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Environmental Influence on the Single-Molecule Magnet Behavior of [Mn(III)(6)Cr(III)](3+): Molecular Symmetry versus Solid-State Effects.
MedLine Citation:
PMID:  23013609     Owner:  NLM     Status:  Publisher    
The structural, spectroscopic, and magnetic properties of a series of [Mn(III)(6)Cr(III)](3+) (= [{(talen(t-Bu(2)))Mn(III)(3)}(2){Cr(III)(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spin-polarization spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr(III)(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [Mn(III)(6)Cr(III)](3+) complexes in the highly symmetric space group R3̅ (3) with a collinear arrangement of the molecular S(6) axes. Incorporation of the spherical anion BPh(4)(-) leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [Mn(III)(6)Cr(III)](3+) complexes, as evidenced by the angle between the approximate molecular C(3) axes taking no specific values in the range of 2°-69°. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U(eff) values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn(III) ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), Ĥ(ex) = -2∑(i<j )J(ij)Ŝ(i)·Ŝ(j)) that is overcome by the stronger antiferromagnetic interaction via the Cr-C≡N-Mn pathway (J(Cr-Mn) = -3.00 to -5.00 cm(-1)), leading to an overall ferrimagnetic coupling scheme with an S(t) = (21)/(2) spin ground state. The differences in U(eff), J(Mn-Mn), and J(Cr-Mn) for the investigated samples are rationalized in terms of subtle variations in the molecular and crystal structures. In particular, a magnetostructural correlation between the Mn-N(C≡N) bond length and the J(Cr-Mn) exchange coupling is inferred from the magnetic measurements and corroborated by DFT calculations. The results of this detailed study on [Mn(III)(6)Cr(III)](3+) allow the formulation of some key recipes for a rational improvement of the SMM behavior.
Veronika Hoeke; Maik Heidemeier; Erich Krickemeyer; Anja Stammler; Hartmut Bögge; Jürgen Schnack; Andrei Postnikov; Thorsten Glaser
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-9-27
Journal Detail:
Title:  Inorganic chemistry     Volume:  -     ISSN:  1520-510X     ISO Abbreviation:  Inorg Chem     Publication Date:  2012 Sep 
Date Detail:
Created Date:  2012-9-27     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0366543     Medline TA:  Inorg Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld , Universitätsstr. 25, D-33615 Bielefeld, Germany.
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