First-principles calculations of the structural and electronic properties of Cu3MN compounds with M = Ni,Cu, Zn,Pd, Ag,and Cd

We have performed accurate ab initio total energy calculations using the full-potential linearized augmented plane wave (FP-LAPW) method to investigate the structural and electronic properties of copper-transition metal nitrides. In its ground state, Cu₃N crystallizes in an anti-ReO₃ type cell and it is a semiconductor material with a small indirect gap. In this paper, we report a study of Cu₃MN compounds with M = Ni, Cu, Zn, Pd, Ag, and Cd. In the calculations, we have used the same anti-ReO₃ type cell of Cu₃N, but with the extra transition metal atom at the center of the cube. In particular, our calculated lattice parameters for copper nitride (a = 3.82 Å) and copper palladium nitride (a = 3.89 Å) are in excellent agreement with the experimental values of a = 3.807 Å and a = 3.86 Å, respectively. In all the cases we have studied, the addition of the transition metal atom modifies the electronic structure of Cu₃N, turning all copper-transition metal nitrides into metals.     

Crystal structure and magnetic properties of the new cobalt tellurite halide Co5(TeO3)4X2 (X = Cl,Br)

Two new cobalt tellurite halides Co₅(TeO₃)₄Cl₂ and Co₅(TeO₃)₄Br₂ have been synthesized and found to be iso-structural with Ni₅(TeO₃)₄X₂ (X = Cl, Br). Co₅(TeO₃)₄X₂ crystallizes in the monoclinic system space group C2/c, and the Br-phase has the lattice parameters a = 20.440(1) Å, b = 5.2760(2) Å, c = 16.4710(7) Å, β = 124.790(5)°, and Z = 4. The crystal structures were solved from single-crystal X-ray data, R1 = 1.90 and 1.77, respectively, for the Cl- and Br-phases. The crystal structure is layered with only weak van der Waals' interactions in between the layers. The layers are built by large [Co₅O₁₆X₂] groups consisting of five edge- and face-sharing Co-octahedra. Each group is connected to adjacent groups via corner sharing through common oxygen atoms as well as through [TeO₃E] groups. Magnetic susceptibility measurements on oriented single crystals reveal pronounced anisotropy in a broad temperature range and clear signs of antiferromagnetic ordering at low temperatures. Anisotropic susceptibility of an iso-structural Ni-based compound was also studied and compared with the corresponding results of Co₅(TeO₃)₄X₂. Magnetic anisotropy is discussed in framework of single-ion anisotropy effects.     

Reduced-dimensionality and direct trajectory calculations for the C(3PJ) + NH2(2B1) reaction

Nonadiabatic transitions through spin–orbit interaction for the C(³P_J) + H₂(²B₁) reaction were investigated by ab initio electronic structure calculations and quantum reactive scattering calculations. It has been found that the reactivity for the J = 0 and J = 1 states is quite large. Ab initio direct trajectory calculations on the lowest doublet potential energy surface have also been carried out in order to understand the HNC production mechanism. We have found that HNC is mostly produced via direct mechanism, in which the H elimination occurs directly from the CNH₂ intermediate, initially formed by the addition of C to NH₂.     

Synthesis and asymmetric catalytic application of chiral imidazolium–phosphines derived from (1R,2R)-trans-diaminocyclohexane

Reaction between a chiral imidazole–amine precursor derived from (1R,2R)-trans-diaminocyclohexane and P¹Cl (where P¹ = PPh₂, P(1,3,5-Me₃C₆H₃)₂, P(2,2′-O,O′-(1,1′-biphenyl), P((R)-(2,2′-O,O′-(1,1′-binaphthyl))) and P((S)-(2,2′-O,O′-(1,1′-binaphthyl)))) followed by RX (where R = ⁿPr, ⁱPr, CHPh₂, X = Br; R = ⁱPr, X = I), respectively, gives a selection of chiral imidazolium–phosphine compounds. Deprotonation of the imidazolium salt gives the corresponding NHC–P ligands that can be used in metal-mediated asymmetric catalytic applications. Catalytic reactions show that NHC–P ligands give a significantly greater rate of reaction for a palladium catalysed allylic substitution reaction in comparison to analogous di-NHC or NHC–imine ligands and that NHC–P hybrids are also effective for iridium catalysed transfer hydrogenation.     

