The paramagnetic properties of iron selenides with NiAs-type structure

The magnetic properties of the ferrimagnetic iron selenides with NiAs type structure between 51 and 59 at % Se have been investigated using a magnetic balance adapted for measurements up to 800°C. The magnetic susceptibilities of monoclinic -Fe_1–x Se and hexagonal -Fe_1–x Se with emphasis on stoichiometric Fe₃Se₄ and Fe₇Se₈ were studied in the paramagnetic region, and from the results phase boundaries and phase transformations derived. TheCurie-Weiss behaviour of alloys with hexagonal structure permitted the calculation of magnetic moments in the paramagnetic state. The deduced number of unpaired d-electronsn between 50 and 60 at % Se is restricted to the range of 4<n<5 assuming spin-only moments. The magnetic moments and their variation with composition evaluated on the basis of the conventional ionic model were found to be in good agreement with the experimental values.

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Paramagnetische Eigenschaften von Eisenseleniden mit NiAs-Struktur

Zusammenfassung Die magnetischen Eigenschaften von ferrimagnetischen Eisenseleniden mit NiAs-Struktur zwischen 51 und 59 At % Se wurden mit einer magnetischen Waage bis 800°C untersucht. Die magnetischen Suszeptibilitäten von monoklinem -Fe_1–x Se und hexagonalem -Fe_1–x Se mit besonderer Berücksichtigung von Fe₃Se₄ und Fe₇Se₈ wurden im paramagnetischen Bereich gemessen und von den Resultaten Phasengrenzen und Umwandlungen abgeleitet. DasCurie-Weiss-Verhalten der Legierungen mit hexagonaler Struktur erlaubte die Berechnung magnetischer Momente im paramagnetischen Zustand. Die daraus abgeleitete Zahl ungepaarter d-Elektronen zwischen 50 und 60 At % Se unter der Annahme von reinen Spinmomenten beschränkt sich auf 4<n<5. Mit Hilfe des konventionellen ionischen Modells berechnete magnetische Momente und ihre Konzentrationsabhängigkeit stimmen gut mit den experimentellen Werten überein.

     

The magnetic and thermoelectric properties of NiAs-type Fe0.89Se

The magnetic structure of NiAs-type Fe_1–x Se is made up by two sets of oppositely aligned ferromagnetic layers parallel to the hexagonal (001) plane. The imbalance of the sublattice magnetizations resulting in ferrimagnetism is usually attributed to the ordered arrangement of the metal vacancies. The results of the present paper provide a direct experimental proof of the correlation between the crystallographic order and the magnetic properties. It could not be distinguished whether the observed effects on the magnetization are due to a combined ordering of vacancies and Fe³⁺ ions or to the ordering of the Fe³⁺ ions only. Partial disorder was obtained by quenching samples of Fe_0.89Se from temperatures high enough to destroy the ordered arrangement. As inferred from the magnetization data the order parameter varied from 0.83 to 0.47 according to quenching temperatures ranging from 670 K to 1 270 K. In contrast to the magnetization the ferri-antiferromagnetic transformation occurred invariantly at about 170 K irrespective of the different degree of order. The thermoelectric power was positive and increased with decreasing temperature reaching +49µVK^–1 at 85 K. The discontinuity observable at about 170 K coincides roughly with the magnetic transformation indicating magnetic contributions to the thermoelectric power.

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Die magnetischen und thermoelektrischen Eigen-schaften von Fe_0.89Se mit NiAs-Struktur

Zusammenfassung Die magnetische Struktur von Fe_0,89Se (NiAs-Typ) besteht aus zwei Sätzen entgegengesetzt gerichteter ferromagnetischer Schichten parallel zur hexagonalen (001)-Ebene. Die Ungleichheit der Magnetisierungen der Untergitter, welche den Ferrimagnetismus verursacht, wird üblicherweise der geordneten Verteilung von Leerstellen zugeschrieben. Die Resultate der vorliegenden Arbeit liefern einen direkten experimentellen Beweis für den Zusammenhang zwischen kristallographischer Ordnung und magnetischen Eigenschaften. Es konnte nicht unterschieden werden, ob die beobachtete Auswirkung auf die Magnetisierung durch die gemeinsame Ordnung der Leerstellen und Fe³⁺-Ionen oder durch die Ordnung der Fe³⁺-Ionen allein bedingt ist. Durch Abschrecken der Proben von Temperaturen, welche hoch genug waren, um die geordnete Verteilung zu zerstören, wurde eine teilweise Entordnung erhalten. Die Ordnungsparameter, welche aus den Magnetisierungsdaten abgeleitet wurden, variierten von 0,83 bis 0,47, entsprechend den Abschrecktemperaturen von 670 K bis 1 270 K. Im Gegensatz zur Magnetisierung vollzog sich die ferri-antiferromagnetische Transformation konstant bei ca. 170 K unabhängig vom unterschiedlichen Ordnungsgrad. Die thermoelektrische Kraft war positiv, nahm mit abnehmender Temperatur zu und erreichte bei 85 K einen Wert von 49µVK^–1. Die Diskontinuität, welche bei 170 K beobachtbar war, fällt mit der magnetischen Transformation zusammen und läßt magnetische Beiträge zur thermoelektrischen Kraft erkennen.

