Proton dynamics in an extended array of hydrogen bonds: normal coordinates, proton transfer and macroscopic quantum entanglement in the ground state

After a brief introduction to neutron scattering techniques, illustrated with the scattering function for harmonic oscillators, some new aspects of proton dynamics in the KHCO₃ crystal are presented. The full scattering function for the proton modes measured on single crystals provides a graphic view of proton dynamics. Vibrational states are fully characterized with three quantum numbers. The effective oscillator mass of 1 amu confirms the decoupling of protons from the lattice. Combining infrared, Raman and inelastic neutron scattering techniques, the double minimum potential for the transfer of a single proton along hydrogen bonds is totally determined. Elastic neutron scattering techniques probe dynamics in the fully degenerate ground state. Quantum entanglement arising from normal coordinates gives rise to quantum interference. With diffraction techniques, the dynamical structure arising from large-scale quantum coherence is observed as ridges of intensity, well separated from Bragg's peaks. The vibrational wave function in the ground state must be regarded as a superposition of non-factorable macroscopic wave function.     

Second-sphere coordination in hexaamminecobalt(III) salt with organic sulphonate anion: Synthesis, characterisation and X-ray crystal structure of [Co(NH3)6](CH3SO3)3

Reaction of hexaamminecobalt(III) chloride with the silver salt of methanesulphonic acid in aqueous medium (1:3 molar ratio) forms hexaamminecobalt(III) methanesulphonate, [Co(NH₃)₆](CH₃SO₃)₃, in high yield. This cobalt(III) complex has been characterized by spectroscopic techniques (UV/visible, IR and NMR) and its solubility product determined. The X-ray crystal structure shows that the [Co(NH₃)₆]³⁺ cations interact at the second sphere by sharing edges with the anions, via N–H  O hydrogen bonds. The structure is related to that of [Co(NH₃)₆]Cl(CH₃SO₃)₂, but is modified to accommodate additional anions in place of Cl⁻.     

Rare gas–iodine complexes in the ion-pair states

Luminescence and luminescence excitation spectra in the vicinity of the optical–optical double resonance transitions to the I₂(, v_f = 8 and 9, J_f ≈ 55) levels have been measured at the bulb conditions for the I₂ + Rg mixtures (Rg = He, Ar, Xe) at the rare gas pressures 2–20 Torr and room temperature. Luminescence attributed to the RgI₂ complexes in the ion-pair states has been observed for the first time. It is argued that the complexes can be formed by direct optical excitation from the complexes or colliding pairs. Besides, the RgI₂ complexes in the ion-pair states can be formed in nonadiabatic internal conversion processes from the one. The complexes have rather long lifetime, especially in the case of Xe, and decay radiatively and nonradiatively forming I₂ molecules in different ion-pair states.     

First examples of ternary lanthanide 5-aminoisophthalate complexes: Hydrothermal syntheses and structures of lanthanide coordination polymers with 5-aminoisophthalate and oxalate

Two new lanthanide coordination polymers with mixed-carboxylates, [Ln(OX)(HAPA)(H₂O)]_n[Ln = Eu (1), Ho (2); H₂APA = 5-aminoisophthalic acid; OX = oxalate] were obtained by hydrothermal reactions, and characterized by single crystal X-ray diffraction, elemental analysis and IR spectra. Complexes 1 and 2 are both 3-D supramolecular structure, in which lanthanide ions are bridged by oxalate and 5-aminoisophthalate ligands forming 2-D metal–organic framework, and 2-D networks are further architectured to form 3-D supramolecular structures by hydrogen bonds. The two carboxylate groups of H₂APA ligand are all deprotonated and exhibit chelating and bridging bidentate coordination modes, respectively, and the amino group in HAPA presents – in the titled complexes. The thermogravimetric analysis was carried out to examine the thermal stability of the titled complexes. And the photoluminescence property of 1 was investigated.     

To what extent are thermodynamic properties of water argon-like?