Double perovskite Sr2FeMoO6−xNx (x=0.3, 1.0) oxynitrides with anionic ordering

Two new oxynitride double perovskites of composition Sr₂FeMoO_6?xN_x (x=0.3, 1.0) have been synthesized by annealing precursor powders obtained by citrate techniques in flowing ammonia at 750 °C and 650 °C, respectively. The polycrystalline samples have been characterized by chemical analysis, x-ray and neutron diffraction (NPD), Mössbauer spectroscopy and magnetic measurements. They exhibit a tetragonal structure with a=5.5959(1) Å, c=7.9024(2) Å, V=247.46(2) Å³ for Sr₂FeMoO_5.7N_0.3; and a=5.6202(2) Å, c=7.9102(4) Å, V=249.85(2) Å³ for Sr₂FeMoO₅N; space group I4/m, Z=2. The nitridation process seems to extraordinarily improve the long-range Fe/Mo ordering, achieving 95% at moderate temperatures of 750 °C. The analysis of high resolution NPD data, based on the contrast existing between the scattering lengths of O and N, shows that both atoms are located at (O,N)2 anion substructure corresponding to the basal ab plane of the perovskite structure, whereas the O1 site is fully occupied by oxygen atoms. The evolution of the 〈Fe–O〉 and 〈Mo–O〉 distances suggests a shift towards a configuration close to Fe⁴⁺(3d⁴, S=2):Mo⁵⁺(4d¹, S=1/2). The magnetic susceptibility shows a ferrimagnetic transition with a reduced saturation magnetization compared to Sr₂FeMoO₆, due to the different nature of the magnetic double exchange interactions through Fe–N–Mo–N–Fe paths in contrast to the stronger Fe–O–Mo–O–Fe interactions. Also, the effect observed by low-temperature NPD seems to reduce the ordered Fe moments and enhance the Mo moments, in agreement with the evolution of the oxidation states, thus decreasing the saturation magnetization.     

Crystal structure and thermal analysis of the tetramethylammonium dichromate and trichromate

The structures of the tetramethylammonium dichromate, [(CH₃)₄N]₂Cr₂O₇ and trichromate, [(CH₃)₄N]₂Cr₃O₁₀, were determined from single-crystal X-ray diffraction data. These compounds crystallize in the orthorhombic system (space group Pnma, with Z=4 and a=17.192(1) Å, b=8.55(1) Å, c=10.637(1) Å), for the dichromate and in the monoclinic system (space group P2₁/n, with Z=4 and a=11.366(2) Å, b=8.493(2) Å, c=20.187(4) Å, β=103.98(3)° for the trichromate. The structures consist of discrete dichromate anions (Cr₂O₇)^2– or trichromate anions (Cr₃O₁₀)^2–, respectively, stabilized by quaternary ammonium [(CH₃)₄N]⁺. Phase transitions in [(CH₃)₄N]₂Cr₂O₇ have been evidenced by differential scanning calorimetry as well as a new allotropic variety of [(CH₃)₄N]₂Cr₂O₇ which was characterized by X-ray powder diffraction. It crystallizes in an orthorhombic system with the unit cell parameters a=24.49(1) Å, b=8.85(1) Å, c=8.705(8) Å.     

