A DSC study of benzoic acid: a suggested calibrant compound

It has been found that cobalt(II, III) oxide, Co₃O₄, lowers the thermal decomposition temperature of Na₂S₂O₈ and K₂S₂O₈ by about 25°C by catalysis, and it therefore acts as a P-type semiconductor at high temperature and atmospheric (air) pressure. Also, this oxide reacts at high temperature with sodium or potassium pyrosulfates to form thermally stable sodium cobalt disulfate, Na₂Co(SO₄)₂ and potassium cobalt trisulfate, K₂Co₂(SO₄)₃, respectively. Binary systems, consisting of a 1 : 3 mole ratio (oxide : persulfate), are established as representing the solid state stoichiometric reaction. X-Ray diffractometry is employed to identify intermediate and final reaction products in general. All calculations are based on data obtained from TG, DTG and DTA curves.     

Sublimation enthalpy of Ni(II) and Cu(II) diethyldithiocarbamate and diethylammonium diethyldithiocarbamate by the sublimation bulb technique

We have used a flow calorimeter and a flow densimeter for measurements leading to apparent molar heat capacities and apparent molar volumes of dilute aqueous solutions of NaIO₃, KMnO₄, and MnCl₂ at 25°C. These apparent molar quantities have been extrapolated to infinite dilution to obtain the corresponding standard state apparent and partial molar heat capacities and volumes. which have then been used for the calculation of conventional ionic heat capacities and volumes.     

Neutral Hexacoordinate Phosphorus: Substituted Carbodiimide Phosphoranes and Other Chelated Substituted 2-Pyridine Derivatives

Abstract

A series of neutral hexacoordinate λ⁶ phosphorus compounds of the general formula X_4-n(CF₃)_nPN(R)C(C1)N(R) (n = 0, 1, 2, 3; R = cyclohexyl, isopropyl) has been prepared. The parent compounds are obtained by “insertion” of carbodiimide into the P-C1 bond of λ⁵-chlorophosphorane. Substituted pyridines also react readily with λ⁵ chloro and fluoro phosphoranes to form 2-methylamino, thio and oxopyridine chelates of the form X₄P(Epy) (E = 0, NMe and S; X = F, Cl) in which the phosphorus achieves six coordination through acceptance of the pyridine nitrogen. Selected reactions and the fluxional behavior of the λ⁶ systems are discussed.     

Neutral Hexacoordinate Phosphorus(V) Compounds Containing Tridentate Dianionic Ligands Obtained from Salicylideneamines, 2,2′-Azodiphenol and a Thio(Diphenol)

Abstract

Neutral hexacoordinate phosphorus(V) compounds of a number of univalent bidentate ligands are known.^l,2 The silylated forms of tridentate, dianionic Schiff base ligands: N-(2-hydroxyphenyl)salicylideneamine H₂L^I, N-(4-tert-butyl-2-hydroxyphenyl)-salicylideneamine H₂L^II, N-(2-hydroxy-4-nitrophenyl)salicylidene-amine H₂L^III, and 2,2′-azodiphenol H₂L^IV gave, with halogeno- and (trifluoromethyl)halogenophosphoranes, neutral hexa-coordinate derivatives with bis-chelate structures. The ligands form bicyclic five- and six-membered chelate rings in a meridional conformation, with two P-O bonds and one N→P donor bond. Hexacoordinate structures were evidenced by high-field ³¹P NMR chemical shifts (-136 to -148 ppm), characteristic J _PF coupling patterns and was further substantiated by crystal structures of Cl₃L^II (A) and F₃PL^II (B).     

Oxidative-Rearrangement Reactions of σ3, λ3 Dialkyl(Silylamino)Phosphines with Chlorophosphines; Formation of a P–P Bond Via a New Road to Phosphinophosphoranimines

Abstract:

Chlorophosphines react with trivalent (silylamino)phosphines via a direct oxidative addition process with elimination of trimethyl silyl chloride to produce phosphino-phosphoranimines with concomitant formation of a P-P bond. Oxidation of the phosphine center with sulfur and an exchange transformation of the phosphine are discussed.     

