Spin-Crossover Phenomena

As well as for Fe complexes spin-crossover effects are observed for Fe complexes Co° complexes (3d ) and, to a lesser extent, for Cr complexes (3d ) and for Mn complexes (3d ). Spin-crossover materials could find applications for the fabrication of rewritable optical, thermal or pressure memories at a nanometre scale. 

N-alkoxysalicylidenyl-N -ethyl-N-ethylenediamine Schiff base ligands, showing 

The transition temperature for the thermal spin-crossover has a more pronounced dependence on the alkyl chain length of the ligands than the transition temperature for the light-induced spin transition (LIESST).  

Seredyuk et al. used a two-step procedure to obtain metallomesogens with a synchronous spin transition and a solid-to-mesophase transition. They started with the selection of an iron(II) complex with triazole ligands 

An interesting property of thin films of the iron(II) complexes in the mesophase is their thermochromism. A reversible colour change from purple (low-spin state) to whitish (high-spin state) was observed by heating or cooling the compound around 60 °C. This work was extended to complexes in which the tosylate counter ions were replaced by tetrafluoro-borate and triflate ions. The resulting compounds were polymeric with a one-dimensional structure. Several of the complexes were liquid-crystalline at room temperature and their mesophase was either hexagonal 

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Giitlich, Garcia and Goodwin (2000) Spin crossover phenomena in Fe(II) complexes [246]. 

Jahn-Teller effects are rarely adopted in theoretical treatments of spin-crossover phenomena, except Kambara s model for Fe(II) complexes [24] and Bersuker s for Fe(III) complexes [19,25]. In the Kambara theory, abrupt spin-crossover transitions are given an FO => LS character, while gradual transitions are of the HS LS type. However, experimental evidences of cooperative Jahn-Teller transitions (FO HS) have not yet been reported for Fe(II) spin-crossover complexes. Kambara s theory ignores the spin-orbit interaction and appears to overestimate the Jahn-Teller coupling, producing an unphysical (for Fe(II) complexes) FO => HS transition. 

The spin-crossover phenomenon in tridentate SB complexes of Fe111, Fe11 and Co11 has been extensively investigated.70-72 Iron(III) SB complexes having a (N20)2 donor set may exhibit spin-crossover phenomena.73-77 The (N20)2 donor set is provided by coordination of two tridentate N20 SBs. Thus, a thermal-induced spin-crossover phenomenon has been observed for Fe111 complexes of the half unit (15a)77 and for other N20 tridentate SBs.76... 

The two-state reactivity concept developed by Schroder et al.136 contributed to emphasize the importance of spin crossover phenomena in organometallic reactions ... 

Some of these show spin crossover phenomena and they arc therefore discussed in Chapter 8. 

Giitlich, P. Goodwin, H. A., Eds. Spin Crossover Phenomena in Transition Metal Compounds, Springer-Verlag Berlin, 2004. 

Recent Topics of Photoinduced Spin-Crossover Phenomena... 

In Section 10.3, we have shown that some complexes exhibit very rare spin-crossover phenomena involving the S = 3/2 spin state such as the one between S = 3/2 and S= I/2, and between S = 3/2 and S = 5/2. Among the complexes with mixed S = 5/2, 3/2 spin state, the mono-imidazole complexes have attracted special attention because they are found in naturally occurring heme proteins such as cytochrome d and peroxidase [19,81]. 

In Chapters I and 2, an introduction is made to the synchrotron Mossbauer spectroscopy with examples. Examples include the/ns/tu Mossbauer spectroscopy with synchrotron radiation on thin films and the study of deep-earth minerals. Investigations of in-beam Mossbauer spectroscopy using a Mn beam at the RIKEN RIBF is presented in Chapter 3. This chapter demonstrates innovative experimental setup for online Mossbauer spectroscopy using the thermal neutron capture reaction, Fe (n, y) Fe. The Mossbauer spectroscopy of radionuclides is described in Chapters 4-7. Chapter 4 gives full description of the latest analysis results of lanthanides Eu and Gd) Mossbauer structure and powder X-ray diffraction (XRD) lattice parameter (oq) data of defect fluorite (DF) oxides with the new defect crystal chemistry (DCC) Oq model. Chapter 5 reviews the Np Mossbauer and magnetic study of neptunyl(+l) complexes, while Chapter 6 describes the Mossbauer spectroscopy of organic complexes of europium and dysprosium. Mossbauer spectroscopy is presented in Chapter 7. There are three chapters on spin-state switching/spin-crossover phenomena (Chapter 8-10). Examples in these chapters are mainly on iron compounds, such as iron(lll) porphyrins. The use of Mossbauer spectroscopy of physical properties of Sn(ll) is discussed in Chapter I I. 

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