Insertion of the p-complex structure of silylenoid H2SiLiF into X–H bonds (X = C,Si, N,P, O,S, and F)

The insertion reactions of the p-complex structure (A) of silylenoid H₂SiLiF into XH_n molecules (X = C, Si, N, P, O, S, and F; n = 1–4) have been studied by ab initio calculations at the G3(MP2) level. The results indicate that the insertion reactions of A into X–H bonds proceed via three reaction paths, I, II, and III, forming the same products, substituted silanes H₃SiXH_n − 1 with dissociation of LiF, respectively, and all insertion reactions are exothermic. All the seven X–H bonds can undergo insertion reactions with A via path I and II, but only four of them, C–H, Si–H, P–H, and S–H, undergo insertion reactions via path III. The following conclusions emerge from this work: (i) the X–H insertion reactions of A occur in a concerted manner via a three-membered ring transition state; (ii) for path I and II, the stabilization energies of the A–XH_n complexes decrease in the order HF > H₂O > H₂S > NH₃ > SiH₄ > CH₄; (iii) for path I and II, the greater the atomic number of heteroatom (X) in a given row, the easier the insertion reaction of XH_n hydrides and the larger the exothermicity, and for the second-row hydrides, the reaction barriers are lower than for the first-row hydrides; (iv) The barriers of path I are lowest in those of three pathways with the exception of A + SiH₄ system, which barrier of path III is lowest. Moreover, the present study demonstrates that both electronic and steric effects play major roles in the course of insertion reactions of A into X–H bonds.     

HF and DFT studies and vibrational spectra of 1,2-bis(2-pyridyl)ethylene and its zinc (II) halide complexes

Ab initio restricted Hartree–Fock and density function theory calculations using BLYP, B3LYP and B3PW91 functionals were carried out to study molecular structure and vibrational spectrum of 1,2-bis(2-pyridyl)ethylene (which is abbreviated as bpe). Comparison of calculated and experimental results indicates the density functional B3LYP and BLYP/6-311G* methods are more accurate in predicting fundamental vibrational frequencies than the scaled other approaches. On the basis of calculated results, assignment of fundamental vibrational modes of bpe was proposed. Complexes of the type Zn(bpe)X₂ [where X = Cl, Br, I] have been studied in the 4000–400 cm⁻¹ region, and assignments of all the observed bands were made. The analysis of the infrared spectra indicates that there is some structure-spectra correlations.     

Potential energy surface and rate constant of the inversion substitution reactions CH3X + O2 → CH3O2• + X• (X = SH,NO2)

The temperature dependence of the rate constant of the inversion substitution reactions CH₃X + O₂ → CH₃O₂^? + X^? (X = SH, NO₂), can be expressed as k = 6.8 × 10^–12(T/1000)^1.49exp(–62816 cal mol^–1/RT) cm³ s^–1 (X = SH) and k = 6.8 × 10^–12(T/1000)^1.26 × × exp(–61319 cal mol^–1/RT) cm³ s^–1 (X = NO₂), as found with the use of high-level quantum chemical methods and the transition state theory.     

Ab initio crystal structure of nickel(II) hydroxy-terephthalate by synchrotron powder diffraction and magnetic study

The structure of the new hybrid compound [Ni₃(OH)₂(tp)₂(H₂O)₄]·2H₂O (tp = C₈H₄O₄²⁻) has been determined ab initio from synchrotron powder diffraction data and refined with the Rietveld method: space group P-1, a = 10.2077(6) Å, b = 8.0135(5) Å, c = 6.3337(4) Å, α = 97.70 (1)°, β = 97.21(1)°, γ = 108.77(1)°, D_x = 2.124 g/cm³, Rp = 0.045, R_B = 0.095 (757 independent reflections). H atoms were placed geometrically and their position optimized by DFT calculation. The repeating structural unit is the chain [Ni(1)O₆]₂Ni(2)O₆, consisting of two edges sharing octahedrons related by the symmetry center and linked via μ3-OH to a vertex of Ni(2) octahedron. The Ni(1) coordination is ensured by two oxygen atoms from two water molecules, two OH and two oxygen atoms from carboxylate groups. The linkage of the chains by the tp anions forms infinite layers parallel to the (010) planes. Interchain hydrogen bonds between the water molecules coordinating the metal ensure the cohesion of the 2D structure. The structural and magnetic properties are compared with that of the 3D fumarate-based compound [Ni₃(OH)₂(fum)₂(H₂O)₄]·2H₂O (fum = C₄H₂O₄²⁻).     

