Calculation of the valence shell correlation effects on ionization potentials. A test on N2, C2N2 and H2NN

Two schemes for the definition of the valence space from an extended basis are proposed and tested for the calculation of ionic states in N₂, C₂N₂ and H₂NN. Good results are obtained with a projection scheme, leading to a 2h-1v model reproducing the essential features of the full basis 2h-1p results. Notably excellent agreement with experiment is obtained for the main ionization potentials in N₂ and C₂N₂. Unsatisfactory results are instead given by a simple extension of the minimal basis set SCF space, indicating the importance of employing accurate occupied orbitals as a starting point.     

Molecular Vibrations and Mean Square Amplitudes. Supplement III Mean Amplitudes of Vibration for Inorganic Six-Atomic Molecules

Review of mean amplitudes of vibration for inorganic six-atomic molecules from spectroscopic calculations and electrondiffraction-data. The work contains new results of spectroscopic mean amplitudes and force constants for a number of molecules, viz.: S₆, N₂O₄, B₂F₄, N₂H₄, N₂F₄, P₂I₄ and SOF₄.     

An extended-valence MC SCF procedure: determination of the dissociation energies of C2, N2, O2, and F2

A series of MC SCF calculations have been carried out on C₂, N₂, O₂, and F₂ with the goal of obtaining compact wavefunctions which recover a significant fraction of the electron correlation effects important for bond dissociation. The active orbital space is varied in size, with the largest spaces including the molecular orbitals derived from 2s, 2p, 3s, 3p and 4p atomic orbitals. Several basis sets ranging in size from 5s3p to 5s4p2d1f are investigated to determine the flexibility in the basis set needed with various choices of the active orbital space. The best extended-valence MC SCF (EVMC) dissociation energies are 0.2–0.5 eV less than the experimental values, indicating that further enlargement of the active orbital space is necessary to achieve 0.1 eV accuracy in the computed dissociation energies. The EVMC calculations reveal that, for the calculation of the dissociation energies, inclusion of non-valence orbitals is much more important for O₂ and F₂ than for C₂ and N₂. The EVMC results are compared with the predictions of full fourth-order perturbation theory, coupled cluster theory, and with the best available CI calculations.     

The structures of 1,4‐diaryl‐5‐trifluoromethyl‐1H‐1,2,3‐triazoles related to J147, a drug for treating Alzheimer's disease

J147 [N‐(2,4‐dimethylphenyl)‐2,2,2‐trifluoro‐N′‐(3‐methoxybenzylidene)acetohydrazide] has recently been reported as a promising new drug for the treatment of Alzheimer's disease. The X‐ray structures of seven new 1,4‐diaryl‐5‐trifluoromethyl‐1H‐1,2,3‐triazoles, namely 1‐(3,4‐dimethylphenyl)‐4‐phenyl‐5‐trifluoromethyl‐1H‐1,2,3‐triazole (C₁₇H₁₄F₃N₃, 1 ), 1‐(3,4‐dimethylphenyl)‐4‐(3‐methoxyphenyl)‐5‐trifluoromethyl‐1H‐1,2,3‐triazole (C₁₈H₁₆F₃N₃O, 2 ), 1‐(3,4‐dimethylphenyl)‐4‐(4‐methoxyphenyl)‐5‐trifluoromethyl‐1H‐1,2,3‐triazole (C₁₈H₁₆F₃N₃O, 3 ), 1‐(2,4‐dimethylphenyl)‐4‐(4‐methoxyphenyl)‐5‐trifluoromethyl‐1H‐1,2,3‐triazole (C₁₈H₁₆F₃N₃O, 4 ), 1‐[2,4‐bis(trifluoromethyl)phenyl]‐4‐(3‐methoxyphenyl)‐5‐trifluoromethyl‐1H‐1,2,3‐triazole (C₁₈H₁₀F₉N₃O, 5 ), 1‐(3,4‐dimethoxyphenyl)‐4‐(3,4‐dimethoxyphenyl)‐5‐trifluoromethyl‐1H‐1,2,3‐triazole (C₁₉H₁₈F₃N₃O₄, 6 ) and 3‐[4‐(3,4‐dimethoxyphenyl)‐5‐(trifluoromethyl)‐1H‐1,2,3‐triazol‐1‐yl]phenol (C₁₇H₁₄F₃N₃O₃, 7 ), have been determined and compared to that of J147 . B3LYP/6‐311++G(d,p) calculations have been performed to determine the potential surface and molecular electrostatic potential (MEP) of J147 , and to examine the correlation between hydrazone J147 and the 1,2,3‐triazoles, both bearing a CF₃ substituent. Using MEPs, it was found that the minimum‐energy conformation of 4 , which is nearly identical to its X‐ray structure, is closely related to one of the J147 seven minima.     

