Room temperature molten fluorometallates: 1-ethyl-3-methylimidazolium hexafluoroniobate(V) and hexafluorotantalate(V)

The first room temperature molten salts containing hexafluorometallate anions of transition metals, 1-ethyl-3-methylimidazolium (EMIm) hexafluoroniobate, EMImNb(V)F₆, and hexafluorotantalate, EMImTa(V)F₆, have been synthesized by the reactions of EMImF·2.3HF with NbF₅ and TaF₅, respectively. They exhibit similar physical properties. Viscosities and conductivities are 49 cP and 8.5 mS cm⁻¹ for EMImNbF₆ and 51 cP and 7.1 mS cm⁻¹ for EMImTaF₆, respectively at 298 K.     

Determination of the enthalpy of fusion of K3TaF8 and K3TaOF6

The areas of the fusion and crystallization peaks of K₃TaF₈ and K₃TaOF₆ have been measured using the DSC mode of the high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities and the temperature dependence of the used calorimetric method sensitivity, the values of the enthalpy of fusion of K₃TaF₈ at temperature of fusion 1039 K: Δ_fusH_m(K₃TaF₈; 1039 K) = (52 ± 2) kJ mol⁻¹ and of K₃TaOF₆ at temperature of fusion 1055 K: Δ_fusH_m(K₃TaOF₆; 1055 K) = (62 ± 3) kJ mol⁻¹ have been determined.     

Infrared and Raman studies of the anion ordering transitions in paramagnetic organometallic radical cation salts [Cp2Mo(dmit)]X (X = PF6, SbF6)

Temperature dependence of infrared and Raman spectra of the two isostructural salts [Cp₂Mo(dmit)]PF₆ and [Cp₂Mo(dmit)]SbF₆ is studied. At room temperature the physical properties of both compounds are very similar but at lower temperatures they undergo phase transitions associated with anion ordering, which are surprisingly different. The phase transitions in [Cp₂Mo(dmit)]PF₆ salt at T₁ = 120 K and T₂ = 89 K have no important influence on infrared and Raman spectra, while the phase transition in [Cp₂Mo(dmit)]SbF₆ salt at T₁ = 175 K causes a splitting of Raman bands assigned to the CC stretching at about 1334 cm⁻¹ and the in-plane Mo(dmit) ring deformation at about 353 cm⁻¹, and also an infrared band at about 939 cm⁻¹ related to the C-S stretching. The splitting of vibrational bands demonstrates a clear distortion of [Cp₂Mo(dmit)]⁺ cations in the [Cp₂Mo(dmit)]SbF₆ salt. This molecular distortion is related to a lattice distortion providing thus a good argument for applicability of the compressible model of the anion ordering transition.     

Structural characteristics of alkylimidazolium-based salts containing fluoroanions

An overview of recent structural studies on alkylimidazolium-based salts containing fluoroanions is presented. Alkylimidazolium cations have been most extensively used for syntheses of ionic liquids (room temperature molten salts) because they usually exhibit low melting points, low viscosities and high conductivities. This review mainly focuses on structures of alkylimidazolium-based salts combined with a fluorocomplex anion ((FH)_nF⁻, BF₄⁻, PF₆⁻, AsF₆⁻, SbF₆⁻, NbF₆⁻, TaF₆⁻), N(SO₂CF₃)₂⁻ (TFSI⁻) and OSO₂CF₃⁻. The first part describes crystal structures of these salts and the second part describes computational, spectroscopic and diffraction studies on their liquid structures. Related studies on ionic liquids of non-alkylimidazolium cation and non-fluoroanion are also briefly summarized.     

