Phase Equilibria in the Sc2S3-Ln2S3 (Ln = Dy,Er, or Tm) Systems

Phase diagrams for the Sc₂S₃-Ln₂S₃ (Ln = Dy, Er, or Tm) systems were designed in the range from 1000 K to melting temperatures. The Ln₃ScS₆ compounds that are formed in these systems crystallize in monoclinic space group P2₁/m, and melt congruently: for Dy₃ScS₆, a = 1.118 nm, b = 1.262 nm, c = 0.354 nm, β = 94.7°, 1800 K, H = 2600 MPa; for Er₃ScS₆, a = 1.113 nm, b = 1.258 nm, c = 0.353 nm, β = 94.5°, 1830 K, H = 2800 MPa; for Tm₃ScS₆, a = 1.112 nm, b = 1.229 nm, c = 0.352 nm, β = 94.3°, 1835 K, H = 2940 MPa. The LnScS₃ (Ln = Dy or Er) complex sulfides, with orthorhombic structures, space group Pnma, melt incongruently: for DyScS₃, a = 0.700 nm, b = 0.637 nm, c = 0.943 nm, 1810 K, H = 3800 MPa; and for ErScS₃, a = 0.697 nm, b = 0.633 nm, c = 0.942 nm, 1800 K, H = 3800 MPa. As the ionic radii rLn3+ and rSc3+ approach Ln Sc to each other in the row Dy-Er-Tm, the solubility in Sc₂S₃ increases, at 1670 K being equal to 13 mol % Dy₂S₃, 30 mol % Er₂S₃, and 40 mol % Tm₂S₃. LnScS₃ (Ln = Dy or Er) forms a two-sided homogeneity region, at 1670 K lying in ranges of 43–56 mol % Ln₂S₃. The eutectic temperatures and compositions are as follows: 1700 K and 66 mol % Dy₂S₃, 1730 K and 81 mol % Dy₂S₃, 1740 K and 65 mol % Er₂S₃, 1700 K and 83 mol % Er₂S₃, 1730 K and 70 mol % Tm₂S₃, and 1755 K and 84 mol % Tm₂S₃.     

Phase diagrams of the Ln2S3-EuS (Ln = La-Gd) systems

The phase diagrams of the Ln₂S₃-EuS (Ln = La-Gd) systems were studied. In these systems, continuous series of solid solutions form between γ-Ln₂S₃ and EuLn₂S₄ (Th₃P₄ structural type), and also eutectics between EuLa₂S₄ and a solid solution based on EuS form at the following coordinates: 71.5 mol % EuS, 2280 K; 66.5 mol % EuS, 2240 K; and 63.5 mol % EuS, 2100 K. The characteristics of the forming compounds are the following: EuLa₂S₄: a = 0.8759 nm, T _melt = 2420 K, and H = 2380 MPa; EuNd₂S₄: a = 0.8615 nm, T _melt = 2380 K, and H = 2530 MPa; and EuGd₂S₄: a = 0.8507 nm, T _melt = 2300 K, and H = 2670 MPa.     

Kinetics of hydroquinone chemisorption at polycrystalline platinum electrodes: The effect of surface roughness

The rate of hydroquinone (HQ) chemisorption from aqueous H₂SO₄ onto annealed (smooth) and platinized (rough) polycrystalline Pt has been studied. Previously, equilibrium adsorption measurements indicated that at smooth Pt surfaces, adsorption of HQ at c_HQ ⩽ 0.1 mM yielded flat (η⁶)-oriented species while adsorption at c_HQ ⩾ 1 mM resulted in edge (2,3-η²)-attached intermediates. Edge-attached species were not formed efficiently at roughened Pt surfaces. The present data show that the rate of η⁶-HQ chemisorption was significantly lower at roughened than at smooth surfaces. Analysis of the rate data gave the following enthalpies and entropies of activation at smooth (sm) and platinized (pt) surfaces: ΔH^≠_sm,0.1mM = 12.5 kJ/mol; ΔH^≠_sm,2mM = 8.3 kJ/mol; ΔS^≠_sm,0.1mM = −83 J/mol K; ΔS^≠_sm,2mM = −117 J/mol K; ΔH^≠_pt,0.4mM = 12.5 kJ/mol; ΔH^≠_pt,2mM = 12.5 kJ/mol; ΔS^≠_pt,0.4mM = −92 J/mol K; ΔS^≠_pt,2mM = −100 J/mol K. The similarity between ΔH^≠_{pt,0.4 mM}, ΔH^≠_{pt,2 mM} and ΔH^≠_{sm,0.1 mM}, and between ΔS^≠_{pt,0.4 mM}, ΔS^≠_{pt,2 mM} and ΔS^≠_{sm,0.1 mM} correlate with the earlier finding that adsorption of HQ onto roughened Pt surfaces occurred primarily in the flat orientation at all concentrations studied.     

