Standard molar Gibbs free energy of formation of Pb5CrO8(s), Pb2CrO5(s), and PbCrO4(s)

Standard molar Gibbs free energy of formation of ternary oxides Pb₅CrO₈(s), Pb₂CrO₅(s), and PbCrO₄(s) were determined by measuring equilibrium oxygen partial pressures over relevant phase fields using manometry and solid oxide electrolyte based emf methods and are given by: ${\mathrm{\Delta }}_f{G}_m^{°}{\text{Pb}}_5{\text{CrO}}_8(s)\pm 0.55/(\text{kJ}·{\text{mol}}^{-1})=-1809.4+0.6845(T/\text{K})(837\le T/\text{K}\le 1008)\text{,}$${\mathrm{\Delta }}_f{G}_m^{°}{\text{Pb}}_2{\text{CrO}}_5(\text{s})\pm 0.30/(\text{kJ}·{\text{mol}}^{-1})=-1161.3+0.4059(T/\text{K})(859\le T/\text{K}\le 1021)\text{,}$${\mathrm{\Delta }}_{\text{f}}{G}_m^{°}{\text{PbCrO}}_4(\text{s})\pm 0.17/(\text{kJ}·{\text{mol}}^{-1})=-909.8+0.3111(T/\text{K})(863\le T/\text{K}\le 1093)\text{,}$     

2-Pyridyloximate clusters of cobalt and nickel

The use of 2-pyridyloximate(-1) ligands, (py)C(R)NO⁻ [R = H, Ph, 2-pyridyl (py)] in cobalt and nickel(II) chemistry has been investigated and led to four families of clusters. A representative member of each family, namely $[{\mathrm{Co}}^{\text{II}}{\mathrm{Co}}_2^{\text{III}}\{(\mathrm{py})\mathrm{C}(\mathrm{ph})\text{NO}{\}}_6]({\mathrm{PF}}_6{)}_2$ (1), $[{\mathrm{Co}}_2^{\text{II}}{\mathrm{Co}}_2^{\mathrm{III}}(\mathrm{OH}{)}_2({\mathrm{O}}_2\mathrm{CMe}{)}_2\{(\mathrm{py}{)}_2\mathrm{CNO}{\}}_4(\mathrm{MeOH}{)}_2]({\mathrm{ClO}}_4{)}_2$ (2), [Ni₉(OH)₄{(py)CHNO}₁₀(H₂O)₈]{N(CN)₂}₃(ClO₄) [3{N(CN)₂}₃(ClO₄)] and [Ni₄(O₂CMe)₄{(py)C(ph)NO}₄(MeOH)₂] (4) is briefly structurally and magnetically described.     

Electrochemical study on determination of diffusivity,activity and solubility of oxygen in liquid bismuth

Diffusivity of oxygen in liquid bismuth was measured by potentiostatic method and is given by$\lg (D_{\mathrm{O}}^{\mathrm{Bi}}/{\mathrm{cm}}^2·{\mathrm{s}}^{-1})(\pm 0.042)=-3.706-1377/(T{\mathrm{K}}^{-1})(804<T/\mathrm{K}<1090)\text{.}$Activityof oxygen in bismuth was determined by coulometric titrations and using the measured data standard free energy of dissolution of oxygen in liquid bismuth was derived for the reaction:$1/2{\mathrm{O}}_2(\mathrm{g})=[\mathrm{O}{]}_{\mathrm{Bi}}(\mathrm{at}\text{.}\%)$and is given by$\mathrm{\Delta }{G}_{\mathrm{O}(\mathrm{Bi})}^{\circ }/(\mathrm{J}·\mathrm{g}\text{-}\mathrm{atom}{\mathrm{O}}^{-1})(\pm 720)=-108784+20.356T{\mathrm{K}}^{-1}(753<T/\mathrm{K}<1020)\text{.}$Using the above data and Gibbs free energy of formation of Bi₂O₃ (s), solubility of oxygen in liquid bismuth was derived as a function of temperature and is given by the following expressions:$\begin{array}{cc}\hfill & \lg (S/\mathrm{at}\%\mathrm{O})(\pm 0.05)=-4476/T{\mathrm{K}}^{-1}+4.05(753<T/\mathrm{K}<988)\text{;}\hfill \\ \hfill & \lg (S/\mathrm{at}\text{.}\%\mathrm{O})(\pm 0.04)=-3786/T{\mathrm{K}}^{-1}+3.36(988<T/\mathrm{K}<1020)\text{.}\hfill \end{array}$The present data on solubility of oxygen in liquid bismuth is compared with the literature data.     

