Control of the magnetic and optical properties in molecular compounds by electrochemical, photochemical and chemical methods

The electrochemical, photochemical and chemical control of the magnetic properties in molecular compounds is described. The preparation of various thin films of CrCr and FeFe Prussian blue on a conducting electrode allowed us to control the magnetic properties by varying the oxidation state of the component metals. The magnetic properties of CrCr Prussian blue show that the critical temperature and coercive field can be drastically modified by electrochemical treatment. That is, the compound, (Cr1.29Cr0.14III)-Cr-II[Cr-III(CN)(6)] has ferrimagnetic properties with T-c (critical temperature)=240 K and H-c (coercive field)=25 G, while the reduced form, (KCr1.21Cr0.14III)-Cr-II[Cr-II(CN)(6)], has T-c=100 K and H-c=220 G Similarly, it was found that the critical temperature of FeFe Prussian blue shifts continuously from paramagnetic to magnetic with T-c=12 K. These changes can be expressed as K4Fe4II[Fe-II(CN)(6)](3) (paramagnetic)reversible arrowFe(14)(III)[Fe-II(CN)(6)](3) (ferromagnetic, T-c=4.5 K) + 4 K+ + 4e(-) and Fe-4(III)[Fe-II(CN)(6)](3) (ferromagnetic, T-c=4.2 K) + 3CI(-) - 3e(-) reversible arrow Fe-4(III)[Fe-III(CN)(6)](3)(Cl)(3) (T-c=12 K). Furthermore, we have discovered that the FeCo Prussian blue and Co valence tautomeric compounds exhibit photo-reversible magnetization effects. The, photoinduced magnetization in FeCo Prussian blue is expressed as Na0.4Co0.3II-HSCoIII-LS[Fe-II(CN)(6)] (paramagnetic) reversible arrow Na0.4Co1.3II-HS[Fe-III(CN)(6)] (ferrimagnetic, T-c=26 K and H-c=6000 G), where HS and LS denote high-spin and low-spin. An example of the photoinduced valence tautomeric behavior is expressed as [COII-LS(3,5-dbsq)(3,5-dbcat)(tmeda)] reversible arrow [CoII-HS(3,5-dbsq)(2)(tmeda)], where tmeda, 3,5-dbsq and 3,5-dbcat represent N,N,N',N'-tetramethylethylenediamine, 3,5-di-tert-butyl-1,2-semiquinonate and 3,5-di-tert-butyl-1,2-catecholate, respectively. Additionally, we succeeded in tuning the phase transition temperature by varying the ligand field of the Co ions in the FeCo Prussian blue. Brief comments are also included regarding the first examples of light-induced excited spin state trapping observed in an Fe-III complex, i.e. [FeIII-LS(pap)(2)]ClO2.H(2)Oreversible arrow [FeIII-HS(pap)(2)]ClO4.H2O (pap=N-2-pyridylmethylidene-2-hydroxy-phenylaminato) and a photoinduced structural change observed in a Cu-II complex, [Cu-II(dieten)(2)](BF4)(2) [dieten=bis(N,N-diethylethylenediamine)].