     

Synthesis and structure of antiferromagnetic dinuclear iron(ii) pivalate with a Chinese-lantern-like structure

Russian Chemical Bulletin -     

The crystal structure and magnetic properties of a new ferrimagnetic semiconductor: Ca21Mn4Sb18

Single crystals of the new transition metal Zintl phase, Ca(21)Mn(4)Sb(18), were prepared by high temperature melt synthesis. The crystal structure was determined by single crystal X-ray diffraction to be monoclinic in the space group C2/c. Crystal information was obtained at 90 K, and unit cell parameters were determined (a = 17.100(2) A, b = 17.073(2) A, c = 16.857(2) A, beta = 92.999(2) degrees, Z = 2, R1 = 0.0540, wR2 = 0.1437). The structure can be described as containing 4 discreet units per formula unit: 1 linear [Mn(4)Sb(10)](22-) anion, 2 dumbbell-shaped [Sb(2)](4-) anions, 4 individual Sb(3-) anions, and 21 Ca(2+) cations. The [Mn(4)Sb(10)](22-) anion contains four edge-shared MnSb(4) tetrahedra with distances between Mn ions of 3.388(4) A, 2.782(4) A, and 2.760(4) A. Electron counting suggests that the Mn are 2+. Temperature dependent magnetization shows a ferromagnetic-like transition temperature at approximately 52 K which is suppressed with increasing magnetic field. The paramagnetic regime is best fit to a ferrimagnetic model, providing a total effective moment of 4.04(2) mu(B), significantly less than that expected for 4 Mn(2+) ions (11.8 mu(B)). Temperature dependent resistivity shows that this compound is a semiconductor with an activation energy of 0.159(2) eV (100-300 K).     

Magnetic properties of chromium sulfide selenides and sulfides

Summary The structural parameters of chromium sulfide selenides are intermediate between those of the sulfides and the selenides. The nature of the dependence of the magnetic properties of the sulfide selenides on temperature and composition has much in common with that for the sulfides. The presence of selenium atoms in the sulfide lattice leads merely to some distortion of the anomalies which are observed for the pure sulfides. In the mixed chalcogenides of chromium, gradual oxidation of the monosulfide by selenium takes place, with the conversion of Cr(II) into Cr(III). The principal contribution to the magnetic moments is made by the spin values, equal to 4.9 _B for Cr(II) and 3.87 _B for Cr(III). The slight increase in the lattice parameters of the sulfide selenides (increase in the Cr–Cr distances) compared with the sulfides leads to a decrease in the exchange interactions in the sulfide selenides compared with the sulfides. This is indicated by the change in the paramagnetic Curie temperature with change in composition.Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 14, No. 1, pp. 163–166, January–February, 1973.     

Preparation and properties of two indium antimony selenides

Crystals of antimony-doped In₂Se₃ were grown by the Bridgeman method. This compound, whose composition is In_1.8Sb_0.2Se₃, appears to be isostructural with In_1.9As_0.1Se₃. The refined unit cell parameters are a = 3.97(1), c = 18.87(1) Å. Orthorhombic crystals of InSbSe₃ were grown from an isothermal melt. The refined unit cell parameters are a = 9.43(1), b = 14.02(5), and c = 3.96(1) Å. These parameters agree with those determined for α-InSbSe₃ by other studies. The observed densities measured by a hydrostatic technique are 5.98(3) g/cm³ for In_1.8Sb_0.2Se₃ and 6.07(2) g/cm³ for InSbSe₃. The room temperature dc resistivity for In_1.8Sb_0.2Se₃ has been found to be 4.4 × 10⁴ Ω-cm, whereas that of InSbSe₃ has been found to be 15.2(1) Ω-cm. A resistivity versus temperature study has beenn carried out for InSbSe₃ between 230 and 400°K. Optical studies indicate that In_1.8Sb_0.2Se₃ is an n-type semiconductor with a band gap of 1.1 eV and InSbSe₃ is a p-type semiconductor with a band gap of 0.92 eV.     

