Molecular Structure of Gaseous Oxopivalate Co(II): Electronic States of Various Multiplicities.

Synchronous electron diffraction/mass spectrometry was used to study the composition and structure of molecular forms existing in a saturated vapor of cobalt(II) oxopivalate at T = 410 K. It was found that monomeric complexes Co4O(piv)6 dominate in the vapor. The complex geometry possesses the C3 symmetry with bond lengths Co-Oc = 1.975(5) Å and Co-O = 1.963(5) Å, as well as bond angles Oc-Co-O = 111.8(3)°, Co-Oc-Co = 110.4(6)°, O-Co-O = 107.1(3)° in the central OcCo4 fragment and four OcCoO3 fragments. The presence of an open 3d shell for each Co atom leads to the possibility of the existence of electronic states of the Co4O(piv)6 complex with Multiplicities 1, 3, 5, 7, 9, 11, and 13. For them, the CASSCF and XMCQDPT2 calculations predict similar energies, identical shapes of active orbitals, and geometric parameters, the difference between which is comparable with the error of determination by the electron diffraction experiment. QTAIM and NBO analysis show that the Co-Oc and Co-O bonds can be attributed to ionic (or coordination) bonds with a significant contribution of the covalent component. The high volatility and simple vapor composition make it possible to recommend cobalt (II) oxopivalate as precursors in the preparation of oxide films or coatings in the CVD technologies. The features of the electronic and geometric structure of the Co4O(piv)6 complex allows for the conclude that only a very small change in energy is required for the transition from antiferromagnetically to ferromagnetically coupled Co atoms.

Thermodynamics of heterogeneous equilibria in the In-In2 O3 system using Knudsen effusion mass spectrometry.

RATIONALE: The In-In2 O3 system is regarded as a potential low-temperature source of gaseous indium oxide (In2 O) when obtaining functional materials by physical vapor deposition techniques. To date the vaporization thermodynamics of the system have been investigated in few studies, the results of which are contradictory. METHODS: The study of the In-In2 O3 system was performed using Knudsen effusion mass spectrometry in the temperature range 930-1210 K, with a magnet mass spectrometer (MS-1301). Quartz effusion cells heated by a resistance furnace were employed. RESULTS: It was established that In(g) and In2 O(g) are the major vapor species over heterogeneous mixtures (In(l) + In2 O3 (s)) and the gaseous oxide In2 O is predominant. The partial pressures of the vapor species were determined and the quantitative vapor composition was calculated. Based on the experimental data, a p-x section of the In-In2 O3 system phase diagram at 1060 K was constructed. The standard enthalpies of reactions accompanying vaporization of the In and In2 O3 mixtures were evaluated using the second- and third-law methods. The standard enthalpy of formation of In2 O(g) was derived from the enthalpies of reactions obtained. CONCLUSIONS: The predominance of In2 O in the equilibrium vapor over heterogeneous mixtures (In(l) + In2 O3 (s)), along with its high partial pressure at relatively low temperatures, substantiate the In-In2 O3 system to be suitable for physical vapor deposition methods. The obtained results can be used for physical vapor deposition parameter adjustment and optimization. The standard enthalpy of formation of In2 O(g) obtained in an independent way in the present work is in good agreement with that from our previous In2 O3 (s) vaporization study.

Vaporization thermodynamics of In2 O3 by Knudsen effusion mass spectrometry. The standard enthalpy of formation of In2 O(g).

RATIONALE: In2 O3 is one of the most important semiconductor oxides in modern electronics. Vacuum deposition methods are often used for the preparation of In2 O3 -based nanomaterials. Thus, vaporization thermodynamics is of key importance for process control and optimization. Since the literature data on the vapor composition and partial pressure values for In2 O3 are contradictory, vaporization thermodynamics of In2 O3 needs to be clarified. METHODS: Vaporization behavior of In2 O3 was studied using the Knudsen effusion technique in the temperature range 1400-1610 K. Quartz effusion cells were employed. A magnet mass spectrometer with an ordinary focus and a sector-type analyzer was used. Heating of samples and molecular beam ionization were performed by electron impact. The operating ionizing electron energy was 75 eV. RESULTS: A specially designed experiment allowed us to determine the individual mass spectrum of the In2 O molecule and, thus, to interpret the mass spectrum of the vapor registered during In2 O3 vaporization. The composition of the equilibrium vapor was quantified and the partial pressures of the vapor species were determined. On the basis of the experimental data, the standard enthalpies of some gaseous and heterogeneous reactions taking place during In2 O3 vaporization and the standard enthalpy of formation of In2 O(g) were calculated. CONCLUSIONS: The presence of In species in the vapor over In2 O3 was confirmed and the vapor composition was quantified. Thermodynamic characteristics of In2 O3 vaporization were obtained and a value of the standard enthalpy of formation of In2 O(g) was recommended. These data can be used for further thermodynamic calculations and for evaluating parameters for the synthesis and exploitation of In2 O3 -containing materials.