Endohedral complexes of fullerene-like silica molecules with H2O, CH4, and CH3NH2 molecules

The possibility of formation of (SiO₂)₆₀@H₂O, (SiO₂)₆₀@CH₄, and (SiO₂)₆₀@CH₃NH₂ endohedral complexes was studied by the density functional (DFT) method (B3LYP exchange correlation functional, 6-31G** basis). The penetration of these molecules into the cavity of fullerene-like silica molecules is hindered by high activation barriers, which ensures the stability of the complexes formed during the synthesis of these molecules.     

Double proton shifts in associates of formic acid with CH4, NH3, H2O,CH3F,NH2F,HOF, and HF molecules

The mechanisms of double synchronous proton transfer in associates of formic acid with solvent molecules of the HC(O)OHX (X = CH₄, NH₃, H₂O, or HF) and HC(O)OHFHY (Y = CH₃F, NH₂F, HOF, F₂, or HF) types have been studied by anab initio (SCF/3G) method. The calculated activation barriers of the reactions are 78.52, 17.72, 9.91, and 7.06 kcal mol^–1 in the former case and 120.1, 259.4, 228.7, 182.8, and 0.35 kcal mol^–1 in the latter case. In the latter case, simultaneously with the double transfer of protons, migration of two fluorine atoms along the chain of the associate occurs.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1690–1700, September, 1995.The present work was carried out with financial support from the Russian Foundation for Basic Research (Project Nos. 93-03-4972 and 93-03-18692) and the International Science Foundation (Grant ISF RNJ 000).     

Perturbed SCF MO calculations. Electrical polarizability and magnetic susceptibility of HF,H2O,NH3 and CH4

The perturbation theory is used to evaluate first order SCF corrections upon Roothaan type molecular wave functions due to one-electron perturbations. The method is applied to the one-center SCF MO wave functions of HF, H₂O, NH₃ and CH₄ to calculate the electrical polarizability and the magnetic susceptibility tensors. The results obtained agree reasonably well with the available experimental data. The effects of the limited number of basis functions upon the final results are discussed.

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Zusammenfassung Es werden Störungen erster Ordnung an SCF-MO-Wellenfunktionen, hervorgerufen durch Einelektronenstöroperatoren, im Rahmen der Störungstheorie behandelt. Insbesondere werden die Tensoren der elektrischen Polarisierbarkeit und der magnetischen Suszeptibilität unter Verwendung von Einzentrumfunktionen für HF, H₂O, NH₃ und CH₄ berechnet. Die Ergebnisse werden mit den verfügbaren experimentellen Daten verglichen. Die Effekte der endlichen Basisgröße auf die Resultate werden diskutiert.

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Résumé La théorie des perturbations est utilisée pour évaleur les corrections SCF du premier ordre, aux fonctions d'onde moléculaires du type Roothaan, dûes à des perturbations monoélectroniques. La méthode est appliquée aux fonctions d'ondes SCF MO à un centre de HF, H₂O, NH₃ et CH₃, pour le calcul des tenseurs de polarisabilité électronique et de susceptibilité magnétique. Les résultats obtenus sont en accord raisonnable avec les données expérimentales disponibles. L'effet du nombre limité de fonctions de base sur le résultat est discuté.

     

Calculation of the isotropic nuclear spin spin coupling constants for H2O,NH3 and CH4

Isotropic nuclear spin spin coupling constants have been evaluated for all possible couplings in H₂O, NH₃ and CH₄ by two different double perturbation techniques. All calculations were performed employing bases of detors constructed with SCF canonical and, for H₂O, localized orbitals, produced by extended STO basis set calculations.     

Extended group function calculations for H2O,NH3 and CH4

Wave functions expressed as antisymmetrized products of strongly orthogonal geminals have been evaluated for H₂O, NH₃ and CH₄. The geminals have been expressed as linear combinations of 2 × 2 detors constructed with localized SCF -MO 's. Several ground state observables have been computed together with the electric polarizabilities and magnetic susceptibilities. In addition, a configuration interaction calculation limited to all possible double group excitations has been carried out.     

