Effect of ionic charge on energy contributions to the interaction of an ion with a polar molecule: ab initio calculations for M⋯H2O (M = Mg,Mg+, Mg2+, Ca,Ca+, Ca2+)

For M?H₂O (M = Mg, Mg⁺, Mg²⁺, Ca, Ca⁺, Ca²⁺) various energy contributions (first-order, induction and charge-transfer, dispersion) are compared. Near the minimum, stability due to the first-order energy decreases and that due to dispersion increases from M²⁺ to M⁰. For M²⁺, dispersion represents only 1–7% of the total energy; it may reach 25% with M⁺ and is largely responsible for stability of the neutral complex.     

Geometry optimised ab initio calculations on disubstituted cyclopropenones (X2C3O,X = F,Cl, OH)

Geometry optimised ab initio molecular orbital calculations are reported for a range of disubstituted cyclopropenones. The effects of the substituents on the σ and π frameworks are noted. Experimentally measurable parameters are calculated and compared with experimental data where available.     

theoretical study of tetrahydroborates and alanates L(MH4)4, HL(MH4)3, H2L(MH4)2, and H3L(MH4) (L = Al, Sc, Ti, V, Cr; M = B, Al)

The structural and energetic characteristics of the lowest-lying structures for isolated molecules and ions of light-metal boro- and aluminohydrides L(MH₄)₄, HL(MH₄)₃, H₂L(MH₄)₂, and H₃L(MH₄) (L = Al, Sc, Ti, V, Cr; M = B, Al) with different coordination modes of BH₄⁻- and AlH₄⁻ groups were calculated by the perturbation theory (MP₂), coupled cluster (CCSD(T)), and density functional theory (B3LYP) methods using the 6-31G*, 6-311+G**, and 6-311++G** basis sets. The results are compared with the computational data obtained at the same level of theory for related complexes L(MH₄)₃, HL(MH₄)₂, H₂L(MH₄), L(MH₄)₂, and HL(MH₄). The preferable coordination modes of the ligands in these complexes are analyzed, and the energies of dissociation with elimination of BH₃ (AlH₃) molecules and BH₄⁻ (AlH₄⁻) anions in various series of related hydroborates and hydroaluminates are estimated. The structure and relative stability of classical hydride and (μ-H₂)-hydrogen complexes in the H₂L (MH₄)₂ and H₃L(MH₄) systems are discussed. Original Russian Text ? O.P. Charkin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 6, pp. 1015–1024.     

MX3(-) superhalogens (M = Be, Mg, Ca; X = Cl, Br): a photoelectron spectroscopic and ab initio theoretical study

Gas-phase alkaline earth halide anions, MgX3(-) and CaX3(-) (X = Cl, Br), were produced using electrospray and investigated using photoelectron spectroscopy at 157 nm. Extremely high electron binding energies were observed for all species and their first vertical detachment energies were measured as 6.60 +/- 0.04 eV for MgCl3(-), 6.00 +/- 0.04 eV for MgBr3(-), 6.62 +/- 0.04 eV for CaCl3(-), and 6.10 +/- 0.04 eV for CaBr3(-). The high electron binding energies indicate these are very stable anions and they belong to a class of anions, called superhalogens. Theoretical calculations at several levels of theory were carried out on these species, as well as the analogous BeX3(-). Vertical detachment energy spectra were predicted to compare with the experimental observations, and good agreement was obtained for all species. The first adiabatic detachment energies were found to be substantially lower (by about 1 eV) than the corresponding vertical detachment energies for all the MX3(-) species, indicating extremely large geometry changes between MX3(-) and MX3. We found that all the MX3(-) anions possess D3h ((1)A1') structures and are extremely stable against dissociation into MX2 and X-. The corresponding neutral species MX3, however, were found to be only weakly bound with respect to dissociation toward MX2 + X. The global minimum structures of all the MX3 neutrals were found to be C2v ((2)B2), which can be described as (X2(-))(MX+) charge-transfer complexes, whereas the MX2...X (C2v, (2)B1) van der Waals complexes were shown to be low-lying isomers.     

Ab initio study of ground state MH2, HMHe+ and MHe2(2+), M = Mg, Ca

The ground states of MH2, HMHe+ and MHe2(2+) (M = Mg, Ca) have been investigated using relativistically-corrected CCSD(T), IC-MRCI and IC-MRCI+Q, in conjunction with ANO-RCC (Mg, Ca) and aug-cc-pVQZ (H, He) basis sets. The ground states of all magnesium species are predicted to be linear, in agreement with predicted trends. Conversely, HCaHe+ and CaHe2(2+) were determined to be quasi-linear species, with linear-inversion barriers of ca. 115 and 3 cm(-1), respectively. For CaH2, a stationary point on the molecular potential energy surface corresponding to a non-linear equilibrium structure was not observed. Trends in bonding, dissociative potential well-depths and spectroscopic constants for these species have been considered with regards to isoelectronic and isovalent reasoning. These trends are consistent with helium and hydrogen forming electrostatic and covalent bonds with the metal ion, respectively.     

