One-dimensional ferromagnetic array compound [Co3(SBA)2(OH)2(H2O)2]n, (SBA = 4-sulfobenzoate)

We report on the syntheses, crystal structure, and magnetic properties of the transition metal coordination polymer [Co₃(SBA)₂(OH)₂(H₂O)₂]_n, (SBA = 4-sulfobenzoate) in which CoO₆ octahedra are linked through their edges, forming one-dimensional (1D) Co(II) arrays running along the crystal a-axis. These arrays are further perpendicularly bridged by SBA ligand to construct a three-dimensional framework. Its magnetic properties have been investigated, and ferromagnetic interactions within the arrays have been found. From heat capacity measurements, we have found that this compound exhibits a three-dimensional ferromagnetic phase transition at T_C = 1.54 K, and the specific heat just above T_C shows a Schottky anomaly which originates from an energy gap caused by uniaxial magnetic anisotropy. These results suggest that [Co₃(SBA)₂(OH)₂(H₂O)₂]_n consists of weakly coupled 1D ferromagnetic Ising arrays.     

Electronic structure and magnetic properties of RuFe3N nitride

Self-consistent band structure calculations were performed on nitride RuFe₃N in order to investigate its magnetic and ground state properties. The Linear Muffin-Tin Orbital (LMTO) method was employed and calculations were performed at several lattice parameters so as to obtain the RuFe₃N equilibrium volume. Nonmagnetic and ferromagnetic LMTO calculations have shown that the RuFe₃N stable stage is ferromagnetic with constant lattice equilibrium of 7.2502 atomic units (a.u.). At equilibrium volume the LMTO calculations have given magnetic moments of 1.25 and 1.63 μ_B at Ru and Fe sites, respectively, and no magnetic moment at N sites. The analysis of states density at equilibrium volume as well as the results for charge transfer illustrates why this ruthenium nitride is ferromagnetic. The LMTO calculations anticipate that the magnetic moment, the hyperfine field (the Fermi contact) and the isomer shift show a strong dependence on the lattice spacing.     

Synthesis and structural characterization of a novel organic-inorganic supermoleculer of [FeII(Phen)3]L2 · 2H2O complex

A new organic-inorganic complex [Fe^II(Phen)₃]L₂ · 2H₂O (Phen = 1,10-phenanthroline, L = 2-mercaptonicotinic acid) was synthesized and characterized. The crystal structure of the complex was determined by single-crystal X-ray diffraction, crystallizing in orthorhombic crystal system, space group Pba2 with the unit cell parameters a = 13.4711(11), b = 17.0021(14), c = 11.7026(9) Å, and Z = 2. The Fe(II) atom was six-coordinated with N(1), N(1A), N(2), N(2A), N(3), and N(3A) from three Phen ligands and formed a slightly distorted octahedral geometry. The base units form a one-dimensional chain via π-π-stacking interaction between 2-mercaptonicotinic acid fragments. A new 3D layered compound was obtained through hydrogen bonding.     

Magnetic and electronic structure of TlCo2S2

An extensive investigation of the ferromagnetic compound TlCo₂S₂ has resulted in new information on the electronic and magnetic structure. Electronic structure calculations showed that magnetic ordering is energetically favorable with a clear driving force for ferromagnetic coupling within the cobalt layers. TlCo₂S₂ is metallic and the conductivity is due to holes in the valence band. XPS single crystal measurements did not show evidence of mixed oxidation states of cobalt. Neutron powder diffraction resulted in a ferromagnetic structure with the magnetic moment in the ab-plane. The derived magnetic moment of the cobalt atom is at 10 K and is in very good agreement with the value, at 10 K, inferred from the magnetic hysteresis curve.     

