NMR study of 1-aryl-1,2-dicarba-closo-dodecaboranes: intramolecular C-H?O hydrogen bonding in solution

Dicarba-closo-dodecaborane(12) (carborane) has recently received much attention as a building block for supramolecular assemblies and bioactive compounds. Among carborane isomers, 1,2-dicarba-closo-dodecaborane(12) (o-carborane) has unique chemical properties, including the ability of the o-carborane C-H hydrogens to form hydrogen bonds. To evaluate intramolecular hydrogen bond formation between the o-carborane C-H hydrogen and various hydrogen bond acceptors in solution, we have designed and synthesized 1-aryl-o-carboranes 2. Intramolecular hydrogen bonding ability was evaluated by means of ¹H NMR measurement of the o-carborane C-H hydrogen signal of 2. The 1-(2-methoxyphenyl)-o-carborane derivative 2m appeared to form an intramolecular hydrogen bond between o-carborane C-H hydrogen and the oxygen atom acting as a hydrogen bonding acceptor. In this study, we present evidence for hydrogen bond formation in solution between the o-carborane C-H and hydrogen bond acceptors positioned with appropriate geometry.     

Thermodynamics of undecanolactone,tridecanolactone, and pentadecanolactone from 0 to 340 K

The heat capacities C_p^o of undercanolactone, tridecanolactone, and pentadecanolactone have been measured between 10 and 370 K in a vacuum adiabatic calorimetric cryostat within about 0.2 per cent. The temperatures and enthalpies of physical transitions have been also estimated. The enthalpies of combustion of the compounds have been measured in an isothermal calorimeter with an accuracy of 0.05 per cent. From the results the functions {H (T) ? H (0)}, S^o(T), and {G^o(T) ? H^o(0)} have been calculated over the range 0 to 340 K, and the values of ΔH_f^o, ΔG_f^o and ΔS_f^o have been evaluated at T = 298.15 K.     

EPR study of mono-o-iminobenzosemiquinonato nickel(II) complexes with Ni-C σ-bond

New square-planar (Ph₃P)Ni^II(o-Tol)(ISQ-Prⁱ) (1), (Ph₃P)Ni^II(o-Tol)(ISQ-Me) (2), (Ph₃P)Ni^II(o-Tol)(ISQ-Bu^t) (3) nickel complexes (where ISQ-Prⁱ = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate, ISQ-Me = 4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate, ISQ-Bu^t = 4,6-di-tert-butyl-N-(2,5-di-tert-butylphenyl)-o-iminobenzosemiquinonate, o-Tol = o-tolyl ligand) have been synthesized. Complexes contain σ-bound o-tolyl and neutral donor ligand Ph₃P. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands lead to the tetrahedral distortion of square-planar configurations of complexes as it was established using EPR spectroscopy.     

The enthalpies of solution of DL-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (298.15 K) of DL-α-alanine in water-organic solvent mixtures were measured at organic component concentrations x ₂ = 0–0.4 mole fractions. The organic solvents used were acetonitrile (ACN), formamide (FA), N,N-dimethylformamide (DMFA), and N,N-dimethylsulfoxide (DMSO). The standard enthalpies of solution Δ_sol H ^o, solvation Δ_solv H ^o, and transfer (Δ_tr H ^o) of DL-α-alanine from water to mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics was considered. The solution of DL-α-alanine in the mixtures studied was endothermic over the whole range of organic component concentrations. The Δ_sol H ^o, Δ_tr H ^o, and Δ_solv H ^o values as functions of x ₂ can pass extrema (DMSO and DMFA), be almost independent of mixed solvent composition (FA), or be exothermic and monotonic functions (ACN). The enthalpy coefficients of pair interactions (h _xy ) between DL-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft equation was used to correlate the h _xy values with the properties of organic solvents.     

