Protonation of ferrocene,ruthenocene, and osmocene: a density functional study

Protonated forms of the ferrocene, ruthenocene, and osmocene molecules in the gas phase were calculated using the density functional approach with the Becke—Lee—Young—Parr functional. The proton affinity energies of ferrocene, ruthenocene, and osmocene were estimated at 214.2, 220.3, and 229.7 kcal mol^–1, respectively. The addition of a proton to carbon atoms of the cyclopentadienyl ring in the ferrocene molecule and to the metal atom in the ruthenocene and osmocene molecules is more energetically favorable. No minimum corresponding to ring protonation was located on the potential energy surface of protonated osmocene. The C—H _endo bond in the ring-protonated [C₁₀H₁₁M]⁺ (M = Fe, Ru) cations is involved in agostic interaction with the metal atom. Transition states of interconversions between the ring-protonated and metal-protonated forms were identified. A specific group of protonated forms of the ferrocene and ruthenocene molecules includes four types of structures, viz., ring-protonated (1a,b) and metal-protonated (2a,b) structures, transition states of the 1 2 interconversion (3a,b), as well as ring-protonated structures with the cyclopentadiene ring folded along the C(2)—C(5) line so that the M—H _endo interaction is virtually negligible. The latter structures are required for [1,5]-sigmatropic shift of the exo-hydrogen atom in the Cp ring to occur. The results obtained were used for the interpretation of the available schemes of electrophilic substitution reactions in metallocenes and of the sigmatropic shift mechanisms.     

Multiple attenuated total internal reflection spectra of ultrathin titanium oxide layers synthesized on a germanium surface

We have realized a vacuum variant for recording the multiple attenuated total internal reflection spectra of ultrathin (2–30 nm) layers of titanium dioxide directly over the course of their synthesis by the molecular lamination method on the surface of germanium single crystals. To a first approximation, there is a linear relationship between the intensity of the bands of the doublet at 890 and 820 cm^–1 (respectivelyv _as andv _s(Ti – O) and the number of molecular lamination cycles (thickness of the synthesized layers); deviations from linearity are due to the effects of the substrate and are expressed in changes in the shape of the contour of the doubletv _as/v _s for thicknesses <10 nm. Redistribution of the intensity in thev _as,v _s bands with an increase in thickness (>20 nm) of the titanium dioxide layer is due to the content of adsorbed H₂O and HCl molecules in the layer, desorption of which when the samples are heated leads to denser packing of the synthesized layers.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 251–255, March–April, 1990.     

Optical response of bimetallic Li x Na8−x (0≦x≦8) and of doped Na8Zn clusters

Total (elastic + inelastic) cross-sections for electron scattering from C, N, O atoms and their simple molecules are studied theoretically. Thee ^–-C, N, O atomic calculations are done in the complex optical potential approach. To study the electron scattering from O₂, N₂, CO, NO, CN, C₂ as well as CO₂, N₂O, NO₂ O₃ targets, we have adopted an additivity rule, wherein the molecular cross-section is an incoherent sum of the cross-sections of the constituent atoms. The cross-sections of C, N & O atoms are presented at incident energiesE _i =10–1000 eV, the molecular cross-sections are presented atE _i =100–1000 eV. The reliability of the additivity rule is discussed against the background of experimental data.     

Ferrocene Compounds. XXVII. Synthesis and Structure of 2-(Ferrocenylmethyl)propane-1,3-diol

