Prussian Blue Compounds Research Articles

Control of the Magnetic and Optical Properties in Molecular Compounds by Electrochemical, Photochemical and Chemical Methods

Abstract 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, CrII1.29CrIII0.14[CrIII(CN)6] has ferrimagnetic properties with Tc (critical temperature) = 240 K and Hc (coercive field) = 25 G, while the reduced form, KCrII1.29CrIII0.14[CrII(CN)6], has Tc = 100 K and Hc = 220 G. Similarly, it was found that the critical temperature of FeFe Prussian blue shifts continuously from paramagnetic to magnetic with Tc = 12 K. These changes can be expressed as K4FeII4[FeII(CN)6]3 (paramagnetic) ←→ FeIII4[FeII(CN)6]3 (ferromagnetic, Tc = 4.5 K) + 4 K+ + 4e− and FeIII4[FeII(CN)6]3 (ferromagnetic, Tc = 4.2 K) + 3Cl− − 3e−←→ FeIII4[FeIII(CN)6]3(Cl)3 (Tc = 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 Na0.4CoII-HS0.3CoIII-LS[FeII(CN)6] (paramagnetic) ←→ Na0.4CoII-HS1.3[FeIII(CN)6] (ferrimagnetic, Tc = 26 K and Hc = 6000 G), where HS and LS denote high-spin and low-spin. An example of the photoinduced valence tautomeric behavior is expressed as [CoIII-LS(3,5-dbsq)(3,5-dbcat)(tmeda)] ←→ [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 FeIII complex, i.e. [FeIII-LS(pap)2]ClO4·H2O ←→ [FeIII-HS(pap)2]ClO4·H2O (pap = N-2-pyridylmethylidene-2-hydroxy-phenylaminato) and a photoinduced structural change observed in a CuII complex, [CuII(dieten)2](BF4)2 [dieten = bis(N,N -diethylethylenediamine)].

On the magnetic properties of Pr[Mn(CN)6]. 4H2O

A Prussian Blue type compound of the nominal composition Pr[Mn(CN)6].4H2O has been prepared. It is shown that the compound exhibits ferrimagnetism with a Curie temperature TC=38.9 K. Observed magnetic relaxation displays a logarithmic behavior.

Theoretical Study of the Charge Transfer Absorption in Cobalt-Iron Cyanide

The photo-induced charge transfer followed by the bidirectional phase transition in Fe-Co Prussian blue compounds is theoretically discussed. The result of ab initio calculations indicates that both the forward and backward transitions are triggered by photo-induced charge transfer excitations between Co-dγ and Fe-dϖ orbitals, although different kinds of Co sites are excited. It is concluded that the charge transfer proceeds by way of the spσ-pπ transition on the nitrogen atom, which can explain such a long range charge transfer between Co and Fe separated by about 5Å.

Magnetic properties of uranium hexacyanomanganate

A Prussian blue type compound of the stoichiometric composition U IV[Mn II(CN) 6]·5H 2O has been prepared. It has been shown that the compound exhibits ferrimagnetism with a Curie temperature T c=36.8 K.

Theoretical Study on Necessary Conditions for Reversible Photoinduced Magnetization: Cobalt-Iron Cyanide System

We study metastability of the Cobalt-Iron Prussian blue compound. DFT calculations are performed for model clusters (a) (NC)5-Fe-CN-Co-(NC)5 and (b) (NC)5-Fe-CN-Co-(NC)3 (H2O)2 and the energy difference between the low spin state (S = 0) and the high spin state (S = 1) is estimated. Correction due to impurity effect is evaluated and screening effect in a solid state is also discussed.

Analysis of Photoinduced Magnetization in a (Co, Fe) Prussian Blue Model

The electronic properties of a modified (Co, Fe) Prussian blue compound, which exhibits interesting photoinduced magnetic properties, are analyzed. For band structure calculations we set realistic models (for the ground and excited states) that involve interstitial potassium ions, crystal water, and lattice defects. The top of the “t2g” block consists mainly of Fe 3d orbitals, the low-lying “eg(1)” block Co 3d, and the high-lying “eg(2)” block Fe 3d. Because of the influence of crystal water coordinating to the Co ion, the “eg(1)”-block bands split into two parts; one is the “eg(1)(N)” block originating from the Co−NC fragment and another the “eg(1)(O)” block from the Co−OH2 fragment. The energy of visible light causing the magnetization enhancement is close to the computed “t2g(Fe-based)−eg(1)(N)” and “t2g(Fe-based)−eg(1)(O)” separations in the ground-state model. It is reasonable from DOS (density of states) analyses that irradiation with visible light causes an electron transfer from the Fe(II) to the Co(III) ions, through which the magnetization is effectively enhanced. Such an electron transfer is not a d−d transition on the same metal ion so that the Laporte rule may not be applied, or if applied, this rule may be relaxed in the (Co, Fe) Prussian blue.

96/06643 The mechanism of SO 2 removal by carbon

The Chernobyl nuclear reactor accident, which resulted in widespread contamination with radiocaesium, led to studies of the use of Prussian Blue (PB) compounds as a countermeasure to reduce the caesium-137 and caesium-134 content of animal products. An important consideration in the practical use of PB compounds in agriculture is their possible toxicity. Hence it is pertinent to assess the work undertaken with laboratory rodents, domesticated animals and humans that has included studies of any toxic effects. Such studies showed that PB compounds had no adverse effects on animal health and production and, in addition, no toxic effects were noted in humans when PB was used experimentally or therapeutically.