An ab initio study of the CH2O adsorption on the MgO (100) surface. Effects of replacing the active Mg ion by different metallic cations

A theoretical analysis of the interaction between formaldehyde, CH₂O, and the MgO (100) surface is reported. Ab initio Hartree-Fock calculations are carried out using an embedded cluster approach in which the environment is described by both total ion potentials and point charges. The cluster selected to describe the CH₂O-surface interaction is CH₂O[MgO₅]⁸⁻, in which the formaldehyde oxygen is coordinated to the Mg²⁺ ion. The effect of the addition of metallic cations to the catalyst is analysed by replacing the cluster Mg²⁺ ion by Na⁺, Al³⁺, Sc³⁺ and Ti⁴⁺ so as to modify the Lewis acid properties of the surface. The different contributions to the adsorbate-surface interaction are analysed, and the theoretical vibrational frequencies are discussed.     

Anion-ligand interactions: ab initio study of the binding of H2O,CO2 and SO2 to the nitrite ion

Binding enthalpies of single attachment of H₂O, CO₂ and SO₂ to NO^?₂ in the gas phase are reproduced with striking accuracy by SCF ab initio computations using a minimal basis set with counterpoise correction. The positions of binding to NO^?₂ are predicted. The charge-transfer character of the binding, small for water, is slightly increased for CO₂ and appreciable for SO₂.     

Ab initio calculations on the clustering energies and stable structures of H(M)+ + M → H(M)2+ (M = CO and N2)

The clustering energies of the reactions, H(M)⁺+ M → H(M)⁺₂ (M = CO and N₂), were calculated by ab initio single configuration LCAO SCF MO and SCEP methods. The calculated energies are in good agreement with the experimental enthalpies.     

尖晶石结构MFe2O4(M=Ca,Mg,Cu,Zn)纳米晶粉末的制备和磁性能

采用新型氨基凝胶自燃法成功制备出尖晶石结构MFe₂O₄（M=Ca,Mg,Cu,Zn）纳米晶粉末。对合成粉体样品的物相、形貌和磁性能进行了详细的研究。经能量色散X射线谱分析确定了合成MFe₂O₄粉末的高纯度。系统地研究了所合成的MFe₂O₄纳米晶粉末的磁性能。所有样品的磁滞回线均较窄,表明了它们具有软磁的特征。经测试得出4种铁氧体的饱和磁化强度（M_s）分别为2.1,29.3,24.1和4.2 emu·g^-1;剩余磁化强度（M_r）分别为0.2,2.3,11.4和0.2 emu·g^-1。这4种铁氧体样品的M_r/M_s值均小于0.5。对CaFe₂O₄和MgFe₂O₄两种典型铁氧体的零场冷却和场冷磁性能作了详细的研究。其中CaFe₂O₄样品的磁化强度在75 K以下有不一致的变化趋势,这是由于其发生了磁相变。     

Electron distribution and chemical bonding in M3(XO4)2 molecules (M = Mg, Cu; X = P, V) as determined by Ab initio calculations

Ab initio quantum-chemical calculations of cage molecules M₃(XO₄)₂ (M = Mg, Cu; X = P, V) have been carried out. Interatomic interactions in them are quantitatively characterized based on analysis of the electronic properties at the critical points in electron density. The Mg-O interaction is close to pure closed-shell interactions, whereas the other interactions can be treated as intermediate with different degrees of covalence. The specific features of the electronic structure of the molecules are revealed with the use of the electron pair localization function. The arrangement of electron pairs in the outer shells of the cores of the transition metals Cu and V corresponds to the Gillespie model of the regions of local concentration of electrons located opposite the ligands, which illustrates the mechanism of bonding of atoms of the third and subsequent periods of the periodic table.     

YbCl3-MCln体系相图的研究(M=Li、Mg、Ca、Pb; n=1,2)

借助于DTA与X射线衍射法研究了YbCl_3-MCl_n(M=Li、Mg、Ca、Pb; n=1或2)二元体系相图．发现YbCl_3-LiCl体系相图属固液异组成型，有化合物Li_3YbCl_6生成，它在481 ℃有一相转变. 其无变点分别为x_(YbCl_s)＝0.410；526 ℃和x_(YbCl_3)=0.340，547 ℃；YbCl_3-MgCl_2属类转熔型相图，在富YbCl_3相区666 ℃有一尚不知其性质的热效应，为x_(YbCl_3)＝0.380，628 ℃；YbCl_3-CaCl_2和YbCl_3-PbCl_2体系皆属简单低共熔型相图，其低共溶点分别为x_(YbCl_3)＝0.530, 615 ℃和x_(YbCl_3)＝0.340, 415 ℃. 后者在固相下有一不稳定化合物PbYbCl_5生成，在392 ℃分解，同时探讨了相图的某些规律．     

