On the Cl···N halogen bond: a rotational study of CF3Cl···NH3

The rotational spectra of six isotopologues (CF(3)(35)Cl···(14)NH(3), CF(3)(37)Cl···(14)NH(3), CF(3)(35)Cl···(15)NH(3), CF(3)(37)Cl···(15)NH(3), CF(3)(35)Cl···(14)ND(3) and CF(3)(37)Cl···(14)ND(3)) of the CF(3)Cl···NH(3) adduct have been investigated and analyzed by pulsed jet Fourier transform microwave spectroscopy. Rotational, centrifugal distortion and quadrupole ((35)Cl, (37)Cl, (14)N) coupling constants have been precisely obtained. The two subunits of the complex are held together via a Cl···N halogen bond interaction. Information on the internal dynamics and on the dissociation energy of the complex is provided.     

Infrared and microwave spectra of the acetylene-ammonia and carbonyl sulfide-ammonia complexes: a comparative study of a weak C-H···N hydrogen bond and an S···N bond

We report a combined high resolution infrared and microwave spectroscopic investigation of the acetylene-ammonia and carbonyl sulfide-ammonia complexes using a pulsed slit-nozzle multipass absorption spectrometer based on a quantum cascade laser and a pulsed nozzle beam Fourier transform microwave spectrometer, respectively. The ro-vibrational transitions of the acetylene-ammonia complex have been measured at 6 μm in the vicinity of the ν(4) band of ammonia for the first time. The previously reported pure rotational transitions have been extended to higher J and K values with (14)N nuclear quadrupole hyperfine components detected and analyzed. The spectral analysis reveals that acetylene binds to ammonia through a C-H···N weak hydrogen bond to form a C(3v) symmetric top, consistent with the previous microwave [Fraser et al., J. Chem. Phys., 1984, 80, 1423] and infrared spectroscopic study at 3 μm [Hilpert et al., J. Chem. Phys., 1996, 105, 6183]. A parallel study has also been carried out for the carbonyl sulfide-ammonia complex whose pure rotational and ro-vibrational spectra at 6 μm have been detected and analyzed for the first time. The spectral and the subsequent structural analyses, in conjunction with the corresponding ab initio calculation, indicate that the OCS-NH(3) complex assumes C(3v) symmetry with S pointing to N of NH(3), in contrast to the T-shaped geometries obtained for the isoelectronic N(2)O-NH(3) and CO(2)-NH(3) complexes.     

Hydrogen bond CH…O in a methanolic solution of hydrogen chloride

The existence of a hydrogen bond in which a methyl group of the (MeOH)₂H⁺ ion acts as a proton donor is examined. The fundamental vibration frequencies of this ion were calculated for different numbers and strengths of CH…O bonds. The atomic charges in neutral ((MeOH) _n ,n=1–4) and protonated ((MeOH) _m H⁺,m=2–6) associates of methanol molecules were also calculated. The experimentally observed decrease in the v(CH) vibration frequencies of the (MeOH)₂H⁺ ion to 2890 cm⁻¹ and 2760 cm⁻¹ is attributable to the fact that each methyl group of the ion is involved in formation of two CH…O bonds with strength of −12.5 kJ mol⁻¹. The proton-donating ability of the CH bond depends on the charge on its H atom; however, it does not correlate with the dipole moment of this bond. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 306–312, February, 1999.     

The R3O+···H+ hydrogen bond: toward a tetracoordinate oxadionium(2+) ion

Oxatriquinanes are tricyclic oxonium ions which are known to possess remarkable solvolytic stability compared to simple alkyl oxonium salts. Their rigid, hemispherical structure presents an oxygen at the apex of three fused five-membered rings. While trivalent oxygen species like these have been well described in the literature, the ability of oxygen to enter into a fourth covalent bonding relationship has been visited in theory and suggested by the outcome of certain reactions conducted in superacidic media, but has never been established by the characterization of a stable, persistent R(3)OH(2+) or R(4)O(2+) ion. In this study, the nucleophilicity of the oxatriquinane oxygen was evaluated first by a series of protonation studies using the Br?nsted superacid H(CHB(11)Cl(11)) both in the solid state and in liquid HCl solution. The interaction of the oxatriquinane oxygen with a bridging carbocation was also examined. A strong case could be made for the occurrence of hydrogen bonding between H(CHB(11)Cl(11)) and oxatriquinane using IR spectroscopy. Under the most forcing protonation conditions, the oxatriquinane ring is cleaved to give a bridged, dicationic, protonated tetrahydrofuran-carbenium ion.     