Die Kristallstruktur des Hydrazinium-monofluorids

The hydrazinium monofluoride N₂H₅F crystallizes with orthorhombic symmetry, space group P2₁2₁2₁,a=4.592 Å,b=8.217 Å,c=12.341 Å, and 8 formula units. The structure was determined by the permutation method in projection, and by the three-dimensionalPatterson function, refined by Full-Matrix-Least-Squares (R=0.056). The structure consists of N₂H₅ ⁺- and F^?-ions, bonded with hydrogen bonds N?H ... N and N?H ... F. Each N₂H₅ ⁺ ion is surrounded by four F^?-ions and two nitrogen atoms of two different N₂H₅ ⁺ ions. Each F^? ion is connected with four different N₂H₅ ⁺ ions.     

Single-determinantal open- and closed-shell FSGO calculations for some diatomic molecules

Open-shell single-determinantal calculations are reported here for the molecular species H₂, Li₂⁺, N₂, O₂ (triplet), O₂^2?;, O₂^?, O₂²⁺, O₂⁺, and F₂; corresponding closed-shell calculations are reported for the species H₂, N₂, O₂ (singlet), O₂^2?, O₂²⁺, and F₂. The floating spherical Gaussian orbital (FSGO ) method was employed. The calculated trend in bond lengths of isonucleic diatomic molecules is in agreement with experiment. For heteronucleic diatomic molecules, however, the experimental trend in bond lengths is not obtained; in this connection, the effect of lone pairs on bond length is discussed. The dissociation energies of H₂ and Li₂⁺ are evaluated. The energy gap between the triplet and singlet states of the oxygen molecule is calculated to be 8.96 eV compared to the experimental value of 4.54 eV.     

Ab initio study of the molecular structures, force fields, and vibrational spectra of alkaline metal fluoride dimers MM′F2 (M, M′=Li, Na, K)

Ab initio calculations of the equilibrium geometrical parameters, force constants, and IR vibration frequencies and intensities of Li₂F₂, Na₂F₂, K₂F₂, LiNaF₂, LiKF₂, and NaKF₂ are reported. The calculations use the Hartree-Fock-Roothaan method and second-order Möller-Plesset perturbation theory along with configuration interaction theory including singly and doubly excited configurations and corrections for quartic excitations with basis sets of grouped Gaussian functions: Li — (9s3p1d/4s3p1d), Na — (12s8p1d/6s4p1d), K — (14s11p3d/9s8p3d), F — (9s5p1d/4s2p1d). According to the results of calculations, the equilibrium structures of the molecules are planar cyclic structures of D_2h (for M₂F₂) and C_2v (for MM′F₂) symmetries. The linear configurations M-F-M′-F (of C_∞v symmetry) are 70–190 kJ/mole less stable than the cyclic ones; for all molecules except M-F-K-F, these configurations correspond to local minima on the potential energy surface. The role of correlation effects in ab initio calculations of the geometry, force fields, and IR characteristics of molecules with highly polar chemical bonds is discussed. The theoretical force fields of the molecules are represented in canonical form in a system of redundant natural vibrational coordinates. The force fields of MM′F₂ molecules are studied. The results of the ab initio calculations are compared with the experimental structural data and vibrational spectra available in the literature.     