Magnetic susceptibility studies of Mn1-xMxO (M = Zn, Mg, Fe)

Magnetic susceptibility studies of Mn_1-xM_xO (M = Zn, x≤0.1; M = Mg, x≤0.12;M = Fe, x≤0.4) in the range 77 to 300 K are reported. The methods of preparation of Mn_1-xM_xO systems preclude the presence of trivalent ions. The M_1-xFe_xO system shows anomalous behaviour aroundx = 0.2–0.3. The results are discussed in terms of competition between the nearest neighbour and the next-near-neighbour interactions, dilution effects and cooperative effects of FeO₆ octahedra.     

Beryllocene, (C5H5)2Be. The He(I) photoelectron spectrum and ab initio molecular orbital calculations

Ab initio molecular orbital calculations with a double-ζ basis have been carrried out on five models of beryllocene, Cp₂Be, with fixed geometries. The lowest energies are obtained for the π-Cp, σ-Cp and D_5d models.

The He(I) photoelectron spectrum of Cp₂Be was recorded and the ionization potentials of the first bands were compared with the orbital energies obtained from the molecular orbital calculations. A satisfactory fit between experiment and calculations was obtained for a slip sandwich model of C_s symmetry. A model of C_5v symmetry is only compatible with the PE spectrum if the Jahn—Teller splitting of the lowest ²E₁ state of the molecular ion is exceptionally large, 1.0 eV.     

Vibrational analysis and ionization potentials of XCH3 (X=Be,Mg,Ca) calculated by hybrid density functional theory and high order ab initio methods

The amount of attention dedicated to the theoretical and experimental investigation of small cationic organometallic systems in the literature is very limited. In this Letter we use the B3LYP method with a variety of basis sets as well as the very advanced CBS-Q, CBS-QB3, G1, G2MP2, G2, G3, and G3B3 ab initio methods in order to analyze the vibrational spectra as well as ionization potentials of BeCH₃,MgCH₃ and CaCH₃. The need for further addition of experimental data to the archives for these systems is discussed, as well as recommendations for which theoretical methods are optimum for a particular result.     

Synthesis, characterization and thermal investigation of M[M(C2O4)3]·xH2O (x=4 for M=Cr(III); x=2 for M=Sb(III) and x=9 for M=La(III))

The complexes, M[M(C₂O₄)₃]·xH₂ O, where x=4 for M=Cr(III), x=2 for M=Sb(III) and x=9 for M=La(III) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR and electronic spectral data, conductivity measurement and powder X-ray diffraction (XRD) studies. The chromium(III)tris(oxalato)chromate(III)tetrahydrate (COT), Cr[Cr(C₂ O₄)₃]·4H₂O, released water in a stepwise fashion. Removal of the last trace of water was accompanied by a partial decomposition of the oxalate group. Thermal investigation using TG, DTG and DTA techniques in air produced Cr₂O₃ at 858°C through the intermediate formation of Cr₂O₃ and CrC₂O₄ at around 460°C. While DSC study in nitrogen up to 670°C produced a mixture of Cr₂O₃ and CrC₂O₄. In antimony(III)tris(oxalato)antimonate(III)dihydrate (AOD), Sb[Sb(C₂O₄)₃]·3H₂O the dehydration took place during the decomposition of precursor at 170–290°C and finally at ca. 610°C Sb₂ O₅ along with trace amounts of Sb₂O₄ were produced. Trace amount of Sb₂O₃ and Sb along with Sb₂O is proposed as the end product at 670°C of AOD in nitrogen. The oxide La₂O₃ is formed at 838°C from the study with TG, DTG and DTA in air of lanthanum(III)tris(oxalato)lanthanum(III)nonahydrate (LON), La[La(C₂O₄)₃]·9H₂O. Intermediate dioxycarbonate, La₂O₂CO₃ was generated at 526°C prior to its decomposition to lanthanum oxide in air; whereas in N₂ the formation of La₂(CO₃)₃ at 651°C was proposed. The thermal parameters have been evaluated for each step of the dehydration and decomposition of COT, AOD and LON using five non-mechanistic equations i.e. Flynn and Wall, Freeman and Carroll, Modified Freeman and Carroll, Coats–Redfern and MacCallum–Tanner equations. Kinetic parameters, such as, E^*, k_o, ΔH^*, ΔS^* etc. were also supplemented by DSC studies in nitrogen for all the three complexes. Some of the intermediate species have been identified by analytical and powder XRD studies. Tentative schemes has been proposed for the decomposition of all three compounds in air and nitrogen.     

