I. V. Kazakov

Vaporization and thermal decomposition of B,B′,B″-tribromoborazine

Vapor pressure as a function of temperature above solid and liquid (BrBNH)3 and the thermodynamic parameters of (BrBNH)3 sublimation and vaporization have been determined using static tensimetry with membrane null-manometer. The thermal decomposition of tribromoborazine has been studied in the saturated and unsaturated vapor regions. Irreversible decomposition occurred at noticeable rates at temperatures higher than 343 K and was accompanied by HBr evolution. In the unsaturated vapor region, thermal decomposition has far lower rates than in the saturated vapor region because of diffusion limitations. The activation energy of condensed-phase thermal decomposition of B,B′,B″-tribromoborazine is 65 ± 3 kJ/mol, and this value proves that tribromoborazine decomposition at low temperatures is not accompanied by opening of the boron-nitrogen cycle.

Structures and stability of molecular InBr3Py(x) (x = 1-3) complexes: unexpected solid state stabilization of dimeric In2Br6Py4 as compared to valence-isoelectronic group 15 and 17 halogen bridging dimers.

Molecular structures of series of InBr3Py(x) complexes (x = 1-3) in the solid state have been determined by single crystal structure analysis. For x = 2, an unexpected dimeric In2Br6Py4 structure, which features a nearly planar In2Br6 unit, has been established. This structure completes the series of known valence-isoelectronic dimeric molecules of group 17 (I2Cl6) and group 15 elements (As2Cl6·2PMe3). Theoretical studies at the B3LYP/def2-TZVP level of theory reveal that all gaseous M2X6Py4 dimers (M = Al, Ga, In, Tl; X = Cl, Br) are energetically unstable with respect to dissociation into MX3Py2 monomers. This finding is in stark contrast to the valence-isoelectronic group 17 and 15 analogs, which are predicted to be energetically stable with respect to dissociation. Thus, additional interactions in the solid state play a crucial role in stabilization of the experimentally observed dimeric In2Br6Py4. Thermal stability and volatility of InBr3Py(x) complexes have been studied by tensimetry and mass spectrometry methods. Mass spectrometry data indicate that, in contrast to the lighter group 13 element halides, species with two In atoms, such as In2Br6Py2, are present in the gas phase. Thermodynamic characteristics for the heterogeneous dissociation processes of InBr3Py(x) (x = 2, 3) complexes with Py evolution have been determined.

An automatic digital tensimeter with a membrane zero-manometer

An automatic setup for measuring vapor pressure and its temperature dependence in a closed volume is designed. The setup can be used to investigate chemical equilibria in both condensed phase–vapor and homogeneous gas-phase systems, along with the kinetics of irreversible processes with the evolution of gas substances. The digital tensimeter offers an improved version of static tensimetry with a membrane zeromanometer. In contrast to conventional optical methods for recording the position of a zero-manometer, an approach based on the Hall effect is used. Automation of the experiment and data acquisition greatly increases the number of experimental points and reduces the errors related to measurements. With processes of irreversible hydrogen release, the method detects hydrogen with a precision of 2 × 10−6 g, remarkably exceeding the possibilities of thermogravimetric methods.

Complex amidoboranes M2[M1(NH2BH3)4] (M1 = Al, Ga; M2 = Li, Na, K, Rb, Cs)

Structural, spectral, and thermodynamic characteristics of complex amidoboranes M2[M1(NH2BH3)4] (M1 = Al, Ga; M2 = Li, Na, K, Rb, Cs) were calculated by the B3LYP/def2-SVPD quantum-chemical method. The procedure for the synthesis of these compounds by reactions of alkali metal amidoboranes with aluminum and gallium chlorides was suggested and experimentally tested. Reaction products were characterized by the NMR and IR spectroscopy and X-ray phase analysis.

Crystal structures and thermal behavior of complexes of group 13 metal halides with pyridine-type ligands

Complexes of group 13 metal halides with pyridine-type ligands (pyridine, pyrazine, and 4, 4´-bipyridine) have molecular, polymeric, or ionic structures containing metal atoms with a coordination number of 4, 5, or 6 depending on the component ratio, the acceptor ability of the halide, the donor ability and the coordination mode of the ligand. The strongest donor-acceptor bond is formed in the 1 : 1 molecular complexes, and their transition to the gas phase is energetically most favorable. The acceptor ability of Lewis acids in the complexes decreases in the series AlCl3 > AlBr3 > GaCl3 > GaBr3 > GaI3. The stability of the complexes with respect to homogeneous dissociation correlates with the donor proton affinity. Group 13 metal trihalides act as catalysts for the pyrolysis of ligands.

