Isolated spin 3/2 plaquettes in Na3RuO4

The crystal structure of Na₃RuO₄ determined by powder neutron diffraction is reported. The structure consists of isolated tetramers of edge sharing RuO₆ octahedra in the ab plane, creating isolated four-member plaquettes of Ru atoms comprised of two equilateral triangles sharing an edge. Magnetic susceptibility measurements reveal an antiferromagnetic transition at ∼29 K, with . Neutron diffraction data indicate the onset of three-dimensional magnetic ordering at 29 K.     

Magneto-structural study on a series of rhenium(IV) complexes containing biimH2, pyim and bipy ligands

Three rhenium(IV) mononuclear compounds of formulae [ReCl₄(biimH₂)] · 2DMF (1), [ReCl₄(pyim)] · DMF (2) and [ReCl₄(bipy)] (3) (biimH₂ = 2,2′-biimidazole, pyim = 2-(2′-pyridyl)imidazole, bipy = 2,2′-bipyridine and DMF = N,N-dimethylformamide) have been prepared and characterized. The crystal structure of 2 was determined by single crystal X-ray diffraction. Compound 2 crystallizes in the monoclinic system with P2₁/c as space group. The rhenium atom is six-coordinated by four Cl atoms and two nitrogen atoms from a bidentate pyim ligand [average values of Re–Cl and Re–N bonds lengths being 2.330(2) and 2.117(4) Å, respectively]. The magnetic properties were investigated from susceptibility measurements performed on polycrystalline samples of 1–3 in the temperature range 1.9–300 K. The magnetic behaviour found is typical of antiferromagnetically coupled systems, and they exhibit susceptibility maxima at 2.8 (1 and 2) and 5.6 K (3). Short Re^IV–Cl?Cl–Re^IV contacts through space account for the antiferromagnetic behaviour observed.     

Hexacyanometallate anions as precursors of two new trinuclear heterobimetallic assemblies: Syntheses,structures and cryomagnetic properties

Two new cyano bridged Cu–Co and Cu–Fe trinuclear bimetallic assemblies, [(CuL)[Co(CN)₆](CuL)]ClO₄ · 3.5H₂O (1) and [(CuL)[Fe(CN)₆](CuL)] · 13H₂O (2) where [L = (3E,5E)-N¹,N⁴-bis((pyridin-2-yl)methylene)butane-1,4-diamine] have been prepared using cyanometallates as anion precursors and characterised by elemental analyses, spectroscopic studies, single crystal X-ray diffraction and cryomagnetic susceptibility measurements. Magneto-structural correlations have been drawn from cryomagnetic susceptibility measurements over a wide temperature range (2–300 K) under 0.5 T magnetic fields. Weak antiferromagnetic interactions with J = −0.81 and −0.73 cm⁻¹ are found for 1 and 2, respectively, showing a very weak coupling, as expected from the diamagnetic long chain –NC–Co–CN–CN– and –NC–Fe–CN–CN– bridges revealed from the single crystal X-ray diffraction studies.     

Magnetic structure and properties of Cu3(OH)4SO4 made of triple chains of spins s=1/2

Cu₃(OH)₄SO₄, obtained by hydrothermal synthesis from copper sulfate and soda in aqueous medium, is isostructural with the corresponding antlerite mineral, orthorhombic, space group Pnma (62), with a=8.289(1) b=6.079(1) and c=12.057(1) Å, V=607.5(2) ų, Z=4. Its crystalline structure has been refined from X-ray single crystal and powder neutron diffraction data at room temperature. It consists of copper (II) triple chains, running in the b-axis direction and connected to each other by sulfate groups. The magnetic structure, solved from powder neutron diffraction data at 1.4 K below the transition at 5 K evidenced by susceptibility and specific measurements, reveals that, inside a triple chain, the magnetic moments of the copper ions (μ_B=0.88(5) at 1.4 K) belonging to outer chains are oriented along the c-axis of the nuclear cell, with ferromagnetic order inside a chain and antiferromagnetic order between the two outer chains. No long-range magnetic order is obtained along the central chain with an idle spin behavior.     