Calorimetric determination of enthalpy changes for the proton ionization of glycine, N,N-bis(2-hyroxyethyl)glycine (“bicine”) and N-tris(hydroxymethyl)methylglycine (“tricine”) in water-methanol mixtures

Enthalpies for the two proton ionizations of glycine, N,N-bis(2-hyroxyethyl)glycine (“bicine”) and N-tris(hydroxymethyl)methylglycine (“tricine”) were obtained in water-methanol mixtures with methanol mole fraction (X_m) from 0 to 0.360. With increasing methanol the ionization enthalpy for the first proton (ΔH₁) of glycine increased from 4.4 to 9.4 kJ mol⁻¹ with a minimum of 4.1 kJ mol⁻¹ at X_m = 0.059. The ionization enthalpy of the second proton (ΔH₂) for glycine decreased from 46.3 to 38.1 kJ mol⁻¹. ΔH₁ of bicine increased from 3.5 to 7.6 kJ mol⁻¹ at X_m = 0.273 before dropping to 4.1 kJ mol⁻¹ at X_m = 0.360. ΔH₂ of bicine increased from 24.9 to 29.4 kJ mol⁻¹. For tricine, ΔH₁ increased from 6.7 to 9.8 kJ mol⁻¹ at X_m = 0.194 then dropped to 7.4 kJ mol⁻¹ at X_m = 0.360. ΔH₂ for tricine first dropped from 30.8 to 28.5 kJ mol⁻¹ at X_m = 0.059 before increasing to 33.3 kJ mol⁻¹ at X_m = 0.273. The solvent composition was selected so as to include the region of maximum structure enhancement of water by methanol. The results were interpreted in terms of solvent-solvent and solvent-solute interactions.     

A new room temperature ionic liquid of oxyfluorometallate anion: 1-Ethyl-3-methylimidazolium oxypentafluorotungstate (EMImWOF5)

The first room temperature ionic liquid (room temperature molten salt) containing oxyfluorometallate anion, 1-ethyl-3-methylimidazolium oxypentafluorotungstate (EMImWOF₅), has been synthesized and characterized compared to other known EMIm fluorocomplex salts. EMImWOF₅ is synthesized by two routes: one is the hydrolysis of EMImWF₇ and the other is the fluoroacid-base reaction of EMIm(HF)_2.3F and WOF₄. EMImWOF₅ is a hydrophilic room temperature ionic liquid but is stable in aqueous solution. From the result of DSC analysis, EMImWOF₅ exhibits a glass transition at 182 K and melts at 253 K. The density, conductivity and viscosity at 298 K are 2.25 g cm⁻³, 3.0 mS cm⁻¹ and 105.1 cP, respectively.     

Protonated MF3 (M = N-Bi): Structure, stability, and thermochemistry of the H-MF3 and HF-MF2 isomers

The structure, stability, and thermochemistry of the H(MF₃)⁺ isomers (M = N-Bi) have been investigated by MP2 and coupled cluster calculations. All the HF-MF₂⁺ revealed weakly bound ion-dipole complexes between MF₂⁺ and HF. For M = N, As, Sb, and Bi they are more stable than the H-MF₃⁺ covalent structures (free energy differences) by 6.3, 14.3, 32.1, and 73.5 kcal mol⁻¹, respectively. H-PF₃⁺ is instead more stable than HF-PF₂⁺ by 21.8 kcal mol⁻¹. The proton affinities (PAs) of MF₃ at the M atom range from 91.9 kcal mol⁻¹ (M = Bi) to 156.5 kcal mol⁻¹ (M = P), and follow the irregular periodic trend BiF₃ < SbF₃ < AsF₃ < NF₃ < PF₃. The PAs at the F atom range instead from 131.9 kcal mol⁻¹ (M = P) to 164.9 kcal mol⁻¹ (M = Bi), and increase in the more regular order PF₃ ≈ NF₃ < AsF₃ < SbF₃ < BiF₃. This trend parallels the fluoride-ion affinities of the MF₂⁺ cations. For protonated NF₃ and PF₃, the calculations are in good agreement with the available experimental results. As for protonated AsF₃, they support the formation of HF-AsF₂⁺ rather than the previously proposed H-AsF₃⁺. The calculations indicate also that the still elusive H(SbF₃)⁺ and H(BiF₃)⁺ should be viable species in the gas phase, exothermically obtainable by various protonating agents.     