The title compound was obtained by reduction of diethyl (ferrocenylmethyl)malonate with lithium aluminium hydride in diethyl ether. The structure of this novel ferrocene derivative was assigned by means of elemental analysis, IR, [¹H]NMR, and [¹³C]NMR spectroscopy. The structure was also confirmed by a single crystal X-ray study. The compound crystallizes in monoclinic P2₁/a space group with unit cell dimensions: a = 9.7360(6), b = 27.040(5), c = 14.767(3) Å, = 103.835(6)°, V = 3774.8(11) ų, Z = 12. The asymmetric unit contains three crystallographically independent molecules. In the ferrocenyl moieties, the Fe–C bond distance values are in the range 2.006(5)—2.051(3) Å and C–C distances in the range 1.366(7)–1.425(4) Å. The cyclopentadienyl rings in each of the molecules are mutually twisted by about 13° from the eclipsed conformation. The hydroxyl groups are involved in the intermolecular O–H...O hydrogen bond formation with O-O distances in the range 2.686(3)–2.801(4) Å forming infinite two-dimensional network in a [0 0 1] plane. The crystal structure is additionally stabilized by C–H-O weak intermolecular hydrogen bonds.     

Hydration of the carboxylate group: Anab initio molecular orbital study of acetate-water complexes

The hydration of the carboxylate group in the acetate anion has been investigated by performingab initio molecular orbital calculations on selected conformers of complexes with the form CH₃CO₂ ^– ·nH₂O·mH₂O, wheren andm denote the number of water molecules in the first and second hydration spheres around the carboxylate group, andn + m 7. The results of RHF/6–31G^* optimizations for all the complexes and MP2/6–31+G^** optimizations for several one-water complexes are reported. The primary consequence of hydration on the structure of the acetate anion is a decrease in the length of the C-C bond. Enthalpy and free energy changes calculated at the MP2/6–31+G^** and MP2/6–311+ +G^** levels are reported for the reactions CH₃CO₂ ^– + [H₂O] _P CH₃CO₂ ^– ·nH₂O ·mH₂O where [H₂O] _P is a water cluster containingp water molecules andp=n+m 7. The calculations show that conformers with the lowest enthalpy change on complex formation are often not those with the lowest free energy change, due to a greater entropic loss in complexes with tighter and more favorable enthalpic interactions. Hydrogen bonding of six water molecules directly to the carboxylate group in CH₃CO₂ ^– is found to account for approximately 40% of the enthalpy change and 37% of the free energy change associated with bulk solvation.     

Freezing temperatures of aqueous solutions of mixtures of amides and polyols. Gibbs energy of interaction of the amide group with the hydroxyl group in aqueous solution

Freezing temperatures of dilute aqueous mixtures of: formamide with myo-inositol, d-mannitol, and cyclohexanol; N,N-dimethylformamide with inositol, mannitol, and cyclohexanol; and acetamide with inositol and mannitol have been measured. These data have been analyzed to yield the pairwise molecular Gibbs energies of interaction between the molecules in an aqueous solution. Using the group additivity principle, the results yield the pairwise functional group Gibbs energies of interaction of the amide group with the hydroxyl group, G _OH,CONH =–31 J-kg-mol^–2.     

Ab initio SCF studies of the molecular structure of XeF6, IF 6 − , and TeF 6 2− in non-octahedral geometries

All-electron SCF calculations in contracted large Gaussian basis sets were performed for the molecules in the isoelectronic series XeF₆, IF ₆ ^– , and TeF ₆ ^2– . Molecular equilibrium geometry of these molecules was studied first in O _h symmetry. Then, the gradient minimization technique was used to determine molecular structure of the studied systems near the local minima corresponding to C _3v and C _2v geometries involved in the internal motion.In the O _h symmetry, TeF ₆ ^2– and IF ₆ ^– are bound by 172 and 104 kcal/mol, respectively. The total energy of XeF₆ is larger than the sum of total energies of the constituent atoms by 192 kcal/mol. Lowering the symmetry to C _3v and C _2v results in an energy gain of about 20 kcal/mol for all studied systems.     