Experimental and theoretical study on the reactivity of phosphorus-containing cubane type clusters [RMPR’]4 (M = Ga, In) toward pyridine

Reactions of cubane type clusters [EtGaPSi(Me)2Thex]4 [Thex = CMe2(Pr-i)] and {EtInP[Si(i-Bu)3]}4 with pyridine were studied. The temperature dependences of vapor pressure over individual solid compounds were measured using a membrane pressure gauge. At a temperature above 200°C the examined clusters undergo irreversible thermal decomposition due to instability of organic substituents. According to the experimental data, the cubane clusters do not react with gaseous pyridine below their decomposition temperature. Thermodynamic parameters for the isomerization of model clusters [HMPH]4 (M = Ga, In) and their gas-phase reactions with pyridine were calculated by quantum-chemical methods. The addition of pyridine is thermodynamically allowed only at low temperatures.

Heat Effects of the Thermal Decomposition of Amidoboranes of Potassium, Calcium, and Strontium

Thermal effects of the decomposition of potassium, calcium, and strontium amidoboranes at 354, 421, and 483 K are determined via drop calorimetry. The processes of decomposition are weakly exothermic and accompanied by the evolution of hydrogen. Upon the decomposition of calcium amidoborane at 421 K, a prolonged exothermic process is first observed; it is then followed by an endothermic effect, due possibly to the slow structural rearrangement of the product of decomposition. The solid products of decomposition are characterized by solid-state 11В NMR, FTIR spectroscopy, and mass spectrometry.

Synthesis and Characterization of Barium Amidoborane

Barium amidoborane was synthesized for the first time by the reaction of metal barium with ammonia borane. The compound was characterized by the methods of the solid-phase 11B NMR and IR spectroscopy and elemental analysis. It was shown by simultaneous thermal analysis that hydrogen is the only volatile product of barium amidoborane decomposition in the temperature range 50–240°C.

Donor–acceptor complexes of inorganic analogs of benzene

GRAPHICAL ABSTRACT ABSTRACT Results of experimental and theoretical studies of inorganic benzene analogs: borazine, substituted borazines, polyborazines, alumazene, and their donor–acceptor complexes are summarized. Structural and energetic aspects of complex formation and thermal stability of heterocycles and their complexes are discussed. A mechanism for the gas-phase acetonitrile polymerization in the presence of alumazene is proposed on the basis of computational studies. It is experimentally shown that solution of B,B′,B″-tribromborazine in deuterobenzene undergoes fast (within minutes) H/D exchange in the presence of Lewis acid AlBr3. The proposed electrophilic substitution mechanism for the exchange is supported by quantum-chemical computations. In contrast, in the presence of AlBr3, unsubstituted borazine in deuterobenzene polymerizes with hydrogen evolution without H/D exchange. The absence of the H/D exchange may be explained by larger stability of the borazonium ion B3N3H7+ which prevents operation of the catalytic cycle. Quantum-chemical computations at B3LYP/TZVP level of theory indicate that upon complexation with AlCl3 both endothermicity and activation energies of hydrogenation processes of borazine and polyborazines are significantly reduced. The use of Lewis acids as catalysts in the processes of regeneration of spent hydrogen fuel is recommended.

Diminished electron density in the Vaska-type rhodium(I) complex trans-[Rh(NCBH3)(CO)(PPh3)2].

Vaska-type complexes, i.e. trans-[RhX(CO)(PPh3)2] (X is a halogen or pseudohalogen), undergo a range of reactions and exhibit considerable catalytic activity. The electron density on the Rh(I) atom in these complexes plays an important role in their reactivity. Many cyanotrihydridoborate (BH3CN(-)) complexes of Group 6-8 transition metals have been synthesized and structurally characterized, an exception being the rhodium(I) complex. Carbonyl(cyanotrihydridoborato-κN)bis(triphenylphosphine-κP)rhodium(I), [Rh(NCBH3)(CO)(C18H15P)2], was prepared by the metathesis reaction of sodium cyanotrihydridoborate with trans-[RhCl(CO)(PPh3)2], and was characterized by single-crystal X-ray diffraction analysis and IR, (1)H, (13)C and (11)B NMR spectroscopy. The X-ray diffraction data indicate that the cyanotrihydridoborate ligand coordinates to the Rh(I) atom through the N atom in a trans position with respect to the carbonyl ligand; this was also confirmed by the IR and NMR data. The carbonyl stretching frequency ν(CO) and the carbonyl carbon (1)JC-Rh and (1)JC-P coupling constants of the Cipso atoms of the triphenylphosphine groups reflect the diminished electron density on the central Rh(I) atom compared to the parent trans-[RhCl(CO)(PPh3)2] complex.