Alla V. Arapova

New type of coordination of phosphorus to carbene analogs. p(π)-Complex of 3a,6a-diaza-1,4-diphosphapentalene with germanium dichloride

Abstract3a,6a-Diaza-1,4-diphosphapentalene (1), as a neutral ligand, displays a new type of complexation, such that the lone pair at the phosphorus atom is not involved in the coordination; instead, the 10π-electron system provides two electrons for the coordination bond formation between the phosphorus atom and the metal. The p(π)-type complex–a molecular adduct of 1 with germanium dichloride — was synthesized and completely characterized. This complex is a coordination polymer with short intermolecular Ge—Ge, Ge—P, P—P, P—Cl, and Ge—C contacts.

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, Cpo (T), Ho(T)-Ho(0), So(T), and Go(T)-Ho(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.

The thermodynamic properties of (2,2′-dipyridyl)bis(4-chloro-3,6-di-tert-butyl-o-benzosemiquinone)cobalt

The heat capacity of paramagnetic (2,2′-dipyridyl)bis(4-chloro-3,6-di-tert-butyl-o-benzosemi-quinone)cobalt was studied over the temperature range 8–390 K by precision adiabatic vacuum and high-accuracy dynamic calorimetry. The physical transformation observed at 309–388 K was caused by the transition of the semiquinone-catecholate to bis-semiquinone form of the complex. Above 388 K, thermal destruction was superimposed on the physical transition. The experimental data were used to calculate the standard thermodynamic functions Cpo (T), Ho(T)−Ho(0), So(T), and Go(T)−Ho(0) at temperatures from T → 0 to 300 K. An analysis of the low-temperature heat capacity of the complex in terms of the Debye theory of the heat capacity of solids and its multifractal generalization led us to conclude that the complex had a predominantly chain structure.

Thermodynamic properties of o-semiquinone complex of Co with Di-(2-pyridyl)amine in the temperature range T → 0 to 370 K

The heat capacity of di-(2-pyridyl)amine-bis-(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt in the temperature range from 7 to 370 K was investigated by means of precise adiabatic vacuum calorimetry. It was established that the phase transition associated with the redox-isomeric transformation of the semiquinone-catecholate form of the complex into the bis-semiquinone form is observed above 260 K; this transition is not completed due to thermal destruction that begins at 367 K. The magnetic moment values in the temperature range from 5 to 350 K and the EPR spectra in the temperature range from 130 to 290 K, which confirm the nature of the phase transition, were obtained for the investigated complex. The standard thermodynamic functions CppO(T), H○(T)-H○(0), S○(T), and G○(T)-H○(0), were calculated from the data on heat capacity in the temperature range from T → 0 to 260 K. Analysis of the low temperature heat capacity on the basis of Debye’s theory of the heat capacity of solids and the multifractional model testifies to the chain-layered structural topology of the investigated complex.

Studying the volatility of pyrazolone complexes of rare-earth elements by means of Knudsen effusion

The temperature dependences of the pressure of saturated vapor of pyrazolone complexes of rare-earth elements Ln(PMIP)3 (where Ln = Y, Ho, Er, Tm, Lu; PMIP = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone) are studied via Knudsen effusion, and the enthalpy of their sublimation is determined. Mass spectra and differential scanning calorimetry data are obtained.

Reaction of benzylidenetriphenylphosphorane with 1,4-dichloro-3а,6а-diaza-1,4-diphosphapentalene

The transylidation between 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalene and benzylidenetriphenylphosphorane (Ph3P=CHPh) results in either mono- or disubstitution of chlorine atoms by the Ph3P=C(Ph) group depending on the reactant molar ratio. In the crystal, the monosubstituted product has the planar diazadiphosphapentalene ring and the P—Cl ionic bond. The 31P NMR spectra of this compound exhibit a strong solvent-dependent behavior, which indicates that it exists both in the ionic form (in CH2Cl2, MeCN) and the molecular form (in THF). In the disubstituted product, the diazadiphosphapentalene skeleton is non-planar and is bent along the N—N bond.

Valence–Tautomeric Interconversion in a Bis(dioxolene)cobalt Complex with Iminopyridine Functionalized by a TEMPO Moiety. Phase Transition Coupled with Monocrystal Destruction

Iminopyridine modified by TEMPO nitroxide was utilized for the synthesis of an octahedral bis(o-semiquinonato)cobalt complex. Variable-temperature magnetic susceptibility measurements detect a valence tautomeric transformation in the temperature range 200-300 K. A reproducible hysteresis loop of about 40 K width is observed on the magnetic moment temperature dependence in the transition region. Differential scanning calorimetry measurements confirm different temperatures of phase transitions accompanying a valence-tautomeric transformation upon heating and cooling. Attempts to study the structural changes associated with the valence-tautomeric transformation by single-crystal X-ray diffraction failed because of the crystal destruction taking place upon cooling from 220 K. The powder X-ray diffraction pattern indicated an essential change of the unit cell upon cooling from 240 K.

Formation of microchannels in thermocured silicone rubber using whiskers of p-aminobenzoic acid

A new method of microchannel formation in silicone rubber cured by heat in the presence of a platinum catalyst was developed using whiskers of p-aminobenzoic acid. Four types of whiskers with lateral dimensions of 10–20, 50–70, 200–300, and 500–600 µm and lengths of 2–3, 5–10, 10–20, and 20–30 mm, respectively, were grown from hot aqueous solutions. A new method for the manufacture of elastic siloxane rubber samples penetrated by open channels with the size corresponding to the size of whiskers is presented. The materials were studied by optical and atomic force microscopy, powder X-ray diffraction, differential scanning calorimetry, gas chromatography—mass spectrometry, and porosimetry.

Thermodynamic properties of o-semiquinonato complexes of cobalt, nickel, and copper in the range T → 0 to 350 K

The heat capacity of bis(3,6-di-tert-butyl-o-benzosemiquinonato)copper, (triethylarsine)bis(3,6-di-tert-butyl-o-benzosemiquinonato)nickel, and (triphenylphosphine)bis(3,6-di-tert-butyl-o-benzosemiquinonato)cobalt was determined in the range of 0 to 350 K by precision adiabatic vacuum calorimetry. The temperature dependences of magnetic moments were studied for the last two complexes. The G-transition in nickel complex, which is presumably caused by a loosening of the molecular degrees of freedom, was determined. The standard thermodynamic functions of complexes were calculated according to the obtained data: Cp○, H○(T)-H○(0), S○(T), and G○(T)-H○(0) for the range of T → 0 to 350 K. It was concluded that our analysis of low-temperature heat capacity based on the Debye theory of the heat capacity of solids and the multifractal model confirms the chain-layer topologies of the structures of the investigated complexes.