A method for determining the mean translational energy of particles desorbed from solid surfaces

A method for determinig the mean molecular translational energy in gas flows of low intensity (10¹²–10¹⁴ molec. s^–1) has been proposed. The method was verified using various gases (H₂, N₂, O₂, and CO₂ flowing into a vacuum out of a heated capillary. The translational energies were determined for CO and N₂ molecules desorbing from the surface of polycrystalline Ir. The translational temperature (T _tr) measured for CO equals 650±90 K and almost coincides with the surface temperature (T _s = 600 K). In the case of nitrogen molecules,T _tr = 4600±500 K atT _s = 500 K. The method proposed is applicable to the determination of the spatial distribution of molecular beam particles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 30–34, January, 1995.The authors express their gratitude to A. V. Sklyarov for fruitful discussions during the elaboration of the theoretical basis and technical realization of the method.The reseach was carried out with the partial financial support of the International Science Foundation (Grant MBN 000).     

The interaction of water with sulfonium ions and the effects of hydration on the energetics of methyl group transfer: An ab initio molecular orbital study of the hydration of (CH3)3S+ and (CH3)2S+CH2CO2 −

The interactions of the sulfonium ions (CH₃)₃S⁺, (CH₃)₂S⁺CH₂CO₂ ^–, and (CH₃)₂S⁺-CH₂CH₂CO₂ ^– with up to four water molecules have been studied by ab initio molecular orbital methods. Complexes of (CH₃)₃S⁺ with one to three water molecules involve strong electrostatic sulfur-oxygen interactions; in contrast, the sulfide (CH₃)₂S interacts with water molecules via weak S-H hydrogen bonds, suggesting that methyl-group transfer from (CH₃)₃S⁺ in aqueous solution involves a significant alteration of the hydration pattern around the sulfur atom. Two conformers of (CH₃)₂S⁺CH₂CO₂ ^– were found that display sulfur-oxygen distances which are approximately 0.3 å less than the sum of the sulfur and oxygen van der Waals radii, indicating a strong intramolecular electrostatic interaction. For the complexes (CH₃)₂S⁺CH₂CO₂ ^–·nH₂O(n =1–4), water interacts primarily with the carboxylate group via hydrogen bonds, rather than electrostatically with the sulfur atom, although in complexes with the three- and four-water complexes, the proximity of the positively charged sulfur atom to the carboxylate group significantly alters the hydration pattern compared to that in the corresponding of complexes CH₃SCH₂CO₂ ^–· Thus, methyl transfer from (CH₃)₂S⁺CH₂CO₂ ^– to an acceptor in aqueous solution also involves substantial changes in the hydration pattern around the carboxylate group.     

A molecular dynamics study on Rh3+ hydration: development and application of a first principles hydrated ion–water interaction potential

The Rh³⁺ aquaion exhibits one of the largest residence times of water molecules in the first hydration shell. The extreme stability of this hexahydrated ion in water solutions makes Rh³⁺ an extremely suitable candidate to be studied using the hydrated ion model. According to this approach, the representative cationic entity in aqueous solution is the ion plus its first hydration shell (i.e. the hydrated ion) and not the bare ion. Our group has successfully applied that concept in the framework of classical statistical simulations based on first principles ion–water interaction potentials. The methodology is now applied to the [Rh(H₂O)₆]³⁺ case based on a previous generalization in which some of the contributions were found to be transferable among the cases already studied (Cr³⁺, Al³⁺, Mg²⁺, Be²⁺). In this contribution a flexible hydrate model is presented, in which rigid first-shell water molecules have rotational and translational degrees of freedom, allowing for internal dynamics of the hydrated ion entity. The potential presented is thoroughly tested by means of a set of molecular dynamics simulations. Structural, dynamical, energetic and spectroscopic information is retrieved from the simulations, allowing the estimation of properties such as ion hydration energy, vibrational spectra of the intermolecular modes, cation mobility, rotational dynamics of the hydrated ion and first-shell water molecules and residence times of the second-shell water molecules. Extension of the Ewald sum to terms r^–4, r^–6 and r^–7 is presented and applied to systems of different size ([Rh(H₂O)₆]³⁺+(n–6)H₂O, n=50, 100, 200, 500, 1000 and 2500) and cutoff radii.Contribution to the Jacopo Tomasi Honorary Issue     

Analytic evaluation of infrared intensities and polarizabilities by two-configuration self-consistent field wave functions