Sc<Subscript>2</Subscript>S<Subscript>3</Subscript>–Cu<Subscript>2</Subscript>S phase diagram

A phase diagram is constructed for the Sc₂S₃–Cu₂S system. The system forms two incongruently melting complex sulfides: hexagonal CuScS₂ (1Cu₂S: 1Sc₂S₃): a = 0.3734 nm, c = 0.6102 nm, space group P3m1, Т_m = 1635 K, ΔH_m = 1670 kJ/mol; and cubic CuSc₃S₅ (1Cu₂S: 3Sc₂S₃), a = 1.0481 nm, space group Fd3m, Т_m = 1835 K. In the 45–62 mol % Cu2S solid solution (ss) range, there is a singular point corresponding to the composition of compound CuScS₂ (50 mol % Cu₂S). The Sc₂S₃-based solubility at 1070 K is 14 mol % Cu₂S. In the γ-Cu₂S-based solid solution range, there is a peritectic point at 7 mol % Sc₂S₃, 1423 K.     

Sm<Subscript>2</Subscript>S<Subscript>3</Subscript>-Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> phase diagram

The Sm₂S₃-Sm₂O₃ phase diagram was studied by physicochemical methods of analysis from 800 K up to melting. Two oxysulfides are formed in the system: Sm₁₀S₁₄O with tetragonal crystal structure (space group I41/acd; unit cell parameters: a = 1.4860 nm, c = 1.9740 nm; microhardness: H = 4700 MPa; solid decomposition temperature: 1500 K) and Sm₂O₂S with hexagonal structure (space group P-3m1; a = 0.3893 nm, c = 0.6717 nm; H = 4500 MPa; congruent melting temperature: 2370 K). Within the extent of the Sm₂O₂S-based solid solution (61–70 mol % Sm₂O₃) at 1070 K, a singular point appears at the compound composition on property-composition curves. The eutectic coordinates: 23 mol % Sm₂O₃ and 1850 K; 80 mol % Sm₂O₃ and 2290 K.     

Phase diagrams of the systems Sc<Subscript>2</Subscript>S<Subscript>3</Subscript>-Ln<Subscript>2</Subscript>S<Subscript>3</Subscript> for Ln = La,Nd, or Gd

Phase diagrams have been designed for the systems Sc₂S₃-Ln₂S₃ where Ln = La, Nd, or Gd. In these systems, complex sulfides crystallize in orthorhombic space group Pnma. The sulfides melt congruently and have the following parameters; for LaScS₃, a = 0.718 nm, b = 0.654 nm, c = 0.960 nm, 2000 K, 3200 MPa; for NdScS₃, a = 0.712 nm, b = 0.646 nm, c = 0.952 nm, 1960 K, 3500 MPa; and for GdScS₃, a = 0.704 nm, b = 0.640 nm, c = 0.946 nm, 1900 K, 3400 MPa. The extents of the solid solutions based on the existing phases increase as the effective ion radii of Ln³⁺ approaches that of Sc³⁺. At 1670 K, the LnScS₃ homogeneity region is 48–52 mol % Nd₂S₃ and 46–54 mol % Gd₂S₃. Sc₂S₃ dissolves 3 mol % Nd₂S₃ and 6 mol % Gd₂S₃. γ-Nd₂S₃ dissolves 2 mol % Sc₂S₃, and γ-Gd₂S₃ dissolves 4 mol % Sc₂S₃. The subsystems Sc₂S₃-LnScS₃ and LnScS₃-Ln₂S₃ are of the eutectic type. The eutectic coordinates are, respectively, 27 mol % La₂S₃, 1880 K; 75 mol % La₂S₃, 1800 K; 30 mol % Nd₂S₃, 1850 K; 74 mol % Nd₂S₃, 1770 K; 33 mol % Gd₂S₃, 1800 K; and 74 mol % Gd₂S₃, 1730 K.     