Crystal structure and magnetic properties of the solid-solution phase Ca3Co2-vMnvO6

The homogeneity range of the Ca₃Co_2-vMn_vO₆ solid-solution phase covers the entire composition interval from v=0 to 1. A systematic powder X-ray and neutron diffraction, magnetic susceptibility, and magnetization study has been carried out to investigate effects of the Mn-for-Co substitution on structural and magnetic properties. The Mn substitution concerns primarily only the octahedral Co1 site of the Ca₃Co1Co2O₆ crystal structure, whereas the trigonal-prismatic Co2 site structurally is left essentially unaffected. The Ca₃Co_2-vMn_vO₆ crystal structure belongs to space group with unit-cell dimensions (in hexagonal setting) 9.084?a?9.134 Å and 10.448?c?10.583 Å. A cut through the magnetic phase diagram at 10 K shows a ferrimagnetic domain for 0?v<∼0.3 and an antiferromagnetic domain for ∼0.50<v<∼1. The magnetic ordering temperatures are quite low (<∼25/18 K), and even so further magnetic transitions appear to take place at still lower temperature. The legitimity and reliability of the different indicators used to establish the magnetic transitions, their individual accuracy, and mutual consistency are briefly discussed. Variable parameters of the crystal and magnetic structures of Ca₃Co1_1-vMn_vCo2O₆ are determined and their variation with v is briefly discussed in relation to chemical bonding. The magnetic structure in the ferrimagnetic region is essentially the same as that of the pristine v=0 phase, but since the moments at the Co2 site decrease and those at the (Co1,Mn) site increase with increasing v; characteristic traits of ferrimagnetism in magnetic susceptibility and magnetization gradually disappear. The magnetic arrangement in the antiferromagnetic region is characterized by differently sized moments at the (Co1,Mn) and Co2 sites, moments at adjacent sites in each of these sublattices being oppositely oriented along [001].     

The magnetic structure of clinopyroxene-type LiFeGe2O6 and revised data on multiferroic LiFeSi2O6

The clinopyroxene compounds LiFeSi₂O₆ and LiFeGe₂O₆ have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are monoclinic, space group P2₁/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi₂O₆ shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P2₁/c′ and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe₂O₆ is different to the silicate: the space group is and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron.     

30-Membered decanuclear manganese metallacrown

A new macrocyclic decanuclear manganese(III) 30-metallacrowns-10, [Mn₁₀(ipbmshz)₈(dmpmshz)₂(DMF)₁₀]. 4DMF (1) has been prepared by supramolecular self-assembly and characterized by X-ray crystal diffraction, where ipbmshz³⁻ is N-(4-isopropylbenzoyl)-3-methylsalicylhydrazide, dmpmshz³⁻ is N-(2,2-dimethylpropanoyl)-3-methylsalicylhydrazide. The single-crystal structure shows that a novel ring formed by the succession of ten structural moieties of the type [Mn(III)–N–N] through hydrazide N–N groups bridging the ring Mn ions. The ligand enforces the Mn³⁺ ions to form the stereochemistry of a propeller configuration with alternate…ΔΛΔΛ…-type chiral forms depending on the steric repulsions between the tail groups. The decanuclear systems measure ∼2.3 nm in diameter and ∼1.2 nm in thickness. The temperature-dependent magnetic properties have been studied and showed the presence of weakly antiferromagnetic couplings between Mn (III) ions.     

Relations of crystal structure to magnetic properties in the quasi-one-dimensional compound PbNi1.88Mg0.12V2O8

