis and characterization of a trinuclear Co(II)(3) triplesalophen complex.

The triplesalophen complex [(baron(Me))Co(II)(3)] has been synthesized and characterized. The low-spin Co(II) ions possess an (2)A2 ground state with the magnetic orbitals of dyz type. These are well oriented for a strong π overlap with the bridging phloroglucinol, which results in the strongest ferromagnetic interactions by the spin-polarization mechanism for a 3d phloroglucinol complex.

Radical-triplet pair mechanism of electron spin polarization. Detailed theoretical treatment.

Specific features of net chemically induced dynamic electron spin polarization (CIDEP) P(n), generated in liquid-phase triplet-radical (TR) quenching, are analyzed in detail within the general model, which allows for fairly simple analysis of CIDEP both numerically and analytically. This model enables one to accurately treat nonadiabatic transitions between the terms of TR-pair spin Hamiltonian, resulting in CIDEP generation. The proposed theory predicts fairly simple analytical dependence of P(n) on parameters of the model. In particular, it is shown that within the wide region of parameters the P(n) dependence on the coefficient of relative TR diffusion D(r) is described by simple linear relation P(n)(-1)(D(r)) ≈ Q0 + q̅(n)D(r) (Q0 and q̅(n) are independent of D(r)). It is also demonstrated that obtained numerical and analytical results are very helpful for the analysis of experimental data, which is demonstrated by analyzing the experimental D(r)-dependence of P(n).

(Eur. J. Inorg. Chem. 27/2014)

Graphical Abstract The back cover picture highlights Werner's legacy, which is celebrated by coordination chemistry contributions describing observations both in the first coordination sphere, the second coordination sphere and beyond. Specific orbital requirements define the geometry of complexes with Tc–Tc multiple bonds (Poineau et al.), and the binding of tetrathiafulvalene ligands to the DyIII dimer results in a single-molecule magnet (Pointillart et al.). In addition, noncovalent interactions can order a system in layers as found for the organometallic Pd–uracil compound (Moriuchi, Hirao et al.), the ordering can be critical for the resulting spin polarization mechanism in cyanido-bearing CoIII/CoII complexes (Alexandru, Marino, Julve et al.) and for the ability of vapochromic PtII complexes to support water binding in the solid state (Kobayashi and Kato). The background shows a group photo of the delegates taken at the 4th Zing Coordination Chemistry Conference held in Mexico in December 2013 (the background photo is used with permission from Zing Conferences Ltd.). Thanks to Guest Editor Debbie Crans for putting the parts of the composite cover together.

Determination of Structural Characteristics of All-Organic Radical Liquid Crystals Based on Analysis of the Dipole–Dipole Broadened EPR Spectra

The angular dependences of g-value and line width of EPR spectra of paramagnetic all-organic liquid crystalline (LC) materials were measured for the quantitative characterization of the nematic, cholesteric, and smectic C phases. The detailed molecular alignment in mesophases was determined by means of numerical spectra simulation focusing on spin exchange and dipole-dipole magnetic interactions of neighboring molecules. The obtained structural data indicate that the spin polarization mechanism between neighboring molecules rather than the direct through-space interactions between paramagnetic centers is responsible for the specific magnetic properties of the studied LC materials.

Switching from antiferromagnetic to ferromagnetic coupling in heptanuclear [M(t)6M(c)](n+) complexes by going from an achiral to a chiral triplesalen ligand.