Complexation of neptunium(V) by salicylate,phthalate and citrate ligands in a pH 7.5 phosphate buffered system

Conditional stability constants, enthalpies and entropies of complexation at pH 7.5 and ionic strength 0.1 have been determined for neptunium(V) complexes of phosphate, salicylate, phthalate and citrate. Phosphate forms a complex with log β = 2.36 ± 0.42 at 25°C, ΔH°_c = ? 69.9 kJ/mole and ΔS°_c = ? 188 J/mole-K. At pH 7.5 salicylate does not form a complex with neptunium(V) due to the low charge density of the NpO₂⁺ ion and incomplete ionization of the salicylate ion. Phthalate forms a complex with log β = 3.43 ± 0.33 at 25°C, ΔH°_c = 33.5 kJ/mole and ΔS°_c = 182 J/mole-K. Citrate forms a complex with log β = 4.84 ± 0.72 at 25°C, ΔH°_c = 14.0 kJ/mole and ΔS°_c = 140 J/mole-K. In all cases, only 1:1 complexes were identified.     

Enthalpy of formation of wulfenite (natural lead molybdate)

A thermochemical study of wulfenite, i.e., natural lead molybdate PbMoO₄ (Kyzyl-Espe field deposit, Central Kazakhstan), is performed on a Setaram high-temperature heat-flux Tian-Calvet microcalorimeter (France). Enthalpies of the formation of wulfenite from oxides Δ_f H _ox ^o (298.15 K) = ?88.5 ± 4.3 kJ/mol and simple substances Δ_f H°(298.15 K) = ?1051.2 ± 4.3 kJ/mol were determined by means of melt calorimetry. The Δ_f G°(298.15 K) of wulfenite corresponding to ?949.1 ± 4.3 kJ/mol was calculated using data obtained earlier for S°(298.15 K) = 161.5 ± 0.27 J/(K mol).     

Phase equilibria in the SrS-Ga2S3 system

In the SrS-Ga₂S₃ system, there exist two individual compounds: SrGa₂S₄ (a = 2.084 nm, b = 2.050 nm, c = 1.220 nm; congruent melting at 1530 K) and Sr₂Ga₂S₅ (a = 1.253 nm, b = 1.203 nm, c = 1.117 nm; peritectic melting at 1330 K); both are orthorhombic. We discovered a compound of composition Sr₄Ga₂S₇; this compound crystallizes in cubic system with the unit cell parameter a = 0.6008 nm, space group Pa3, and decomposes by a solid-phase reaction at 870 K. Eutectic compositions are 42 and 73 mol % Ga₂S₃; eutectic melting temperatures are 1210 and 1170 K, respectively. The SrS solubility in γ-Ga₂S₃ at 1070 K reaches 4 mol %.     

Phase equilibria in the systems SrS-Cu<Subscript>2</Subscript>S-Ln<Subscript>2</Subscript>S<Subscript>3</Subscript> (Ln = La or Nd)

Phase equilibria in the systems SrS-Cu₂S-Ln₂S₃ (Ln = La or Nd) have been studied along the isothermal section at 1050 K and vertical sections CuLnS₂-SrS and Cu₂S-SrLnCuS₃, which are partially quasibinary joins. Compounds SrLnCuS₃ with Ln = La or Nd have been synthesized for the first time. They crystallize in orthorhombic space group Pnma, the BaLaCuS₃ structure type, with the following unit cell parameters: for SrLaCuS₃, a = 1.1157(2) nm, b = 0.41003(6) nm, c = 1.1545(2) nm; for SrNdCuS₃, a = 1.1083(1) nm, b = 0.40887(7) nm, c = 1.1477(2) nm. Noticeable homogeneity regions for SrLnCuS₃ are not found. The compounds melt congruently by the reaction SrLnCuS₃ ? SrS + L at 1365 K for SrLaCuS₃ and 1400 K for SrNdCuS₃. The tie-lines at 1050 K in the systems SrS-Cu₂S-Ln₂S₃ radiate from SrLnCuS₃ toward phases SrS, Cu₂S, CuLnS₂, and SrLn₂S₄, lying between the phases CuLnS₂ and compositions from the γ-Ln₂S₃-SrLn₂S₄ solid-solution field. Eutectics are formed between the compounds CuLaS₂ and SrLaCuS₃ at 21.0 mol % SrS, T = 1345 K; between the compounds CuNdS₂ and SrNdCuS₃ at 31.0 mol % SrS, T = 1310 K; and between the phases Cu₂S and SrLnCuS₃ at 14.0 mol % SrLaCuS₃, T = 1075 K and 8.0 mol % SrNdCuS₃, T = 1055 K.     