A new view on the role of H-bonds in water, arising from the principle of corresponding states and Hilbert’s principle is presented. It is shown that the relative values of the H-bond contributions to the fraction volume and the heat of evaporation per molecule do not exceed 5%, although H-bonds are responsible for the non-monotone behavior of the fraction volume. It is established that the average number of H-bonds per molecule everywhere on the vapor–liquid coexistence curve is given by the formula n_H(T) ≈ 4(1 − 0.83t), where and is the critical temperature of water.     

Complex dynamics of proton and deuteron transfer in double hydrogen bond of benzoic acid isotopes

This paper deals with spin-lattice relaxation due to classical jumps and incoherent tunnelling of protons and deuterons in hydrogen bonds in solids. An analysis of experimental spin-lattice relaxation data for carboxylic acids suggests that tunnelling does not contribute to spin-lattice relaxation above the temperature at which the thermal energy of molecules and the potential barrier height are equal. It is also shown that contributions to the spin-lattice relaxation rate due to classical motion and incoherent tunnelling in excited vibrational states are negligible for fast proton transfer. However, for deuterons this contribution to spin-lattice relaxation is significant.     

Synthesis and characterization of a novel two-dimensional layered vanadate complex containing double helical chains

A novel two-dimensional layered vanadate complex 1 [Ni(phen)H₂O][V₂O₆] has been hydrothermally synthesized and characterized by elemental analyses, i.r., x.p.s., t.g. and single crystal X-ray diffraction. The single crystal X-ray diffraction analysis reveals that compound 1 consists of the chains covalently linked by [Ni(phen)H₂O]²⁺ subunits to form two-dimensional layered polyoxovanadate. It is interesting that the compound 1 consists of left-handed and right-handed helical chains, which are further interconnected to produce the double helical chains. The adjacent two-dimensional layers interact with each other via extensive hydrogen bonds and π–π stacking interactions to form a three-dimensional supramolecular framework.     

Intercalation of poly(methyl methacrylate) into tyramine-modified layered silicates through hydrogen-bonding interaction

Layered silicates modified with tyramine hydrochloride () were prepared and subsequently used in the preparation of polymer–layered silicate nanocomposites. Accordingly, surfaces of tyramine-modified silicate layers are partially covered with the phenol groups, which are able to form hydrogen bonds with the carbonyl groups of PMMA. In this study the solution-mediated process was applied to prepare two PMMA-based nanocomposites from tyramine-modified montmorillonite and Laponite (TAMMT and TALAP). Through hydrogen bonding, PMMA molecules are absorbed onto the silicate surfaces, and hence silicate layers can be dispersed in the polymer matrix. In the case of using TAMMT whose size is 300–500 nm, the intercalated nanocomposite is obtained. While using TALAP which has the much smaller diameter (25–50 nm) compared to TAMMT, the corresponding nanocomposite exhibits a mixed intercalated/exfoliated morphology. The nano-morphology of the nanocomposites was characterized by means of X-ray diffraction and TEM. FTIR was used to verify the presence of hydrogen bonds between PMMA and the surface phenol groups, and in addition, the interaction between PMMA and the surface oxygens of silicates.     

Vibronic dynamics in the low-lying coupled electronic states of methyl cyanide radical cation

Static and dynamic aspects of the Jahn–Teller (JT) and pseudo-Jahn–Teller (PJT) interactions between the ground and first excited electronic states of the methyl cyanide radical cation are theoretically investigated here. The latter involves construction of a theoretical model by ab initio computation of electronic potential energy surfaces and their coupling surfaces and simulation of the nuclear dynamics employing time-independent and time-dependent quantum mechanical methods. The present system represents yet another example belonging to the (E + A)  e JT–PJT family, with common JT and PJT active degenerate (e) vibrational modes. The theoretical results are found to be in very good accord with the recent experimental data revealing that the JT interactions are particularly weak in the ground electronic manifold of methyl cyanide radical cation, On the other hand, the PJT interactions of this ground electronic manifold with the first excited electronic state of the radical cation are stronger which cause an increase of the spectral line density. The effect of deuteration on the JT–PJT dynamics of the methyl cyanide radical cation is also discussed.     

