Mössbauer, Electron Paramagnetic Resonance, and Magnetic Susceptibility Studies on Members of a New Family of Cyano-Bridged 3d-4f Complexes. Demonstration of Anisotropic Exchange in a Fe−Gd Complex

Abstract

The synthesis and crystallographic characterization of a new family of M(μ-CN)Ln complexes are reported. Two structural series have been prepared by reacting in water rare earth nitrates (Ln III = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho) with K 3 [M(CN) [CoGd] 10). The hexamethylenetetramine molecules contribute to the stabilization of the crystals by participating in an extended network of hydrogen bond interactions. In both series the aqua ligands are hydrogen bonded to the nitrogen atoms from both the terminal CN groups and the hmt molecules. The [FeGd] complex has been analyzed with 57 Fe Mössbauer spectroscopy, EPR, and magnetic susceptibility measurements. We have also analyzed the [FeLa] complex, in which the paramagnetic Gd III is replaced by diamagnetic La III , to obtain information about the low-spin Fe III site that is not accessible in the presence of a paramagnetic ion at the complementary site. For the same reason, the [CoGd] complex, containing diamagnetic Co III , was studied with EPR and magnetic susceptibility measurements, which confirmed the S = 7/2 spin of Gd III . Prior knowledge about the paramagnetic sites in [FeGd] allows a detailed analysis of the exchange interactions between them. In particular, the question of whether the exchange interaction in [FeGd] is isotropic or anisotropic has been addressed. Standard variable-temperature magnetic susceptibility measurements provide only the value for a linear combination of J x , J y , and J z but contain no information about the values of the individual exchange parameters J x , J y , and J z . In contrast, the spin-Hamiltonian analysis of the variable-field, variable-temperature Mössbauer spectra reveals an exquisite sensitivity on the anisotropic exchange parameters. Analysis of these dependencies in conjunction with adopting the g-values obtained for [FeLa], yielded the values J x = Ŝ 1 · J · Ŝ 2 +0.11 cm −1 , J y = +0.33 cm −1 , and *To whom correspondence should be addressed emunck@cmu.edu; marius.andruh@dnt.ro; eb7g@andrew.cmu.edu. Supporting Information Available Details of the analysis of the magnetic susceptibilities, an explicit derivation of eq 1 as well as a proof for the validity of the subtraction method in the analysis of χT vs. T of [FeGd] are presented. Complete crystallographic data, structure, solution and refinement are available. This material is available free of charge via internet from http://pubs.acs.org. NIH Public AccessAuthor Manuscript Inorg Chem. Author manuscript; available in PMC 2011 April 5. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript J z = +1.20 cm −1 (convention). The consistency of these results with magnetic susceptibility data is analyzed. The exchange anisotropy is rooted in the spatial anisotropy of the low-spin Fe III ion. The condition for anisotropic exchange is the presence of low-lying orbital excited states at the ferric site that (i) effectively interact through spin-orbit coupling with the orbital ground state and (ii) have an exchange parameter with t...

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model To Improve Density Functional Calculations

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Short-range correlations in d–f cyanido-bridged assemblies with XY and XY-Heisenberg anisotropy

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Cyanometallate-Bridged Didysprosium Single-Molecule Magnets Constructed with Single-Ion Magnet Building Block

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