Sterically crowded cyclohexanes - 81). Synthesis,crystal structure,conformation and dynamics of pentaspiro[2.0.2.0.2.0.2.0.2.1]hexadecane,pentaspiro[3.0.2.0.3.0.2.0.3.1]- nonadecane and pentaspiro[3.0.3.0.3.0.3.0.3.1] heneicosane

The synthesis, crystal structure (7,8), conformation and dynamics of pentaspiro[2.0.2.0.2.0.2.0.2.1] hexadecane 6, pentaspiro [3.0.2.0.3.0.2.0.3.1] nonadecane 7 and pentaspiro [3.0.3.0.3.0.3.0.3.1] heneicosane 8 are described. Chair conformations have been found in the solid state (7,8) and in solution (6,7,8). The activation parameters of the chair-to-chair interconversion have been determined from bandshape analyses of exchange broadened ¹H-NMR (6,7) and¹³ C-NMR spectra (8), respectively. The results were as follows: 6: ΔH³ = 48.9 ± 0.8 kJ/mol, ΔS³ = -20.7 ± 2.8 J/mol, grd, ΔG³₂₉₈ = 55.0 ± 0.1 kJ/mol; 7: ΔH³=51.2±0.7 kJ/mol, ΔS³ = -12.0±2.4 J/mol, grd, ΔG³₂₉₈ = 54.8±0.1 kJ/mol; 8: ΔH³ - 74.2±0.6 kJ/mol, ΔS³ =-21.9 ± 1.5 J/mol, grd, ΔG³₂₉₈ = 80.7 ± 0.2 kJ/mol. On the basis of these values the barrier of inversion of the still unknown hexaspirane 5 is predicted to exceed 160 kJ/mol.     

Low-temperature heat capacity and high-temperature thermal behavior of sodium lutetium molybdate phosphate Na<Subscript>2</Subscript>Lu(MoO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)

The low-temperature heat capacity of Na₂Lu (MoO₄)(PO₄) was measured by adiabatic calorimetry in the range of 7.47–345.74 K. The experimental data were used to calculate the thermodynamic functions of Na₂Lu (MoO₄)(PO₄). At 298.15 K, the following values were obtained: C _p ⁰ (298.15 K) = 237.7 ± 0.1 J/(K mol), S ⁰(298.15 K) = 278.1 ± 0.8 J/(K mol), H ⁰(298.15 K) ? H ⁰ (0 K) = 42330 ± 20 J/mol, and Φ⁰(298.15 K) = 136.1 ± 0. 3 J/(K mol). A heat capacity anomaly was found in the range of 10-67 K with a maximum at T _tr = 39.18 K. The entropy and enthalpy of transition are ΔS = 12.39 ± 0.75 J/(K mol) and ΔH = 403 ± 16 J/mol. The thermal investigation of sodium lutetium molybdate phosphate in the high-temperature range (623–1223 K) was performed using differential scanning calorimetry. It was found that during melting in the range of 1030–1200 K, Na₂Lu(MoO₄)(PO₄) degrades to simpler compounds; the degradation scenario is verified by X-ray powder diffraction.     

Temperature dependent near-UV molar absorptivities of aliphatic aldehydes and ketones in aqueous solution

Temperature dependent molar absorptivities are reported for acetone, 2-butanone, 2-pentanone, 3-pentanone, acetaldehyde, propionaldehyde, and n-butyraldehyde in aqueous solution. Molar absorptivities are given at eight temperatures in the range 6.5–69.5°C for wavelengths greater than 200 nm, a spectral resolution of 2.0 nm, and a spacing of 2.5 nm. For both ketones and aldehydes a shift to shorter wavelengths of approximately 10 nm is observed in the aqueous phase absorption spectrum relative to that found in the gas phase. For the ketones, there is an increase in the total intensity of the spectrum of approximately 5% over the range of temperatures studied. For the aldehydes a much larger change in the intensity of the absorption spectrum is observed, due to the temperature dependence of the hydration reaction RCHO + H₂O ⇄ RCH(OH)₂; K_hyd = [RCH(OH)₂/[RCHO]. The change in the spectral intensity with temperature is used to determine thermodynamic parameters for the hydration reaction, giving the following results (at 25°C): acetaldehyde, K_hyd = 1.13 ± 0.06, ΔH = −19.7±0.6kJ/mol, ΔS= −65.0±2.5J/mol-K; propionaldehyde, K_hyd=1.02±0.06, ΔH=-20.8±0.8kJ/mol, ΔS=-69.6±3.1J/mol-K; n-butyraldehyde, K_hyd=0.50±0.05, ΔH=-27.0±2.2kJ/mol, ΔS= −96.5± 8.2 J/mol-K. The implications of these results for aqueous phase atmospheric chemistry are discussed.     