Self-consistent field calculations using two-body density functionals for correlation energy component: II. Small molecules

In part I of this series, self-consistent calculations using two-body density functionals for correlation energy were done and applied to atomic systems, giving very good results. We now apply the same scheme to small molecules. The examples studied include diatomic (H₂, Li₂, B₂, C₂, N₂, O₂, F₂, HLi, HBe, HB, HF, and HCl) as well as polyatomic (H₂O, NH₃, H₂O₂, and O₃) molecules at their ground states. The values reported for equilibrium geometries, atomization energies, vibrational frequencies, and dipole moments are compared with experimental and other theoretical calculations, with good agreement in most cases. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1899–1908, 1998     

A method for molecular correlation energy calculations. Application to the determination of dissociation energies of diatomic and polyatomic molecules

A simple and economical method for molecular correlation energy calculations is developed. In this method, the internal part of the correlation energy is calculated by means of a CI in a minimal basis set and the non-internal part (semi-internal and all-external) is evaluated using an original atoms-in-molecule method. It is successfully applied to the determination of dissociation energies of some diatomic (H₂, NH, C₂, CN, N₂, CO, NO, O₂, F₂) and polyatomic (H₂O, N₂O, CO₂, N₃H, CH₂N₂, CH₂CO, C₂N₂) molecules. The results are compared to those obtained using very elaborate variational methods.Aspirant du Fonds National Belge de la Recherche Scientifique.     

正硅酸乙酯水解过程的半经验量子化学研究

通过半经验量子化学方法研究了正硅酸乙酯的最优化分子几何结构并推断了催化水解机理。通过用MNDO方法求得正硅酸乙酯在不同条件下水解反应过程的位能曲线,研究了不同催化剂对正硅酸乙酯水解反应过程的影响。计算结果表明,碱催化过程是一个放热过程,硅原子可从原先的4配位的正四面体结构向6配位的八面体结构转变。而在酸性条件下,水合质子作为亲电试剂,可以使正硅酸乙酯的烷氧基质子化,从而增加了正硅酸乙酯的亲电能力。质子化后的正硅酸乙酯容易被亲核试剂所进攻,进攻过程是一个S_N2亲核取代反应过程。计算结果表明,在有氟离子参与的反应过程中,氟离子对正硅酸乙酯亲核进攻所形成的6配位结构易与亲核试剂水分子发生亲核反应。这些结论对实验研究将起到很重要的指导意义。     

Correlated polarization propagator calculations of static polarizabilities

We present a systematic comparison of the correlation contribution at the level of the second-order polarization propagator approximation (SOPPA ) and MP 2 to the static dipole polarizability of (1) Be, BeH^?, BH, CH⁺, MgH^?, AIH, SiH⁺, and GeH⁺; (2) BH₃, CH₄, NH₃, H₂O, HF, BF, and F₂; and (3) N₂, CO, CN^?, HCN, C₂H₂, and HCHO . Fairly extended basis sets were used in the calculations. We find that the agreement with experimental values is improved in SOPPA and MP .2 over the results at the SCF level. The signs and magnitudes of the correlation contribution in SOPPA are similar to those obtained in analytical derivative MP 2 calculations. However, it is not possible to say, in general, which method gives the largest correlation contribution or the best agreement with experiment, nor is it possible to make a priori prediction of the sign of the correlation contribution. For the first group of molecules, which have a quasi-degenerate ground state, additional CCDPPA and CCSDPPA calculations were performed and compared with polarizabilities obtained as analytical/numerical derivatives of the CCD and CCSD energies. The CCSDPPA results were found to be in better agreement with other calculations than were the SOPPA results, demonstrating the necessity of using methods based on infinite-order perturbation theory for these systems. © 1994 John Wiley & Sons, Inc.     