The chiral triplesalen ligand H6chand(RR) has been used to synthesize the chiral heptanuclear complexes [{(chand(RR))Mn(III)3}2{Fe(II)(CN)6}](ClO4)2 ((RR)[Mn(III)6Fe(II)](ClO4)2) and [{(chand(RR))Fe(III)3}2{Fe(II)(CN)6}](ClO4)2 ((RR)[Fe(III)6Fe(II)](ClO4)2), which have been characterized by single-crystal X-ray diffraction, mass spectrometry, elemental analysis, FT-IR, Mössbauer, and UV-vis spectroscopies, electrochemistry, as well as DC and AC magnetic susceptibility measurements. The half-wave potential of the Fe(III)/Fe(II) couple in (RR)[Mn(III)6Fe(II)](2+) and (RR)[Fe(III)6Fe(II)](2+) is E1/2 = +0.21 and +0.75 V vs. Fc(+)/Fc, respectively, which (i) corresponds to a strong stabilization of the reduced Fe(II) species compared to the redox couple of free [Fe(II/III)(CN)6](4-/3-) and (ii) indicates a significant difference of the electronic coupling with the {(chand(RR))M(t)}(3+) units (M(t) = Mn(III), Fe(III)). Analysis of the DC magnetic data (μeffvs. T, VTVH) of both complexes by a full-matrix diagonalization of the spin-Hamiltonian including isotropic exchange, zero-field splitting with full consideration of the relative orientation of the D tensors and Zeeman interactions reveals ferromagnetic interactions of JMn-Mn = +0.17 ± 0.02 cm(-1) with DMn = -3.4 ± 0.3 cm(-1) for (RR)[Mn(III)6Fe(II)](2+) and JFe-Fe = +0.235 ± 0.005 cm(-1) with DFe = 0 for (RR)[Fe(III)6Fe(II)](2+). The comparison of the molecular structures of (RR)[Mn(III)6Fe(II)](2+) and (RR)[Fe(III)6Fe(II)](2+) with those of the heptanuclear complexes [M(t)6M(c)](n+) using the achiral triplesalen ligand (talen(t-Bu2))(6-) reveals significant differences in the ligand folding, smaller C-C bond distances in the central phloroglucinol ring and larger HOMA values. This indicates more aromatic character and less heteroradialene contribution in (RR)[Mn(III)6Fe(II)](2+) and (RR)[Fe(III)6Fe(II)](2+), which explains the switching from antiferromagnetic coupling in [M(t)6M(c)](n+) to ferromagnetic coupling in (RR)[M(t)6M(c)](n+) by a stronger contribution of the spin-polarization mechanism. This establishes a magnetostructural correlation between the structural parameters describing the aromaticity of the central phloroglucinol unit and the observed exchange couplings JMn-Mn.

Electronic and Exchange Coupling in a Cross-Conjugated D–B–A Biradical: Mechanistic Implications for Quantum Interference Effects

A combination of variable-temperature EPR spectroscopy, electronic absorption spectroscopy, and magnetic susceptibility measurements have been performed on Tp(Cum,Me)Zn(SQ-m-Ph-NN) (1-meta) a donor-bridge-acceptor (D-B-A) biradical that possesses a cross-conjugated meta-phenylene (m-Ph) bridge and a spin singlet ground state. The experimental results have been interpreted in the context of detailed bonding and excited-state computations in order to understand the excited-state electronic structure of 1-meta. The results reveal important excited-state contributions to the ground-state singlet-triplet splitting in this cross-conjugated D-B-A biradical that contribute to our understanding of electronic coupling in cross-conjugated molecules and specifically to quantum interference effects. In contrast to the conjugated isomer, which is a D-B-A biradical possessing a para-phenylene bridge, admixture of a single low-lying singly excited D → A type configuration into the cross-conjugated D-B-A biradical ground state makes a negligible contribution to the ground-state magnetic exchange interaction. Instead, an excited state formed by a Ph-NN (HOMO) → Ph-NN (LUMO) one-electron promotion configurationally mixes into the ground state of the m-Ph bridged D-A biradical. This results in a double (dynamic) spin polarization mechanism as the dominant contributor to ground-state antiferromagnetic exchange coupling between the SQ and NN spins. Thus, the dominant exchange mechanism is one that activates the bridge moiety via the spin polarization of a doubly occupied orbital with phenylene bridge character. This mechanism is important, as it enhances the electronic and magnetic communication in cross-conjugated D-B-A molecules where, in the case of 1-meta, the magnetic exchange in the active electron approximation is expected to be J ~ 0 cm(-1). We hypothesize that similar superexchange mechanisms are common to all cross-conjugated D-B-A triads. Our results are compared to quantum interference effects on electron transfer/transport when cross-conjugated molecules are employed as the bridge or molecular wire component and suggest a mechanism by which electronic coupling (and therefore electron transfer/transport) can be modulated.

