Infrared spectroscopic evidence of the Mg3O3 molecule formed by reaction of magnesium and oxygen atoms in inert gas matrices at 20.4°K

The reaction of magnesium and oxygen atoms in argon, krypton, xenon and oxygen matrices at 20.4° K was studied by infrared spectroscopy between 200 and 4000 cm^?1. The appearance of a band in the magnesium-oxygen stretching region, reproducible in all the matrices, indicates that reaction takes place. Oxygen-13 isotopic substitution suggests that the absorption is due to Mg₃O₃, whose formation is supported by the crystal structure of the solid phase. The force constants are calculated as f_R = 2.3 mdyne/Å and F_?/R² = 0.44 mdyne/Å assuming a planar six-membered ring of alternate magnesium and oxygen atoms with bond angles O-Mg-O 100° and Mg-O-Mg 140°.     

Autoionizing rydberg states of. The Li2 molecule: Molecular constants for Li2+

Autoionizing Rydberg series of Li₂ have been observed in the two-step optical cxcitation of a supersonic lithium beam. The series limits are vibrational states of Li₂⁺. In the most probable assignment IP(Li₂) = 41236.4 ± 2.5 cm^?1 and for Li₂⁺ω_e = 263.45 ± 1.3 cm^?1; ω_eχ_e = 1.35 ± O.2 cm^?1; r_e = 3.032 ± 0.01 Å; D_e = 10807 ± 150 cm^?1.     

A new approach to electron diffraction analysis of symmetric triatomic molecules with large-amplitude bending motion: The equilibrium geometry,force field and vibrational frequencies of BaI2 as determined by electron diffraction

Diffraction data on BaI₂, analyzed by a new approach, indicate an anharmonic potential with a barrier of 71(12) cm^?1 at a linear geometry. The structural and vibrational parameters were found to be r_e^h(Ba-I_o) = 3.150(7)Å, ∠_eIBaI = 148.0(9) °, f_q = 0.69(8) mdyn/Å,f_qq= 0.14(6) mdyn/Å, k₂ = ?0.0075(15) mdyn/Å, k₄ = 0.0025(9) mdyn/ų, v₁ = 106(12) cm^?1 and v₃ = 145(21) cm^?1. The bending frequency v₂ is predicted to be near 16 cm^?1.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.     

The interaction of aromatic hydrocarbons with organometallic compounds of the main group elements. : IV. The preparation and structure of the novel selenide K[CH3Se{Al(CH3)3}3] · 2C6H6

The crystal structure of K[CH₃Se {Al(CH₃)₃}₃] · 2C₆H₆ has been determined from single-crystal X-ray diffraction data collected by counter methods. The compound crystallizes in the triclinic space group P$\text{1}$ with cell dimensions a = 17.165(7), b = 10.144(7), c = 10.156(7)Å, α = 119.26(5), β = 104.07(5), ψ = 80.51(5)°, and Dc = 1.12 gcm^?3 for Z = 2. Least-squares refinement gave a final R value of 0.083 for 1967 independent observed reflections. One of the two benzene molecules in the asymmetric unit has been located by difference Fourier techniques. Because of either extreme disorder or high thermal motion, the aromatics make practically no contribution to the X-ray scattering. The selenium atom in the anion exhibits tetrahedral coordination. The Al-Se bond lengths average 2.578(5)Å, and the Se-C distance is 1.93(2)Å.     

Synthese,structure cristalline et analyse vibrationnelle de l'hexathiohypodiphosphate de lithium Li4P2S6