The crystal structure of the quasi-one-dimensional oxide PbNi_1.88Mg_0.12V₂O₈ has been studied by Rietveld analysis of combined high-resolution neutron and X-ray powder diffraction data at 300 K and at low temperatures. The (Ni/Mg)O₆ octahedral units share a common edge and form spiral chains along the c-axis of the tetragonal unit cell, without deviating the I4₁cd (Z=8) symmetry upon cooling. DC magnetic susceptibility measurements show that the system undergoes a magnetic phase transition below T_N≅3.4 K. Rietveld analysis of the medium resolution neutron powder diffraction data confirms that impurity-induced antiferromagnetic order (with propagation vector, ) takes over from the Haldane ground state of the parent compound. The power-law [β=0.31(3)] temperature evolution of the strongest magnetic Bragg peak intensity indicates three-dimensional Ising-type magnetic interactions, while the reduced magnitude of the Ni²⁺ moment [〈μ〉=0.98(3) μ_B] suggests important zero-point spin fluctuations. Structural considerations are consistent with small changes in the interatomic distances around the bridging tetrahedral VO₄ entities separating the chains. However, no bulk structural phase transition concurrent to the Néel ordering is found. We show that the modification of intra- and inter-chain Ni-Ni distances upon cooling promotes the magnetic coupling of the end-of-chain liberated S=1/2 spins and leads to antiferromagnetic ordering.     

A novel tetra(μ3-phenoxo) bridged copper(II) Schiff base complex containing a Cu4O4 cubane core: Synthesis,structural aspects and magneto-structural correlations

A novel tetranuclear complex, [Cu₄L₄] · Na · ClO₄ (1) has been prepared from an interesting multidentate Schiff base ligand H₂L resulting from the 1:1 condensation of 3-methoxysalicylaldehyde with benzhydrazide. The prepared complex has been characterized by elemental analysis, FT-IR, UV–Vis spectroscopy, electrochemical studies and single crystal X-ray diffraction analysis. The Cu₄O₄ cubane core consists of four μ₃-phenoxo-bridged copper(II) atoms giving an approximately cubic array of alternating copper(II) and oxygen atoms. Magneto-structural correlations have been drawn from cryomagnetic susceptibility measurements over a wide range of temperature (2–300 K) under 0.5 T magnetic field. The measurements reveal both ferromagnetic and antiferromagnetic interactions in a 2J model [J₁₁ = +13.6(4) cm⁻¹ and J₁₂ = −34.9(4) cm⁻¹] which in turn results in an overall antiferromagnetic behaviour of the magnetic system.     

Photoactivity of mechanochemically prepared nanoparticulate titanium dioxide investigated by EPR spectroscopy

Titanium dioxide nanopowders were prepared by mechanochemical synthesis in a high-energy ball mill using TiOSO₄·xH₂O and Na₂CO₃ followed by annealing in the temperature range 200–800 °C. The UVA photonic efficiency of radical processes on synthesized TiO₂ powders was determined by in situ EPR spectroscopy, using, as indicators, the N-oxide spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide and 5-(diisopropoxy-phosphoryl)-5-methyl-1-pyrroline N-oxide) or the radical cation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate, ABTS⁺). The results obtained by monitoring the photoinduced generation of hydroxyl radical spin adducts correlated with those found by the investigation of the photoreduction of ABTS⁺. The presence of iron and chromium ions, which were evidenced in samples milled in steel, decreased the photonic efficiency of radical processes. The presence of a sulfate salt matrix during the annealing process distinctly inhibits the transformation of anatase to rutile. The highest photocatalytic activity was shown by anatase samples which were prepared by milling in corundum and annealed at 700 °C. They were composed of crystallites with a mean size of 25–30 nm and well developed crystal faces.     

Magnetic and thermodynamic properties of NdT2Ge2 (T=Pd, Ag) compounds

Physical properties of NdPd₂Ge₂ and NdAg₂Ge₂, crystallizing with the tetragonal ThCr₂Si₂-type crystal structure, were investigated by means of magnetic, calorimetric, electrical transport as well as by neutron diffraction measurements. The specific heat studies and neutron diffraction measurements were performed down to 0.30 K and 0.47 K, respectively. Both compounds exhibit antiferromagnetic ordering below T_N equal to 1.5 K for NdPd₂Ge₂ and 1.8 K for NdAg₂Ge₂. Neutron diffraction data for the latter germanide indicate antiferromagnetic collinear structure described by the propagation vector k=(0.5, 0, 0.5). The Nd magnetic moments equal to 2.24(5) μ_B at 0.47 K are aligned along the a-axis and have the +− sequence within the crystal unit cell. For NdPd₂Ge₂ only very small Bragg peaks of magnetic origin were observed in the neutron diffraction patterns measured below T_N, thus hampering determination of the magnetic structure. Both compounds exhibit metallic-like electrical conduction. From the specific heat data the crystal electric field (CEF) levels schemes were determined. Difference between the overall CEF splitting in the two compounds is correlated with their structural parameters.     