Studies of any toxicological effects of Prussian blue compounds in mammals—A review

The Chernobyl nuclear reactor accident, which resulted in widespread contamination with radiocaesium, led to studies of the use of Prussian Blue (PB) compounds as a countermeasure to reduce the caesium-137 and caesium-134 content of animal products. An important consideration in the practical use of PB compounds in agriculture is their possible toxicity. Hence it is pertinent to assess the work undertaken with laboratory rodents, domesticated animals and humans that has included studies of any toxic effects. Such studies showed that PB compounds had no adverse effects on animal health and production and, in addition, no toxic effects were noted in humans when PB was used experimentally or therapeutically.

Electrochemical behaviour of persulphate on carbon paste electrodes modified with Prussian blue and analogous compounds

Peroxodisulphate (“persulphate”) may be determined by direct current voltammetry (DCV) using carbon paste electrodes chemically modified with Prussian Blue, iron(III)-hexacyanoruthenate(II) or iron(III)-hexacyano-osmate(II). The determination is based on the exploitation of catalytic currents from the reduction of the modifiers. Best results are obtained for iron(III)-hexacyanoosmate(II) yielding a detection limit of 1 μg O22−/ml (as persulphate) when using HCl (10−2 mol/l) as supporting electrolyte and measuring in the DCV-mode. Electrodes doubly-modified with the osmium compound and a liquid anion-exchanger (Amberlite LA2) allow determinations of persulphate after preconcentration under open circuit conditions, in the presence of hydrogen peroxide and perborate, with a detection limit of 20 ng O22−/ml (as persulphate).

Manganese hexacyanomanganate: Magnetic interactions via cyanide in a mixed valence Prussian blue type compound

A Prussian blue type compound of the stoichiometric composition Mn(CN)3⋅xH2O (x=0.57) is formed as the final product of hydrolysis of Na3[Mn(CN)6] in perchloric acid. IR and visible spectra as well as structural and magnetic data show that it is a mixed valence compound consisting of sixfold N-coordinated Mn(II) and sixfold C-coordinated Mn(IV) in a cubic face-centered lattice. The compound exhibits ferrimagnetism with a Curie temperature of 48.7 K. A molecular field treatment assuming two collinear spin sublattices provides an adequate description of the observed magnetic behavior. The calculation of exchange integrals, which was based on a Heisenberg model, reveals that the magnetic ordering is almost exclusively induced by an antiferromagnetic interaction between Mn(II) and Mn(IV) ions. This interaction is described in terms of a super exchange involving cyanide as bridging ligand.

Bonding nature and semiconductivity of Prussian blue and related compounds

Bonding nature and semiconductivity of Prussian blue and related compounds

A comparison of two Prussian blue models: Tracer and Fe-56 labeled Mössbauer studies

Selective labeling of compounds containing one element in two or more chemical environments with Mössbauer inactive Fe-56 and with Mössbauer active Fe-57 isotopes has been used to study the nature of the three iron environments in Prussian blue type compounds. The effect of the intersititial ion in Prussian blue upon the nitrogen bonded and carbon bonded irons was studied by exchanging interstitial K + with cations from Group IA, Group IIA, and including NH 4 +, H +, and Al +3. For the interstitial Group IA precipitates, the isomer shift values became more positive as the electronegativities decreased and the ionic radii increased. The Cs Prussian blue data were significantly different for both iron environments, giving very broad peaks with a distinct shoulder on the carbon hole active iron peak. This shoulder was found to be due to nitrogen hole iron indicating that the large cesium interstitial iron distorted the lattice in such a way as to permit exchange of the carbon and nitrogen hole irons. This isotope labeling technique is inexpensive and should be widely applicable to Mössbauer studies for atoms in multiple environments in which there is no exchange.

The crystal structure of manganese(II) hexacyanochromate(III), Mn 3[Cr(CN) 6] 2·xH 2O

The crystal structure of Mn 3[Cr(CN) 6] 2·xH 2O has been determined from three dimensional X-ray diffraction data measured by counter methods. The cubic face centered unit cell with space group O 3F432 or H h 5Fm3m has a = 10.761(4) Å and contains 1 1 3 formula units, the measured and calculated densities are 1.50 and 1.48 g/cm 3, respectively. The structure was determined by application of a general structural model for Prussian Blue analog compounds. Least squares refinement of the positional and individual isotropic thermal parameters led to a final R value for the observed reflections of 0.054. The crystal structure is very closely related to the structures of other Prussian Blue analog compounds. Manganese and chromium atoms occupy the positions 4a (0 0,0) and 4b (0.5, 0.5, 0.5), respectively, of the unit cell. Carbon and nitrogen atoms are situated at positions 24e (x,0,0) and two different kinds of oxygen atoms (O(1) and O(2)) are distributed in general positions with O(1) (coordinated water) close to the nitrogen position and O(2) (zeolitic water) close to the special position Sc (0.25, 0.25, 0.25). One third of all Cr(CN) 6 groups are statistically absent so that each manganese atom has a mixed coordination, its average composition being MnN 4O 2. All cyanide groups are bridged between chromium and manganese atoms, with the carbon atoms bonded to chromium. The Cr-C, C-N, Mn-N, and Mn-O(1) distances are 2.06(1), 1.12(2), 2.20(1), and 2.36(4) Å respectively.

Retention of Radiocaesium by the Rat as Influenced by Prussian Blue and Other Compounds

The effectiveness of several compounds in suppressing the enteral absorption of 137Cs in rats was tested. All agents were found to be ineffective, with the exception of sodium tetraphenylborate, potassium ferrocyanide and, in particular, ferric ferrocyanide (Prussian Blue). The decrease in enteral absorption of 137Cs by oral administration of PB is dependent upon dose and time of administration. The maximal effect achieved is the reduction of the body-burden by 99%. Repeated oral administration of PB also enhances substantially the excretion of parenterally administered 137Cs. This effect was found to be independent on the time when treatment was started. No toxic side effects of PB were observed.