CN Mn Research Articles

Cyanide-bridged trinuclear MnIII–FeIII assembly: Crystal structure, magnetic and photoluminescence behavior

A trinuclear cyanide-bridged MnIII–FeIII compound, [NEt4][Mn(3,5-ClL)2(MeOH)]2Fe(CN)6], [3,5-ClLH2=N,N′-bis(3,5-chlorosalicylidenato)-1,2-diamino propane)], 1, has been characterized by X-ray analyses, magnetic and photoluminescence measurements. The structure assumes a two-dimensional network consisting of Mn–NC–Fe–CN–Mn (Fe1–C19–N4=175.9(3)°, C19–N4–Mn1=145.5 (3)°). The magnetic properties of this compound indicate antiferromagnetic coupling between low-spin Fe(III) and high-spin Mn(III) through the cyanide bridges. Furthermore, solid state photoluminescence properties of complex 1 have been investigated at room temperature.

Crystal structure refinement of the electron-transfer-active potassium manganese hexacyanoferrates and isomorphous potassium manganese hexacyanocobaltates

We report on the crystal structure refinements in the novel electron-transfer-active Prussian Blue analogs (PBA) KMn4II[Co1−xIIIFexIII(CN)6]3·nH2O (n≃12). The series of novel PBA with the end members of KMn4[Co(CN)6]3·11.8H2O and KMn4[Fe(CN)6]3·10.5H2O have been synthesized for the first time, all showing a number of extra-reflections incompatible with ordinary face-centered cell of the Fm-3m symmetry group. We have analyzed the Rietveld patterns for x=0,0.53,1 and found that the extra-reflections could be well fitted using several primitive (P) cell symmetries. The best fitting quality was obtained using the noncentrosymmetric space group (S.G.) P4¯3m (Z=1) with the origin of coordinate system shifted into a zeolitic site. In this structure model, the Co–CN–Mn entities are bent owing to the charge introduced by the K+ insertion that induces also the electron transfer between Mn and Fe. Using Mössbauer spectroscopy the electron transfer activity is identified with the appearance of unsplit resonance at the isomer shift of typically −0.15mm/s evidencing the low-spin state for Fe3+ and Fe2+ species. In the same P4¯3m phases doped with Fe2+57 into the Mn site, a sequence of discrete values of quadrupole splitting (0mm/s, 0.9mm/s, 1.8mm/s) is observed and attributed to different conformations of the polyhedra, in which the ground states are orbital triplet, doublet and singlet, respectively.

Magneto–Structural Correlations in Discrete MnII‐WV Cyano‐Bridged Assemblies with Polyimine Ligands

AbstractWe present the magneto–structural correlations for two novel discrete cyano‐bridged assemblies based on cationic complexes of manganese(II) with diimine ligands and octacyanotungstate(V) ions. The crystal structure of [MnII(terpy)(dmf)(H2O)2][MnII(terpy)(H2O)(dmf)(μ‐NC)WV(CN)7]2·6H2O (1) (terpy = 2,2′;6′,2″‐terpyridine, dmf = dimethylformamide) contains dinuclear {MnIIWV}– cyano‐bridged anions, while the crystal structure of [MnII(phen)3]2[MnII(phen)2(μ‐NC)2WV(CN)6]2(ClO4)2·9H2O (2) (phen = 1,10‐phenanthroline) is built of tetranuclear {MnII2WV2}2– square anions. Intramolecular Mn–W magnetic interactions through the cyano bridges are represented by magnetic coupling constants J = –39 cm–1 for the {MnIIWV}– unit in 1 and J1 = –25.7 and J2 = –16.7 cm–1 for the {MnII2WV2}2– unit in 2. J and J1 represent relatively strong W–CN–Mn interactions and are ascribed to the bridges in b positions of TPRS‐8 (trigonal prism square‐face bicapped) of [W(CN)8]3– polyhedra, favoring the strongest electronic interactions between the d–d orbital of W and the π* orbitals of CN–, whereas J2 is related to the m vertex of [W(CN)8]3–. The magnetic properties of 1 and 2 are compared with reference compounds and discussed in the context of the type of coordination polyhedra of [W(CN)8]3– as well as the metric parameters of cyano‐bridged W–CN–Mn linkages. We found the type of coordination polyhedra and bridging mode of [W(CN)8]3– to be the most important factors influencing the magnitude of the Mn–W magnetic interaction.