For more than a few molecular electronic states, the simplest qualitatively correct picture of the electronic structure is provided by the two-configuration self-consistent-field (TCSCF) method. Here, analytic methods are reported for the evaluation of TCSCF infrared intensities and polarizabilities. These new methods have been implemented and applied to the molecules CH₂(¹A₁), CF₂, CH ₃ ^– , NH₃, HF and O₃. Nine different basis sets, ranging from 3–21G to triple zeta plus double polarization (TZ + 2P), have been used. In several cases one finds qualitative differences between the analogous SCF and TCSCF predictions.     

Auration of ruthenocene: synthesis and molecular structure of mono- and diaurated derivatives

Ruthenocene, like ferrocene, reacts with (Ph₃PAu)₃O⁺BF₄ ^– to afford agem-diaurated derivative CpRuC₅H₄(AuPPh₃)₂ ⁺BF₄ ^–, which is converted into CpRuC₅H₄AuPPh₃ when treated with PPh₃. X-ray structural analysis revealed substantial Ru-Au interaction in the diaurated derivative.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1335–1337, July, 1994.This work was supported by the Russian Foundation for Basic Research (projects 03-93-5827 and 03-93-18559).     

Conformational Stability from Variable-Temperature Infrared Spectra of Krypton Solutions, Ab Initio Calculations, and r o Structural Parameters of Chlorocyclopentane

The infrared spectra (3500–400 cm^–1) of krypton solutions of chlorocyclopentane, c-C₅H₉Cl, at variable temperatures (–101 to –150°C) have been recorded and the fundamental vibrations of the axial conformer and several of those for the equatorial form have been assigned. Utilizing two pairs of fundamentals for the two conformers in the krypton solution, an enthalpy difference of 145±15 cm^–1 (1.73±0.18 kJ-mol^–1) has been obtained with the axial conformer the more stable form. It is estimated that there is 67±2% of the axial conformer present at ambient temperature. Convincing spectroscopic evidence shows that a significant percentage of the chlorocyclopentane molecules are undergoing pseudorotation at ambient temperature. The conformational stabilities, harmonic force constants, fundamental frequencies, infrared intensities, and Raman activities have been obtained from MP2/6-31G(d) calculations with full electron correlation and these quantities have been compared to the experimental values when appropriate. The optimized geometries and conformational stabilities have also been obtained from ab initio MP2 calculations as well as by density functional theory (DFT) by the B3LYP method with several different basis sets. The adjusted r ₀ structural parameters have been obtained for both conformers by combining the ab initio data with the previously reported microwave rotational constants. These new values of the structural parameters for both conformers are compared to those previously reported from electron diffraction and microwave studies. These results are compared to the corresponding quantities of some similar molecules.     

Co-hydrolysis products of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions: Part 2 [1]

²⁹Si NMR peaks due to species with the double four-membered ring siloxane backbone composed of both Si(O^–)_4/2 and CH₃Si(O^–)_3/2 units, (CH₃) _n Si₈O _{20 – n} ^{/(8 – n) –} (n=1–3), formed by co-hydrolysis of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions in methanol have been assigned. It has been found that ²⁹Si NMR peaks due to Si(OSi)₃(O^–) units shift to lower frequencies by replacement of the adjacent Si(O^–)_4/2 units by CH₃Si(O^–)_3/2 units, in other words, with increasing m value in Si[OSi(O^–)₃]_{3 – m} [OSi(CH₃) (O^–)₂] _m (O^–) (m=0–2). Peaks from CH₃ Si(OSi)₃ units in the species have also appeared as separated due to the kind of neighbor structural units. On the basis of the assignments, positions of CH₃Si(O^–)_3/2 units in the cubic octameric siloxane framework of (CH₃) _n Si₈O _{20 – n} ^{/(8 – n) –} (n=2, 3), for both of which three isomers are present, have been estimated.     