Neutron diffraction study of the HF adducts containing a hydrogen bond F-H?O

Single-crystal structures of HF adducts of acid salts CsH₂PO₃·HF, KH₂PO₄·HF, and CsH₂PO₄·HF were determined by neutron diffraction using the Laue method. In the crystals, HF molecules are connected to anions by means of new type of hydrogen bonds, F-H?O, which are significantly shorter (F?O distances 2.356-2.386(3) Å) than strong O-H?O or O-H?F hydrogen bonds. The H-F distances in the structures of these adducts, 1.020-1.027(5) Å, are compared with those in crystalline HF and hydrofluoride anions.     

On the thermal decomposition of [Fe2NiO(CH3COO)6(H2O)3]·2H2O

The heteronuclear-oxoacetate with the composition [Fe₂NiO(CH₂COO)₆(H₂O)₃]·2H₂O decomposed on heating, forming nickel ferrite NiFe₂O₄ and (depending on the decomposition conditions) in part other solid phases. H₂O, CH₃COOH, acetone and CO₂ were also formed in the decomposition. A reaction scheme is given for the decomposition. The products were porous powders with grain diameters between 3 and 10m. On increase of the temperature of decomposition from 300 to 800 C, the BET surface area and the surface area of the pores decreased, but only a small alteration in grain size was observed. As a result of thermal treatment in the temperature region abone 800C, larger aggregates of grains were formed in sintering processes.

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Zusammenfassung Heteronukleare-Oxoazetate der Zusammensetzung [Fe₂NiO(CH₃COO)₆(H₂O)₃]·2H₂O werden durch Erhitzen zersetzt, wobei Nickelferrite NiFe₂O₄ und — in AbhÄngigkeit von den Bedingungen der Zersetzung — mit einem Teil anderer fester Phasen gebildet wird. In der Zersetzungsreaktion werden auch H₂O, CH₃COOH, Azeton und CO₂ gebildet. Es wird ein Reaktionsschema für die Zersetzung angegeben. Die Produkte sind poröse Pulver mit einem Korndurchmesser zwischen 3 und 10 m. Wird die Zersetzungstemperatur von 300 auf 800C erhöht, nimmt die BET-OberflÄche und die PorenoberflÄche ab, wobei sich die Korngrö\e aber nur wenig verÄndert. Im Ergebnis der WÄrmebehandlung im Temperaturbereich oberhalb 800C werden durch Sinterprozesse grö\ere Partikelaggregate gebildet.

     

Theoretical study of the N—H···O red-shifted andblue-shifted hydrogen bonds

Theoretical calculations are performed to study the nature of the hydrogen bonds in complexes HCHO···HNO, HCOOH···HNO, HCHO···NH3, HCOOH···NH3, HCHO···NH2F and HCOOH···NH2F. The geomet- ric structures and vibrational frequencies of these six complexes at the MP2/6-31 G(d,p), MP2/6-311 G(d,p), B3LYP/6-31 G(d,p) and B3LYP/6-311 G(d,p) levels are calculated by standard and counterpoise-corrected methods, respectively. The results indicate that in complexes HCHO···HNO and HCOOH···HNO the N—H bond is strongly contracted and N—H···O blue-shifted hydrogen bonds are observed. While in complexes HCHO···NH3, HCOOH···NH3, HCHO···NH2F and HCOOH···NH2F, the N—H bond is elongated and N—H···O red-shifted hydrogen bonds are found. From the natural bond orbital analysis it can be seen that the X—H bond length in the X—H···Y hydrogen bond is controlled by a balance of four main factors in the opposite directions: hyperconjugation, electron density redistribu- tion, rehybridization and structural reorganization. Among them hyperconjugation has the effect of elongating the X—H bond, and the other three factors belong to the bond shortening effects. In complexes HCHO···HNO and HCOOH···HNO, the shortening effects dominate which lead to the blue shift of the N—H stretching frequencies. In complexes HCHO···NH3, HCOOH···NH3, HCHO···NH2F and HCOOH···NH2F where elongating effects are dominant, the N—H···O hydrogen bonds are red-shifted.     

Small heterocyclics as hydrogen bond acceptors and donors: the case of the C2H3XS···NH3 complexes (X = H, F and CH3)

B3LYP/6-311++G(d,p) calculations were employed in order to examine the molecular parameters of the C₂H₃XS···NH₃ heterocyclic hydrogen-bonded complexes with X = H, F and CH₃. Intermolecular criteria were taken into account when studying the formation of these hydrogen-bonded complexes, such as geometry analysis, charge density quantification and interpretation of the harmonic vibrational spectrum, in which case the appearance of red-shift and blue-shift effects was discussed. It was assumed from the outset that many hydrogen bond types may exist in these systems, and these were investigated using the results of topological integrations from the quantum theory of atoms in molecules (QTAIM) and intermolecular charge transfer calculations using the ChelpG scheme. The proton donor/acceptor behavior of C₂H₃XS was interpreted in terms of hydrogen bond energies, whose values were corrected using the basis sets superposition error (BSSE) and zero point energy (ZPE). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