Cocrystals of 2,3,5,6‐tetrafluorobenzene‐1,4‐diol with diaza aromatic compounds

2,3,5,6‐Tetrafluorobenzene‐1,4‐diol easily forms cocrystals with heteroaromatic bases containing the pyrazine unit. In the 1:1 complexes with pyrazine, C₆H₂F₄O₂·C₄H₄N₂, (I), and quinoxaline, C₆H₂F₄O₂·C₈H₆N₂, (II), the crystal components are linked via O—H...N hydrogen bonds into one‐dimensional chains. With the largest base, phenazine, the 1:2 benzenediol–phenazine complex, C₆H₂F₄O₂·2C₁₂H₈N₂, (III), was obtained, with the molecules linked via O—H...N interactions into a discrete heterotrimer. In all three cocrystals, the two types of molecules are organized into layers via softer C—H...O and C—H...F interactions and π–π stacking interactions, with stronger hydrogen bonds linking molecules of adjacent layers. In (II) and (III), molecules are arranged into heterostacks, whereas in (I) separate stacks are formed by the heterocyclic base and the benzenediol molecule.     

Correlated and gauge origin independent calculations of magnetic properties

Summary We have applied a gauge origin invariant method for calculations of nuclear magnetic shielding constants to the singly bonded molecules BF, F₂, BH₃, CH₄, NH₃, H₂O, and HF as well as to the¹H shielding constants of HCN and C₂H₂. The calculations were performed at the RPA and second order polarization propagator (SOPPA) level of theory. For most molecules the correlation contribution in SOPPA is less diamagnetic than in the comparable MP2 calculations. For F₂, SOPPA gives a large paramagnetic correlation correction whereas the MP2 method gives a very small correlation contribution. For all molecules agreement with experimental results is generally improved at the SOPPA level compared to RPA. We have also demonstrated that second order gauge origin invariant, common and local origin (SOLO) methods do not necessarily give the same shielding even in the limit of a converged basis set.     

Hydrazinium(1+) hexafluorogermanate(IV) and hydrazinium(2+) hexafluorogermanate(IV) difluoride

(N₂H₅)₂GeF₆ and (N₂H₆)₂(GeF₆)F₂ have been prepared by reactions of N₂H₄·H₂O and N₂H₆F₂ with fluorogermanic acid. The solids have been characterized by chemical analysis and vibrational spectra. X-ray diffraction study has shown that crystals of (N₂H₅)₂GeF₆ are monoclinic, space group P 2₁/n, with unit-cell dimensions a = 6.015 (2), b = 5.249 (1), c = 11.181 (2) Å, β = 100.15 (2)^o, and Z = 2. There are N₂H₅⁺ cations and GeF₆^2? anions in the crystals interconnected by hydrogen bonds of the type NH····F and NH····N.     

π-Complexation and C—H hydrogen bonding in the formation of colored cocrystals

The present study evaluates the potential combination of charge-transfer electron-donor–acceptor π–π complexation and C—H hydrogen bonding to form colored cocrystals. The crystal structures of the red 1:1 cocrystals formed from the isomeric pyridines 4- and 3-{2-[4-(dimethylamino)phenyl]ethynyl}pyridine with 1-[2-(3,5-dinitrophenyl)ethynyl]-2,3,5,6-tetrafluorobenzene, both C₁₄H₄F₄N₂O₄·C₁₅H₁₄N₂, are reported. Intermolecular interaction energy calculations confirm that π-stacking interactions dominate the intermolecular interactions within each crystal structure. The close contacts revealed by Hirshfeld surface calculations are predominantly C—H interactions with N, O, and F atoms.     

Two new zinc(II) and mercury(II) complexes based on N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide): synthesis,crystal structures and antibacterial activities