On the photodissociation of ozone in the range of 5–9 eV

The photoabsorption spectrum of ozone in the UV range (5–9 eV) is calculated from a short-time wave packet propagation using six potential energy surfaces obtained from ab initio electronic structure calculations. It is shown that the (unnamed) band around 7 eV, which is immediately adjacent to the intense Hartley band, is primarily due to excitation of three electronic states: 5 ¹A′ (3 ¹A₁), 6 ¹A′ (4 ¹A₁), and 4 ¹A″ (2 ¹B₁). Excitation of the state 8 ¹A′ (¹B₂) leads to a broad and intense band starting around 8 eV with a maximum near 9.1 eV. In full accord with the recent experimental study of Brouard et al. [M. Brouard, R. Cireasa, A.P. Clark, G.C. Groenenboom, G. Hancock, S.J. Horrocks, F. Quadrini, G.A.D. Ritchie, C. Vallance, J. Chem. Phys. 125 (2006) 133308], the excitation at 193 nm (6.42 eV) involves at least two states (5 ¹A′ and 4 ¹A″) different from the state excited in the Hartley band (3 ¹A′). The dynamics along the dissociation path is discussed in terms of one-dimensional potential curves. Several avoided crossings among the excited ¹A′ as well as the ¹A″ states point to a complicated fragmentation process. Although a quantitative analysis of branching ratios is not possible on the basis of the present calculations, we surmise, that in addition to and O(¹D) + O₂(¹Δ_g), the next higher spin-allowed channel, , also is likely to be a major product channel, in agreement with experimental observations.     

A theoretical study of the excited electronic states of the SiCN system

Ab initio methods have been used to study the lowest-lying electronic states of the SiCN radical, which has two stable linear isomers in its electronic ground state, SiCN and SiNC. Vertical excitation energies and oscillator strengths have been computed for a number of states lying up to 8 eV. The geometries of the lowest-lying doublet and quartet states have been determined. The lowest-lying excited doublet state of SiNC (1²Σ⁺, 4.0 eV) arises from a HOMO–LUMO excitation (3π → 10σ), although the 1²Δ state (9σ → 3π) is very close in energy. In the case of the SiCN isomer the lowest excited state is 1²Δ, which arises from an excitation from the highest occupied σ orbital into the HOMO (9σ → 3π) and lies 3.6 eV above the ground state. SiCN should present very strong absorptions at 4.9 and 6.1 eV whereas SiNC should have relatively strong absorptions in the region of 5.7–5.9 eV. The smallest adiabatic energy gaps with respect to the ground state of SiNC and SiCN are very close (about 2.8 eV) and the excited state is the same 1²A′, which has angular equilibrium geometries for both isomers. We have determined accurate values for enthalpies of formation of the two linear doublet forms and .     

A tetra-nuclear copper(II) complex stabilizes an extended structure of a water nonamer: Synthesis and characterization of [Cu4(C54H46N4O14)(OH)2] · 10H2O

A tetra-nuclear copper(II) complex [Cu₄(C₅₄H₄₆N₄O₁₄)(OH)₂] · 10H₂O (1) has been synthesized starting from l-tyrosine, NaOH, 2,6-diformyl-4-methylphenol (dfp) and CuSO₄ · 5H₂O. Compound 1 crystallizes from an ethanol–water mixture in triclinic space group. In the crystal of 1, two binuclear copper units, related by a center of symmetry, are bridged by two hydroxo bridges and results in the formation of a tetra-nuclear {Cu₄} structure. Five lattice water molecules, located in the asymmetric unit, interact among themselves and form an unusual form of a water nonamer. In the crystal, the water nonamer is again hydrogen bonded to the next nonamer forming a chainlike polymer. Each {Cu₄} complex unit attaches four such water nonamer chains. Variable temperature magnetic data fit to the Bleaney–Bower’s equation with a Curie type of impurity of S = 0.5. The best fit of the magnetic data to this equation yielded 2J = −217, g = 2.019 and a TIP value of 60 × 10⁻⁶ cm³ mol⁻¹.     