O–H···C hydrogen bond in the methane–water complex

Quantum chemical calculations were performed at different levels of theory (SCF, DFT, MP2, and CCSD(T)) to determine the geometry and electronic structure of the HOH···CH₄ complex formed by water and methane molecules, in which water is a proton donor and methane carbon (sp³) is an acceptor. The charge distribution on the atoms of the complex was analyzed by the CHelpG method and Hirshfeld population analysis; both methods revealed the transfer of electron charge from methane to water. According to the natural bond orbital (NBO) analysis data, the charge transfer upon complexation is caused by the interaction between the σ orbital of the axial С–H bond of methane directed along the line of the O–H···C hydrogen bridge and the antibonding σ* orbital of the О–H bond of the water molecule. Topological analysis of electron density in the HOH···CH₄ complex by the AIM method showed that the parameters of the critical point of the bond between hydrogen and acceptor (carbon atom) for the O–H···C interaction are typical for Н-bonded systems (the magnitude of electron density at the critical point of the bond, the sign and value of the Laplacian). It was concluded that the intermolecular interaction in the complex can be defined as an Н bond of O–H···σ(С–H) type, whose energy was found to be 0.9 kcal/mol in MP2/aug-cc-pVQZ calculations including the basis set superposition error (BSSE).     

Quantum-chemical study of compounds containing intramolecular O-H…O=C bond

New results of the study of stable intermediates containing an intramolecular hydrogen bond O-H…O=C in the gas phase and solvents, carbon tetrachloride and dioxane, were analyzed. The structural and energy characteristics of the stable conformers of these compounds were determined by a MR2/6-311++G(d, p) method. The most stable is the hydrogen-bonded conformer of 1-hydroxy-1-chloroethyl acetate molecule. The approaches to accounting for the effects of the O-H…O=C intramolecular hydrogen bonding on the molecules reactivity were discussed.     

Experimental study of the pyrolysis path of CaSO3·1/2H2O

Journal of Thermal Analysis and Calorimetry - Simultaneous DSC-TGA (SDT) and Fourier transform infrared spectrometer (FTIR) and diffuse reflectance in situ Fourier transform spectroscopy (DRIFTs)...     

A photoionization study of the ion-neutral complexes CH3CH +CH 3 · CH2CH3] and CH3CH2CH+CH 3 · CH3 in the gas phase: Formation,H-transfer and C—C bond formation between partners,and channeling of energy into dissociation

Photoionization mass spectrometry was used to investigate the dynamics of ion-neutral complex-mediated dissociations of the n-pentane ion (1). Reinterpretation of previous data demonstrates that a fraction of ions 1 isomerizes to the 2-methylbutane ion (2) through the complex CH₃CH⁺CH ₃ ^· CH₂CH₃ (3), but not through CH₃CH⁺CH₂CH ₃ ^· CH₃ (4). The appearance energy for C₃Hin ₇ ⁺ formation from 1 is 66 kJ mol^?1 below that expected for the formation of n-C₃H ₇ ⁺ and just above that expected for formation of i-C₃H ₇ ⁺ . This demonstrates that the H shift that isomerizes C₃H ₇ ⁺ is synchronized with bond cleavage at the threshold for dissociation to that product. It is suggested that ions that contain n-alkyl chains generally dissociate directly to more stable rearranged carbenium ions. Ethane elimination from 3 is estimated to be about seven times more frequent than is C-C bond formation between the partners in that complex to form 2, which demonstrates a substantial preference in 3 for H abstraction over C-C bond formation. In 1 → CH₃CH⁺CH₂CH₃ + CH₃ by direct cleavage of the C1–C2 bond, the fragments part rapidly enough to prevent any reaction between them. However, 1 → 2 → 4 → C4H ₈ ⁺ + CH₄ occurs in this same energy range. Thus some of the potential energy made available by the isomerization of n-C₄H₉ in 1 is specifically channeled into the coordinate for dissociation. In contrast, analogous formation of 3 by 1 → 3 is predominantly followed by reaction between the electrostatically bound partners.     

A partial proton transfer in hydrogen bond O-H···O in crystals of anhydrous potassium and rubidium complex chloranilates

Hydrogen bonding and proton transfer in the solid state are studied on the crystals of isostructural anhydrous potassium and rubidium complex chloranilates by variable-temperature single crystal X-ray diffraction, solid state (1)H NMR and IR spectroscopies, and periodic DFT calculations of equilibrium geometries, proton potentials, and NMR chemical shifts. Their crystal structures reveal neutral molecules of chloranilic acid and its dianions connected into a chain by O-H···O hydrogen bond. A strong hydrogen bond with a large-amplitude movement of the proton with NMR shift of 13-17 ppm and a broad continuum in IR spectra between 1000 and 500 cm(-1) were observed. Periodic DFT calculations suggest that proton transfer is energetically more favorable if it occurs within a single pair of chloranilate dianion and chloranilic acid molecule but not continuously along the chains of long periodicity. The calculated chemical shifts confirm the assumption that the weak resonance signals observed at lower magnetic fields pertain to the case when the proton migrates to the acceptor side of the hydrogen bond. The detected situation can be described by a partial proton transfer.     