Vaporization of DyI3(s) and thermochemistry of the homocomplexes (DyI3)2(g) and (DyI3)3(g)

The vaporization of DyI₃(s) was investigated in the temperature range between 833 and 1053 K by the use of Knudsen effusion mass spectrometry. The ions DyI₂⁺, DyI₃⁺, Dy₂I₄⁺, Dy₂I₅⁺, Dy₃I₇⁺, and Dy₃I₈⁺ were detected in the mass spectrum of the equilibrium vapor. The gaseous species DyI₃, (DyI₃)₂, and (DyI₃)₃ were identified and their partial pressures determined. Enthalpies and entropies of sublimation resulted according to the second- and third-law methods. The following sublimation enthalpies at 298 K were determined for the gaseous species given in brackets: 274.8±8.2 kJ mol⁻¹ [DyI₃], 356.0±11.3 kJ mol⁻¹ [(DyI₃)₂], and 436.6±14.6 kJ mol⁻¹ [(DyI₃)₃]. The enthalpy changes of the dissociation reactions (DyI₃)₂=2 DyI₃ and (DyI₃)₃=3 DyI₃ were obtained as Δ_dH°(298)=193.3±5.6 and 390.3±13.0 kJ mol⁻¹, respectively.     

Calorimetric determination of enthalpy changes for proton ionization of N-[2-hydroxyethyl]piperazine-N′-[2-ethane sulfonic acid] (HEPES) and N-[2-hydroxyethyl]piperazine-N′-[2-hydroxypropane sulfonic acid] (HEPPSO) in water-methanol mixtures

Enthalpies for the two proton ionizations of the biochemical buffers N-[2-hydroxyethyl]piperazine-N′-[2-ethane sulfonic acid] (HEPES) and N-[2-hydroxyethyl]piperazine-N′-[2-hydroxypropane sulfonic acid] (HEPPSO) were obtained in water-methanol mixtures with methanol mole fraction (X_m) from 0 to 0.360. With increasing methanol, the ionization enthalpy for the first proton (ΔH₁) of HEPES increased steadily from 8.4 to 15.3 kJ mol⁻¹ whereas that for HEPPSO rose to a maximum of 21.0 kJ mol⁻¹ at X_m = 0.123 before dropping to 18.4 kJ mol⁻¹ at X_m = 0.360. The ionization enthalpy for the second proton (ΔH₂) of HEPES varied from 20.8 kJ mol⁻¹ in water to 13.6 kJ mol⁻¹ at X_m = 0.360 with a maximum of 24.8 kJ mol⁻¹ at X_m = 0.194. For HEPPSO, ΔH₂ increased steadily from 23.4 to 29.2 kJ mol⁻¹. The solvent composition was selected so as to include the region of maximum structure enhancement of water by methanol. The results were interpreted in terms of solvent-solvent and solvent-solute interactions.     

Energetics of cobalt phosphate frameworks: α, β, and red NaCoPO4

Thermal behavior, relative stability, and enthalpy of formation of α (pink phase), β (blue phase), and red NaCoPO₄ are studied by differential scanning calorimetry, X-ray diffraction, and high-temperature oxide melt drop solution calorimetry. Red NaCoPO₄ with cobalt in trigonal bipyramidal coordination is metastable, irreversibly changing to α NaCoPO₄ at 827 K with an enthalpy of phase transition of −17.4±6.9 kJ mol⁻¹. α NaCoPO₄ with cobalt in octahedral coordination is the most stable phase at room temperature. It undergoes a reversible phase transition to the β phase (cobalt in tetrahedra) at 1006 K with an enthalpy of phase transition of 17.6±1.3 kJ mol⁻¹. Enthalpy of formation from oxides of α, β, and red NaCoPO₄ are −349.7±2.3, −332.1±2.5, and −332.3±7.2 kJ mol⁻¹; standard enthalpy of formation of α, β, and red NaCoPO₄ are −1547.5±2.7, −1529.9±2.8, and −1530.0±7.3 kJ mol⁻¹, respectively. The more exothermic enthalpy of formation from oxides of β NaCoPO₄ compared to a structurally related aluminosilicate, NaAlSiO₄ nepheline, results from the stronger acid-base interaction of oxides in β NaCoPO₄ (Na₂O, CoO, P₂O₅) than in NaAlSiO₄ nepheline (Na₂O, Al₂O₃, SiO₂).     

Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts containing simultaneously tetrahedral BF4 and octahedral AF6 anions

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄)(PF₆) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å³ at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF₄⁻ and PF₆⁻ anions. In the analogous system with AsF₅ instead of PF₅ the compound Ba(BF₄)(AsF₆) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å³ at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF₆⁻ and four F atoms from BF₄⁻ anions. When the system BaF₂/BF₃/AsF₅/aHF is made basic with an extra addition of BaF₂, the compound Ba₂(BF₄)₂(AsF₆)(H₃F₄) was obtained. It crystallizes in a hexagonal P6₃/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å³ at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF₄⁻, three AsF₆⁻ and three H₃F₄⁻ anions. All F atoms, except the central atom in H₃F₄ moiety, act as μ₂-bridges yielding a complex 3-D structural network.     

Heat-capacity measurements and thermodynamic functions of crystalline adenine; revised thermodynamic properties of aqueous adenine

The standard molar heat capacity C^°_p,m of adenine(cr) has been measured using adiabatic calorimetry over the range 6<(T/K)<310 and the results used to derive thermodynamic functions for adenine(cr) at smoothed temperatures. At T=298.15 K, C^°_p,m=(142.67±0.29) J · K⁻¹ · mol⁻¹ and the third law entropy S^°_m=(145.62±0.29) J · K⁻¹ · mol⁻¹. The standard molar Gibbs free energy of formation Δ_fG^°_m at T=298.15 K for crystalline adenine was calculated, using the standard molar enthalpy of formation for the compound and entropies of the elements from the literature, and found to be Δ_fG^°_m=(301.4±1.0) kJ · mol⁻¹. The results were combined with solution calorimetry and solubility measurements from the literature to yield revised values for the standard molar thermodynamic properties of aqueous adenine at T=298.15 K: Δ_fG^°_m=(313.4±1.0) kJ · mol⁻¹, Δ_fH^°_m=(129.5±1.4) kJ · mol⁻¹, and S_m^°=(217.68±0.44) J · K⁻¹ · mol⁻¹.     

Tutorial review: Bohr circular orbit diagrams for some fluorine-containing molecules

Examples are provided of Bohr circular orbit diagrams to represent the electronic structures of some fluorine-containing molecules. The orbit diagrams are constructed from a 2n × n factorisation of the atomic shell-structure formula 2n², with n = 1, 2, 3, … Particular attention is given to orbit diagrams and the associated valence bond structures for the hypercoordinate molecules and ions PF₅ and NF₅, F₃⁻ and XeF₂, IF₅ and XeF₅⁺, XeF₅⁻, IF₈⁻, XeF₈²⁻, ReF₈⁻ and TaF₈³⁻, ZrF₈⁴⁻, ZrF₇³⁻, Re₂F₈²⁻, and high-spin CoF₆³⁻.Aspects of the electronic structures of D_3h-symmetry PF₅ and NF₅ are contrasted via the use of orbital valence bond considerations, and the results of STO-3G valence bond calculations are reported for these species.     

Syntheses, structures and Raman spectra of Cd(BF4)(AF6) (A = Ta, Bi) compounds

The compounds, Cd(BF₄)(TaF₆) and Cd(BF₄)(BiF₆), have been synthesized and characterized by single-crystal X-ray diffraction and Raman spectroscopy. Both isostructural compounds crystallize in the monoclinic P2₁/c space group with a = 8.2700(6) Å, b = 9.3691(6) Å, c = 8.8896(7) Å, β = 94.196(3)°, V = 686.94(9) Å³ for Cd(BF₄)(TaF₆) and a = 8.3412(8) Å, b = 9.4062(8) Å, c = 8.9570(7) Å, β = 93.320(5)°, V = 701.58(11) Å³ for Cd(BF₄)(BiF₆). Eight fluorine atoms (4 BF₄⁻ + 4 AF₆⁻) form a surrounding around the cadmium atom in the shape of distorted square antiprism. These compounds are not isostructural with mixed-anion analogues of Ca, Sr, Ba and Pb studied earlier.     