Ab-initio calculation of structural, electronic, and optical characterizations of the intermetallic trialuminides ScAl3 compound

We present first-principles study of the electronic and the optical properties for the intermetallic trialuminides ScAl₃ compound using the full-potential linear augmented plane wave method within density-functional theory. We have employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for calculating the electronic band structure and optical properties. The electronic specific heat coefficient (γ), which is a function of density of states, can be calculated from the density of states at Fermi energy N(E_F). The N(E_F) of the phase L1₂ is found to be lower than that of D0₂₂ structure which confirms the stability of L1₂ structure. We found that the dispersion of the band structure of D0₂₂ is denser than L1₂ phase. The linear optical properties were calculated. The evaluations are based on calculations of the energy band structure.     

Synthesis and structure of a complex of copper(II) bromide with bis(benzotriazol-1-yl)methane

The preparation technique of a complex of copper(II) bromide with bis(benzotriazol-1-yl)methane (L), (Cu₂L₂Br₄)_n, is developed. The compound is studied by single crystal and powder X-ray diffraction and static magnetic susceptibility techniques. According to single crystal XRD data, the complex has a layered structure determined by bidentate bridging coordination of L with N(3) and N(3′) atoms to copper(II). The elementary unit of {Cu₂(μ-Br)₂Br₂} polymer has a binuclear structure. The coordination polyhedron is a trigonal pyramid, and the coordination core is CuN₂Br₃. The temperature dependence of effective magnetic moment is studied within an interval of 2–300 K. The nature of the μ_eff(T) dependence indicates that antiferromagnetic exchange interactions dominate in exchange clusters of the complex with an even number of paramagnetic centers. Original Russian Text Copyright ? 2007 by E. V. Lider, A. S. Potapov, E. V. Peresypkina, A. I. Smolentsev, V. N. Ikorskii, A. I. Khlebnikov, and L. G. Lavrenova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No.3, pp.543–547, May–June, 2007.     

Circumventing the perovskite pattern: Linear ruthenate(V) polyoxoanions in Bi2NaRuO6

Phase pure, coarse crystalline Bi₂NaRuO₆ was synthesized in a hydrothermal approach. It displays a new crystal structure (Pnma (62), a = 12.1408(1) Å, b = 7.49282(6) Å, c = 12.1163(1) Å, Z = 8), which is characterized by a quasi-1D poly-oxoanion composed of (RuO6) octahedra sharing oxygen atoms in trans position. The magnetic response at high temperatures is described by a Curie-Weiss law reflecting strong antiferromagnetic interactions. The obtained effective magnetic moment complies with the d³ configuration for Ru⁵⁺. Below 208 K a weakly ferromagnetic state evolves while no phase transition could be observed in a heat capacity measurement. The compound displays activated electrical conduction. The overall composition and the ionic radii ratios of the constituents encourage to apply elevated hydrostatic pressure in order to realize the title compound in a double perovskite type arrangement, instead of the chain-like structure encountered at ambient conditions.     

Layered Monophosphate Tungsten Bronzes [Ba(PO4)2]WmO3m−3: 2D Metals with Locked Charge-Density-Wave Instabilities

Phosphate tungsten and molybenum bronzes represent an outstanding class of materials displaying textbook examples of charge-density-wave (CDW) physics among other fundamental properties. Here we report on the existence of a novel structural branch with the general formula [Ba(PO₄)₂][W_mO_3m−3] (m=3, 4 and 5) denominated ′layered monophosphate tungsten bronzes′ (L-MPTB). It results from thick [Ba(PO₄)₂]⁴⁻ spacer layers disrupting the cationic metal-oxide 2D units and enforcing an overall trigonal structure. Their symmetries are preserved down to 1.8 K and the compounds show metallic behaviour with no clear anomaly as a function of temperature. However, their electronic structure displays the characteristic Fermi surface of previous bronzes derived from 5d W states with hidden nesting properties. By analogy with previous bronzes, such a Fermi surface should result into CDW order. Evidence of CDW order was only indirectly observed in the low-temperature specific heat, giving an exotic context at the crossover between stable 2D metals and CDW order.     

A novel 3D lead(II) organometallic framework with four lead(II) nuclei as a secondary building unit: Synthesis and characterization

A new 3D layered compound, [Pb₂(L)₂H₂O] _n (L is phenylmalonic acid) was hydrothermally synthesized and characterized by single-crystal X-ray diffraction. In the compound, lead has four coordination modes. The compound has formed a 2D surface shape structure through these coordinate modes with the ligand, and this 2D layer piles through C-H...π forms the 3D compound.     