Observation of the Fixed Fe–CN–Mn Cluster in Cesium Manganese Hexacyanoferrate

The temperature-induced phase transition of cesium manganese hexacyanoferrate is based on the charge transfer between transition metal ions, and the behavior is complex. To clarify the mechanism for the phase transition, X-ray absorption and magnetic susceptibility were measured. The magnetic susceptibility behavior was different from that of rubidium manganese hexacyanoferrate. X-ray data analyses suggested that the phase transition of cesium manganese hexacyanoferrate is the result of a local charge transfer in the fixed Fe–CN–Mn cluster and the interaction among the clusters. Calculation of the Gibbs free energy of the mean-field model indicates that the cluster interaction influences the phase transition behavior of cesium manganese hexacyanoferrate.

A cyano-bridged bimetallic ferrimagnet: Synthesis, X-ray structure and magnetic study

Mixing of trans-[Mn(cyclam)Cl 2]Cl (cyclam = 1,4,8,11-tetraazacyclotetradecane) and potassium hexacyanochromate (K 3[Cr(CN) 6]) aqueous solutions instantaneously yields a 1D infinite chain complex {[Mn(cyclam)(μ-CN) 2Cr(CN) 4]·H 2O} n ( 1). The crystal structure of 1, crystallizing in the monoclinic system with space group P2 1/ n has been solved from X-ray powder diffraction data following direct space approach and refined by the Rietveld method. The structure analysis of 1 reveals alternating [Cr(CN) 6] 3− and [Mn(cyclam)] 3+ ions generating one-dimensional polymeric (–Cr–CN–Mn–NC–) n chain propagating along the [0 0 1] direction. The coordination environment of both the metal ions, Mn(III) and Cr(III), is octahedral. While a notable distortion in the coordination environment around Mn(III) centers was observed in complex 1, Cr(III) centers have suffered no such distortion. A ferrimagnetic interaction between the heterobimetallic centers was evidenced through variable temperature magnetic susceptibility measurements. The AC susceptibility measurement reveals that the compound 1 undergoes spontaneous ferrimagnetic ordering. Ferrimagnetic ordering has been rarely observed among the cyano-bridged compounds in the previous studies.

Photoinduced charge-transfer process in rubidium manganese hexacyanoferrate probed by Raman spectroscopy

The photoinduced charge-transfer process in Rb(0.94)Mn[Fe(CN)(6)](0.98).0.2H(2)O is investigated by observing the valence states of the metal ions by Raman spectroscopy. The sample in the high-temperature phase is irradiated at the ligand to metal, CN(-)-->Fe(III) and charge-transfer band (lambda=395 nm). The Fe(III)-CN-Mn(II) pair valence state corresponding to the high-temperature configuration is totally depleted after prolonged irradiation, and the Fe(II)-CN-Mn(III) pair valence state corresponding to the low-temperature configuration appears. In addition, two kinds of CN stretching modes, ascribed to Fe(II)-CN-Mn(II) and Fe(III)-CN-Mn(III) pair valence states, are found. The photoproduction process of each pair valence states is well reproduced by a kinetic model assuming a charge transfer from Mn(II) to Fe(III). During irradiation, continuous shifts of the Raman peaks are found and ascribed to a release of the strain due to the lattice mismatching between the high-temperature and the photoinduced phases. This behavior indicates that the photoinduced phase created locally in the high-temperature-phase lattice grows up to a photoinduced phase domain. The conversion efficiency is lowered with decreasing temperature, indicating the existence of an energy barrier. We propose a model, which can explain the existence of an energy barrier in the electronic excited state.

Syntheses, crystal structures and magnetic properties of cyano- and phenoxide-bridged Fe(iii)Mn(iii) tetramers containing fac-Fe(iii) tricyanides and Mn(iii) Schiff bases

