Synthesis, heat capacity and enthalpy of formation of [Ho2(l-Glu)2(H2O)8](ClO4)4·H2O

A complex of holmium perchlorate coordinated with l-glutamic acid, [Ho₂(l-Glu)₂(H₂O)₈](ClO₄)₄·H₂O, was prepared with a purity of 98.96%. The compound was characterized by chemical, elemental and thermal analysis. Heat capacities of the compound were determined by automated adiabatic calorimetry from 78 to 370 K. The dehydration temperature is 350 K. The dehydration enthalpy and entropy are 16.34 kJ mol⁻¹ and 16.67 J K⁻¹ mol⁻¹, respectively. The standard enthalpy of formation is −6474.6 kJ mol⁻¹ from reaction calorimetry at 298.15 K.     

Low-temperature heat-capacity and standard molar enthalpy of formation of copper l-threonate hydrate Cu(C4H6O5)·0.5H2O(s)

The solid copper l-threonate hydrate, Cu(C₄H₆O₅)·0.5H₂O, was synthesized by the reaction of l-threonic acid with copper dihydrocarbonate and characterized by means of chemical and elemental analyses, IR and TG-DTG. Low-temperature heat-capacity of the title compound has been precisely measured with a small sample precise automated adiabatic calorimeter over the temperature range from 77 to 390 K. An obvious process of the dehydration occurred in the temperature range between 353 and 370 K. The peak temperature of the dehydration of the compound has been observed to be 369.304 ± 0.208 K by means of the heat-capacity measurements. The molar enthalpy, Δ_dH_m, of the dehydration of the resulting compound was of 16.490 ± 0.063 kJ mol⁻¹. The experimental molar heat capacities of the solid from 77 to 353 K and the solid from 370 to 390 K have been, respectively, fitted to tow polynomial equations with the reduced temperatures by least square method. The constant-volume energy of combustion of the compound, Δ_cU_m, has been determined as being −1616.15 ± 0.72 kJ mol⁻¹ by an RBC-II precision rotating-bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of formation of the compound, , has been calculated to be −1114.76 ± 0.81 kJ mol⁻¹ from the combination of the data of standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities.     

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.     

Calorimetric study and thermal analysis of [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O (Gly: glycin)

Two solid-state coordination compounds of rare earth metals with glycin, [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O and [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 342.90 K, while [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol⁻¹ and 53.9 J K⁻¹ mol⁻¹ for [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, 1.82 kJ mol⁻¹ and 5.5 J K⁻¹ mol⁻¹ for [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed.     

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.     

Synthesis, crystal structure and thermochemical behaviour of a barium complex [Ba(5-OH-BDC)(H2O)3] [5-OH-H2BDC = 5-hydroxyisophtalic acid]

A novel complex [Ba(5-OH-BDC)(H₂O)₃] [5-OH-H₂BDC = 5-hydroxyisophtalic acid] was synthesized and characterized by X-ray crystallography. The complex is Monoclinic P2₁/c, a = 11.1069(4), b = 14.8192(6), c = 6.5005(2) Å, β = 103.465(3)° and Z = 4, which exhibits a three-dimensional framework formed by linkage of adjacent two-dimensional (6, 3) layers via intermolecular hydrogen bonds. The title complex has been studied by IR spectrum and TG-DTG. The constant-volume combustion energy of the complex, Δ_cU, was determined as being (−3210.45 ± 1.41) kJ mol⁻¹ by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpy of combustion, , and the standard enthalpy of formation, , were calculated as being (−3207.97 ± 1.41) and (−1922.80 ± 1.76) kJ mol⁻¹, respectively. A calculation model for determining the specific heat capacity of the complex with an improved RD496-III microcalorimeter is also derived. The specific heat capacity of the complex was (6158.387 ± 0.187) J mol⁻¹ K⁻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.     