Highly electrochemiluminescent Ru(II) complexes containing 1,3-dihydro-1,1,3,3-tetramethyl-7,8-diazacyclopenta[1]phenanthren-2-one ligand

A series of new ruthenium(II) complexes containing 1,3-dihydro-1,1,3,3-tetramethyl-7,8-diazacyclopenta[1]phenanthren-2-one (DTDP) ligand, such as [Ru(DTDP)_n(L)_3−n]²⁺ (L = 2,2′-bipyridyl (bpy), 4,4′-dimethyl-2,2′-bipyridyl (dmbpy), o-phenanthroline (o-phen), 5-chloro-o-phenanthroline (o-phen-Cl), 2,2′-bipyridine-4,4′-dicarboxaldehyde (bpy-(CHO)₂), n = 1, 2, 3) were synthesized and examined as ECL materials. All the complexes were characterized in terms of electrochemical redox potential and relative ECL intensity, and were compared to the well-known tris(o-phenanthroline) ruthenium(II) complex. Most of the synthesized Ru(II) complexes containing the DTDP ligand exhibited more intense ECL emissions than [Ru(o-phen)₃]²⁺. In particular, the ECL intensities of [Ru(DTDP)(o-phen)₂]²⁺ and [Ru(DTDP)(bpy-(CHO)₂)₂]²⁺ were observed to be as high as 9-fold and 20-fold greater, respectively, than the ECL intensity of [Ru(o-phen)₃]²⁺.     

Ion-pair effects on the electroreduction and electrochromic properties of ortho-chloranil in dipolar aprotic solvents

The use of ortho-chloranil (o-CA) as an electrochromic material requires three conditions to operate properly: (1) the reversibility of the electronic transfer of the reaction

; (2) the formation of a visible-light absorbing charge-transfer complex between o-Ca⁻ and the counterion M⁺, and (3) the use of an insoluble salt o-CA⁻M⁺ as a film adherent to the electrode surface. The behavior of the redox o-CA/o-CA⁻ couple has been investigated in different solvents and in the presence of several alkaline and alkaline earth cations (M^z+). The reversibility of the electron transfer and the formation of an adhesive salt layer on the electrode are strongly related to the counter ion M^z+. The ion-pair formation depends on the solvent and particularly on its weak electron donor character. The best electrochromic properties of o-CA were obtained in 0.1 M NaClO₄ acetonitrile solutions.     

Thermodynamic properties of molybdenum pentafluoride vapor

There are calculated for 298 K and higher temperatures the standard entropies of the liquid and the important gas species (monomer, dimer, and trimer) of MoF₅, and their differences in enthalpy and Gibbs energy. Besides estimated mean heat capacities, the input data are: the vapor pressure at one temperature and the saturated-vapor density at two temperatures (based on measurements in this laboratory); the standard entropies of the three gas species (estimated from published spectroscopic data on the crystal and monomer); and an ion-abundance proportion (from a published mass-spectral study). This ion proportion is corrected for fragmentation after demonstrating that changes in the ion proportions for a similar fluoride, RhF₅, can be explained by assuming that the rates of fragmentation of the dimer and trimer are equal. For those input data considered most uncertain (the vapor pressure, the entropies of dimer and trimer, and the ratios of mass-spectral ionization efficiencies) several sets of values covering their respective estimated ranges of uncertainty are used alternatively in the calculations. Results at 298.15 K—expressed in the form “preferred value (probable range due to uncertainty)”, with H^o and G^o relative to the liquid, and S^o—are as follows: liquid, S^o = 46 (44.5 to 49) cal_th K^?1 mol^?1; monomer, H^o = 19 (17 to 22) kcal_th mol^?1, G^o = 8.5 (7.5 to 11.5) kcal_th mol^?1, S^o = 80.6 cal_thK^?1; dimer, H^o = 15.7 (15 to 16) kcal_th mol^?1, G^o = 6.48 (6.45 to 6.51) kcal_th mol^?1, S^o = 123 (121 to 127) cal_th K^?1 mol^?1; trimer, H^o = 17.7 (16 to 21) kcal_th mol^?1, G^o = 8.4 (8.1 to 8.7) kcal_th mol^?1, S^o = 169 (161 to 185) cal_th K^?1 mol^?1. The calculated mole fractions of monomer, dimer, and trimer in the saturated vapor at 298.15 K average 0.027, 0.94, and 0.035, respectively.     