The crystalline compound Li₄P₂S₆ is obtained either by devitrification of Li₄P₂S₇ glass at 450°C with sulfur formation or by crystallisation at 450°C of a Li₂S, P and S melt. The structure determination has been solved by X-ray diffraction on a monocrystal. The unit cell is hexagonal $\text{P6}{}_3\text{mcm}$ with a = 6.070(4), c = 6.577(4) Å, V = 209 ų, Z = 1. Intensities were collected at 293°K with Kα (λ = 0.71069 Å) Mo radiation on an automatic Nonius CAD-4 diffractometer. The structure was solved under the assumption of random disorder of P atoms over two sites (occupancy factor of 0.5). Anisotropic least-squares refinement with W = 1 gave R = 0.047 for 90 independent reflections and 9 variables. The structure is built according to an ABAB sequence sulfur packing. Per unit cell, four out of six octahedral sites are occupied by Li ions, and the other two are statistically filled (0.5) by PP pairs. The PP central bond (2.256(13) Å) links two staggered PS₃ groups (PS = 2.032(5) Å) to form the D_3d symmetry P₂S^4?₆ anion. Infrared and Raman spectra show features very similar to those of Na₄P₂S₆, 6H₂O and M^IIPS₃ compounds. A new assignment in terms of symmetry species is proposed for the P₂S₆ internal modes, which is confirmed by a normal coordinate calculation using a valence force field; the stretching force constants f_PP and f_PS are equal to 1.6 and 2.7 mdyne Å^?1, respectively.     

Molecular structure of t-butyl-phenylphosphinic acid (−)-menthyl ester: a comparison of solid state and solution

The molecular structure of t-butyl-phenylphosphinic acid (?)-menthyl ester (1eS) has been determined by X-ray analysis and the results compared with the findings of a detailed NMR-study. 1eS crystallises in the monoclinic space group P2 ₁ with a = 9.304(2), b = 10.678(4), c = 12.681(4) Å, β = 124.91(1)°, Z = 2, D_x = 1.08 g cm^?3. The structure was refined to R = 0.035 for 1842 independent reflections. The absolute configuration was confirmed as S_(p). Both methyl functions of the menthyl-iso-propyl substituent take up positions close to the phenyl ring system.     

Zinc(II) complexes with the tetradentate schiff base ligand N,N′-bis(1-pyridin-2-yl-ethylidene)propane-1,3-diamine: Synthesis and crystal structures

Two new zinc(II) complexes [ZnL(N₃)]·BF₄ (1) and [ZnBrL]·BF₄ (2), derived from the tetradentate Schiff base ligand N,N′-bis(1-pyridin-2-yl-ethylidene)propane-1,3-diamine (L), are prepared and characterized by physicochemical methods and single crystal X-ray crystallography. The crystal of (1) is triclinic: space group P-1, a = 8.593(1) Å, b = 8.752(1) Å, c = 13.393(2) Å, α = 97.153(1)°, β = 93.046(1)°, γ = 91.577(1)°, V = 997.4(2) ų, Z = 2. The crystal of (2) is triclinic: space group P-1, a = 8.351(1) Å, b = 8.956(1) Å, c = 13.139(2) Å, α = 92.716(1)°, β = 94.241(2)°, γ = 95.016(1)°, V = 974.8(2) ų, Z = 2. The geometries of the penta-coordinated zinc atoms in both complexes are intermediate between the square pyramid and the trigonal bipyramid having the Addison parameters of 0.39 and 0.47 respectively. The syntheses of the complexes show distinct preference for the anions in the order Br^? > N ₃ ^? > CH₃COO^?.     

Crystal structure of [Pd3(μ-OH)(μ-CH3COO)5]

The crystals of the [Pd₃(μ-OH)(μ-CH₃COO)₅] complex are obtained and characterized using powder and single crystal X-ray diffraction and IR spectroscopy. The crystal structure (a = 15.6942(6) Å, b = 11.7190(3) Å, c = 9.7871(3) Å, V = 1800.05(10) ų, space group Pna2₁, Z = 4) is formed from neutral trinuclear cyclic molecules of [Pd₃(μ-OH)(μ-CH₃COO)₅], in which the OH^? group, together with five CH₃COO^? anions, is a bridge ligand.     