Synthesis,structure, and characterization of a new two-dimensional lead(II) vanadate,Ba3PbV4O14

A new two-dimensional lead(II) vanadate, Ba₃PbV₄O₁₄ has been synthesized by standard solid state techniques using BaCO₃, PbO, and V₂O₅ as reagents. The structure of Ba₃PbV₄O₁₄ was determined by single-crystal X-ray diffraction. Ba₃PbV₄O₁₄ crystallizes in the triclinic space group P-1 (no. 2), with a = 7.2997(15) (Å), b = 7.2932(15) (Å), c = 13.379(3) (Å), α = 93.68(3)°, β = 99.68(3)°, γ = 91.49(3)°, V = 700.2(2) (ų) and Z = 2. Ba₃PbV₄O₁₄ exhibits a novel two-dimensional layered structure consisting of corner shared VO₄ tetrahedra that are linked by edge shared PbO₇ polyhedra, in which the Ba²⁺ cations occupy the interlayer region. The Pb²⁺ cations are in asymmetric coordination environments attributable to its lone pair. Infrared, Raman, and UV–vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dipole moment calculations are also presented.     

Unprecedented multistability in dodecanuclear complex compound observed by Mössbauer spectroscopy

The precursors [Fe(III)(^5XL)Cl] (^5XLH₂ = N,N′-bis(1-hydroxy-2-benzyliden)-1,6-diamino-3-X-hexane, X = N,S) are high-spin (S = 5/2) complexes. This precursors are combined with the bridging unit [(NC)₅Fe(II)-CN-Co(III)(CN)₅]⁶⁻ to yield star-shaped dodecanuclear clusters, [(^5XLFe(III)-NC)₅Fe(II)-CN-Co(III)(CN-Fe(III)^5XL)₅]Cl₄. The star-shaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers in the N-star switch to the low-spin state as proven by Mössbauer spectroscopy, i.e. multiple electronic transitions, while the S-star remains in the high-spin state.     

Syntheses,structures and single-molecule magnetic behaviors of two dicubane Mn4 complexes

The reaction of MnX₂ · 4H₂O (X = Cl or Br) with 2,6-bis(hydroxymethyl)-4-methylphenol (H₃L) and NaOH in methanol solution yielded two tetranuclear manganese complexes, [Mn₄(HL)₄(MeOH)₄Cl₂] (1) and [Mn₄(HL)₄(MeOH)₄Br₂] (2). Both compounds crystallize in the monoclinic space group C₂/c with cell parameters: a = 26.0945(19) Å, b = 11.4999(8) Å, c = 21.2188(16) Å, β = 121.050(1)° and z = 4 for 1 · 2Et₂O; a = 25.8145(3) Å, b = 11.6734(2) Å, c = 21.3956(3) Å, β = 120.1277(6)° and z = 4 for 2 · 2Et₂O. Both complexes consist of a mixed-valence dicubane structure, which comprises two Mn^II and two Mn^III ions. Magnetic susceptibilities and magnetization of complexes 1 and 2 in the solid state indicate that two clusters have an S = 9 ground state. Frequency-dependent out-of-phase signals of alternating current magnetic susceptibilities were observed in the low temperature range (<3 K) for both complexes indicating a slow magnetic relaxation.     