Four Discrete Transition Metal Complexes Involving Pyridyl-substituted Nitronyl Nitroxide: Syntheses, Crystal Structures, and Magnetic Properties

Four discrete metal-radical complexes, [Cu(p-MePh-COO)2(NITpPy)2] (1), [Ni(m-MePhCOO)2(NITpPy)2(H2O)2]·(CH3-OH)2 (2), [Mn(p-MePhCOO)2(NITpPy)2(H2O)2] (3), and [Mn(m-MePhCOO)2(NITpPy)2(H2O)2] (4) [NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide] were synthesized and characterized by elemental analyses, IR spectroscopy, PXRD, single-crystal X-ray diffraction, and magnetic susceptibility. For the four complexes, the crystal structural analyses indicate that the two radical ligands coordinated to the metal ions by the nitrogen atoms of the pyridine rings form three spin complexes, where toluates act as co-ligands. Weak antiferromagnetic interactions [JCu–Rad = –6.75 cm–1 (1), JCo–Rad = –4.15 cm–1 (2), JMn–Rad = –0.22 cm–1 (3), and JMn–Rad = –3.74 cm–1 (4)] were observed, spin polarization mechanism and orbital symmetry are used to explain the magnetic coupling in these complexes.

Dynamic nuclear polarization in InGaAs/GaAs and GaAs/AlGaAs quantum dots under nonresonant ultralow-power optical excitation

We study experimentally the dependence of dynamic nuclear spin polarization on the power of nonresonant optical excitation in two types of individual neutral semiconductor quantum dots: InGaAs/GaAs and GaAs/AlGaAs. We show that the mechanism of nuclear spin pumping via second-order recombination of optically forbidden (``dark'') exciton states recently reported in InP/GaInP quantum dots [E. A. Chekhovich et al., Phys. Rev. B 83, 125318 (2011)] is relevant for material systems considered in this work. In the InGaAs/GaAs dots this nuclear spin polarization mechanism is particularly pronounced, resulting in Overhauser shifts up to $\ensuremath{\sim}$80 $\ensuremath{\mu}$eV achieved at ultralow optical excitation power, $\ensuremath{\sim}$1000 times smaller than the power required to saturate ground state excitons. The Overhauser shifts observed at ultralow power pumping in the interface GaAs/AlGaAs dots are generally found to be smaller (up to $\ensuremath{\sim}$40 $\ensuremath{\mu}$eV). Furthermore in GaAs/AlGaAs we observe dot-to-dot variation and even sign reversal of the Overhauser shift which is attributed to the dark-bright exciton mixing originating from electron-hole exchange interaction in dots with reduced symmetry. Nuclear spin polarization degrees reported in this work under ultralow-power optical pumping are comparable to those achieved by techniques such as resonant optical pumping or above-gap pumping with high-power circularly polarized light. Dynamic nuclear polarization via second-order recombination of ``dark'' excitons may become a useful tool in single quantum dot applications, where manipulation of the nuclear spin environment or electron spin is required.

An ion-pair complex [TTF][Pd(mnt)2]: synthesis, crystal structure, magnetic property, and electrical conductivity

A new ion-pair complex, [TTF][Pd(mnt)2] (1), where TTF+ = tetrathiafulvalene and mnt2− = maleonitriledithiolate, was synthesized and characterized structurally. Compound 1 crystallizes in triclinic space group P-1, with a = 8.008(5) Å, b = 11.333(8) Å, c = 11.373(6) Å, α = 108.112(7)°, β = 91.550(5)°, γ = 95.232(5)°, and V = 975.2(11) Å3. The [TTF]+ cations (C) and [Pd(mnt)2]− anions (A) form mixed stacks in …AACCAACC… fashion, and the neighboring mixed stacks are held together via van der Waals forces in the crystal. Compound 1 shows weak Curie/Weiss-type magnetic behavior from 2 to 370 K; theoretical investigation disclosed the existence of strongly antiferromagnetic coupling in both [Pd(mnt)2]2 2− and [TTF]2 2+ dimer pairs via frontier orbitals overlap mechanism and weakly ferromagnetic coupling between the face-to-face overlapped [TTF]+ and [Pd(mnt)2]− via spin polarization mechanism within a mixed stack. The powdered pellet electrical conductivity measurement indicated that 1 shows semiconductor character with activation energy of 1.1(3) eV.