Thermodynamic properties of second generation poly(phenylene-pyridyl) dendrimer

The temperature dependence of heat capacity C _p ^o = f (T) of second generation hard poly(phenylene-pyridyl) dendrimer (G2-24Py) was measured by a adiabatic vacuum calorimeter over the temperature range 6–320 K for the first time. The experimental results were used to calculate the standard thermodynamic functions: heat capacity C _p ^o (T), enthalpy H ^o(T)–H ^o(0), entropy S ^o(T)–S ^o(0) and Gibbs function G ^o(T)–H ^o(0) over the range from T → 0 K to 320 K. The standard entropy of formation at T = 298.15 K of G2-24Py was calculated. The low-temperature heat capacity was analyzed based on Debye’s heat capacity theory of solids. Fractal treatment of the heat capacity was performed and the values of the temperature characteristics and fractal dimension D were determined. Some conclusions regarding structure topology are given.     

Reaction of vanadocene and vanadocene dichloride with ortho-iodobenzoic acid

At the interaction of bis (η⁵-cyclopentadienyl)vanadium with iodobenzoic acid or trimethylsilyl o-iodobenzoate in toluene depending on the ratio of the initial reagents bis(η⁵-cyclopentadienyl)vanadium(o-iodobenzoate) or η⁵-cyclopentadienylvanadium-bis-o-iodobenzoate were obtained in high yields. The latter was also formed in the reaction of bis(η⁵-cyclopentadiene)vanadium dihloride with trimethylsilyl o-iodobenzoate.     

Optical spectroscopic studies of the polymerization of (SN)on radicals to (SN)x in thin films

Optical absorption measurements between 300 and 50000 cm^?1 in the 12 to 300 K temperature range, on thin films of (SN)^o_n radicals deposited from (SN)_x vapors, are presented. The spectrum of a thin film deposited at 12 K is interpreted as arising from the SN vibrational modes and electronic transitions of the ring S₄N₄ molecule, the linear (SN)^o_x radical and an (SN)^o_n radical longer chain length. The temperature induced evolution of the optical spectrum and the probable nature of the polymerized blue—black films, shown by preliminary X-ray data to be non-crystalline, are discussed.     

Influence des effets de substituants sur la protonation de la pyridine

Standard thermodynamic values of proton ionisation of 3 substituted (Cl?, Br?, I?, C₂H₅? and CH₂CN?) pyridine derivatives are determined at 25°C, in an aqueous medium of ionic strength 0.5 M KNO₃.Free energies are deduced from equilibrium constants log K potentiometrically calculated. Enthalpies are obtained from calorimetric measurements.ΔG^o, ΔH^o and ΔS^o values are discussed in the context of the results of our earlier studies on this subject.The Hammett plot corresponding to the thirteen systems examined gives the proton ionisation constant of a substituted pyridine from the equation log K = 5,48 – 5,94Σσ.Besides, a linear relationship is found between ΔG^o and ΔH^o, which confirms the observation made previously in other series of pyridine derivatives.     

Influence of the composition of aqueous dimethylsulfoxide solvent on thermodynamics of complexing between 18-crown-6-ether and D,L-alanine

Standard thermodynamic parameters (logK ^o, ??_r H ^o, T??_r S ^o) of complexing 18-crown-6 ether (18C6) with D,L-alanine (Ala) in mixed water-dimethysulfoxide (H₂O-DMSO) solvents are calculated on the basis of calorimetric titration results. A rise in the DMSO concentration in mixed solvent is found to increase stability and increase the exothermicity of the formation of [Ala-18C6] molecular complex. Changes in the reaction energetic are shown to be determined by changes in the solvation state of 18C6 that is the characteristic of the reactions of molecular complex formation between 18C6 and D,L-alanine or glycine in water-organic solvents.     