Molecular geometries of H2S···ICF3 and H2O···ICF3 characterised by broadband rotational spectroscopy

The rotational spectra of three isotopologues of H(2)S···ICF(3) and four isotopologues of H(2)O···ICF(3) are measured from 7-18 GHz by chirped-pulse Fourier transform microwave spectroscopy. The rotational constant, B(0), centrifugal distortion constants, D(J) and D(JK), and nuclear quadrupole coupling constant of (127)I, χ(aa)(I), are precisely determined for H(2)S···ICF(3) and H(2)O···ICF(3) by fitting observed transitions to the Hamiltonians appropriate to symmetric tops. The measured rotational constants allow determination of the molecular geometries. The C(2) axis of H(2)O/H(2)S intersects the C(3) axis of the CF(3)I sub-unit at the oxygen atom. The lengths of halogen bonds identified between iodine and sulphur, r(S···I), and iodine and oxygen, r(O···I), are determined to be 3.5589(2) ? and 3.0517(18) ? respectively. The angle, φ, between the local C(2) axis of the H(2)S/H(2)O sub-unit and the C(3) axis of CF(3)I is found to be 93.7(2)° in H(2)S···ICF(3) and 34.4(20)° in H(2)O···ICF(3). The observed symmetric top spectra imply nearly free internal rotation of the C(2) axis of the hydrogen sulphide/water unit about the C(3) axis of CF(3)I in each of these complexes. Additional transitions of H(2)(16)O···ICF(3), D(2)(16)O···ICF(3) and H(2)(18)O···ICF(3) can be assigned only using asymmetric top Hamiltonians, suggesting that the effective rigid-rotor fits employed do not completely represent the internal dynamics of H(2)O···ICF(3).     

MO investigations on lignin model compounds: IX. A PCILO study of the hydrogen bond O-H…O and O-H…N type formed by phenol with some proton acceptors

A systematic PCILO study has been carried out on the intermolecular hydrogen bond formed by phenol with proton acceptors such as acetone, ether, p-benzoquinone, N,N-dimethylformamide, trimethylamine, pyridine, acetonitrile and acrylonitrile. The complexes studied form hydrogen bonds with energy intervals of 20 − 45 kJ mol⁻¹ at distances R_O…Y = 0.265 − 0.300 nm (Y=N,0). For the system phenol-pyridine both the 1:1 complex PhPy and the 2:1 complex Ph₂Py were also studied. The calculated hydrogen bond energies are compared and discussed with experimental data from the literature. The calculated hydrogen bond and O-H stretching force constants are in range expected.     

Microwave spectroscopic and theoretical studies on the phenylacetylene···H2O complex: C-H···O and O-H···π hydrogen bonds as equal partners

Rotational spectra of five isotopologues of the title complex, C(6)H(5)CCH···H(2)O, C(6)H(5)CCH···HOD, C(6)H(5)CCH···D(2)O, C(6)H(5)CCH···H(2)(18)O and C(6)H(5)CCD···H(2)O, were measured and analyzed. The parent isotopologue is an asymmetric top with κ = -0.73. The complex is effectively planar (ab inertial plane) and both 'a' and 'b' dipole transitions have been observed but no c dipole transition could be seen. All the transitions of the parent complex are split into two resulting from an internal motion interchanging the two H atoms in H(2)O. This is confirmed by the absence of such doubling for the C(6)H(5)CCH···HOD complex and a significant reduction in the splitting for the D(2)O analog. The rotational spectra, unambiguously, reveal a structure in which H(2)O has both O-H···π (π cloud of acetylene moiety) and C-H···O (ortho C-H group of phenylacetylene) interactions. This is in agreement with the structure deduced by IR-UV double resonance studies (Singh et al., J. Phys. Chem. A, 2008, 112, 3360) and also with the global minimum predicted by advanced electronic structure theory calculations (Sedlack et al., J. Phys. Chem. A, 2009, 113, 6620). Atoms in Molecule (AIM) theoretical analysis of the complex reveals the presence of both O-H···π and C-H···O hydrogen bonds. More interestingly, based on the electron densities at the bond critical points, this analysis suggests that both these interactions are equally strong. Moreover, the presence of both these interactions leads to significant deviation from linearity of both hydrogen bonds.