Dicopper(II) Metallacyclophanes with Oligo(p-phenylene-ethynylene) Spacers: Experimental Foundations and Theoretical Predictions on Potential Molecular Magnetic Wires

Two novel double-stranded dicopper(II) metallacyclophanes of formula (nBu4N)4[Cu2(dpeba)2]·4MeOH·2Et2O (1) and (nBu4N)4[Cu2(tpeba)2]·12H2O (2) have been prepared by the Cu(II)-mediated self-assembly of the rigid ('rod-like') bridging ligands N,N'-4,4'-diphenylethynebis(oxamate) (dpeba) and N,N'-1,4-di(4-phenylethynyl)phenylenebis(oxamate) (tpeba), respectively. Single crystal X-ray diffraction analysis of 1 confirms the presence of a dicopper(II)tetraaza[3.3]4,4'-diphenylethynophane metallacyclic structure featuring a very long intermetallic distance between the two square planar Cu(II) ions [r = 14.95(1) Å]. The overall parallel-displaced π-stacked conformation of the two nearly planar para substituted diphenylethyne spacers [dihedral angle (ψ) of 7.8(1)°] leads to important deviations from the perpendicular orientation of the copper mean basal planes with respect to the facing benzene planes [dihedral angles (φ) of 56.4(1) and 58.4(1)°]. X-band EPR spectra together with variable-temperature magnetic susceptibility and variable-field magnetization measurements of 1 and 2, both in solution and in the solid state, show the occurrence of a non-negligible, moderate to weak intramolecular antiferromagnetic coupling [-J = 3.9-4.1 (1) and 0.5-0.9 cm(-1) (2); H = -JS1·S2 with S1 = S2 = SCu = 1/2]. Density functional calculations on the BS singlet (S = 0) and triplet (S = 1) spin states of the model complexes 1 and 2 with an ideal orthogonal molecular geometry (ψ = 0° and φ = 90°) support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the dxy orbital of each square planar Cu(II) ion through the predominantly π-type orbital pathway of the double p-diphenylethyne (1) and di(phenylethynyl)phenylene spacers (2). Time-dependent density functional calculations reproduce the observed bathochromic shift of the main intraligand (IL) π-π* transition in the electronic absorption spectra of 1 and 2 [λ1 = 308 (1) and 316 nm (2)]. In the series of orthogonal model complexes 1-5 with linear oligo(p-phenylene-ethynylene) (OPE) spacers, -C6H4(C≡CC6H4)n- (n = 1-5), a linear increase of the IL π-π* transition energy with the reciprocal of the intermetallic distance is theoretically predicted [νmax = 1.99 × 10(4) + 2.15 × 10(5) (1/r) (S = 0) or ν = 2.01 × 10(4) + 2.18 × 10(5) (1/r) (S = 1)], which clearly indicates that the effective π-conjugation length increases with the number of phenylethyne repeating units. This is accompanied by an exponential decay of the antiferromagnetic coupling with the intermetallic distance [-J = 1.08 × 10(3) exp(-0.31r)], which supports the ability of the extended π-conjugated OPEs to mediate the exchange interaction between the unpaired electrons of the two Cu(II) centers with intermetallic distances in the range of 1.5-4.3 nm. Further developments may be then envisaged for this new family of oxamato-based dicopper(II) oligo-p-phenylethynophanes on the basis of the unique ligand capacity to act as a molecular antiferromagnetic wire.