Three cyanide-linked Fe(iii)Mn(iii) bimetallic clusters, [(Tp)Fe(CN)(3)](2)[Mn(acphen)](2) [; acphen = N,N'-ethylenebis(2-hydroxyacetophenylideneiminato) dianion], [(Tp)Fe(CN)(3)](2)[Mn(5-Bracphen)](2) [; 5-Bracphen = N,N'-ethylenebis(5-bromo-2-hydroxyacetophenylideneiminato) dianion], and [(Tp)Fe(CN)(3)](2)[Mn(salen)](2).6H(2)O [; salen = N,N'-ethylenebis(salicylidineiminato) dianion], were prepared by self-assembling a facial [(Tp)Fe(CN)(3)](-) [Tp = hydrotris(pyrazolyl)borate] precursor and respective Mn(iii) Schiff bases. X-Ray crystal structure analyses revealed that each complex is composed of a central Mn(iii) dimer doubly linked by phenoxides of the tetradentate N(2)O(2) Schiff bases and the terminal [(Tp)Fe(CN)(3)](-) groups connecting to the center through cyanides. Using the spin Hamiltonian H = -2J(1)(S(Fe1).S(Mn1) + S(Mn1a).S(Fe1a)) - 2J(2)(S(Mn1).S(Mn1a)), where J(1) stands for the exchange coupling constant between Fe(iii) (S(Fe) = 1/2) and Mn(iii) (S(Mn) = 2) through cyanides and J(2) between Mn(iii) ions via phenoxides, the best fits corresponded to J(1) = 2.61 cm(-1) and J(2) = 0.85 cm(-1) for , J(1) = 2.50 cm(-1) and J(2) = 1.30 cm(-1) for , and J(1) = -2.15 cm(-1) and J(2) = 0.55 cm(-1) for . The phenoxide routes transmit ferromagnetic interactions in all cases, while ferromagnetic or antiferromagnetic couplings occur through the cyanide linkage. Although the geometric parameters relevant to the magnetic Fe-C[triple bond, length as m-dash]N-Mn pathways are analogous to each other their magnetic natures are varied across the compounds, which supports that a degree of orbital overlap is quite sensitive to a subtle structural change in the present system.

Influence of octacyanoniobate(IV)-bridging geometry on Tc in Mn 2Nb ferrimagnets of identical 3D topology

A novel 3D cyano-bridged hybrid ferrimagnet { Mn 2 II ( imH ) 2 ( H 2 O ) 4 [ Nb IV ( CN ) 8 ] } · 4 H 2 O 1 (imH = imidazole) of T c = 25 K is reported. Its 3D inorganic –Nb–CN–Mn– framework is built of two groups of mutually parallel 1D-ladders cross-linked at niobium centers. Imidazole molecules reveal terminal coordination mode only. We discuss structural features in the context of 3D –Nb–CN–Mn– framework of 1, comparing it with that of { Mn 2 II ( pzdo ) ( H 2 O ) 4 [ Nb IV ( CN ) 8 ] } · 5 H 2 O 2 ferrimagnet with T c = 37 K reported by us [Inorg. Chem. 46 (2007) 10416]. The differences in T c are explained in respect to the metric parameters and positions of bridging linkages at [Nb(CN) 8] 4− polyhedra. Comparison of infrared spectra of 1 and free imH is also provided.

Observation of phase transition of cesium manganese hexacyanoferrates by X-ray absorption spectroscopy

Cesium manganese hexacyanoferrates exhibit an interesting phenomenon of temperature-induced phase transition accompanied by a variation in the magnetic susceptibility. We observed the variation in the electronic state of Mn during the phase transition by using X-ray absorption spectroscopy. The results of the analyses showed that the content ratio of Fe II–CN–Mn III and Fe III–CN–Mn II systematically varied during the phase transition. However, the ratio of Fe II–CN–Mn II remained constant at almost all temperatures. These results suggest that the charge transfer between Fe and Mn ions in the Fe III–CN–Mn II or the Fe II–CN–Mn III bond produces the phase transition.

Effects of vibronic interaction in cyano-bridged clusters containing Mn(III) and Mn(II) ions

The effects of vibronic interaction in the formation of the barrier for magnetization reversal in the cyanide-based binuclear Mn(III)–CN–Mn(II) clusters containing octahedrally coordinated Mn(III) and Mn(II) ions were examined. Along with the orbitally dependent superexchange between the Mn(II) and Mn(III) ions the model includes an axial component of the crystal field, spin–orbit coupling and vibronic interaction operating within the ground 3 T 1 ( t 2 4 ) term of the low-spin Mn(III) ion. The vibronic coupling parameters for the Mn(III) ion in the octahedral surrounding of six carbon ions have been evaluated in the framework of the exchange charge model of the crystal field accounting for the exchange and covalence effects. The dominating role of the tetragonal vibrations for the 3T 1 term of a single Mn(III) ion was demonstrated. The ability of the investigated complex to act as a Single-Molecule Magnet was analyzed as a function of both the temperature and the strength of vibronic coupling with the tetragonal vibrations. Very strong vibronic interaction strongly facilitates tunneling through the barrier, i.e., suppresses the barrier for magnetization reversal and prevents from long life time of magnetization.