Determination calorimetrique de l'enthalpie de formation des alliages (Al,Ba) riches en aluminum

The heats of formation of some aluminium-barium alloys have been determined by drop calorimetry at high temperature. The heats of mixing of pure liquid Al and Ba to give the liquid alloy are Δ_mH(x_Ba=O.056, 1215 K)=?6.6 kJ mole^?1 and Δ_mH(x_Ba=O.333, 1215 K)=?31.0 kJ mole^-1. To measure its heat of formation, the solid compound Al₄Ba was precipitated by addition of pure barium from a liquid (Al, Ba) bath. It was found that Δ_fH(Al_0.8Ba_O.2, solid, 1215 K)=-(37.1 ? 1.5) kJ mole^?1 with reference to the pure metals in the solid state.     

Synthesis, crystal structure, and properties of triphenylguanidinium perrhenate hemihydrate

Triphenylguanidinium perrhenate hemihydrate, [(C₆H₅NH)₃C]ReO₄ · 0.5H₂O (I), is synthesized, and its crystal structure and some properties are studied. The colorless extended plate-like crystals of compound I are triclinic (space group $P\bar 1$ , Z = 4, 293 K, a = 9.8716(17), b = 14.093(2), c = 15.439(3)Å, α = 99.632(9)^○, β = 101.802(9)^○, γ = 95.361(10)^○). Compound I has no isostructural analogs, and the conformations of both crystallographically independent triphenylguanidinium cations differ by a higher symmetry (C _3h ) from those for cations of this type in all other structurally studied compounds. The following parameters are determined: the upper limit of the temperature stability of compound I (383 K), the melting point of anhydrous [(C₆H₅NH)₃C]ReO₄ (Ia) of 441 K, the enthalpy of dehydration of compound I (ΔH _dehydr ^{(383 K)} = 10.0(8) kJ/mol), and the enthalpy of melting of anhydrous Ia (ΔH _m ^{(441 K)} = 16.6(9) kJ/mol).     

Phase diagram of the MgS-Ga2S3 system

The MgGa₂S₄ phase, which forms in the MgS-Ga₂S₃ system, crystallizes in monoclinic system with the parameters a = 1.275 nm, b = 2.255 nm, c = 0.641 nm, β = 108.8°. Its congruent melting temperature is 1365 K. The eutectics have compositions of 31 and 62 mol % Ga₂S₃ and melt at 1280 and 1140 K, respectively. The MgS solubility in γ-Ga₂S₃ at 1070 K reaches 7 mol % MgS.     

Sm–Sm<Subscript>2</Subscript>Se<Subscript>3</Subscript> phase diagram and properties of phases

A Sm–Sm2Se3 phase diagram has been studied from 1000 K until melting. This system forms three congruently melting compounds: SmSe (ST NaCl, a = 0.6200 nm, T_m = (2400 ± 50) K, and H = 2750 MPa), Sm₃Se₄ (ST Th₃P₄, a = 0.8925 nm, T_m = (2250 ± 30) K, and H = 3350 MPa), and Sm₂Se₃ (ST Th₃P₄, a = 0.8815 nm, T_m = (2150 ± 40) K, and H = 5300 MPa). There are eutectics between Sm and SmSe phases and between SmSe and Sm₃Se₄ phases at 2.5 at % Se, 1300 K and at 54.5 at % Se, 2100 K, respectively. Within the extent of Sm₂₊ Sm₂³⁺ Se4–Sm₂³⁺Se₃ solid solution (ST Th₃P₄), the experimentally determined percentages of Sm₂₊ ions correspond with the values calculated from the formula compositions of samples. The bandgap width for SmSe_1.45 and SmSe_1.48 phases is ΔE = (1.90 ± 0.05) eV.     