Enthalpies of combustion and formation of 3-formylchromones

The enthalpies of combustion of 3-formylchromone (3F), 3-formyl-6-methylchromone (3F6M) and 3-formyl-6-isopropylchromone (3F6I) were determined by combustion calorimetry. The molar combustion energies () of the 3F, 3F6M and 3F6I are: −(4452.4 ± 1.8), −(5115.6 ± 2.7) and −(6411.4 ± 2.5) kJ mol⁻¹, respectively. The formation enthalpies in the crystalline state () are: −(340.2 ± 2.2), −(355.1 ± 3.1) and −(415.5 ± 3.0) kJ mol⁻¹, respectively.s     

Gas-phase reactivities of charged platinum dimers with ammonia: A combined experimental/theoretical study

Computational and experimental studies of with ammonia are reported. While ammonia is dehydrogenated with either cluster type, the reaction efficiencies are quite different with  = 0.27 for [K. Koszinowski, D. Schröder, H. Schwarz, J. Phys. Chem. A 107 (2003) 4999.] and  = 0.0033 for . DFT-based relativistic calculations are consistent with this distinct behavior, with maximum energies along the reaction path of −13.3 kcal/mol for the cationic and +1.4 kcal/mol for the anionic clusters relative to the reactants. The recently proposed mechanism for the system [D. Xu. X.-Y. Chen, S.-G. Wang, Int, J. Quant. Chem. 107 (2007) 1985.] needs to be modified to account for the experimental findings.     

Crystal structure, phase transition and thermal behaviour of dabcodiium hexaaquacopper(II) bis(sulfate), (C6H14N2)[Cu(H2O)6](SO4)2

A new organically templated metal sulfate has been synthesized and characterized. At room temperature, dabcodiium hexaaquacopper(II) bis(sulfate), (C₆H₁₄N₂)[Cu(H₂O)₆](SO₄)₂ crystallizes in the monoclinic symmetry (space group P2₁/n) with the following unit cell parameters: a = 6.9533(2), b = 12.5568(2), c = 9.9434(2) Å; β = 90.526(1)° and Z = 2. Its crystal structure is built from isolated [Cu(H₂O)₆]²⁺, and disordered ions linked together by a hydrogen-bonding network. The title compound undergoes a reversible phase transition of the first-order type at 265.7/281.8 K on heating–cooling runs. Below the phase transition temperature, the structure is fully ordered.     

Ion pairing, H-bonding, and π–π interactions in copper(II) complex-organo-networks derived from a proton-transfer compound of the 1,10-phenanthroline-2,9-dicarboxylic acid

The one-pot reaction between the novel proton transfer compound (pydaH₂)²⁺(phendc)²⁻, LH₂, and Cu(II) afforded the compounds (pydaH)₂[Cu(phendc)₂]·10H₂O, 1, and (pydaH)₂[Cu(phendc)(phendcH)]₂·5H₂O, 2, where pyda=2,6-diaminopyridine, and phendcH₂=1,10-phenanthroline-2,9-dicarboxylic acid. The single crystal X-ray diffraction analysis of 1 and 2 revealed that these are two novel self-assembled 3D Cu(II) complex-organo-networks, in which (pydaH)⁺ ions and [Cu(phendc)₂]²⁻ or complex units are held together by ion pairing, H-bonding, and π–π interactions. Magnetic measurements over the temperature range 1.8–310 K revealed no significant magnetic coupling between Cu(II) centers in 1 or 2.     

The limiting partial molar volume and apparent molar volume of glycylglycine in aqueous KCl solution at 298.15 and 308.15 K

Apparent molar volumes V_Φ of glycylglycine in aqueous KCl solutions have been obtained from densities at 298.15 and 308.15 K measured with a vibrating-tube densimeter. These data have been used to deduce partial molar volumes of transfer from water to different KCl–water mixtures. values are positive. This result arises from the interaction of KCl with the charged centers of glycylglycine. The results show that depends less on temperature. Hydration numbers are calculated from data and are interpreted in terms of various interactions.     