Kinetic study of the reaction H2O2+H→H2O+OH by ab initio and density functional theory calculations

Theoretical investigations on the kinetics of the elementary reaction H₂O₂+H→H₂O+OH were performed using the transition state theory (TST). Ab initio (MP2//CASSCF) and density functional theory (B3LYP) methods were used with large basis set to predict the kinetic parameters; the classical barrier height and the pre-exponential factor. The ZPE and BSSE corrected value of the classical barrier height was predicted to be 4.1 kcal mol⁻¹ for MP2//CASSCF and 4.3 kcal mol⁻¹ for B3LYP calculations. The experimental value fitted from Arrhenius expressions ranges from 3.6 to 3.9 kcal mol⁻¹. Thermal rate constants of the title reaction, based on the ab initio and DFT calculations, was evaluated for temperature ranging from 200 to 2500 K assuming a direct reaction mechanism. The modeled ab initio-TST and DFT–TST rate constants calculated without tunneling were found to be in reasonable agreement with the observed ones indicating that the contribution of the tunneling effect to the reaction was predicted to be unimportant at ambient temperature.     

Quantum mechanical scattering calculations on a spline-fitted ab initio surface: the He + H+2 (ν = 0, 1, 2) → HeH+ + H reaction

All-channel time-dependent quantum mechanical reaction probabilities are reported for the collinear He + H⁺₂(ν = 0, 1, 2) → HeH⁺ + H reaction at a total energy of 1.2 eV on previously reported diatomics-in-molecule (DIM) and spline fitted ab initio (SAI) surfaces. These results are in agreement with the previous quasiclassical trajectory results in that there is vibrational enhancement of the reaction probability on the SAI surface but not on the DIM surface. This agreement lends support to our previously drawn conclusion that small differences in the potential-energy surface can lead to substantially different dynamic results.     

Infrared study of νOD modes in isotopically dilute (HDO) isostructural compounds M(HCOO)2·2H2O (M=Mn,Fe,Co,Ni,Cu,Zn) with matrix-isolated guest ions (Cu in M(HCOO)2·2H2O and M in Cu(HCOO)2·2H2O)

The infrared spectra of isotopically dilute (matrix-isolated HDO molecules) isostructural compounds M(HCOO)₂·2H₂O (M=Mn,Fe,Co,Ni,Zn,Cu) are presented and discussed in the region of the OD stretching modes. According to the structural data the compounds under study are divided into two groups: in M(HCOO)₂·2H₂O (M=Mn,Ni,Zn) the H₂O(1) molecules form stronger hydrogen bonds as compared to H₂O(2); in M(HCOO)₂·2H₂O (M=Fe,Co,Cu) the H₂O(2) molecules form stronger hydrogen bonds as compared to the H₂O(1) molecules. The influence of the metal–water interactions (synergetic effect) and the unit-cell volumes (repulsion potential of the lattice) on the hydrogen bond strength within the isostructural series is discussed. The wavenumbers of the uncoupled OD stretching modes of the HDO molecules influenced by guest ions (Cu²⁺ ions matrix-isolated in M(HCOO)₂·2H₂O and M²⁺ ions matrix-isolated in Cu(HCOO)₂·2H₂O) are presented and commented. For example, the analysis of the spectra reveals that when Cu²⁺ ions are included in the structure of M(HCOO)₂·2H₂O the hydrogen bonds of the type M–OH₂OCHO–Cu are considerably weaker as compared to those of the same type formed when M²⁺ ions are included in the structure of Cu(HCOO)₂·2H₂O if the cations remain unchanged.     

Geminal interactions in ClZ(CH3)2X molecules (Z = C, Si, Ge) according to ab initio calculations

The structure and electronic parameters of ClZ(CH₃)₂X molecules (Z = C, Si, Ge, X = CH₃, OCH₃) were calculated by the RHF/6–31G(d) and RHF/6–311G(d,p) methods with full geometry optimization; calculations of ClZ(CH₃)₂OCH₃ molecules were also performed by the RHF/6–31G(d) method with partial geometry optimization. The ³⁵Cl NQR frequencies calculated from the populations of less diffuse 3p constituents of valence p orbitals of chlorine [RHF/6–31G(d)] were in agreement with the experimental values. The ³⁵Cl NQR frequencies for molecules with X = OCH₃ are lower than those for molecules with X = CH₃ (the Z atom being the same), due mainly to direct through-field polarization of the Z-Cl bond, induced by the effect of unshared electron pair of the oxygen atom in the trans position with respect to that bond. The difference in the ³⁵Cl NQR frequencies decreases in going from Z = C to Z = Si, Ge, in parallel with variation of the Z-Cl bond polarization as the size of Z increases.