Disordered crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane dibromide dihydrate

The disordered crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane dibromide dihydrate, [H₂(2.2.2-Crypt)]²⁺·2Br^?2H₂O (I) was studied by X-ray diffraction (XRD) analysis. The orthorhombic structure of I (space group Aba2, a = 21.036(3) Å, b = 14.453(2) Å, c = 8.525(1) Å, Z = 4) was solved by direct methods and refined by full-matrix least squares in anisotropic approximation to R = 0.045 over all 2695 independent (taking into account anomalous scattering) reflections collected (CAD-4 automatic diffractometer, λCuK_α).     

X-ray scattering by water molecules studied by using synchrotron radiation

The energy spectra of free water molecules were measured at scattering angles 2θ ranging from 10.5° to 75.7°, using an angle-dispersive-type diffractometer and synchrotron radiation as an X-ray source. A silicon (111) monochrometer was used to obtain incident X-rays with the wavelengths of (1.543/n) Å (n = 1,3,4,5). Observed inelastic scattering peaks are clearly separated from eleastic ones at s values [s = (4π/λ) sin Å] larger than 8 Å^?1. The increase of the separation with an increasing s value was consistent with the classical theory of the Compton shift. The total (elastic plus inelastic) intensities were obtained over a range of s = 0.74–5.0 Å^?1. Experimental difference intensities Δσ_ee and Δσ_ne were obtained separately by combining the X-ray and high-energy electron scattering data. The experimental results are in reasonable agreement with the theoretical intensities calculated from SCF and CI molecular wave functions with a basis set of double-zeta plus polarization functions. © 1994 John Wiley & Sons, Inc.     

Crystal structure of polymer hexaaqua-hexakis(2-thiobarbiturato)dieuropium(III)

Complex [Eu₂(HTBA)₆(H₂O)₆] _n (I), where H₂TBA is 2-thiobarbituric acid C₄H₄N₂O₂S, is synthesized. Its structure is determined by X-ray diffraction analysis (CIF file CCDC 987519). The crystals of complex I are monoclinic: a = 14.1033(4) Å, b = 10.0988(4) Å, c = 15.4061(5) Å, β = 110.003(1)°, V = 2061.9(1) ų, space group P2/n, Z = 2. All three independent ligands HTBA^? are coordinated to Eu³⁺ through oxygen atoms. Six HTBA^? ions (two terminal and four bridging) and two water molecules are coordinated to one of the independent Eu³⁺ ions. The second Eu³⁺ ion is bound to four bridging HTBA^? ions and four water molecules. The coordination polyhedra are square antiprisms. The bridging HTBA^? ions join the antiprisms into layers. The structure is stabilized by numerous hydrogen bonds and the π-π interaction between HTBA^?.     

Synthesis and crystal structure of platinum(II) acetamidates [Pt(2,2′-bipy)(NHCOCH3)2] and [enPt(μ-NHCOCH3)(μ-OH)Pten](NO3)2

The diamines PtbipyCl₂, and PtenCl₂ and their aqua and hydroxy derivatives react with acetonitrile to give the Pt(II) acetamidates [Pt(2,2′-bipy)(NHCOCH₃)₂] · 4.125 H₂O (I) and [enPt(μ-NHCOCH₃(μ-OH)Pten](NO₃)₂ · H₂O (II), which are characterized by X-ray diffraction. The crystals of I are triclinic, a = 7.137(10) Å, b = 12.655(3) Å, c = 21.914(6) Å, α = 81.82(2)°, β = 82.12(2)°, γ = 77.72(2)°, V = 1908.6(7) ų, space group P $\overline 1 $ , Z = 4, R = 0.033 for 3700 reflections. Complex I is a mononuclear acetamidate with terminal (NHCOCH₃)^? ligands. The crystals of II are monoclinic, a = 11.413(2) Å, b = 10.981(2) Å, c = 14.385(3) Å, β = 105.90(3)°, V = 1733.8(6) ų, space group P2₁/n, R = 0.028 for 2797 reflections. Complex II is a dimer with bridging (NHCOCH₃)^? and (OH)^? groups. The Pt-Pt distance is 3.1667(7) Å.     