Thermodynamic properties of CaTiF5(s)

Calcium titanofluoride CaTiF₅(s) was prepared by solid-state reaction of CaF₂(s) with TiF₃(s) and characterized by X-ray diffraction method. The standard molar isobaric heat capacity $(C_{p\text{,m}}^{\circ })$ of CaTiF₅(s) was determined by a power compensated differential scanning calorimeter in the temperature from 230 K to 710 K. A solid-state galvanic cell with CaF₂ as electrolyte was used to determine the standard molar Gibbs energy of formation $({\mathrm{\Delta }}_{\text{f}}{G}_{\text{m}}^{\circ })$ of CaTiF₅ in the temperature range from 803 K to 1005 K. The galvanic cell can be depicted as:$(-)\text{Pt,}{\text{O}}_2(\text{g,}101.325\text{kPa})/\{\text{CaO(s)}+{\text{CaF}}_2(\text{s})\}//{\text{CaF}}_2//\{{\text{CaTiF}}_5(\text{s})+{\text{CaTiO}}_3(\text{s})\}/{\text{O}}_2(\text{g,}101.325\text{kPa})\text{,Pt}(+)$The second law analysis of present data were carried out to derive the standard entropy $S_{\text{m}}^{\circ }(298.15\text{K})$ and the enthalpy of formation ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{\circ }(298.15\text{K})$ and the values derived are 68.7 J · K⁻¹ · mol⁻¹ and −2848.4 kJ · mol⁻¹, respectively.     

Role of entropy in the stability of cobalt titanates

The standard molar Gibbs free energy of formation of Co₂TiO₄, CoTiO₃, and CoTi₂O₅ as a function of temperature over an extended range (900 to 1675) K was measured using solid-state electrochemical cells incorporating yttria-stabilized zirconia as the electrolyte, with CoO as reference electrode and appropriate working electrodes. For the formation of the three compounds from their component oxides CoO with rock-salt and TiO₂ with rutile structure, the Gibbs free energy changes are given by:$\begin{array}{cc}\hfill & {\mathrm{\Delta }}_{\text{f}}{G}_{(\text{ox})}^{°}({\text{Co}}_2{\text{TiO}}_4)\pm 104/(\text{J}·{\text{mol}}^{-1})=-18865-4.108(T/\text{K})\hfill \\ \hfill & {\mathrm{\Delta }}_{\text{f}}{G}_{(\text{ox})}^{°}({\text{CoTiO}}_3)\pm 56/(J·{\text{mol}}^{-1})=-19627+2.542(T/\text{K})\hfill \\ \hfill & {\mathrm{\Delta }}_{\text{f}}{G}_{(\text{ox})}^{°}({\text{CoTi}}_2{O}_5)\pm 52/(\text{J}·{\text{mol}}^{-1})=-6223-6.933(T/\text{K})\hfill \end{array}$Accurate values for enthalpy and entropy of formation were derived. The compounds Co₂TiO₄ with spinel structure and CoTi₂O₅ with pseudo-brookite structure were found to be entropy stabilized. The relatively high entropy of these compounds arises from the mixing of cations on specific crystallographic sites. The stoichiometry of CoTiO₃ was confirmed by inert gas fusion analysis for oxygen. Because of partial oxidation of cobalt in air, the composition corresponding to the compound Co₂TiO₄ falls inside a two-phase field containing the spinel solid solution Co₂TiO₄–Co₃O₄ and CoTiO₃. The spinel solid solution becomes progressively enriched in Co₃O₄ with decreasing temperature.