Effects of conjugation and the conformational structure of aromatic selenides

Conclusions In the aromatic selenides, in contrast to the corresponding sulfides, the partial steric inhibition of the conjugation of the Se atom with the aromatic -system occurs. The appreciable content (30%) of the plane conformer is observed in compounds with the tertiary and quaternary -carbon atoms of the alkyl group; this explains the weak -donor properties of Se in relation to the aromatic fragment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 64–69, January, 1989.The authors thank V. M. Bzhezovskii for helpful discussions, as well as V. I. Mamatyuk, R. G. Kostyanovskii, and I. I. Chervin for allowing the possibility of registering the¹³C NMR spectra of some of the investigated compounds.     

Synthesis,crystal structures and magnetic properties of two iron (II) tris(pyridyl)phosphine selenides complexes

We reported the synthesis of tris(pyridyl)phosphine selenide (TppSe) and tris(4-methylpyridin-2-yl)phosphine selenide (MeTppSe), which were prepared by a simple and straightforward one-pot method with red phosphorus in a KOH/DMSO suspension, and treatment of resulted phosphines with selenium in hot toluene. These compounds were characterized by mass spectroscopy, ¹H, ¹³C and ³¹P NMR spectroscopies and the structure of MeTppSe was characterised by a single-crystal X-ray diffraction. Furthermore, The reactions of selenides with Fe(ClO₄)₂·6H₂O afforded two new iron(II) mononuclear metal complexes [Fe(TppSe)₂][ClO₄]₂·3DMF (1) and [Fe(MeTppSe)₂][ClO₄]₂·2DMF (2). Detailed structural analyses and magnetic susceptibility measurements confirm no spin transition from low-spin to the high-spin state between 2 and 300 K in two iron(II) complexes.     

Thermodynamic properties of titanium selenides with variable composition TiSe2-TiSe1.80

The thermodynamic investigation of the system TiSe₂-TiSe_1.80 was carried out by the static method of vapor pressure measurements using the quartz membrane-zero manometers in the temperature range from 713 to 1395 K. The analysis of the p _Se-T-x dependences obtained showed that titanium diselenide formed a continuous solid solution. The enthalpies and entropies of dissociation processes of TiSe _x were derived from the experimental data. The standard enthalpies of formation, the absolute entropies, and the free Gibbs energies of formation of selenides belonging to the homogeneity region of TiSe₂ were estimated using literature data. The obtained set of thermodynamic characteristics may be used for the calculation of phase equilibria and for thermodynamic modeling in the system Ti-Se.     

Formation and properties of the nanocluster structure of iron oxides

Nanostructures based on iron oxide clusters 1–300 nm in size were synthesized and studied. Thermodynamic models of nanocluster nucleation resulting in the formation of both primary nanoclusters and nanocluster aggregates with the sizes up to 70–80 nm were considered. Models of heat capacity of the nanoclusters were examined, and the twofold increase in the heat capacity of the iron oxide clusters 2–3 nm in size compared to that of the bulk iron oxide samples was found. The size of the primary nanoclusters and the intercluster interaction make it possible to vary the magnetic properties of the nanostructures in a wide range from paramagnetic to magnetically ordered α-Fe₂O₃-γ-Fe₂O₃ nanostructures with the first-order magnetic phase transitions, magnetic twinning, and a strong magnetic field (10 Oe) effect on the magnetization increase at low temperatures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1693–1704, October, 2006.     

Two metal-organic frameworks constructed from one-dimensional cobalt(II) ferrimagnetic chains with alternating antiferromagnetic/ferromagnetic and AF/AF/FM interaction: synthesis, structures, and magnetic properties

Here, we report two three-dimensional metal-organic frameworks of formula [Co(2)(4-ptz)(2)(bpp)(N(3))(2)](n) (1) and [Co(3)(OH)(2)(bdt)(2)(bpp)(2)(H(2)O)(2)](n) (2), which were synthesized by hydrothermal reaction from the respective tetrazole ligand (5-(4-pyridyl)tetrazole (4-H-ptz) for 1 and 5,5'-(1,4-phenylene)bis(1-H-tetrazole) (H(2)bdt) for 2), long and flexible pyridyl-containing ligand 1,3-bi(4-pyridyl)propane (bpp), NaN(3), and CoCl(2). Both 1 and 2 consist of well-isolated one-dimensional cobalt(II) alternating chains further linked by the bpp and/or the tetrazole ligand, while their chain structures are totally different. The chains of 1 are formed by Co(2+) ions bridged by single μ-EE-N(3) and triple (μ-EO-N(3))(μ-tetrazole)(2) alternately, whereas the Co(2+) ions are bridged by μ(3)-OH to form Co(3)(OH)(2) chains in compound 2. Magnetic measurements demonstrate that compound 1 contains an alternating antiferromagnetic (AF)/ferromagnetic (FM) ferrimagnetic chain, while compound 2 exhibits the coexistence of spin canting, slow magnetic dynamics, and finite-size effect, with alternating AF/AF/FM ferrimagnetic chains.     

