More user-friendly phosphines? Molecular structure of methylphosphine and its adduct with borane, studied by gas-phase electron diffraction and quantum chemical calculations

The molecular structures of methylphosphine (CH(3)PH(2)) and methylphosphine-borane (CH(3)PH(2).BH(3)) have been determined from gas-phase electron diffraction data and rotational constants, employing the SARACEN method. The experimental geometric parameters generally showed a good agreement with those obtained using ab initio calculations and previous microwave spectroscopy studies. In order to assess the accuracy of the calculated structures a range of ab initio methods were used, including the CCSD(T) method, with correlation-consistent basis sets. The structural environment around the phosphorus atom was found to change significantly upon complexation with borane, with the P-C bond length shortening and the bond angles widening.     

A study of the structure and energy of β-diketonates. XVIII. Molecular structure of chromium and cobalt tris-acetylacetonates according to quantum chemical calculations and gas electron diffraction

The molecular structure of chromium and cobalt tris-acetylacetonates is studied by the synchronous electron diffraction and mass spectrometric experiment and quantum chemically. It is found that molecules have the D ₃ symmetry with internuclear distances r _h1(Cr-O) = 1.960(4) Å r _h1(Co-O) = 1.893(4) Å. Quantum chemical calculations by the DFT methods with different basis sets yield a structure well consistent with that found in the experiment. Changes in the structural parameters of chromium and cobalt β-diketonate complexes whose ligands differ in ?CH₃, ?C(CH₃)₃, ?CF₃ substituents are considered.     

Structure and energetics of β-diketonates. XVI. Molecular structure and vibrational spectrum of zinc acetylacetonate according to gas-phase electron diffraction and quantum-chemical calculations

The molecular structure of zinc acetylacetonate was studied in a simultaneous electron diffraction and mass spectrometric experiment at 376(7) K and by quantum-chemical calculations. The Zn(acac)₂ molecule has a structure of D _2d symmetry with the chelate rings lying in mutually perpendicular planes. The main geometrical parameters of the molecule are r _h1(Zn-O) = 1.942(4) Å, r _h1(C-O) = 1.279(3) Å, r _h1(C-C_r) = 1.398(3) Å, r _h1(C-C _m ) = 1.504(5) Å, ∠(O-Zn-O) = 93.2(7)°, ∠(Zn-O-C) = 125.9(7)°, ∠(C-C_r-C) = 125.8(14)°, ∠(O-C-C _m ) = 115.2(9)°. The effective rotation angle of methyl groups is close to 30°, which is indicative of the free rotation of these groups. The vibration frequencies were obtained by quantumchemical calculations, and the IR spectrum of the Zn(acac)₂ molecule was interpreted.     

Molecular structure of N,N′-o-phenylene-bis(salicylideneaminato)copper(II) studied by gas-phase electron diffraction and quantum-chemical calculations

The molecular structure of N,N′-o-phenylene-bis(salicylideneaminato)copper(II) (Cu(saloph)) was determined using the combination of gas-phase electron diffraction (GED), mass spectrometry, and quantum-chemical calculations. According to both experimental and theoretical approaches the molecule of Cu(saloph) is planar and possesses C _2v symmetry. Main structural parameters determined by GED experiment are the following (total error is given in a brackets): r _h1(Cu–N) = 1.960(20) Å, r _h1(Cu–O) = 1.913(17) Å, ∠NCuN = 82.7(18)°, ∠OCuO = 91.6(21)°, ∠NCuO = 92.9(9)°. The experimental structural parameters of Cu(saloph) molecules determined by X-ray single crystal analysis and GED experiments were discussed and compared to the theoretical ones.

     

Propane transformations on aluminum chloride—cobalt chloride clusters: a quantum chemical study

Density functional PBE/TZ2p quantum chemical calculations of activated complexes and pathways of model catalytic transformations of propane under the action of aluminum chloride-cobalt chloride ionic bimetallic complexes were carried out. The formation of an intermediate with a broken C-C bond can occur on the cationic cluster CoAlCl₄ ⁺ characterized by the strongest coordination of propane molecule. The activation barrier to the reaction is ΔG = 25.0 kcal mol⁻¹. Activation of alkane C-H bonds follows the alkyl pathway involving the formation of bimetallic alkyl complexes. The interaction of activated hydrocarbon fragments bound to transition metal atoms in cobalt-chloroaluminate clusters can result in alkane metathesis products (in this case, ethane and a polymetallic cluster containing an extendedchain alkyl radical).     