Synthesis, crystal structure and magnetic properties of a three-dimensional cyano-bridged heterometallic complex of manganese(II) and molybdenum(IV)

A bimetallic cyano-bridged complex {[Mn(ImH)(H2O)2]2[Mo(CN)8]·4H2O} n (ImH = imidazole) has been prepared and characterized. Single-crystal X-ray analysis reveals that the complex crystallizes in space group C2/c with a = 15.665(2), b = 14.616(2), c = 12.307(2) Å, α = 90, β = 108.31(1), γ = 90°. The structure of the complex demonstrates a three-dimensional network through cyano-bridges. Each Mo(IV) atom has six –CN–Mn linkages and two terminal cyano ligands arranged in a square antiprismatic arrangement. The Mn(II) atom is in a distorted octahedral environment formed by three MoCN → Mn linkages along with one imidazole and two water molecules in cis configuration. Variable temperature magnetic susceptibility shows an antiferromagnetic coupling between Mn2+ ions through the NC–MoIV–CN diamagnetic bridges within the three-dimensional network. The IR spectra have also been investigated.

Metal-to-metal electron transfer and magnetic interactions in a mixed-valence Prussian Blue analogue

In search of a new Prussian Blue analogue exhibiting fascinating magnetic properties, potassium manganese hexacyanoferrate, K 0.2 Mn 0 . 66 II Mn 1.44 III [ Fe 0.2 II Fe 0.8 III ( CN ) 6 ] O 0.66 ( CH 3 COO ) 1.32 ] , 7.6H 2O, has been synthesized. This compound undergoes a paramagnetic to ferrimagnetic transition at 10 K. Temperature and magnetic field-dependent magnetization studies of this compound have revealed different spin alignments below and above 3 K. The nature of possible magnetic interactions between the nearest neighbor magnetic centers has been discussed in order to explore the origin of the observed magnetic interactions. Mössbauer spectroscopic study at different temperatures demonstrates the presence of both Fe III and Fe II in low-spin states in this compound. Quantitative analysis of the Fe III and Fe II ions, and their temperature dependence exhibits the existence of an electron transfer phenomenon between Mn and Fe ions [Fe III ( t 2 g 5 , S = 1 / 2 )–CN–Mn II ( t 2 g 3 e g 2 , S = 5 / 2 )]⇔[Fe II ( t 2 g 6 , S = 0 )–CN–Mn III ( t 2 g 3 e g 1 , S = 2 )]. This electron transfer has been remarkably enhanced in the magnetically ordered region.

Optical switching between bistable phases in rubidium manganese hexacyanoferrate at room temperature

The phase transition from Fe(II)(S=0)–CN–Mn(III)(S=2) to Fe(III)(S=1∕2)–CN–Mn(II)(S=5∕2) in Rb0.98Mn1.01[Fe(CN)6]∙0.2H2O was observed at room temperature with a one-shot-laser-pulse (λ=532nm; pulse width: 6ns) irradiation. The quantum yield (Φ) depended on the laser power density (P) and Φ=38 was achieved with a 24mJcm−2pulse−1. In this photochemical reaction, only when the P value was above 6mJcm−2pulse−1 (Pth), the low-temperature phase was converted to the high-temperature phase. The threshold in laser power density and large Φ value were thermodynamically considered using a mean field model that contains cooperative interaction.

One-shot-laser-pulse-induced demagnetization in rubidium manganese hexacyanoferrate

We report on the photomagnetic effect in Rb0.91Mn1.05[Fe(CN)6]⋅0.6H2O ferromagnet. Magnetization of this system was reduced by irradiation with only one-shot of laser pulse (532 nm) at 3 K. This photodemagnetization was observed only when the laser power density (P) was above 9.3 mJ cm−2 pulse−1. The quantum yield was above one and reached 4.5 at P=43 mJ cm−2 pulse−1, showing that this phenomenon is driven by a cooperative effect such as the photoinduced domino effect. Infrared spectra before and after the irradiation indicated that this photomagnetic effect was caused by a photoinduced phase transition from the Fe(II)–CN–Mn(III) phase to the Fe(III)–CN–Mn(II) phase.