Crystal structure and magnetic properties of dinuclear iron(III) complex with ONNO-donor ligand

A new dinuclear Fe(III) complex, [Fe(5-MeOL1)(OH)_0.86(CH₃O)_0.14]₂?2(CH₃OH), [H₂-5-MeOL1 = N,N′-bis(5-methoxy-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine], 1 has been synthesized and characterized by single crystal structure analysis. The structure of 1 consists of two Fe(III) centers with one tetradentate schiff base ligand (N₂O₂) which are bridged by dihydroxo/dimethoxo groups to yield a Fe₂O₂ core. Complex 1 exhibits weak antiferromagnetic exchange interaction between Fe(III) ions with J = ?0.21 cm^–1.     

The novel azomethine ligands for binuclear copper(II) complexes with ferro- and antiferromagnetic properties

A series of novel binuclear ferro- and antiferromagnetic Cu(2+) chelates of structurally broadly varied Schiff bases (derived from o-tosylamino(hydroxyl)benzaldehydes and monoalkylated o-phenylenediamine, o-aminophenol, o-aminothiophenol, 1,2-diaminobenzimidazole, 1-aminobenzimidazoline-2-thione) and β-diketimines (derived from 2,6-di-i-Pr-aniline) has been prepared. The tautomerism of the ligands and structureof their copper complexes have been studied with the use of IR, ¹H NMR EPR and EXAFS spectroscopy. Molecular and crystal structure of a β-diketimine copper dimer has been determined by X-ray crystallography. The magnetic measurements (2–300?K) performed for all the complexes showed that the ferro- and antiferromagnetic character of the exchange interaction depends both on the structure of the coordination site (origin of the ligating centers) and the structure of the ligands (in particular, on the type of the cycle annelated to the bridging fragment). Whereas S-binding metal chelates 13 (X?=?NTs, Y?=?S, R?=?H) are diamagnetic, the complexes 15 with annelated azole moieties are ferromagnetic.     

The reaction of selenophosphonates with carbonyl compounds. Vinylic selenides

Selenophosphonates of the general formula (EtO)₂P(O)CHRSePh were prepared and their reactions with aldehydes and ketones investigated. The products formed are vinylic selenides having predominantly the E configuration. Hydrolytic cleavage of these products gives the corresponding ketones.     

The UV spectra of arsines and arsine selenides

Short-wavelength n_Se ^* and long-wavelength n_Se ^* bands are observed in the UV spectra of saturated trialkylarsine selenides in the near-UV region. The n_x ^* band in going from arsine selenides to arsine sulfide and then to arsine oxides is shifted hypsochromically, as in the corresponding phosphorus compounds. The n_x ^* band is only slightly sensitive to the chalcogen. Saturated trialkylarsines, in contrast to alkylphosphines, absorb in the near UV region (the n_As ^* band is at 208 nm).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 940–942, April, 1990.     

Computational modeling of structure and magnetic properties of dinuclear di-o-benzoquinone iron complexes with linear polycyclic linkers

Density functional theory (DFT UTPSSh/6-311++G(d,p)) quantum chemical modeling of geometry, energy and magnetic characteristics of binuclear iron complexes, in which iron atoms coordinated by 2,11-diaza[3.3](2,6)pyridinophane bases are connected by di-o-benzoquinone ligands with acene linkers, was performed. It is established that the energy diff erence between electromeric forms of the studied compounds is determined by the type of the alkyl substituents at the nitrogen atoms of the tetraazamacrocyclic ligand and does not depend on the structure of the polycyclic chain. The possibility of controlling magnetic properties of the molecules of this type by means of external influences is predicted based on the facts that terminal metal-containing fragments are capable of undergoing thermally induced spin-state switching rearrangements, while the singlet-triplet transition of the acene linker can be induced by light irradiation.

     

The structure and reactivity of iron nitride complexes

The structure and reactivity of discrete iron nitride complexes is described. Six-coordinate, four-fold symmetric nitrides are thermally unstable, and have been characterized at cryogenic temperatures by an arsenal of spectroscopic methods. By contrast, four-coordinate, three-fold symmetric iron nitrides can be prepared at room temperature. A range of diamagnetic iron(IV) nitrides have been reported and in some cases, isolated. Among these are the isolable, yet reactive, tris(carbene)borate iron(IV) nitrides. These complexes can effect two-electron nitrogen atom transfer to a range of substrates, in some cases with complete atom transfer occuring through Fe-N bond cleavage. These nitrides are also active in single electron pathways, including the synthesis of ammonia by a mechanism involving hydrogen atom transfer to the nitride ligand. One-electron oxidation of a tris(carbene)borate iron(IV) nitride leads to an isolable iron(V) complex that is unusually reactive for a metal nitride.