An Investigation of 1:1 Adducts of Gallium Trihalides with Triarylphosphines by Solid‐State 69/71Ga and 31P NMR Spectroscopy

Several 1:1 adducts of gallium trihalides with triarylphosphines, X₃Ga(PR₃) (X=Cl, Br, and I; PR₃=triarylphosphine ligand), were investigated by using solid‐state ^69/71Ga and ³¹P NMR spectroscopy at different magnetic‐field strengths. The ^69/71Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the ⁷¹Ga quadrupolar coupling constants (C_Q(⁷¹Ga)) range from approximately 0.9 to 11.0 MHz . The spans of the gallium magnetic shielding tensors for these complexes, δ₁₁?δ₃₃, range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for In^III–phosphine complexes. This experimental trend, attributed to spin‐orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of C_Q(^69/71Ga) for some of the adducts were determined from the analysis of the ³¹P NMR spectra acquired with magic angle spinning (MAS). The ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga, ³¹P) values, as well as their signs, were also determined; values of ¹J(⁷¹Ga,³¹P) range from approximately 380 to 1590 Hz. Values of ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga,³¹P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi‐contact and spin‐dipolar Fermi‐contact mechanisms make important contributions to the ¹J(^69/71Ga,³¹P) tensors. The ³¹P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single‐crystal X‐ray diffraction data for Br₃Ga[P(p‐Anis)₃] and I₃Ga[P(p‐Anis)₃] were obtained.     

Core photoelectron spectroscopy of some acetylenic molecules

Carbon 1s binding energies have been measured for CH₃CCH, CH₃CCCH₃, CF₃CCH and CF₃CCCF₃ and compared to a verified value for acetylene. Assignments are based on the application of a CNDO potential model with relaxation corrections which is quite successful in predicting binding energy shifts and upon qualitative considerations. Substitution of CF₃ groups shifts the acetylenic C 1s binding energy from 291.2 (HCCH) to 292.2 in CF₃CCH and 292.7 eV in CF₃CCCF₃. The unequal substitutional shifts are probably due to a saturation of substituent effect expected in competitive situations. With reservations arising from uncertainties in assignment due to lack of resolution, it appears that acetylenic C 1s binding energies decrease [to 290.7 (av.) in CH₃CCH and to 290.1 eV in CH₃CCCH₃] upon replacement of H by CH₃ groups. Although the decrease in acetylenic binding energies agrees with the chemical notion that CH₃ groups are electron donating with respect to unsaturated portions of the molecule, theoretical calculations available in the literature indicate that actual electron withdrawal or donation does not occur in these differently substituted molecules. The shifts of apparent binding energy correlate reasonably well with a ground state potential model which accounts for the effect of the charge on the adjacent atoms as well as on the photoionized atom. Even better correlation is obtained if the atomic potentials are corrected for electronic redistribution (relaxation) effects which occur during the photoionization process, and it is suggested that relaxation effects make a significant contribution to shifts of apparent binding energies. Surprisingly ground state potential and relaxation corrected potential calculations with the CNDO method suggest a large difference in C 1s binding energies of the two acetylenic carbon atoms in CH₃CCH which is not verified experimentally nor mirrored by calculations on CF₃CCH. The CH₃ binding energies are 291.8 eV in CH₃CCH and 291.3 eV in CH₃CCCH₃, both higher than values assigned to CH₄ or C₂H₆.     

Influence of geometry on reductive elimination of hydrocarbyl-palladium-carbene complexes

The influence of spectator ligand bite angle and the twist angle of the carbene on the reductive elimination of N-heterocyclic carbenes (NHCs) from palladium bis-phosphine complexes has been investigated using density functional theory. The spectator bite angle was found to have a significant influence on both the activation energy (E(act)) and the enthalpy of reaction. Widening of the bite angle was found to lower E(act) and increase the enthalpy of reaction. In contrast, rotation of the carbene with respect to the PdL(2) plane was found to have little influence on E(act). At carbene twist angles approaching 0 degrees however, relief of the increased steric strain provides a considerable driving force for the decomposition reaction.