Features of the Diels-Alder reaction between 9,10-diphenylanthracene and 4-phenyl-1,2,4-triazoline-3,5-dione

The Diels-Alder reaction between substituted anthracenes 1a?1j and 4-phenyl-1,2,4-triazoline-3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10-atoms of substituted anthracenes. The orthogonality of the two phenyl groups at the 9,10-position of diene 1a is found to shield 9,10-reactive centers. No dienophiles with C=C bonds are shown to participate in the Diels-Alder reaction with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4-phenyl-1,2,4-triazoline-3,5-dione. It is shown that attachment occurs on the less active but sterically accessible 1,4-reactive center of diene 1a. The structure of adduct 3a is proved by ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. The following parameters are obtained for reaction 1a + 2 ? 3a in toluene at 25°C: K _eq = 2120 M^?1, ΔH _f ^≠ = 58.6 kJ/mol, ΔS _f ^≠ = ?97 J/(mol K), ΔV _f ^≠ = ?17.2 cm³/mol, ΔH _b ^≠ = 108.8 kJ/mol, ΔS _b ^≠ = 7.3 J/(mol K), ΔV _b ^≠ = ?0.8 cm³/mol, ΔH _r-n = ?50.2 kJ/mol, ΔS _r-n = ?104.3 J/(mol K), ΔV _r-n = ?15.6 cm³/mol. It is concluded that the values of equilibrium constants of the reactions 1a?1j + 2 ? 3a?3j vary within 4 × 10¹?10¹¹ M^?1.     

Stereochemical nonrigidity of the square complex (PPh3)2Pt(HgGePh3)(GePh3)

³¹P, ¹⁹⁵Pt and ¹⁹⁹Hg NMR spectra of complex (PPh₃)₂Pt(HgGePh₃)(GePh₃) (I) have been studied. The spectra at temperatures below ?40°C prove that (I) is a cis-isomer with the square-planar coordination of the Pt atom. The reversibility of temperature dependences of spectra, insensitivity of line shape to the solvent, concentration and presence of free phosphine establish the fluxional behaviour of (I). The activation parameters of the intramolecular rearrangement which is realized, most probably, through a digonal twist, are: Δ^≠₂₉₈ = 51.5 ± 2.9 kJ/mol, ΔH^≠ = 59.3 ± 2.9 kJ/mol, ΔS^≠ = 26.2 ± 9.7 J/mol. K.     

The Formation and Stability of the [FePy3Cl3]· Py Clathrate in the Pyridine–Iron(III) Chloride System: Phase Diagram and Solid–Gas Equilibria Study

The phase diagram of the pyridine–iron(III) chloride system has been studied for the 223–423 K temperature and 0–56 mass-% concentration ranges using differential thermal analysis (DTA) and solubility techniques. A solid with the highest pyridine content formed in the system was found to be an already known clathrate compound, [FePy₃Cl₃]·Py. The clathrate melts incongruently at 346.9 ± 0.3 K with the destruction of the host complex: [FePy₃Cl₃]·Py_(solid)=[FePy₂Cl₃]_(solid) + liquor. The thermal dissociation of the clathrate with the release of pyridine into the gaseous phase (TGA) occurs in a similar way: [FePy₃Cl₃]·Py_(solid)=[FePy2Cl₃]_(solid) + 2 Py_(gas). Thermodynamic parameters of the clathrate dissociation have been determined from the dependence of the pyridine vapour pressure over the clathrate samples versus temperature (tensimetric method). The dependence experiences a change at 327 K indicating a polymorphous transformation occurring at this temperature. For the process ${1 \over 2}[\hbox{FePy}_{3}\hbox{Cl}_{3}]\cdot \hbox{Py}_{\rm (solid)} = {1 \over 2}[\hbox{FePy}_{2}\hbox{Cl}_{3}]_{\rm (solid)} + \hbox{Py}_{\rm (gas)}$ in the range 292–327 K, ΔH $^{0}_{298}$ =70.8 ± 0.8 kJ/mol, ΔS $^{0}_{298}$ =197 ± 3 J/(mol K), ΔG $^{0}_{298}$ =12.2 ± 0.1 kJ/mol; in the range 327–368 K, ΔH $^{0}_{298}$ =44.4 ± 1.3 kJ/mol, ΔS $^{0}_{298}$ =116 ± 4 J/(mol K), ΔG $^{0}_{298}$ =9.9 ± 0.3 kJ/mol.