Reaction between LiF and MF5 (M = Ta, Nb) in a fluorine atmosphere

LiMF₆ (M = Ta, Nb) was prepared by the reaction between LiF and MF₅ (M = Ta, Nb) in F₂ gas. Pure LiMF₆ (M = Ta, Nb) salts were obtained by using the reaction at temperatures higher than 473 K under 80 kPa (F₂) for 24 h. The x values in LiMF_x (M = Ta, Nb) were confirmed as 5.7-6.0 by XRD-Rietveld analysis. Results showed that LiMF₆ (M = Ta, Nb) has a trigonal structure (, Z = 3). The respective lattice parameters of LiTaF₆ and LiNbF₆ are a₀ = 0.533 nm, c₀ = 1.362 and a₀ = 0.532 nm, c₀ = 1.360. The equivalent conductivities of both LiMF₆ (M = Ta, Nb) in propylene carbonate (PC) are equal at 15.2 Ω⁻¹ cm² mol⁻¹ at 0.01 mol dm⁻³. The electrochemical potential window of TaF₆⁻ is 7.0 V, which is 0.4 and 0.2 V wider, respectively, than those of BF₄⁻ and PF₆⁻.     

Kinetics of the CH3 + HCl/DCl → CH4/CH3D + Cl and CD3 + HCl/DCl → CD3H/CD4 + Cl reactions: An experimental H atom tunneling investigation

The kinetics of the radical reactions of CH₃ with HCl or DCl and CD₃ with HCl or DCl have been investigated in a temperature controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃ (or CD₃) radical, R, was produced homogeneously in the reactor by a pulsed 193 nm exciplex laser photolysis of CH₃COCH₃ (or CD₃COCD₃). The decay of CH₃/CD₃ was monitored as a function of HCl/DCl concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature, typically from 188 to 500 K. The rate constants of the CH₃ and CD₃ reactions with HCl had strong non-Arrhenius behavior at low temperatures. The rate constants were fitted to a modified Arrhenius expression k = QA exp (−E_a/RT) (error limits stated are 1σ + Students t values, units in cm³ molecule⁻¹ s⁻¹): k(CH₃ + HCl) = [1.004 + 85.64 exp (−0.02438 × T/K)] × (3.3 ± 1.3) × 10⁻¹³ exp [−(4.8 ± 0.6) kJ mol⁻¹/RT] and k(CD₃ + HCl) = [1.002 + 73.31 exp (−0.02505 × T/K)] × (2.7 ± 1.2) × 10⁻¹³ exp [−(3.5 ± 0.5) kJ mol⁻¹/RT]. The radical reactions with DCl were studied separately over a wide ranges of temperatures and in these temperature ranges the rate constants determined were fitted to a conventional Arrhenius expression k = A exp (−E_a/RT) (error limits stated are 1σ + Students t values, units in cm³ molecule⁻¹ s⁻¹): k(CH₃ + DCl) = (2.4 ± 1.6) × 10⁻¹³ exp [−(7.8 ± 1.4) kJ mol⁻¹/RT] and k(CD₃ + DCl) = (1.2 ± 0.4) × 10⁻¹³ exp [−(5.2 ± 0.2) kJ mol⁻¹/RT] cm³ molecule⁻¹ s⁻¹.     

Low-temperature heat capacity and thermodynamic properties of endo-Tricyclo[5.2.1.0]decane

Endo-Tricyclo[5.2.1.0^2,6]decane (CAS 6004-38-2) is an important intermediate compound for synthesizing diamantane. The lack of data on the thermodynamic properties of the compound limits its development and application. In this study, endo-Tricyclo[5.2.1.0^2,6]decane was synthesized and the low temperature heat capacities were measured with a high-precision adiabatic calorimeter in the temperature range from (80 to 360) K. Two phase transitions were observed: the solid-solid phase transition in the temperature range from (198.79 to 210.27) K, with peak temperature 204.33 K; the solid-liquid phase transition in the temperature range from 333.76 K to 350.97 K, with peak temperature 345.28 K. The molar enthalpy increments, ΔH_m, and entropy increments, ΔS_m, of these phase transitions are ΔH_m=2.57 kJ · mol⁻¹ and ΔS_m=12.57 J · K⁻¹ · mol⁻¹ for the solid-solid phase transition at 204.33 K, and, Δ_fusH_m=3.07 kJ · mol⁻¹ and Δ_fusS_m=8.89 J · K⁻¹ · mol⁻¹ for the solid-liquid phase transition at 345.28 K. The thermal stability of the compound was investigated by thermogravimetric analysis. TG result shows that endo-Tricyclo[5.2.1.0^2,6]decane starts to sublime at 300 K and completely changes into vapor when the temperature reaches 423 K, reaching the maximal rate of weight loss at 408 K.     