Synthesis, Crystal Structure and Magnetic Properties of a Two-Dimensional Heterometallic Assembly ∣[Mn(salen)]∣2∣[Ni(CN)4∣·1/2H2O

A heterometallic assembly, [Mn(salen)]2[Ni(CN)4 ]·1/2H2O (where salen=N, N'-ethylene-bis(salicylideneiminato)-dianion), has been prepared from the reaction of [Mn(salen)H2O]ClO4 ·H2O with K2 [Ni(CN)4 ]·H2O in methanol/water. The compound crystallizes in the tetragonal space group P 4/ncc with the cell dimensions of a =14.604(2) Å, c =16.949(3) Å, and Z=4. The compound assumes a two-dimensional distorted square network structure, formed from Ni―CN―Mn(salen)―NC―Ni linkages with dimensions of Ni―C = 1.867(7)Å, Mn―N - 2.312(6) Å, Mn―N―C - 163.8(6)° Ni―C―N = 178.4(6)°. The two metal atoms Ni(II) and MN(III) have square and slightly distorted octahedral arrangements, respectively. Magnetic susceptibility measurements indicate the presence of an intramolecular antiferro-magnetic interaction and gives a Mn―Mn exchange integral of −3.2cm−1.

High-pressure effects on a manganese hexacyanomanganate ferrimagnet with TN=29 K

The effects of high pressure, up to 1 GPa, on a Mn-based Prussian blue ferrimagnet, Mn 3 II[Mn III(CN) 6] 2·12H 2O·1.7(CH 3OH) with T N=29 K, were studied. The transition temperature gradually increases with an increase in pressure and becomes ∼40 K at 1 GPa. The pressure dependence of T N can be semi-quantitatively interpreted in terms of the shrinkage of the Mn–CN–Mn superexchange pathway.

Redoxchemie, Zweikernkomplexe und Ru 3 ‐Clusterderivate des ”︁Liganden”︁ [Cp(Co) 2 Mn–CN] −

Redox Chemistry, Dinuclear Complexes, and Ru3,-Cluster Derivatives of the “Ligand” [Cp(CO)2Mn - CN]− By means of the compounds Na[Cp(CO)2MnCN] (1a, b) the abilities of the cyanide ion to link different organometallic units and to stabilize unusual electron counts in organometallic complexes were tested. The dinuclear complexes [Cp(CO)2Mn–CN–M]- [form M = MnCp(CO)2 and W(CO)5 as PPN salts 2a, 3a] as well as Cp(CO)2Mn–Cn–M [for M = MoCp(CO)3 and NiCpPPh3, 4a, 5a] were obtained in a pure state. From the reactions with Ru3(CO)12 the cluster derivatives HRu3(CO)10[μ-NC–Mn(CO)2Cp] (6a, b) and Ru3(CO)10[μ-NC–Mn(CO)2Cp]2 (7b) were characterized. One-electron transfers were investigated for the starting complex and for the two anionic dinuclear complexes 2a, 3a. Crystal structures were determined of the dinuclear Mn–CN–Mn compex 2a and of the two cluster derivatives 2b, 7b.

Koordinationsambivalenz und elektronenstruktur ein- und zweikerniger methylcyclopentadienyldicarbonylmangan-komplexe der cyanpyridine und terephthalsäuredinitrile

The ambident cyanopyridine ligands form N(pyridine) and N′(nitrile) coordinated mono- and binuclear complexes with the (C 5H 4CH 3)(CO) 2Mn fragment. All three possible forms for 4-cyanopyridine could be isolated, whereas mononuclear compounds were obtained as most stable species in N 1-coordinated form with 3-cyanopyridine and in CN 2-coordinated form with the 2-isomer. IR, NMR, and UV/VIS spectroscopy as well as electrochemistry and ESR spectroscopy of the anion radicals demonstrate superior π back-bonding via the pyridine nitrogen centers, the isolation of nitrile coordinated complexes is attributed to the kinetic stability of the CNMn bond. While terephthalonitrile was found to form exclusively mononuclear neutral complexes, its anion radical prefers to coordinate to a second metal fragment, illustrating the excellent coordination properties of reduced nitriles. A neutral binuclear complex could be isolated with the stronger π-acceptor, tetrafluoroterephthalonitrile.