Synthesis,thermal behaviour and crystal structure of RbSrP3O9·3 H2O

Rubidium strontium cyclo-triphosphate trihydrate, RbSrP₃O₉·3 H₂O, was synthesized by reaction between cyclo-triphosphoric acid H₃P₃O₉ and rubidium and strontium carbonates. It crystallizes in the othorhombic system, space group Pnma, with a = 9.120(1) Å, b = 8.141(1) Å, c = 15.234(1) Å, V = 1 131.1(3) Å³, Z = 4. Crystal structure determination from single crystal data collected at 300 K shows that the P₃O₉ groups exhibit C_s symmetry and are not connected to each other. Rubidium (distorted octahedron) and strontium (distorted square antiprism) are coordinated by oxygen and water molecules yielding the formation of infinite chains interconnected to each other and to the P₃O₉ groups. The IR valence vibration bands of the P₃O₉ cycle have been identified in the domain 1 400–650 cm^–1 and related to the structural results. After water loss, the anhydrous phase crystallizes from an intermediate amorphous phase and further decomposes into Rb₂SrP₄O₁₂ and SrP₂O₆.     

Structure elucidation of BaSi2O2N2 – A host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs

BaSi₂O₂N₂ is a promising host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs. Applying a combined approach, its orthorhombic average structure (space group Cmcm (no. 63), a = 14.3902(3) Å, b = 5.3433(1) Å, c = 4.83256(7) Å and V = 371.58(2) Å³, Z = 4) has been elucidated by electron diffraction and structure solution from X-ray and neutron powder diffraction data with subsequent Rietveld refinement (wRp = 0.0491 for X-ray data). The structure contains layers of highly condensed SiON₃ tetrahedra with O terminally bound to Si. The Ba²⁺ ions are situated between the layers and are surrounded by a cuboid of O atoms capped by two N atoms. In the structure, there is only one Ba site and one Si site, respectively, which is in accordance with a single sharp ²⁹Si NMR signal observed at ?52.8 ppm typical for SiON₃ tetrahedra in MSi₂O₂N₂ type oxonitridosilicates. Lattice energy calculations support the results of the structure determination.     

Crystal structure and ionic conductivity of AgCr2(PO4)(P2O7)

Single crystals of a new phosphate AgCr₂(PO₄)(P₂O₇) have been prepared by the flux method and its structural and the infrared spectrum have been investigated. This compound crystallizes in the monoclinic system with the space group C2/c and the parameters are, a = 11.493 (3) Å, b = 8.486 (3) Å, c = 8.791 (2) Å, β = 114.56 (2)°, V = 779.8 (3) ųand Z = 4. Its structure consists of CrO₆ octahedra sharing corners with P₂O₇ units to form undulating chains extending infinitely along the [110] direction. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the Ag⁺ ions are located. The infrared spectrum of this compound was interpreted on the basis of P₂O₇^4? and PO₄^3? vibrations. The appearance of ν_sP–O–P in the spectrum suggests a bent P–O–P bridge for the P₂O₇^4? ions in the compound, which is in agreement with the X-ray data. The electrical measurements allow us to obtain the activation energy of (1.36 eV) and the conductivity measurements suggest that the charge carriers through the structure are the silver captions.     

Synthesis and structure of 1-benzyl-5-amino-1H-tetrazole in the solid state and in solution: Combining X-ray diffraction, 1H NMR,FT–IR,and UV–Vis spectra and DFT calculations

Compound 1-benzyl-5-amino-1H-tetrazole (BAT) was synthesized and characterized by ¹H NMR, FT–IR, and UV–Vis spectroscopies and elemental (CHNS) analysis. The crystal structure was further elucidated by single-crystal X-ray diffraction. Density functional theory (DFT) calculations with B3LYP and PBE1PBE functionals of the BAT were performed to provide structural and spectroscopic information and guide spectral assignments. The compound crystallizes in monoclinic primitive system space group P2(1)/c with a = 14.91 Å, b = 5.12 Å, c = 11.19 Å, V = 852 Å³, Z = 4, R₁ = 0.0428 at 298 K. The structure exhibits intermolecular hydrogen bonds of the type N–H(amino)···N(tetrazole). Simultaneous hydrogen bonds between amino···tetrazole and tetrazole···amino establish a dimeric intermolecular structure, whereas another hydrogen bond between the remaining H atom of the amino group and the other N atoms of the tetrazole ring extends the structure into another dimension. The crystal structure of BAT is properly reproduced by DFT calculations only when a dimeric or tetrameric model is employed in the modeling. Comparisons between experimental and calculated spectral properties suggest that the monomeric form of BAT is dominant in aprotic, polar, hydrogen-bonding solvents, such as DMSO and DMF.     