Homoleptic [M(XeF2)6] cations of copper(II) and zinc(II)—Syntheses and crystal structures of [M(XeF2)6](SbF6)2 (M = Cu, Zn)

[Cu(XeF₂)₆](SbF₆)₂ crystallizes in the rhombohedral symmetry with a = 1003.6(2) pm, c = 2246.5(12) pm at 200 K and Z = 3, space group (No. 148). [Zn(XeF₂)₆](SbF₆)₂ is isostructural to [Cu(XeF₂)₆](SbF₆)₂ with a = 1007(2) pm and c = 2243(6) pm. The structures are characterized by isolated homoleptic [M(XeF₂)₆]²⁺ (M = Cu, Zn) cations and of [SbF₆]⁻ octahedra.Reactions of M(SbF₆)₂ (M = Cu, Zn) with XeF₂ in anhydrous hydrogen fluoride (aHF) and reactions of MF₂ with Xe₂F₃SbF₆ in aHF always yield a mixture of [M(XeF₂)₆](SbF₆)₂, Xe₂F₃SbF₆ and MF₂.     

N,N′-Bis(aryl)pyridine-2,6-dicarboxamide complexes of ruthenium: Synthesis,structure and redox properties

Reaction of five N,N′-bis(aryl)pyridine-2,6-dicarboxamides (H₂L-R, where H₂ denotes the two acidic protons and R (R = OCH₃, CH₃, H, Cl and NO₂) the para substituent in the aryl fragment) with [Ru(trpy)Cl₃](trpy = 2,2′,2″-terpyridine) in refluxing ethanol in the presence of a base (NEt₃) affords a group of complexes of the type [Ru^II(trpy)(L-R)], each of which contains an amide ligand coordinated to the metal center as a dianionic tridentate N,N,N-donor along with a terpyridine ligand. Structure of the [Ru^II(trpy)(L-Cl)] complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru^II(trpy)(L-R)] complexes shows a Ru(II)–Ru(III) oxidation within 0.16–0.33 V versus SCE. An oxidation of the coordinated amide ligand is also observed within 0.94–1.33 V versus SCE and a reduction of coordinated terpyridine ligand within −1.10 to −1.15 V versus SCE. Constant potential coulometric oxidation of the [Ru^II(trpy)(L-R)] complexes produces the corresponding [Ru^III(trpy)(L-R)]⁺ complexes, which have been isolated as the perchlorate salts. Structure of the [Ru^III(trpy)(L-CH₃)]ClO₄ complex has been determined by X-ray crystallography. All the Ru(III) complexes are one-electron paramagnetic, and show anisotropic ESR spectra at 77 K and intense LMCT transitions in the visible region. A weak ligand-field band has also been shown by all the [Ru^III(trpy)(L-R)]ClO₄ complexes near 1600 nm.     

Thermal properties of the pyrochlore, Y2Ti2O7

The thermal conductivity and heat capacity of high-purity single crystals of yttrium titanate, Y₂Ti₂O_7, have been determined over the temperature range 2 K?T?300 K. The experimental heat capacity is in very good agreement with an analysis based on three acoustic modes per unit cell (with the Debye characteristic temperature, θ_D, of ca. 970 K) and an assignment of the remaining 63 optic modes, as well as a correction for C_p−C_v. From the integrated heat capacity data, the enthalpy and entropy relative to absolute zero, are, respectively, H(T=298.15 K)−H₀=34.69 kJ mol⁻¹ and S(T=298.15 K)−S₀=211.2 J K⁻¹ mol⁻¹. The thermal conductivity shows a peak at ca. θ_D/50, characteristic of a highly purified crystal in which the phonon mean free path is about 10 μm in the defect/boundary low-temperature limit. The room-temperature thermal conductivity of Y₂Ti₂O₇ is 2.8 W m⁻¹ K⁻¹, close to the calculated theoretical thermal conductivity, κ_min, for fully coupled phonons at high temperatures.