Electronic structure of hydantoin studied by He I photoelectron spectroscopy and MNDO quantum—chemical calculations

The He I photoelectron spectra of hydantoin, 1-methyl-hydantoin, 3-methylhydantoin and 1,3-dimethylhydantoin are reported. Displacement of the bands upon the N-methylsubstitution indicates that HOMO and the third highest occupied MO are localized on the nitrogen atoms, the former on the amidic nitrogen and the latter on the imidic one. The second and the fourth highest occupied MO's are oxygen lone pairs. The MNDO method provides the same picture.     

Molecular structure of nickel(II) and copper(II) N,N′-ethylene-bis(acetylacetoneiminates) MO2N2C12H18 according to gas-phase electron diffraction data and quantum-chemical calculations

The molecular structure of nickel(II) and copper(II) N,N′-ethylene-bis(acetylacetoneiminates), NiO₂N₂C₁₂H₁₈ and CuO₂N₂C₁₂H₁₈, at 442(5) K and 425(5)K, respectively. Both molecules have C ₂ symmetry with a nearly planar MN₂O₂ coordination site and internuclear distances r _h1(M-O) = 1.862(10)/1.923(17) Å and r _h1(M-N) = 1.879(10)/1.947(18) Å for Ni(acacen) and Cu(acacen), respectively. The structure of free molecules is close to the structure of molecules in crystal. The DFT/3LYP quantum-chemical calculations (CEP-31G and 6-31G* basis sets) gave a molecular structure that agreed satisfactorily with the one found in experiment. The low-spin ¹ A and high-spin ³ A states of the Ni(acacen) molecule were considered. It was found that a change in multiplicity caused significant changes in the geometrical and electronic structure of the MN₂O₂ coordination site. As shown by experiment and calculations for the NiO₂N₂C₁₂H₁₈ molecule, the low-spin ¹ A state is the ground state. The internal rotation of CH₃(CN) and CH₃(CO) methyl groups was studied by the 3LYP/CEP-31G method. It was shown that steric hindrances led to a high rotation barrier of the CH₃(CN) group.     

VOPO4·H2O: a stacking faults structure studied by X-ray powder diffraction and DFT-D calculations

The dehydration process of VOPO(4)·2H(2)O occurs in two steps corresponding to successive elimination of the two crystallographically distinct water molecules. The intermediate phase VOPO(4)·H(2)O has been stabilized for X-ray powder diffraction studies. The resulting data suggest a tetragonal cell (a = 6.2203(2) ? and c = 6.18867(7) ?), but an important anisotropy in the line broadening points out the necessity of considering a not perfectly organized structure. Because of the layered structure of this compound, density functional theory calculations including dispersion corrections have been carried out to evaluate the possible presence of stacking faults. The results of these calculations give information about the nature of the translations and their probabilities using a Boltzmann distribution. DIFFaX+ simulations of the X-ray powder diffraction pattern have been carried out using the results of the theoretical calculations and confirm the presence and nature of stacking faults.     

NMR property calculations and experimental study of the 1,6-epoxycarvone and α-epoxypinene: a comparison of models

This work aims at using theoretical calculations of shielding tensors (σ) through different methods [gauge-independent atomic orbital (GIAO), continuous set of gauge transformations (CSGT) and individual gauges for atoms in molecules (IGAIM)] and spin-spin coupling constants J using GIAO method to compare these methods and to corroborate the data obtained with the assignment of all of (1)H and (13)C NMR signals and the relative stereochemistry of the 1,6-epoxycarvone and the α-epoxypinene. All the (1)H and (13)C NMR signals were assigned unequivocally. The stereochemistry for the epoxides is trans and the B3LYP theory level with CSGT and IGAIM methods is the best choice to evaluate theoretical chemical shifts for compounds studied.     

Host-guest complex of nabumetone: β-cyclodextrin: quantum chemical study and QTAIM analysis

The aim of the present work is the investigation of the inclusion complex of nabumetone (NAB) and β-cyclodextrin (β-CD) using PM3, DFT, DFT-D and ONIOM2 methods. The results indicate that the most energetically favorable structure predicts a preference of the methoxy group to enter the cavity of β-CD from its wide rim. Consequently, the butanone moiety is positioned outside the cavity on the side of the secondary hydroxyls, with a total insertion of naphthalene group. The semi-empirical PM3 results are in good agreement with those obtained by the DFT optimization (with and without dispersion correction). The donor–acceptor interactions between drug and the cavity wall of the host, studied on the basis of natural bonding orbital (NBO) analysis, show the presence of weak intermolecular hydrogen bonds in addition to the most important van der Waals interactions. Furthermore, it is revealed that among the DFT and DFT-D techniques selected to quantify these interactions, WB97X-D functional provides the greatest values of stabilization energies E⁽²⁾. Finally, a detailed topological charge density analysis based on the quantum theory of atoms in molecules (QTAIM), developed by Bader and co-workers, has been accomplished using the WB97X-D and B3LYP methods on the most favorable complexes. A good correlation between the structural parameters and the electronic density is found.     