Syntheses and structures of nine-coordinate K3[DyIII(nta)2(H2O)]·5H2O and eight-coordinate (NH4)3[DyIII(nta)2] complexes

K₃[Dy^III(nta)₂(H₂O)]·5H₂O and (NH₄)₃[Dy^III(nta)₂] have been synthesized in aqueous solution and characterized by IR, elemental analysis and single-crystal X-ray diffraction techniques. In K₃[Dy^III(nta)₂(H₂O)]·5H₂O the Dy^III ion is nine coordinated yielding a tricapped trigonal prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 15.373(5) Å, b = 12.896(4) Å, c = 26.202(9) Å; β = 96.122(5)°, V = 5165(3) ų, Z = 8, D _c = 1.965 g·cm^?3, μ = 3.458 mm^?1, F(000) = 3016, R ₁ = 0.0452 and wR ₂ = 0.1025 for 4550 observed reflections with I ≥ 2σ(I). In (NH₄)₃[Dy^III(nta)₂] the Dy^III ion is eight coordinated yielding a usual dicapped trigonal anti-prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 13.736(3) Å, b = 7.9389(16) Å, c = 18.781(4) Å; β = 104.099(3)°, V = 1986.3(7) ų, Z = 2, D _c = 1.983 g·cm^?3, μ = 3.834 mm^?1, F(000) = 1172, R ₁ = 0.0208 and wR ₂ = 0.0500 for 2022 observed reflections with I ≥ 2σ(I). The results indicate that the difference in counter ion also influences coordination numbers and structures of rare earth metal complexes with aminopolycarboxylic acid ligands.     

An ab initio calculation of the potential surface and rotation—vibration energies of the silyl radical

We have calculated 64 points on the ground electronic state potential energy surface of the silyl radical (SiH₃) using the MRD CI technique. This potential surface gives an inversion barrier of 1951 cm^?1 and an equilibrium geometry of r_e = 1.480 Å and α_e(HSiH) = 111.2°. Using the non-rigid invertor Hamiltonian with this potential we determine for SiH₃ that ν₁ = 2424 cm^?1, ν₂ = 778 cm^?1, ν₃ = 2106 cm^?1, and ν₄ = 976 cm^?1; the inversion splitting is calculated to be 0.11 cm^?1. Rotational constants and centrifugal distortion constants have also been calculated.     

Crystal structure of bis[Ba(Aet)(OH2)5]bis(Aet)·4H2O

An X-ray crystallographic study is conducted of single crystals with the composition [Ba₂(Aet^?)₂·10(H₂O)]²⁺·2(Aet^?)·4H₂O, where Aet^? = (C₁₀H₁₁N₄O₂S₂)^? is the ethazole (2-(para-aminobenzenesulfamido)-5-ethyl-1,3,4-tiadiazole) anion. The crystals are monoclinic; the space group is P2₁/c, Z = 2; a = 9.793(2) Å, b = 15.408(4) Å, and c = 22.553(6) Å; β = 94.98(2)°; and R = 0.047. The independent part of the compound’s structural formula, [Ba(Aet)(OH₂)₅](Aet)·2H₂O, is isostructural with the analogous compound with the Sr atom. The ethazole anion is coordinated to the complexing metal atom by oxygen and nitrogen atoms to form a four-membered ring.     

Diagrammatic perturbation theory: Potential curves for the ground state of the carbon monoxide molecule

Diagrammatic many-body perturbation theory is used to calculate the potential energy function for the X¹ σ+ state of the CO molecule near the equilibrium nuclear configuration. Spectroscopic constants are derived from a number of curves which are obtained from calculations taken through third order in the energy. By forming [2/1] Padé approximants to the constants we obtain: r_e = 1.125 Å (1.128 Å), B_e = 1.943 cm^?1 (1.9312 cm^?1), a^B_e = 0.0156 cm^?1 (0.0175 cm^?1), W_e = 2247 cm^?1 (2170 cm^?1), W_eX_e = 12.16 cm^?1 (13.29 cm^?1), where the experimental values are given in parenthesis.     