Crystal structure and magnetic properties of tetra(monomethylammonium)hexachloroytterbatochloride(CH3NH3)4YbCl7

(CH₃NH₃)₄YbCl₇ has been synthesized from a solution of CH₃NH₃Cl and YbCl₃ in a mixture of ethnole/acetonitrile. The structure was solved from 1464 single crystal data by Patterson methods and refined to a final R_w = 0.035 space group P2, a = 9.972(6) Å, b = 7.605(5) Å, c = 12.866(6) Å, β = 90.53(4)°. The structure consists of alternating [YbCl₆]^3? octahedra and of tetrahedrally arranged [(CH₃NH₃)₄Cl]³⁺ units. Raman spectra display a splitting of frequencies related to the CH₃NH₃⁺ group in agreement with the structure determination. The magnetic susceptibility shows a remarkable deviation from a Curie-Weiss law below 170 K which may be explained by crystal field effects of Yb³⁺.     

Degenerate lithium-hydrogen exchange reactions: Ab initio models for metallation mechanisms involving H2, CH4, NH3, H2O,and HF

Hydrogen exchange reactions between lithium and sodium compounds, MX (M=Li: X=H, CH₃, NH₂, OH, F; M=Na: X=CH₃), and the corresponding hydrides, HX, have been modelled by means of ab initio calculations including electron correlation and zero point energy (ZPE) corrections. Small or no activation barriers (from the initial complexes) are encountered in systems involving lone pairs (10.8, 2.4, 0.0 kcal/mol for X=NH₂, OH, F, respectively). Since the association energies of the initial complexes are much larger (21.0, 20.4, 23.5 kcal/mol, respectively; MP2/6–31+G*/6–31+G* + ZPE), such exchange reactions should occur spontaneously in the gas phase. The methyl systems (X=CH₃) have the largest barriers: 26.7 (M=Li) and 31.7 (M=Na) kcal/mol (MP2/6–31+G*/6–31G* + ZPE), and the initial complexes are only weakly bound. The significance of these systems as models for hydrogen exchange reactions in complexes of electropositive transition metals is discussed. However, the gegenion-free exchange of hydrogen between CH₃ and CH₄ has a much lower, 11.8 kcal/mol barrier (MP2/6–31+G*/6–31+G* + ZPE). All the transition structures are highly ionic (charges on the metals > +0.8). The effect of aggregation has been considered by examining the hydrogen exchange between (LiX)₂ and HX(X=H, CH₃, NH₂, OH). Although these dimer reactions formally involve six, instead of four electrons, no “aromatic” preference is observed.     

Double orbital exponent SCF functions for H2O,NH3, CH4

The results of an investigation on best double orbital exponents for Hydrogen in H₂O, NH₃, CH₄ are reported. An error analysis for calculations with extended basis sets is presented. This analysis is based on the hypothesis that the errors on the integrals are small so that it is possible to use statistical methods.     

Theoretical study on H2 elimination pathways of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

Ab initio molecular orbital calculations have been performed to explore the reaction potential energy surfaces of silylenoid H₂SiLiF with XH _n hydrides, where XH _n = CH₄, NH₃, H₂O, HF, SiH₄, PH₃, H₂S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H₂SiLiF + H-XH _{n − 1} → H _n XSiLiF + H₂, which involves H₂ elimination following the initial formation of an association complex via a four-membered ring transition state to form the substituted three-membered ring silylenoid H _n XSiLiF and a H₂ molecule. This theoretical calculations suggest that (i) for H₂ eliminations there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in periodic table, and (ii) for the second-row hydrides, the H₂ elimination reactions are less exothermic than for the first-row hydrides and the reaction barriers are lower for X–S and Cl. Compared to the insertions of H₂SiLiF into XH _n , the H₂ elimination pathways should be unfavorable with higher barrier and lower exothermic.     