Synthesis,crystal structure and magnetic studies of cis-configuration copper(II)—M(II) (M = Ba,Ca) complexes of novel Schiff bases derived from salicylaldehyde and dipeptides

The novel heteronuclear complexes [M(CuL)₂]₂ · nH₂O [M = Ba (1), Ca (2); H₂L = N-salicylideneglycylglycine] were synthesized and characterized, and the crystal structure of complex (1) was determined by X-ray diffraction. The entire structure is held together by an extensive network of H-bonds and – interactions. Variable-temperature magnetic susceptibility measurements (75–300 K) revealed the occurrence of an intramolecular antiferromagnetic interaction in (1) and (2).     

PbMn(SO4)2: A new chiral antiferromagnet

PbMn(SO₄)₂ has been synthesized in an evacuated quartz tube. The nuclear and magnetic crystal structures have been determined using powder X-ray and neutron diffraction. This material crystallizes in the enantiomorphic space group pair P4₁2₁2(92) and P4₃2₁2(96), forming a double-helical arrangement of Pb²⁺ and Mn²⁺ cations. The Mn²⁺O₆ octahedra are distorted. Each 3d⁵ Mn²⁺ has four nearest-neighbors and four next-nearest-neighbors adopting a frustrating arrangement. The compound orders antiferromagnetically at 5.5 K. Field dependent specific heat and magnetization measurements show that T_N is suppressed to 3.3 K when μ₀H=9 T.     

Magnetic and Crystallographic Properties of LnCrO4 (Ln=Nd, Sm, and Dy)

Zircon-type compounds LnCrO₄ (Ln=Nd, Sm, and Dy) were prepared. Their precise crystal structures at room temperature were determined from X-ray diffraction measurements. These compounds have a tetragonal system with space group I4₁/amd. Magnetic susceptibility and specific heat measurements have been performed for all the compounds in the temperature range between 1.8 and 300 K. For NdCrO₄, an antiferromagnetic transition was found at 25.2 K. SmCrO₄ and DyCrO₄ show magnetic transitions at 15.0 and 22.8 K, respectively. In addition, structural phase transitions were observed at 58.5 and 31.2 K, respectively. For DyCrO₄, the crystal structure below the transition temperature was determined by low-temperature powder X-ray diffraction measurements to be orthorhombic with space group Imma.     

Effects of gamma irradiation on the single crystal ergosterol: An EPR study

Single crystals of ergosterol were investigated by Electron Paramagnetic Resonance (EPR) technique, with γ irradiation of the crystals at different orientations in the magnetic field between temperatures of 120 and 380 K, and the spectra were found to be slightly dependent on temperature. Because of the importance of ergosterol it is important to determine the irradiation effects on this molecule.Taking into consideration the chemical structure and the experimental spectra of the irradiated single crystal ergosterol, we found that two paramagnetic species which were labeled as radical A, CH_2αH_β, and radical B, CH_αH_βH_γH_σ, were produced in the host crystal. The EPR parameters; spectroscopic splitting factor, g, and hyperfine coupling constant, a, were determined for each radical.     

Coordination behaviour of Schiff base 2-acetyl-2-thiazoline hydrazone (ATH) towards cobalt(II), nickel(II) and copper(II)

The synthesis and characterization of Co(II), Ni(II) and Cu(II) complexes of 2-acetyl-2-thiazoline hydrazone (ATH) are reported. Elemental analysis, IR spectroscopy, UV–Vis–NIR diffuse reflectance and magnetic susceptibility measurement, as well as, in the case of copper complex EPR spectroscopy, have been used to characterize the complexes. In addition, the structure of [NiCl₂(ATH)₂] (2) and [{CuCl(ATH)}₂(μ-Cl)₂] (3) have been determined by single crystal X-ray diffraction. In all complexes, the ligand ATH bonds to the metal ion through the imine and thiazoline nitrogen atoms. X-ray data indicates that the environment around the nickel atom in 2 may be described as a distorted octahedral geometry with the metallic atom coordinated to two chlorine atoms, two thiazoline nitrogen atoms and two imino nitrogen atoms. With regard to 3, it can be said that its structure consists of dimeric molecules in which copper ions are bridge by two chlorine ligands. The geometry about each copper ion approximates to a distorted square pyramid with each copper atom coordinated to one thiazoline nitrogen atom, one imine nitrogen atom, one terminal chlorine ligand and two bridge chlorine ligands. In compound 3, magnetic susceptibility measurements in the temperature range 2–300 K show an intradimer antiferromagnetic interaction (J = −7.5 cm⁻¹).     