Cesium chromate,Cs2CrO4: heat capacity and thermodynamic properties from 5 to 350 K

The heat capacity of a sample of Cs₂CrO₄ was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure C_p^o(298.15 K), the entropy S^o(298.15 K), the enthalpy {H^o(298.15 K) - H^o(0)} and the function $\text{? {G}{}^{\mathrm{o}}\text{(298.15}\text{K}\text{) - H}{}^{\mathrm{o}}\text{(0)}}\text{298.15}\text{K}$ were found to be (146.06 ± 0.15) J K^?1 mol^?1, (228.59 ± 0.23) J K^?1 mol^?1, (30161 ± 30) J mol^?1, and (127.43 ± 0.13) J K^?1 mol^?1, respectively. The heat capacity C_p^o(298.15 K) and entropy S^o(298.15 K) and entropy S^o(298.15 K) of Rb₂CrO₄ are estimated to be (146.0 ± 1.0) J K^?1 mol^?1 and (217.6 ± 3.0) J K^?1 mol^?1, respectively.     

Synthesis, characterisation and solid state structures of α-diimine cobalt(II) complexes: Ethylene polymerisation tests

A series of cobalt(II) compounds of the type [CoX₂(α-diimine)] were synthesised by direct reaction of anhydrous CoCl₂ or CoI₂ and the corresponding α-diimine ligand, in CH₂Cl₂: [CoI₂(o,o′,p-Me₃C₆H₂-DAB)] (1), [CoI₂(o,o′-ⁱPr₂C₆H₃-DAB)] (2), (where Ar-DAB = 1,4-bis(aryl)-2,3-dimethyl-1,4-diaza-1,3-butadiene), and [CoCl₂(o,o′,p-Me₃C₆H₂-BIAN)] (3), [CoCl₂(o,o′-ⁱPr₂C₆H₃-BIAN)] (4), and [CoI₂(o,o′-ⁱPr₂C₆H₃-BIAN)] (5) (where Ar-BIAN = bis(aryl)acenaphthenequinonediimine). All compounds were characterised by elemental analyses, IR, mass spectrometry, and X-ray diffraction whenever possible. The crystal structures of compounds 2-4 showed, in all cases, distorted tetrahedral geometries about the Co, built by two halogen atoms and two nitrogen atoms of the α-diimine ligand. Compounds 3 and 4, as well as [CoCl₂(o,o′,p-Me₃C₆H₂-DAB)] (1a), and [CoCl₂(o,o′-ⁱPr₂C₆H₃-DAB)] (2a), were activated by methylaluminoxane (MAO) and tested as catalysts for ethylene polymerisation, showing low catalytic activities. Selected polyethylene (PE) samples were characterised by ¹H and ¹³C NMR and FT-IR spectroscopies, and by differential scanning calorimetry (DSC), revealing branching microstructures (2.5-5.5%).     

Synthesis and spectroscopy of cis-configured mononuclear palladium(II) and platinum(II) complexes of chalcogeno o-carboranes and structures of [Pt(SCboPh)2(dppm)], [Pt(SeCboPh)2(dppm)], [Pt(SCboS)(PMe2Ph)2] and [Pt(SCboS)(PMePh2)2]

The reactions of [MCl₂(P^∩P)] and [MCl₂(PR₃)₂)] with 1-mercapto-2-phenyl-o-carborane/NaSeCb^oPh and 1,2-dimercapto-o-carborane yield mononuclear complexes of composition, [M(SCb^oPh)₂(P^∩P)], [M(SeCb^oPh)₂(P^∩P)] (M = Pd or Pt; P^∩P = dppm (bis(diphenylphosphino)methane), dppe (1,2-bis(diphenylphosphino)ethane) or dppp (1,3-bis(diphenylphosphino)propane)) and [M(SCb^oS)(PR₃)₂] (2PR₃ = dppm, dppe, 2PEt₃, 2PMe₂Ph, 2PMePh₂ or 2PPh₃). These complexes have been characterized by elemental analysis and NMR (¹H, ³¹P, ⁷⁷Se and ¹⁹⁵Pt) spectroscopy. The ¹J(Pt–P) values and ¹⁹⁵Pt NMR chemical shifts are influenced by the nature of phosphine as well as thiolate ligand. Molecular structures of [Pt(SCb^oPh)₂(dppm)], [Pt(SeCb^oPh)₂(dppm)], [Pt(SCb^oS)(PMe₂Ph)₂] and [Pt(SCb^oS)(PMePh₂)₂] have been established by single crystal X-ray structural analyses. The platinum atom in all these complexes acquires a distorted square planar configuration defined by two cis-bound phosphine ligands and two chalcogenolate groups. The carborane rings are mutually anti in [Pt(SCb^oPh)₂(dppm)] and [Pt(SeCb^oPh)₂(dppm)].     