Theoretical study on the substitution reactions of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

DFT calculations at the B3LYP/6-31G(d,p) level have been performed to explore the substitution reactions of silylenoid H(2)SiLiF with XH(n) hydrides, where XH(n) = CH(4), NH(3), H(2)O, HF, SiH(4), PH(3), H(2)S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H(2)SiLiF + XH(n) --> H(3)SiF + LiXH(n-1), which involved the initial formation of an association complex via a five-membered cyclic transition state to form an intermediate followed by the substituted product H(3)SiF with LiXH(n-1) dissociating. These theoretical calculations suggest that (i) there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in the periodic table, and (ii) for the second-row hydrides, the substitution reactions are more exothermic than for the first-row hydrides and the reaction barriers are lower. The solvent effects were considered by means of the polarized continuum model (PCM) using THF as a solvent. The presence of THF solvent disfavors slightly the substitution reaction. Compared to the previously reported insertions and H(2)-elimination reactions of H(2)SiLiF and XH(n), the substitution reactions should be most favorable.     

Theoretical study on the insertion reactions of Ti+(2F) with HF,HCl, H2O,H2S,NH3, PH3, CH4, and SiH4

The insertion reactions of the titanium atom cation Ti⁺(²F) into HF, HCl, H₂O, H₂S, NH₃, PH₃, CH₄, and SiH₄ have been studied by ab initio molecular orbital theory. All these reactions involve the initial formation of an intermediate complex followed by a hydrogen migration process via a transition state to inserting product. The Ti⁺(²F) insertion into eight compounds' reactions show that the reaction with hydride of the right‐hand group is more exothermic than that of the left‐hand group and has a lower overall barrier, and that the reaction with the second‐row hydride has a lower overall barrier and is less exothermic than with the first‐row hydride. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 47–54, 1999     

Synthesis,X-ray powder structure,and magnetic properties of layered NiII methylphosphonate, [Ni(CH3PO3)(H2O)], and NiII octadecylphosphonate, [Ni(CH3-(CH2)17-PO3)(H2O)

[Ni(CH(3)PO(3))(H(2)O)] (1) and [Ni(CH(3)-(CH(2))(17)-PO(3))(H(2)O)] (2) were synthesised by reaction of NiCl(2).6 H(2)O and the relevant phosphonic acid in water in presence of urea. The compounds were characterised by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy, and their magnetic properties were studied by using a SQUID magnetometer. The crystal structure of 1 was determined "ab initio" from X-ray powder diffraction data and refined by the Rietveld method. The crystals of 1 are orthorhombic, space group Pmn2(1), with a=5.587(1), b=8.698(1), c=4.731(1) A. The compound has a hybrid, layered structure made up of alternating inorganic and organic layers along the b direction of the unit-cell. The inorganic layers consist of Ni(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one oxygen atom from the water molecule. These layers are separated by bilayers of methyl groups and van der Waals contacts are established between them. A preliminary structure characterisation of compound 2 suggests the crystallisation in the orthorhombic system with the following unit-cell parameters: a=5.478(7), b=42.31(4), c=4.725(3) A. The oxidation state of the Ni ion in both compounds is +2, and the electronic configuration is d(8) (S=1), as determined from static magnetic susceptibility measurements above 50 K. Compound 1 obeys the Curie-Weiss law at temperatures above 50 K; the Curie (C) and Weiss (theta) constants were found to be 1.15 cm(3) K mol(-1) and -32 K, respectively. The negative value of theta indicates an antiferromagnetic exchange coupling between near-neighbouring Ni(II) ions. No sign of 3D antiferromagnetic long-range order is observed down to T=5 K, the lowest measured temperature. Compound 2 is paramagnetic above T=50 K, and the values of C and theta were found to be 1.25 cm(3) K mol(-1) and -24 K, respectively. Below 50 K the magnetic behavior of 2 is different from that of 1. Zero-field cooled (zfc) and field-cooled (fc) magnetisation plots do not overlap below T=21 K. The irreversible magnetisation, DeltaM(fc-zfc), obtained as a difference from fc and zfc plots starts to increase at T=20 K, on lowering the temperature, and it becomes steady at T=5 K. The presence of spontaneous magnetisation below T=20 K indicates a transition to a weak-ferromagnetic state for compound 2.     