Disubstituted Rubidium Orthoperiodate Rb2H3IO6: Crystal and Molecular Structures and Properties

The crystal and molecular structures of acid salt Rb₂H₃IO₆ were determined. The anion part of the structure is united via a hydrogen bonding system to form a layer parallel to the xy plane. The proton conductivity in the temperature range of 40–60°C was found to be 10^–7–5 × 10^–6 Ohm^–1cm^–1, E _a = 2 eV.     

Crystal and molecular structure of 1,1′-<Emphasis Type="Italic">bis</Emphasis>-(acetoacetyl)ferrocene

Using physicochemical methods, the crystal and molecular structure of 1,1-bis-(acetoacetyl)ferrocene is studied. The compound crystallizes in the form of two crystallographically independent molecules with slightly different conformations and mutually perpendicular orientation. Crystals are monoclinic, C₁₈H₁₈FeO₄, a = 35.68(1) ?, b = 5.733(2) ?, c = 30.30(1) ?; β = 96.831(5)°; V= 6154(3) ?³, Z= 16, d_x = 1.529 g/cm³, C2/c space group. The molecule consists of the ferrocene fragment and two acetylacetonyl substituents.     

Conformational Studies of Methyl Vinyl Silane from Temperature-Dependent FT–IR Spectra of Xenon and Krypton Solutions

Variable-temperature (–55 to –155°C) studies of the infrared spectra (3500–400 cm^–1) of methyl vinyl silane, CH₂CHSiH₂CH₃, dissolved in liquid xenon and krypton have been recorded. Utilizing three sets of conformer doublets due to the cis and gauche rotamers, the enthalpy difference has been determined to be 133 ± 11 cm^–1 (1.59 ± 0.13 kJ/mol) with the gauche conformer the more stable form in the krypton solution. In the xenon solution, the enthalpy difference could not be determined because the infrared bands become so broad and the overlap was so extensive that meaningful areas could not be determined. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G(2d,2p) from which structural parameters and conformational stabilities have been determined. With the largest basis set, the cis conformer is predicted to be the more stable conformer, which is inconsistent with the experimental results. Utilizing previously reported microwave rotational constants for both conformers along with the ab initio predicted distances and angles, r ₀ parameters have been obtained for both the cis and gauche conformers. The spectroscopic and theoretical results are compared to the corresponding quantities for some similar molecules.     

Untersuchungen an Kristallhydraten anorganischer Salze, 8. Mitt. Interpretation der Schwingungsspektren vonM(BF4)2·6H2O fürM=Fe2+, Co2+, Ni2+

The infrared and Raman spectra were recorded in the range 4000–160 cm^–1 forM(BF₄)₂·6 H₂O whereM=Fe²⁺, Co²⁺, Ni²⁺. The spectroscopic data support the X-ray structural data in showing that in the crystal hydrates studied two kinds of hydrogen bonds are present: H₂O...H₂O and OH₂... F₄B^–. The energies and molecular force constants (f _OH and fH₂O) andr _OH for OH₂...F₄B^– were calculated for the three crystal hydrates. It was found that the bond OH₂... F₄B^– is comparatively weak, with mean energy 3.7–3.3 kcal/mol. Two types of water molecule with different structures are existing as the first are participating in H₂O...H–O–H...F₄B^– and the second in BF₄ ^–...H–O–H...F₄B^–.     

Tables of accurate STF HF wavefunctions from B to Ca

Accurate Slater type function (STF) Hartree-Fock (HF) wavefunctions are calculated and tabled from B to Ca. The STF's have a form of r ⁿ e ^-r and the powers (n) of r are carefully determined. The total atomic energies agree with those of numerical HF (NHF) within the error of 4×10^–6 a.u. and 1×10^–5 a.u. for B to F and for Ne to Ca, respectively. The STF HF basis sets given will be useful to benchmark calculations for the molecular, solid, and atomic electronic states. Applications of the STF HF basis to molecular calculations are given and briefly discussed. Sample calculations are performed on the N₂ and P₂ molecules.