Synthesis,crystal structure,and kinetics of thermal decomposition of the Zn(II) complex with vanillin

A complex [Zn(C₈H₇O₃)₂(H₂O)₂] (C₈H₈O₃ is vanillin) has been synthesized and characterized by IR, elemental analysis, and X-ray diffraction single-crystal analysis. The crystals are monoclinic, space group C2/c, a = 22.236(8) Å, b = 10.594(2) Å, c = 7.8190(16) Å, α = 89.90(3)°, β = 106.87(4)°, γ = 89.99(3)°, V = 1762.6(8) ų, Z = 4, F(000) = 832, S = 1.079, ρ _c = 1.521g cm^?3, R = 0.0221, R _w = 0.0604, μ = 1.433 mm^?1. The Zn²⁺ ion is six-coordinated with a distorted octahedron geometry. The complex forms a three-dimensional network through intermolecular hydrogen bonds. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal conditions by the TG and DTG methods. The kinetic equation can be expressed as dα/dt = Ae^?E/RT 2(1 ? α)[1 ? ln(1 ? α)]^1/2. The kinetic parameters (E, A), activation entropy ΔS ^≠, and activation free-energy ΔG ^≠ were also gained.     

CEPA calculations on open-shell molecules

Ab initio calculations at SCF and CEPA levels using large Gaussian basis sets have been performed for the two lowest electronic states,X ² Σ⁺ andA ² Π, of HeAr⁺. Spin-orbit coupling (SOC) effects have been added using a semiempirical treatment. The resulting potential curves for the three statesX,A ₁, andA ₂ have been used to evaluate molecular constants such as vibrational intervals ΔG(v + 1/2) and rotational constantsB _v as well as — by means of a Dunham expansion — equilibrium constants such asR _e , ω _e ,B _e etc. Comparison with the experimental data from UV emission spectroscopy shows that the calculated potential curves are slightly too shallow and have too large equilibrium distances:D _e = 242 cm^?1 andR _e = 2.66 Å compared to the experimental values of 262 cm^?1 and 2.585 Å, respectively, for theX ²Σ⁺ ground state. However, the ab initio calculations yield more bound vibrational levels than observed experimentally and allow for a more complete Dunham analysis, in particular for theA ₂ state. The experimental value of 154 cm^?1 for the dissociation energyD _e of this state is certainly too low; our best estimate is 180±5 cm^?1. For theA ₁ state our calculations are predictions since this state has not yet been observed experimentally.     

A crystal chemical study of stishovite

The crystal structure of stishovite, SiO₂, a = 4.1773(1), c = 2.6655(1)Å, space group $\text{P4}{}_2\text{mnm}$, with Z = 2, has been refined with 217 graphite-monochromatized MoKα data (2θ max = 120°) to R = 0.012 (R_w = 0.014). Electron deformation density maps show a modest accumulation of charge density ascribed to partial covalent bonding in both the equatorial and axial bonds together with a delocalization of density in and around the shared octahedron edges with the shorter equatorial bonds showing higher peaks (0.47 eÅ^?3) than the longer axial bonds (0.29 eÅ^?3). Net atomic charges for Si and O determined by a population and κ refinement by varying the occupancy and shape of their valence shells are +1.71 and ?0.86(15) e, respectively. The observed structural distortions and charge distributions conform with the results of ab initio molecular orbital calculations undertaken on molecules designed to mimic the local geometry of the structure of stishovite. The SiO bond length (1.73 Å) calculated for a neutral molecule with 6-coordinated Si is slightly shorter than that observed on the average (1.76 Å) for silicates and molecular crystals with 6-coordinated Si. In addition, the calculated geometrical parameters of two edge-sharing octahedra agree to within ～5% of the observed geometry of stishovite. The calculated charge on Si is indicated to increase with coordination number and bond length in agreement with the larger net charge recorded for stishovite as compared with that recorded for α-quartz, Q(Si) = +1.0 e. Observed deformation maps are compared with theoretical ones calculated in the equatorial plane of the 6-coordinated molecule using molecular orbital theory with a split valence s,p basis supplemented with d-type polarization functions on Si.