Undoped Layered Perovskite Oxynitride Li2LaTa2O6N for Photocatalytic CO2 Reduction with Visible Light

Oxynitrides are promising visible‐light‐responsive photocatalysts, but their structures are almost confined with three‐dimensional (3D) structures such as perovskites. A phase‐pure Li₂LaTa₂O₆N with a layered perovskite structure was successfully prepared by thermal ammonolysis of a lithium‐rich oxide precursor. Li₂LaTa₂O₆N exhibited high crystallinity and visible‐light absorption up to 500 nm. As opposed to well‐known 3D oxynitride perovskites, Li₂LaTa₂O₆N supported by a binuclear Ru^II complex was capable of stably and selectively converting CO₂ into formate under visible light (λ>400 nm). Transient absorption spectroscopy indicated that, as compared to 3D oxynitrides, Li₂LaTa₂O₆N possesses a lower density of mid‐gap states that work as recombination centers of photogenerated electron/hole pairs, but a higher density of reactive electrons, which is responsible for the higher photocatalytic performance of this layered oxynitride.     

Synthesis and characterization of a new layered organic-inorganic hybrid nickel(II) 1,4:5,8-naphthalenediimide bis-phosphonate, exhibiting canted antiferromagnetism, with Tc∼21 K

A new Ni(II) layered hybrid organic-inorganic compound of formula Ni₂[(NDI-BP)(H₂O)₂]·2H₂O has been prepared in very mild conditions from N,N′-bis(2-phosphonoethyl)napthalene-1,4:5,8-tetracarboximide (NDI-BP ligand) and NiCl₂. The X-ray powder structure characterization of the title compound suggests a pillared layered organic-inorganic hybrid structure. The distance between the organic and inorganic layers has been found to be 17.8 Å. The inorganic layers consist of corner sharing [NiO₅(H₂O)] octahedra and they are pillared by the diphosphonate groups. DC and AC magnetic measurements as a function of temperature and field indicate the presence of 2D antiferromagnetic exchange interactions between the nearest-neighbor Ni(II) ions below 100 K. A long-range magnetic ordering at T_c∼21 K has been established and is attributed to the presence of spin canting. AC magnetic measurements as a function of temperature at different frequencies confirm the occurrence of the magnetic ordering temperature at T=21 K and the presence of a slight structural disorder in the title compound.     

Bitriazole bridged manganese(II) framework with weak ferromagnet behavior

An asymmetric bridging ligand 3,4′-bi-1,2,4-triazole (Hbtr) was used for constructing transition metal coordination polymer, and yielding a manganese(II) compound [Mn(btr)₂]_n (1) with a unique three-dimensional (3D) framework. Single-crystal X-ray diffraction reveals that 1 crystallizes in the orthorhombic space group Fdd2 and the structure is 3D (3, 6)-connected topological framework constructed from manganese ions and μ₃-btr ligands. The magnetic investigation for compound 1 shows that it is an antiferromagnetically coupled 3D array of high-spin manganese(II) ions with long-range ordering below T = 2.6 K, which is a weak ferromagnetic state due to spin-canting.     

New metal phosphonates containing coordination piperazine or pyridyl groups

Reactions of transition metal(II) salts with three aminophosphonic acids, 1-[(H₂O₃PCH₂)₂NCH₂CH₂−]-piperazine-4-CH₂PO₃H₂ (H₆L¹), 3-pyridyl-CH₂N(CH₂PO₃H₂)₂ (H₄L²) and 4-pyridyl-CH₂N(CH₂PO₃H₂)₂ (H₄L³) afforded three new metal phosphonates, namely, Cu(H₄L¹)·2H₂O (1), Co(H₃L²)₂·H₂O (2) and [Co(H₂L³)(H₂O)]·H₂O (3). The structure of compound 1 features a 1D chain in which the CuN₂O₃ and CPO₃ polyhedra are interconnected by bridging phosphonate ligands to form 1D chains. Compound 2 has a layered structure. The cobalt(II) ions in the octahedral coordination geometries and {CPO₃} tetrahedra are interconnected into an inorganic chain via -N(CH₂PO₃H)₂ moieties, and adjacent chains are further bridged by the coordination pyridyl groups of H₃L² into a 2D layer. The structure of compound 3 features a 2D double layered structure, in which the Co(II) ions are interconnected by bridging phosphonate groups into a 1D chain along b-axis. Neighboring chains are interconnected by coordination pyridyl groups into a double layer perpendicular to the c-axis.     

