Quantifying magnetic exchange in doubly-bridged Cu-X(2)-Cu (X = F, Cl, Br) chains enabled by solid state synthesis of CuF(2)(pyrazine).
Chemical communications (Cambridge, England) 49:34 (2013) 3558-3560
Abstract:
Solid state techniques involving pressure and temperature have been used to synthesize the fluoride member of the CuX(2)(pyrazine) (X = F, Cl, Br) family of coordination polymers that cannot be crystallized by solution methods. CuF(2)(pyrazine) exhibits unique trans doubly-bridged Cu-F(2)-Cu chains that provide an opportunity to quantify magnetic superexchange in an isostructural Cu-X(2)-Cu series.Giant Ising-type magnetic anisotropy in trigonal bipyramidal Ni(II) complexes: experiment and theory.
Journal of the American Chemical Society 135:8 (2013) 3017-3026
Abstract:
This paper reports the experimental and theoretical investigations of two trigonal bipyramidal Ni(II) complexes, [Ni(Me(6)tren)Cl](ClO(4)) (1) and [Ni(Me(6)tren)Br](Br) (2). High-field, high-frequency electron paramagnetic resonance spectroscopy performed on a single crystal of 1 shows a giant uniaxial magnetic anisotropy with an experimental D(expt) value (energy difference between the M(s) = ± 1 and M(s) = 0 components of the ground spin state S = 1) estimated to be between -120 and -180 cm(-1). The theoretical study shows that, for an ideally trigonal Ni(II) complex, the orbital degeneracy leads to a first-order spin-orbit coupling that results in a splitting of the M(s) = ± 1 and M(s) = 0 components of approximately -600 cm(-1). Despite the Jahn-Teller distortion that removes the ground term degeneracy and reduces the effects of the first-order spin-orbit interaction, the D value remains very large. A good agreement between theoretical and experimental results (theoretical D(theor) between -100 and -200 cm(-1)) is obtained.Elucidating magnetic exchange and anisotropy in weakly coupled Mn(III) dimers.
Inorganic chemistry 52:2 (2013) 718-723
Abstract:
High-frequency Electron Paramagnetic Resonance (HFEPR) measurements have been performed on both a single-crystal and powder samples of a weakly coupled antiferromagnetic dinuclear [Mn(III)](2) molecular magnet, [Mn(III)(2)L(2)(py)(4)], where L is the trianion of 3-(3-oxo-3-phenylpropionyl)-5-methylsalicylic acid, and py is pyridine. The experimental results were analyzed on the basis of a multispin Hamiltonian using both a perturbative approach and numerical simulations. It is found that the single-crystal HFEPR results provide a direct and simple means of determining both the axial anisotropy of the individual Mn(III) ions and the isotropic exchange coupling between them. Previously unpublished low-temperature magnetization data are then simulated using the same model Hamiltonian, yielding excellent agreement. This work highlights the limitations of widely used protocols for analyzing magnetic and powder EPR data obtained for multinuclear molecular magnets in which the exchange and single-ion anisotropies are comparable, thus emphasizing the value of single-crystal, multifrequency EPR measurements.Synthetic, structural, spectroscopic and theoretical study of a Mn(III)-Cu(II) dimer containing a Jahn-Teller compressed Mn ion.
Dalton transactions (Cambridge, England : 2003) 42:1 (2013) 207-216
Abstract:
The heterobimetallic complex [Cu(II)Mn(III)(L)(2)(py)(4)](ClO(4))·EtOH (1) built using the pro-ligand 2,2'-biphenol (LH(2)), contains a rare example of a Jahn-Teller compressed Mn(III) centre. Dc magnetic susceptibility measurements on 1 reveal a strong antiferromagnetic exchange between the Cu(II) and Mn(III) ions mediated through the phenolate O-atoms (J = -33.4 cm(-1)), with magnetisation measurements at low temperatures and high fields suggesting significant anisotropy. Simulations of high-field and high frequency powder EPR data suggest a single-ion anisotropy D(Mn(III)) = +4.45 cm(-1). DFT calculations also yield an antiferromagnetic exchange for 1, though the magnitude is overestimated (J(DFT) = -71 cm(-1)). Calculations reveal that the antiferromagnetic interaction essentially stems from the Mn(d(x(2)-y(2)))-Cu(d(x(2)-y(2))) interaction. The computed single-ion anisotropy and cluster anisotropy also correlates well with experiment. A larger cluster anisotropy for the S = 3/2 state compared to the single-ion anisotropy of Mn(III) is rationalised on the basis of orbital mixing and various contributions that arise due to the spin-orbit interaction.Slow magnetic relaxation induced by a large transverse zero-field splitting in a Mn(II)Re(IV)(CN)2 single-chain magnet.
Journal of the American Chemical Society 134:17 (2012) 7521-7529