Reaction of N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide), C₂₀H₁₈F₂N₄O₂, ( L^F ), with zinc chloride and mercury(II) chloride produced different types and shapes of neutral coordination complexes, namely, dichlorido[N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide)‐κ²N,O]zinc(II), [ZnCl₂(C₂₀H₁₈F₂N₄O₂)], ( 1 ), and dichlorido[N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide)‐κ⁴O,N,N′,O′]mercury(II), [HgCl₂(C₂₀H₁₈F₂N₄O₂)], ( 2 ). The organic ligand and its metal complexes are characterized using various techniques: IR, UV–Vis and nuclear magnetic resonance (NMR) spectroscopies, in addition to powder X‐ray diffraction (PXRD), single‐crystal X‐ray crystallography and microelemental analysis. Depending upon the data from these analyses and measurements, a typical tetrahedral geometry was confirmed for zinc complex ( 1 ), in which the Zn^II atom is located outside the bis(benzhydrazone) core. The Hg^II atom in ( 2 ) is found within the core and has a common octahedral structure. The in vitro antibacterial activities of the prepared compounds were evaluated against two different bacterial strains, i.e. gram positive Bacillus subtilis and gram negative Pseudomonas aeruginosa bacteria. The prepared compounds exhibited differentiated growth‐inhibitory activities against these two bacterial strains based on the difference in their lipophilic nature and structural features.     

Hirshfeld surface analysis of two bendroflumethiazide solvates

Bendroflumethiazide, or 3‐benzyl‐6‐(trifluoromethyl)‐3,4‐dihydro‐2H‐1,2,4‐benzothiadiazine‐7‐sulfonamide 1,1‐dioxide, is reported to crystallize as 1:1 solvates with acetone, C₁₅H₁₄F₃N₃O₄S₂·C₃H₆O, and N,N‐dimethylformamide, C₁₅H₁₄F₃N₃O₄S₂·C₃H₇NO. A detailed investigation of the crystal packing and intermolecular interactions is presented by means of Hirshfeld surface analysis. This analysis confirms the atomic positions of methyl H atoms of the solvent molecules that were inferred from the X‐ray data and provides a useful tool for structure validation.     

Free Radical Reactions of N2O Molecules

Experimental data are presented on the spectral (ESR, IR, and optical) and thermochemical characteristics of a complex between the (Si–O)₃Si^.radical and an N₂O molecule. The rate constants of separate reactions in the systems (Si–O)₃Si^.+ N₂O and (Ge–O)₃Ge^.+ N₂O are found. The results of quantum chemical calculations of potential energy surfaces and spectral characteristics are presented for the following systems: H^.+ N₂O, H₃C^.+ N₂O, H₃Si^.+ N₂O, F₂HSi^.+ N₂O, F₃Si^.+ N₂O, and F₃Ge^.+ N₂O. The latter three systems served as molecular models for experimentally found systems. Based on experimental and theoretical data, the product of N₂O addition to (Si–O)₃Si^.has the structure Si–N=N–O^.. The reactions of free radicals H^., H₃C^., H₃Si^., F₂HSi^., F₃Si^., (Si–O)₃Si^., and (Ge–O)₃Ge^.with N₂O are compared. The spectrum of optical absorbance of the (Si–O)₃Si–O^.radical is recorded and qualitatively characterized.     

Synthese et application de nouveaux sulfures a chaine perfluoree

Metallation of thiols R_FC₂H₄SH followed by alkylation with iodides R′_FC₂H₄I leads either to symmetrical or to unsymmetrical sulphides R_FC₂H₄SC₂H₄R′_F (with R_F=R′_F or R_F ≠ R′_F). All compounds obtained are good solvents of gases (particularly O₂, CO, CO₂, N₂).This property allows their application as biological carriers of dissolved gases.     

Nucleophilic aromatic substitution; kinetics of fluorine-18 substitution reactions in polyfluorobenzenes. Isotopic exchange between 18F− and polyfluorobenzenes in dimethylsulfoxide. A kinetic study

Nucleophilic aromatic substitution reactions of C₆F₆, C₆XF₅ (XH, Cl, Br), C₆H₂F₄, oC₆H₄FNO₂ and pC₆H₄FNO₂ by the fluoride anion were studied in DMSO utilizing fluorine-18. Substitution of fluorine by fluorine-18 is the only reaction observed with a C₆F₆ substrate. With other substrates fluorine substitution is predominant. The kinetic studies provide results consistent with a S_NAr two step mechanism and suggest an intermediate analogous to that for electrophilic aromatic substitution. Consideration of σ^? indicates consistency with methoxide ion substitution results with similar substrates. The possible utility of these reactions in labeling aromatic compounds is noted.