Mechanism of a Strongly Anisotropic MoIII-CN-MnII Spin-Spin Coupling in Molecular Magnets Based on the [Mo(CN)7]4- Heptacyanometalate: A New Stra
详细信息 查看全文
- 作者：Vladimir S. Mironov ; Liviu F. Chibotaru ; and Arnout Ceulemans
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：August 13, 2003
- 年：2003
- 卷：125
- 期：32
- 页码：9750 - 9760
- 全文大小：259K
- 年卷期：v.125,no.32(August 13, 2003)
- ISSN：1520-5126
文摘
Unusual spin coupling between MoIII and MnII cyano-bridged ions in bimetallic molecular magnetsbased on the [MoIII(CN)7]4- heptacyanometalate is analyzed in terms of the superexchange theory. Due tothe orbital degeneracy and strong spin-orbit coupling on MoIII, the ground state of the pentagonal-bipyramidal[MoIII(CN)7]4- complex corresponds to an anisotropic Kramers doublet. Using a specially adapted kineticexchange model we have shown that the MoIII-CN-MnII superexchange interaction is extremelyanisotropic: it is described by an Ising-like spin Hamiltonian J
for the apical pairs and by the Jz
+ Jxy(
+ 
) spin Hamiltonian for the equatorial pairs (in the latter case Jz and Jxy canhave opposite signs). This anisotropy resulted from an interplay of several Ising-like (
) andisotropic (SMoSMn) ferro- and antiferromagnetic contributions originating from metal-to-metal electron transfersthrough the 
and 
orbitals of the cyano bridges. The MoIII-CN-MnII exchange anisotropy is distinct fromthe anisotropy of the g-tensor of [MoIII(CN)7]4-; moreover, there is no correlation between the exchangeanisotropy and g-tensor anisotropy. We indicate that highly anisotropic spin-spin couplings (such as theIsing-like J
) combined with large exchange parameters represent a very important source of theglobal magnetic anisotropy of polyatomic molecular magnetic clusters. Since the total spin of such clustersis no longer a good quantum number, the spin spectrum pattern can differ considerably from the conventionalscheme described by the zero-field splitting of the isotropic spin of the ground state. As a result, the spinreorientation barrier of the magnetic cluster may be considerably larger. This finding opens a new way inthe strategy of designing single-molecule magnets (SMM) with unusually high blocking temperatures. Theuse of orbitally degenerate complexes with a strong spin-orbit coupling (such as [MoIII(CN)7]4- or its 5danalogues) as building blocks is therefore very promising for these purposes.
for the apical pairs and by the Jz + Jxy( + ) spin Hamiltonian for the equatorial pairs (in the latter case Jz and Jxy canhave opposite signs). This anisotropy resulted from an interplay of several Ising-like ( ) andisotropic (SMoSMn) ferro- and antiferromagnetic contributions originating from metal-to-metal electron transfersthrough the and orbitals of the cyano bridges. The MoIII-CN-MnII exchange anisotropy is distinct fromthe anisotropy of the g-tensor of [MoIII(CN)7]4-; moreover, there is no correlation between the exchangeanisotropy and g-tensor anisotropy. We indicate that highly anisotropic spin-spin couplings (such as theIsing-like J ) combined with large exchange parameters represent a very important source of theglobal magnetic anisotropy of polyatomic molecular magnetic clusters. Since the total spin of such clustersis no longer a good quantum number, the spin spectrum pattern can differ considerably from the conventionalscheme described by the zero-field splitting of the isotropic spin of the ground state. As a result, the spinreorientation barrier of the magnetic cluster may be considerably larger. This finding opens a new way inthe strategy of designing single-molecule magnets (SMM) with unusually high blocking temperatures. Theuse of orbitally degenerate complexes with a strong spin-orbit coupling (such as [MoIII(CN)7]4- or its 5danalogues) as building blocks is therefore very promising for these purposes.