Synthesis and Characterization of a One-dimensional Coordination Polymer Generated from Unsymmetrical Bridging Organosulfur Ligand

A new one-dimensional（1D） coordination polymer [Zn（MMTA）2]n（MMTA=5-mercapto-l-methyl-tetrazole） was synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction. This compound crystallizes in the monoclinic space group C2/c, with cell parameters： a=1.4938（7） nm, b=1.3599（5） nm, c=1.2180（4） nm, fl=120.84（3）^＊, V=2.1243（2） nm^3, and Z=8. The deprotonated HMMTA molecule as a/a2-1igand links the zinc center, forming ID chains, which are luther linked by weak C--H...N hydrogen bonds, forming a three-dimensional supramolecular framework. The compound exhibits intense photoluminescence at room temperature. On the basis of the results of TG/DTA analyses, the structure is thermally stable up to -280 ℃.     

Neutron diffraction study on protonated and hydrated layered perovskite

A layered perovskite compound with Na⁺, D₃O⁺ ions (H₃O⁺) and D₂O molecules (H₂O) in the interlayer, D_xNa_1−xLaTiO₄·yD₂O, has been prepared by an ion-exchange/intercalation reaction with dilute DCl solution, using an n=1 Ruddlesden-Popper phase, NaLaTiO₄. Its structure has been analyzed in order to clarify the interlayer structure by Rietveld method, using powder neutron diffraction data. The structure analysis revealed that the layered structure changed from the space group P4/nmm-I4/mmm after the ion-exchange/intercalation reaction, and it induced the transformation of perovskite layers from staggered to an eclipsed configuration. The D₂O molecules and D₃O⁺ ions loaded in the interlayer statistically occupied the sites around a body center position of rectangular space surrounded by eight apical O atoms of TiO₆ octahedra in upper and lower layers.     

Magnetic order and heavy fermion behavior in CePd1+xAl6−x: Synthesis, structure, and physical properties

The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of single crystals are reported for the compound CePd_1+xAl_6−x (x=0.5) which crystallizes in the tetragonal SrAu₂Ga₅-type structure (space group P4/mmm). The compound was grown from an excess of molten Al flux from the respective elements and the crystal structure was established from single-crystal X-ray diffraction. Anomalies in the low temperature specific heat C_p(T) and electrical resistivity ρ(T) show that the compound undergoes ferromagnetic order at T_C=2.8 K. In the ordered state, CePd_1.5Al_5.5 displays heavy fermion behavior with a Sommerfeld coefficient of ca. 500 mJ/mol-K².     

β‐CuN3: The Overlooked Ground‐State Polymorph of Copper Azide with Heterographene‐Like Layers

An unexpected polymorph of the highly energetic phase CuN₃ has been synthesized and crystallizes in the orthorhombic space group Cmcm with a=3.3635(7), b=10.669(2), c=5.5547(11) Å and V=199.34(7) ų. The layered structure resembles graphite with an interlayer distance of 2.777(1) Å (=1/2 c). Within a single layer, considering N₃^? as one structural unit, there are 10‐membered almost hexagonal rings with a heterographene‐like motif. Copper and nitrogen atoms are covalently bonded with Cu? N bonds lengths of 1.91 and 2.00 Å, and the N₃^? group is linear but with N? N 1.14 and 1.20 Å. Electronic‐structure calculations and experimental thermochemistry show that the new polymorph termed β‐CuN₃ is more stable than the established α‐CuN₃ phase. Also, β‐CuN₃ is dynamically, and thus thermochemically, metastable according to the calculated phonon density of states. In addition, β‐CuN₃ exhibits negative thermal expansion within the graphene‐like layer.     