Host–guest complexes of mixed glycol-phenanthroline cryptands: prediction of ion selectivity by quantum chemical calculations IV

Abstract Structures and complex-formation energies, calculated with DFT (B3LYP/LANL2DZp) for the cryptands [2.2.phen] and [2.phen.phen] with endohedrally complexed alkali and alkaline earth metal ions, were utilized to predict their ion selectivity. Both cryptands [2.2.phen] and [2.phen.phen] have a cavity size smaller than [2.2.2], [phen.phen.phen] and [bpy.bpy.bpy], and prefer to bind K⁺ and Sr²⁺, whereas [2.2.phen] that is larger than [2.phen.phen], has a preference for Ba²⁺, and [2.phen.phen] favours Na⁺ and Ca²⁺. The cryptand flexibility is mainly attributed to the presence of CH₂–N_SP3···N_SP3–CH₂ groups. Graphical abstract Host–Guest Complexes of mixed Glycol-Phenanthroline Cryptands—Prediction of Ion Selectivity by Quantum Chemical Calculations III Ralph Puchta* and Rudi van Eldik Keywords Cation selectivity Host–guest DFT DFT-studies allow a sensitive analysis of selectivity and cage size. Calculations predict a favourable binding of K⁺, Sr²⁺ and Ba²⁺ by [2.2.phen], and binding of K⁺, Na⁺, Ca²⁺ and Sr²⁺ by [2.phen.phen]. The cryptands fold around the ions by twisting their torsion angles in order to reach the best coordination mode for each cation. For “Prediction of ion selectivity by quantum chemical calculations III” see, R. Puchta, R. van Eldik. Aust. J. Chem. 60, 889–897 (2007).     

Structure and energetics of β-diketonates. IX. Molecular structure of Sr(DPM)2 according to gas phase electron diffraction data

Simultaneous electron diffraction and mass spectrometric investigation of overheated vapor of strontium dipivaloyl methanate was carned out. It was found that at 437(5)°C one molecular form, Sr(DPM)₂, prevails in the vapor. The r_a, r_g, and r_α structural parameters of the Sr(DPM)₂ monomeric molecule were determined; the molecule was found to have D_2d symmetry. The structural characteristics are compared in the series Ca(DPM)₂—Sr(DPM)₂—Ba(DPM)₂.     

Investigation of the structure and energetics of Β-diketonates. VIII. Molecular structure of the Ba(dpm)2 monomer according to gas phase electron diffraction data

A combined electron diffraction and mass spectrometric study of the overheated vapor over barium dipivaloylmethanate was performed. It was found that at 488°C the monomeric molecular form predominates in the vapor. The Ba(dpm)₂ molecule has D_2d symmetry. Its r_a, r_g, and r_α parameters were determined.     

Molecular structure and conformation of triphenylsilane from gas-phase electron diffraction and theoretical calculations, and structural variations in H4?nSiPhn molecules (n?=?1–4)

The molecular structure of triphenylsilane has been investigated by gas-phase electron diffraction and theoretical calculations. The electron diffraction intensities from a previous study (Rozsondai B, Hargittai I, J Organomet Chem 334:269, 1987) have been reanalyzed using geometrical constraints and initial values of vibrational amplitudes from calculations. The free molecule has a chiral, propeller-like equilibrium conformation of C ₃ symmetry, with a twist angle of the phenyl groups τ = 39° ± 3°; the two enantiomeric conformers easily interconvert via three possible pathways. The low-frequency vibrational modes indicate that the three phenyl groups undergo large-amplitude torsional and out-of-plane bending vibrations about their respective Si–C bonds. Least-squares refinement of a model accounting for the bending vibrations gives the following bond distances and angles with estimated total errors: r _g(Si–C) = 1.874 ± 0.004 ?, 〈r _g(C–C)〉 = 1.402 ± 0.003 ?, 〈r _g(C–H)〉 = 1.102 ± 0.003 ?, and ∠_aC–Si–H = 108.6° ± 0.4°. Electron diffraction studies and MO calculations show that the lengths of the Si–C bonds in H_4−n SiPh _n molecules (n = 1–4) increase gradually with n, due to π → σ*(Si–C) delocalization. They also show that the mean lengths of the ring C–C bonds are about 0.003 ? larger than in unsubstituted benzene, due to a one hundredth angstrom lengthening of the C_ipso–C_ortho bonds caused by silicon substitution. A small increase of r(Si–H) and decrease of the ipso angle with increasing number of phenyl groups is also revealed by the calculations.     