Heat of immersion of iron(III) oxides in water at 25°C

The heat of immersion in water was measured at 25°C for three iron(III) oxides using a twin-type microcalorimeter. One of the samples was commercial α-Fe₂O₃ (sample C) and the other two (samples M and F) were prepared by calcining magnetite and iron(III) hydroxide in air at various temperatures, T_p, from 300 to 700°C. The samples were evacuated at outgassing temperature, T_o, between room temperature and 500°C at a pressure of 1 × 10^?2?2.7 × 10^?2N m^?2 for 6 h. The heat of immersion, h_i(J m^?2), of samples C and M increased with an increase in T_o and showed the maximum h_i at T_o =400°C, while sample F did not show the maximum up to T_o =500°C. The systematic correlation was not observed between h_i and T_p of sample F. The heat of reproduction of the surface hydroxyl group on sample F was approximately estimated as 6.6 × 10⁴ J mole^?1 H₂O.     

Syntheses,interconversions and reactivity of heteropalladacycles made from aryl isocyanates and various phenanthroline Pd(II) precursors with small molecules

The synthesis and full characterisation of new families of palladacycles such as (o-phen)PdN(Ar)C(O)N(Ar)C(O) (2/2a–g), (o-phen)PdN(Ar)C(O)N(Ar)C(O)N(Ar) (3/3a–c) and (o-phen)PdN(Ar)C(O)N(Ar) (4/4a–b) is reported (o-phen = 2,2’-phenanthroline), as well as the X-ray structure of the six-member palladacycle (o-phen)PdN(Tol)C(O)N(Tol)C(O)N(Tol) (3c·Et₂O). The reactivity of these palladacycles with small molecules like CO, PhNCO and H⁺ is also investigated. This contribution reveals a rich chemistry and provides a complete picture of the possible interconversions existing between members of different families. Analysed in the context of the catalytic carbonylation of nitroaromatics, this study also gives some clues to understanding the disappointing results reported for (Pd/o-phen/H⁺) catalytic systems when the transformation is attempted in the absence of alcoholic solvent. Notably, the formation of five-member palladacycles like 2 under these conditions could be at the origin of the catalyst deactivation.     

The Thermodynamic Properties of (α,α′-Dipyridyl)bis(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt over the Temperature Range from T → 0 to 320 K

The heat capacity of (g?,g?′-dipyridyl)bis(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt over the temperature range 7–320 K was studied by precision adiabatic vacuum calorimetry. A physical transformation observed at 134–222 K accompanied the reversible transition of the semiquinone-catecholate complex of low-spin cobalt into the bis-semiquinone adduct of high-spin cobalt. The enthalpy and entropy of this redox-isomeric transition were determined. The data obtained were used to calculate the standard thermodynamic functions of the complex, C _p ^o (T), H^o(T)-H^o(0), S^o(T), and G ^o (T)-H ^o (0), over the temperature range from T → 0 to 320 K. The low-temperature heat capacity of the complex was analyzed using the Debye theory of the heat capacity of solids and its multifractal generalization. The conclusion was drawn that the complex had a predominantly chain structure.     

Doubly-excited 1,3Po autoionization states of He between the N = 4 and N = 6 thresholds of He+ ions

The method of complex-coordinate rotation is used to investigate the doubly-excited ^1,3P^o autoionization states of He between the N = 4 and N = 6 thresholds of He⁺ ions. Resonance energies and total widths for 51 ¹P^o and 51 ³P^o states are reported in the present work. For the singletspin and triplet-spin states, lower-lying resonances for all nine Rydberg series converging on the He⁺ (N = 5) threshold are calculated. For resonances below the He⁺ (N = 6) threshold, we report lower-lying states for eleven and ten Rydberg series for the singlet-spin states and triplet-spin states, respectively. Our results are compared with the experimental observations and with other theoretical calculations when available.