Unimolecular reactions of the isolated immonium ions CH3CH = NH+C4H9, CH3CH2Ch = NH+C4H9 and (CH3)2C = NH+C4H9

The reactions of ten metastable immonium ions of general structure R¹R²C?NH⁺C₄H₉ (R¹ = H, R² = CH₃, C₂H₅; R¹ = R² = CH₃) are reported and discussed. Elimination of C₄H₈ is usually the dominant fragmentation pathway. This process gives rise to a Gaussian metastable peak; it is interpreted in terms of a mechanism involving ion-neutral complexes containing incipient butyl) cations. Metastable immonium ions ontaining an isobutyl group are unique in undergoing a minor amount of imine (R¹R²C?NH) loss. This decomposition route, which also produces a Gaussian metastable peak, decreases in importance as the basicity of the imine increases. The correlation between imine loss and the presence of an isobutyl group is rationalized by the rearrangement of the appropriate ion-neutral complexes in which there are isobutyl cations to the isomeric complexes containing the thermodynamically more stable tert-butyl cations. A sizeable amount of a third reaction, expulsion of C₃H₆, is observed for metastable n-C₄H₉ ⁺NH?CR¹R² ions; in contrast to C₄H₈ and R¹R²C?NH loss, C₃H₆ elimination occurs with a large kinetic energy release (40–48 kJ mol^?1) and is evidenced by a dish-topped metastable peak. This process is explained using a two-step mechanism involving a 1,5-hydride shift, followed by cleavage of the resultant secondary open-chain cations, CH₃CH⁺ CH₂CH₂NHCHR¹R².     

Substituent Effects on the Hydrogen Bonding between 4-Substituted Phenols and HF, H2O, NH3

Density function theory UB3LYP/6-31 g(d) calculations were performed to study the hydrogen bonds between para-substituted phenols and HF, H2O, or NH3. It revealed that many properties of the non-covalent complexes, such as the interaction energies, donor-acceptor distances, bond lengths and vibration frequencies, showed well-defined substituent effects. Therefore, from the substituent effects not only the mechanism of a certain non-covalent interaction can be better understood, but also the interaction energies and structures of a certain non-covalent complex, which otherwise might be very hard or resource-consuming to estimate, can be easily predicted.     

GF Calculations for some tricyclic molecules: C3H6, C3H4, C2H4NH,C2H4O and C2H4S

We have functions expressed as antisymmetrized products of strongly orthogonal geminals have been evaluated for some three membered ring molecules. GF results are compared with previously computed SCF-MO results, obtained employing the same atomic basis. Transferability features of bonds and inner shells are shown.     

Synthesis of a layered zinc phosphate, [NH3(CH2)2NH2(CH2)3NH3][Zn2(PO4)(HPO4)2].H2O,and its transformation to a extra-large pore three-dimensional zinc phosphate, [NH3(CH2)2NH2(CH2)3NH3][Zn3(PO4)(HPO4)3

An unusual two-dimensional zinc phosphate with pendant phosphate groups, projecting into the inter-lamellar space between the layers, has been synthesized and is shown to transform into a three-dimensional structure with 16-membered bifurcated channels, giving evidence for the building up process in the formation of open-framework structures.     

[NH3(CH2)5NH3][Fe2{O3PC(CH3)(OH)(PO3H)}2]@2H2O:一个新的二膦酸亚铁化合物的合成、结构与性质研究（英文）

通过水热合成得到一个新的有机二膦酸亚铁化合物[NH3(CH2)5NH3][Fe2Ⅱ(O3PC(CH3)(OH)(PO3H)}2]·2H2O,该化合物包含阴离子型共价双链[Fe2Ⅱ{O3PC(CH3)(OH)PO3H}2]n2n-,质子化的戊二胺和结晶水,双链之间通过强氢键构成一个开放型的骨架结构.另外,观察到亚铁离子之间存在弱铁磁性相互作用.     

Magnetic properties of polyatomic molecules. III. Magnetic shielding constants of heavy nuclei in H217O, 14NH3, 13CH4 and 13CH3F

The nuclear magnetic shielding tensor components for ¹⁷O in H₂¹⁷O. ¹⁴N in ¹⁴NH₃ and ¹³C in both ¹³CH₄ and ¹³CH₃F have been evaluated by coupled HF perturbation theory. All quantities needed to calculate the tensor components for any gauge are also reported. The gauge-invariance of the computed quantities is not uniformly good for the various examples investigated.     

Ionization gauge sensitivities of N2, O2, N2O,NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^?1 Pa≤p≤1.3·10^?3Pa. Nitrogen was used as a calibration standard.