Synthesis, crystal structures and magnetic properties of Cu(II) compounds bridged by the terephthalate ligand and hydrogen bonds

A 3D network [Cu(tmen)(tp)(H₂O)₂]_n (1) (tmen = N,N,N′,N′-tetramethylethylenediamine; tp = terephthalate) and a 2D sheet [Cu(pyrazole)₂(tp)]_n (2), featuring 1D chains interwoven by hydrogen bonds, have been prepared and characterized by means of X-ray analyses and magnetic measurements. For 1, coordinative zigzag chains contain Cu(II) centers capped by the chelate ligand tmen, in which the tetragonal structure is elongated due to Jahn–Teller distortion. Coordinated water molecules are hydrogen-bonded to two free carboxylate oxygens of tp bridges, leading to the observed 3D structure. The use of the non-chelating capping ligand pyrazole produced the covalent-bonded 1D linear compound 2 with hydrogen bonds. A severe octahedral distortion of the Cu(II) center arises from a small bite angle (52.3(1)°) of two carboxylate oxygen atoms of tp, which are in turn hydrogen-bonded to the N–H groups of pyrazole ligands coordinated to Cu(II) atoms in neighboring chains. Magnetic data were fitted with the high-temperature series expansion for the Heisenberg chain spin Hamiltonian H = −J∑_iS_i · S_i + 1 together with consideration of the molecular field approximation (zJ′). Both compounds interestingly exhibit ferromagnetic interactions with g = 2.17, J = 4.08 cm⁻¹, zJ′ = −0.28 cm⁻¹ for 1 and g = 2.09, J = 1.47 cm⁻¹, zJ′ = −0.04 cm⁻¹ for 2. By taking into account structural parameters of distances between Cu atoms, it is reasonably assigned that the ferromagnetic couplings (J > 0) in these systems originate from the hydrogen bonds. The spin density of the d_x²-y² orbital on a Cu(II) atom in a chain is propagated and induced over the d_z² orbital of another Cu(II) atom in an adjacent chain. This orbital orthogonality gives rise to such interactions. The negative zJ′ term suggests that the tp bridges communicate only tiny antiferromagnetic interactions.     

A study on copper(II)-Schiff base-azide coordination complexes: Synthesis, X-ray structure and luminescence properties of [Cu(L)(N3)]X (L = Schiff bases; X = ClO4, PF6)

Two Schiff bases N,N′-(bis(pyridin-2-yl)benzylidene)propane-1,3-diamine (pbpd) and N,N′-(bis(pyridin-2-yl)formylidene)butane-1,4-diamine (pfbd) have been prepared and used to synthesize copper(II) complexes. Four complexes of the type [Cu(L)(N₃)]X (1–4) [L = pbpd; X = ClO₄ (1); L = pbpd; X = PF₆ (2); L = pfbd; X = ClO₄ (3); L = pfbd; X = PF₆ (4)] have been synthesized and characterized on the basis of microanalytical, spectroscopic, magnetic, electrochemical, luminescence and other physicochemical properties. Two representative complexes of the series, 2 and 3, have been characterized by single crystal X-ray diffraction measurements which reveal that in each complex the copper(II) ion assumes a distorted trigonal bipyramidal environment through coordination of the metal centre by two pyridine N atoms and two imine N atoms of the Schiff base with the fifth position occupied by a N atom of a terminal . They display intraligand ¹(π–π^*) fluorescence at room temperature and intraligand ³(π–π^*) phosphorescence in glassy solutions (MeOH at 77 K). A band (492 nm) observed for the complexes in their solid-state emission spectra is an excimeric emission arising due to an aromatic π–π interaction. Electrochemical electron transfer study reveals Cu^II–Cu^I reduction in methanolic solutions.     

ERAS modeling of the excess molar enthalpies of binary liquid mixtures of 1-pentanol and 1-hexanol with acetonitrile at atmospheric pressure and 288, 298, 313 and 323 K

This work reports experimental data on the excess molar enthalpy as a function of composition of acetonitrile + 1-pentanol and acetonitrile + 1-hexanol mixtures at 288.15, 298.15, 313.15 and 323.15 K under atmospheric pressure. The data show positive values over the whole composition range for both systems and for all temperatures studied, they also increase with temperature and with alkanol chain length. The experimental curves have a parabolic shape with maximum point around 0.5 mole fraction. The extended real associated solution (ERAS) model was applied to correlate the experimental data. The ERAS model adequately described the main features of the behavior of the mixtures.