First one-dimensional homochiral stairway-like Cu(ii) chains: crystal structures, circular dichroism (CD) spectra, ferroelectricity and antiferromagnetic properties

The reactions of enantiopure chiral ligands (+)/(−)-4,5-pinenepyridyl-2-pyrazine (LS/LR) with CuCl2·2H2O in CH3OH/CH2Cl2 solution led to the formations of one-dimensional homochiral enantiomeric pairs with the formula [Cu(LR/S)Cl2]n·2H2O (R-1 and S-1, the isomers containing the LR and LS ligands, respectively). The circular dichroism (CD) spectra verified their chiroptical activities and enantiomeric natures. Their structures have been determined by X-ray single-crystal analyses, showing stairway-like and mirror-symmetric features, which represent the first examples of homochiral metal complexes with stairway-like structures. The ferroelectric property measurement indicated that R-1 exhibits ferroelectricity with the remnant polarization (Pr) value of 0.02 μC cm−2 under an applied electric field of 6.1 kV cm−1 at room temperature. The magnetic investigation of R-1 showed a weak intrachain antiferromagnetic coupling between Cu(II)–Cu(II) ions mediated by pyrazine, which can be interpreted by a spin-polarization mechanism. All these results suggested that R-1 and S-1 are potential multifunctional molecule-based materials combining optical activity, ferroelectricity and magnetism within one molecule.

Magnetic properties of two 2D complexes based on 1D chain containing [Fe(bpy)(CN)4]−unit

Two heterobimetallic 2-dimensional layer complexes, {[Fe(bpy)(CN)(4)](2)M(4,4'-bipyridine)}·4H(2)O [bpy = 2,2'-bipyridine, M = Mn (1), Cu (2)] have been prepared by diffusion and their structures determined by single crystal X-ray diffraction. 1 and 2 are isomorphous, made of neutral bimetallic [Fe(bpy)(CN)(4)](2)M(4,4'-bipyridine)] layers and uncoordinated water molecules located between the layers. Interestingly, complex 2 shows the compression of the Jahn-Teller distortion around the copper(II) ion. Magnetic investigation shows antiferromagnetic coupling between the manganese(II) and iron(III) ions mediated by bridging CN(-) in 1, while ferromagnetic coupling between the copper(II) and iron(III) ions is seen in 2. Both complexes 1 and 2 reveal a metamagnetic-like behaviour with different critical fields (H(c), at 1.8 K): 2.0 kOe (1) and 3.2 kOe (2). The weak interchain antiferromagnetic interaction can be illustrated by the spin-polarization mechanism.

Synthesis, crystal structures and magneto-structural correlations study of three 3d metal–radical heterospin complexes

Three heterospin complexes [M(NIT4Py)2(cda)H2O] (M=Cu(II) (1), Ni(II) (2), Co(II) (3)) with various paramagnetic 3d metal ions and pyridyl-substituted nitronyl nitroxide radical (NIT4Py=2-(4′-pyridyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, H2cda=4-hydroxy-pyridine-2,6-dicarboxylic acid) have been synthesized, characterized structurally and magnetically. The single crystal structures show that complexes 1–3 are isomorphic, and have 2D supramolecular network consisting of [M(NIT4Py)2(cda)H2O] with three paramagnetic centers. The magnetic measurements indicated that complexes 1–3 exhibit all antiferromagnetic interactions between M(II) and radicals with JCu–rad=−7.30cm−1, JNi–rad=−3.58cm−1 and JCo–rad=−1.85cm−1, respectively. Their magnetic behaviors were interpreted in terms of the spin polarization mechanism of the π-electrons of NIT4Py and the orthogonality of 3d magnetic orbital of M(II) ion and the 2pπ orbital on the pyridine rings of NIT4Py.

Theoretical Study of Hyperfine Interactions in Small Arsenic-Containing Radicals

Various density functional theory (DFT) and ab initio MP2 and CCSD methods were employed in calculations of arsenic isotropic and anisotropic hyperfine parameters in three small radicals, AsH(2), AsO(2), and H(2)AsO. Convergent basis sets for these calculations were specially derived starting from Dunning's correlation-consistent sets. DFT methods proved to be particularly appropriate choice, because the results obtained with the suitable functionals are in accordance with the available experimental values. Additionally, mechanisms of hyperfine couplings were investigated by examining individual orbital contributions to spin density. The spin polarization mechanism in AsH(2) was studied by evaluating one- and two-electron integrals in spin-restricted and unrestricted case. Apart from nonrelativistic, scalar-relativistic Douglas-Kroll-Hess DFT calculations were performed to examine relativistic impacts on spin density distribution.