Subsolidus phase relations,crystal chemistry and cation-transport properties of sodium iron antimony oxides

Subsolidus phase relations in Na₂O–Fe₂O₃–Sb₂O_x system (excluding Na-rich and Sb-rich corners) were studied using powder X-ray diffraction. Samples were prepared by conventional solid-state reactions at 980–1030 °C followed by quenching. Sb substitution for Fe stabilizes the low-temperature rhombohedral α form of NaFeO₂ and enhances ionic conductivity: σ(300 °C) = 0.5 S/m, E_a = 0.38(3) eV, t_e < 0.01 for Na_0.8Fe_0.9Sb_0.1O₂ ceramics. Besides known orthorhombic Na₂Fe₃SbO₈, three new compounds have been identified: trigonal Na₄FeSbO₆, a superlattice of α-NaFeO₂ type, a = 5.4217(7) Å, c = 16.2715(1) Å, possible space group P3₁12; orthorhombic Na₂FeSbO₅, possibly related to brownmillerite, Pbcn, a = 10.8965(13) Å, b = 15.7178(13) Å, c = 5.3253(4) Å, and one more phase with empirical formula Na₄Fe₃SbO₉, whose pattern could not be indexed. Ion-exchange reactions lead to a delafossite-type superlattice Ag₃(NaFeSb)O₆ (a = 5.4503(12) Å, c = 18.7747(20) Å, possible space group P3₁12).     

Synthesis and structural characterization of two new hexagonal osmates: Ba2Fe0.92Os1.08O6 and Ba2Co0.77Os1.23O6

Two complex oxides of osmium, Ba₂Fe_0.92Os_1.08O₆ and Ba₂Co_0.77Os_1.23O₆, have been prepared as single crystals from molten potassium hydroxide. Both oxides crystallize in the hexagonal space group P6₃mc with a = 5.7403(1) Å and c = 14.0771(6) Å and a = 5.7745(2) Å and c = 14.0946(7) Å for Ba₂Fe_0.92Os_1.08O₆ and Ba₂Co_0.77Os_1.23O₆, respectively. The structure of these compounds is related to the 6H–BaTiO₃ structure but exhibit mixed occupancy of both metals on the three crystallographically independent metal sites.     

Crystal growth of barium rhenates from hydroxide fluxes

Single crystals of two new barium rhenate compositions, Ba₁₆Re₆O₃₇ and Ba₁₀Re₃O₁₆(OH)₃, and of one new polymorph, orthorhombic Ba₅Re₂O₁₂, were grown out of a barium hydroxide flux in sealed silver tubes. Ba₁₆Re₆O₃₇ and Ba₁₀Re₃O₁₆(OH)₃ crystallize into the monoclinic C2/m system, with a = 20.577(4) Å, b = 5.8897(10) Å, c = 15.438 (3) Å, β = 92.255(10) ° and a = 1938342(9) Å, b = 5.8172(3) Å, c = 10.2925(5) Å, β = 91.7460(10) °, respectively. The orthorhombic polymorph of Ba₅Re₂O₁₂ crystallizes in the space group Pnma, with a = 19.6728(10) Å, b = 5.8491(3) Å and c = 10.4648(5) Å. All the three crystal structures are related and consist of a framework of BaO_x polyhedra (where x varies from six to twelve) with interpenetrating layers of ReO₆ octahedra.