Study of Nα-benzoyl-L-argininate ethyl ester chloride, a model compound for poly(ester amide) precursors: x-ray diffraction, infrared and Raman spectroscopies, and quantum chemistry calculations

Poly(ester amide)s (PEAs) are lacking in structural and spectroscopic information. This paper reports a structural and spectroscopic characterization of N(α)-benzoyl-L-argininate ethyl ester chloride (BAEEH(+)·Cl(-)), an important amino acid derivative and an adequate PEAs' model compound. Crystals of BAEEH(+)·Cl(-) obtained by slow evaporation in an ethanol∕water mixture were studied by different complementary techniques. X-ray analysis shows that BAEEH(+)·Cl(-) crystallizes in the chiral space group P2(1). There are two symmetry independent cations (and anions) in the unit cell. The two cations have different conformations: in one of them, the angle between the least-squares planes of the phenyl ring and the guanidyl group is 5.1(2)°, and in the other the corresponding angle is 13.3(2)°. There is an extensive network of H-bonds that assembles the ions in layers parallel to the ab plane. Experimental FT-IR and Raman spectra of BAEEH(+)·Cl(-) were recorded at room temperature in the 3750-600 cm(-1) and 3380-100 cm(-1) regions, respectively, and fully assigned. Both structural and spectroscopic analysis were supported by quantum chemistry calculations based on different models (in vacuo and solid-state DFT simulations).     

Neutron diffraction analysis at 15 K and ab initio molecular orbital calculations for α-cyanoacetohydrazide: A crystal structure with a high energy conformer

The crystal structure of α-cyanoacetohydrazide, C₃H₅N₃O, is refined using single-crystal neutron diffraction data at 15 K. Nuclear equilibrium geometries of the isolated molecules are calculated using GAUSSIAN-82 for the eight possible conformers having C_s symmetry. The conformation observed in the crystal has the eighth highest calculated energy, 36.6 kJ mol⁻¹ above the lowest energy conformer, and the largest calculated dipole moment, 8.6 D, with a HF/6-31G* basis. In the crystal the molecule is distorted from the ideal C_s symmetry. These distortions add another 20.3 kJ mol⁻¹ in energy, calculated with HF/6-31G*. All the hydrogens, including the CH, are involved in intermolecular hydrogen-bonding which is unusual in that it is formed entirely by three-center bonds. These bonds form a network which includes dimer and chain configurations.     

Molecular recognition of endocrine disruptors by synthetic and natural 17β-estradiol receptors: a comparative study

A β-estradiol receptor binding mimic was synthesised using molecular imprinting. Bulk polymers and spherical polymer nanoparticles based on methacrylic acid and ethylene glycol dimethacrylate as the functional monomer and crosslinker, respectively, were prepared in acetonitrile. The selectivity was evaluated by radioligand binding assays. The imprinted polymers were very specific to β-estradiol since the control polymers bound virtually none of the radioligand. The bulk polymer was then employed to screen endocrine disrupting chemicals. Structurally related steroids like α-estradiol, estrone and ethynylestradiol showed, respectively, 14.0, 5.0 and 0.7% of relative binding to the β-estradiol polymer, whereas most unrelated chemicals did not bind at all. These results are compared to those obtained with a bioassay using stably transfected yeast cells in culture bearing the human estrogen receptor. The receptor was activated by several estrogen-like chemicals and to a lesser extent by some structurally related chemicals. Figure A molecularly imprinted polymer that was a synthetic receptor for beta-estradiol was used for the screening of endocrine disrupting chemicals that are structurally related or unrelated to beta-estradiol. The results were compared with the recognition of the compounds by the biological estrogen receptor expressed in yeast cells. Related steroids like alpha-estradiol, estrone and ethynylestradiol showed significant binding to the beta-estradiol imprinted polymer, whereas most unrelated chemicals did not bind. The biological receptor was activated by several estrogen-like chemicals, and to a lesser extent by some structurally related chemicals     

Theoretical study of the structure and properties of complexes formed by lithium and a boron α sheet

The ability of lithium to form complexes with a boron α sheet and the occurrence of ionic conduction in the compounds formed were evaluated using quantum-chemical methods. The obtained materials were established to be stable, and the weight fraction of lithium can reach 0.32. It was concluded that a low potential barrier for migration of lithium ions over the surface indicates the presence of ionic conduction.