Crystal structure and magnetic properties of Cu3(TeO3)2Br2—a layered compound with a new Cu(II) coordination polyhedron

The new compound Cu₃(TeO₃)₂Br₂ crystallizes in the monoclinic spacegroup C2/m. The unit cell parameters are a=9.3186(18)Å, b=6.2781(9)Å, c=8.1999(16)Å, β=107.39(2)°, Z=2. The structure is solved from single crystal data, R₁=0.021. The new compound shows a layered structure where only weak van der Waals interactions connect the layers. There are two crystallographically different Cu(II) atoms; one having a square planar [CuO₄] coordination and one showing an unusual [CuO₄Br] trigonal bi-pyramidal coordination, the Br-ion is located in the equatorial plane. The Te(IV) atom has a tetrahedral [TeO₃E] coordination where E is the 5s² lone-pair. Within the layers the Cu-polyhedra are connected by corner- and edge sharing to form chains. The chains are separated by the Te atoms. The magnetic properties are dominated by long range magnetic ordering at . Evidence for a coexistence of ferromagnetic and antiferromagnetic interactions exists.     

Spin canting and metamagnetism in the first hybrid cobalt-hypoxanthine open framework with umr topology

Hydrothermal reactions generated a cobalt–hypoxanthine framework [Co₃(OH)₄(Hpxt)₂]?2 H₂O (H₂pxt=6‐hydroxypurine, 1 ?2 H₂O), which became a microporous framework [Co₃(OH)₄(Hpxt)₂] ( 1 ) through a single‐crystal‐to‐single‐crystal transformation. Compound 1 ?2 H₂O shows a three‐dimensional umr topological structure with two types of spiral channels constructed by rod‐shaped {Co₃(μ‐OH)₄(N‐C‐N)₂(N‐C‐C‐O)₂} second building units (SBUs). The larger channel is filled by fourfold spiral water chains. An unprecedented μ₅‐O6,N3,N7,N9 coordination mode of the Hpxt anion was observed. Both complexes 1 ?2 H₂O and 1 qualitatively show similar metamagnetism from anti‐parallel to parallel ferromagnetic cobalt‐hydroxide chains. Compared with 1 ?2 H₂O, a smaller Curie constant and more negative Weiss constant in 1 indicate that the helical water chains tend to suppress antiferromagnetic coupling between Co₃(OH)₄ ferromagnetic chains. Detailed magnetic studies of 1 ?2 H₂O revealed that the competitive interactions between interchain antiferromagnetic exchange coupling and single‐ion anisotropy of Co^II resulted in a partly canted antiferromagnetic sate in low fields. Anti‐parallel arrangement of adjacent ferromagnetic chains in middle fields gives 3D antiferromagnetic ordering, and magnetic ground states in high fields are a parallel arrangement of ferromagnetic chains.     

Ion-exchange properties of P2-NaxMnO2: evidence of the retention of the layer structure based on chemical reactivity data and electrochemical measurements of lithium cells

The ion-exchange properties of two P2-type layered Na_xMnO₂ bronzes (x=0.6, 0.75) with a differential microstructure were studied in LiCF₃SO₃ solutions in acetonitrile under ambient conditions. Na⁺ ions are readily exchanged with Li⁺, but the reaction causes a significant loss of crystallinity that results in some amorphization. The feasibility of the process increases with increasing structural disorder in the parent compound; conversion, however, is incomplete. The ability of the exchanged material to intercalate water in the air is consistent with the formation of an Li-Mn-O compound that retains the layered framework. Also, the electrochemical data obtained for this material as cathode in lithium cells are consistent with retention of the layer structure and exclude a potential spinel transition due to the ion-exchange reaction. However, the cycling properties of cells made from these layered compounds are quite modest, probably because of the strong structural disorder induced by the lithium reaction.