Transition metal complexes of 2-amino-3-chloro-5-trifluoromethylpyridine: syntheses,structures, and magnetic properties of [(TMCAPH)2CuBr4] and [(TMCAPH)2CuCl4]

The reaction of CuX₂ (X = Br or Cl) with 2-amino-3-chloro-5-trifluoromethylpyridine in aqueous acids (HX; X = Br or Cl) yields bis(2-amino-3-chloro-5-trifluoromethylpyridinium)tetrabromocuprate(II) (1) and bis(2-amino-3-chloro-5-trifluoromethylpyridinium)tetrachlorocuprate(II) (2). These compounds have been characterized by IR, powder X-ray diffraction (XRD), single crystal XRD, combustion analysis, and temperature-dependent magnetic susceptibility. Compound 1 crystallizes in the monoclinic space group P2₁/c with three ions in the asymmetric unit, whereas 2 crystallizes in the triclinic space group P 1, and the asymmetric unit contains 18 ionic moieties. Both compounds exhibit antiferromagnetic exchange via the double halide exchange pathway and singlet ground states, with stronger exchange observed for 1. Both compounds exhibit multiple potential magnetic exchange pathways, but fitting of the data to available analytical models suggests that the magnetic exchange constants 2J/k _B are ～50 K in 1 and ～6 K in 2, respectively.     

Synthesis,structure, and properties of 2-(triphenylstannyloxy)-3,6-di-tert butyl-1,4-benzoquinone

2-(Triphenylstannyloxy)-3,6-di-tert-butyl-1,4-benzoquinone (1) was obtained from the potassium salt of 3,6-di-tert-butyl-2-hydroxy-1,4-benzoquinone and triphenyltin bromide in methanol and characterized by x-ray diffraction analysis, electronic, IR, and NMR spectroscopy. According to x-ray diffraction data, the single crystal of1 has the structure of a chain metal polymer with bridging hydroxy-para-quinone ligands; the coordination number of tin is six. Complex1 is reduced by cobaltocene to the corresponding radical anion. In solutions,1 reacts with metal-centered radicals , and with formation of paramagnetic binuclearortho-semiquinone complexes.Institute of Organometallic Chemistry, Russian Academy of Sciences, 603600 Nizhnii Novgorod. A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2798–2804, December, 1992.     

Influence of the position of the nitro group on the structural and spectroscopic characteristics of N"-(nitrobenzylidene)isonicotinic hydrazides in the crystalline state

N"-Substituted isonicotinic hydrazides of the general formula Py—C(=O)—N(H)-N"=C(H)—R, where R is o- (1), m- (2), or p-nitrophenyl (3), were studied by IR spectroscopy and X-ray diffraction analysis. The position of the nitro group in these compounds has no effect on the type of the crystal structure. The crystal packings are based on stacks consisting of antiparallel planar molecules. The molecules from the adjacent stacks are linked to each other via the N—H...N_Py hydrogen bonds. Depending on the position of the nitro group, the N...N_Py distance increases in the series 3 > 1 > 2 and the energy of the hydrogen bonds decreases (according to the IR spectroscopic data) from 3.9 to 3.1 kcal mol^–1. Analysis of the IR spectra demonstrated that the intensity of absorption in the (C—H) stretching region of the pyridine ring increases substantially as the the N—H...N_Py hydrogen bond is strengthened. Some regularities of the changes, which are observed for the (NO₂) bands in the spectra of the nitrophenyl-containing conjugated molecules in solutions, persist in the crystalline state.