Change in mechanistic pathway of hydroboration: A detailed kinetic study of H2BBr·SMe2 and HBBr2·SMe2

Hydroboration reactions of 1-octene and 1-hexyne with H₂BBr·SMe₂ in CH₂Cl₂ were studied as a function of concentration and temperature, using ¹¹B NMR spectroscopy. The reactions exhibited saturation kinetics. The rate of dissociation of dimethyl sulfide from boron at 25 °C was found to be (7.36 ± 0.59 and 7.32 ± 0.90) × 10⁻³ s⁻¹ for 1-octene and 1-hexyne, respectively. The second order rate constants, k₂, for hydroboration worked out to be 7.00 ± 0.81 M s⁻¹ and 7.03 ± 0.70 M s⁻¹, while the overall composite second order rate constants, k K, were (3.30 ± 0.43 and 3.10 ± 0.37) × 10⁻² M s⁻¹, respectively at 25 °C. The entropy and enthalpy values were found to be large and positive for k₁, whilst for k₂ these were large and negative, with small values for enthalpies. This is indicative of a limiting dissociative (D) for the dissociation of Me₂S and associative mechanism (A) for the hydroboration process. The overall activation parameters, ΔH^≠ and ΔS^≠, were found to be 98 ± 2 kJ mol⁻¹ and +56 ± 7 J K⁻¹ mol⁻¹ for 1-octene whilst, in the case of 1-hexyne these were found out to be 117 ± 7 kJ mol⁻¹ and +119 ± 24 J K⁻¹ mol⁻¹, respectively. When comparing the kinetic data between H₂BBr·SMe₂ and HBBr₂·SMe₂, the results showed that the rate of dissociation of Me₂S from H₂BBr·SMe₂ is on average 34 times faster than it is in the case of HBBr₂·SMe₂. Similarly, the rate of hydroboration with H₂BBr·SMe₂ was found to be on average 11 times faster than it is with HBBr₂·SMe₂. It is also clear that by replacing a hydrogen substituent with a bromine atom in the case of H₂BBr·SMe₂ the mechanism for the overall process changes from limiting dissociative (D) to interchange associative (I_a).     

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.     

Heat capacity and thermodynamic functions of LuPO4 in the range 0-320 K

The heat capacity of LuPO₄ was measured in the temperature range 6.51-318.03 K. Smoothed experimental values of the heat capacity were used to calculate the entropy, enthalpy and Gibbs free energy from 0 to 320 K. Under standard conditions these thermodynamic values are: (298.15 K) = 100.0 ± 0.1 J K⁻¹ mol⁻¹, S⁰(298.15 K) = 99.74 ± 0.32 J K⁻¹ mol⁻¹, H⁰(298.15 K) − H⁰(0) = 16.43 ± 0.02 kJ mol⁻¹, −[G⁰(298.15 K) − H⁰(0)]/T = 44.62 ± 0.33 J K⁻¹ mol⁻¹. The standard Gibbs free energy of formation of LuPO₄ from elements Δ_fG⁰(298.15 K) = −1835.4 ± 4.2 kJ mol⁻¹ was calculated based on obtained and literature data.     

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.     

Thermochemistry of NaRb[B4O5(OH)4]·4H2O

The enthalpies of solution of NaRb[B₄O₅(OH)₄]·4H₂O in approximately 1 mol dm⁻³ aqueous hydrochloric acid and of RbCl in aqueous (hydrochloric acid + boric acid + sodium chloride) were determined. From these results and the enthalpy of solution of H₃BO₃ in approximately 1 mol dm⁻³ HCl(aq) and of sodium chloride in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(5128.02 ± 1.94) kJ mol⁻¹ for NaRb[B₄O₅(OH)₄]·4H₂O was obtained from the standard molar enthalpies of formation of NaCl(s), RbCl(s), H₃BO₃(s) and H₂O(l). The standard molar entropy of formation of NaRb[B₄O₅(OH)₄]·4H₂O was calculated from the Gibbs free energy of formation of NaRb[B₄O₅(OH)₄]·4H₂O computed from a group contribution method.     

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).     

Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity X_m = 1.60 ± 0.23 mmol g⁻¹, β = −0.00654 ± 0.00017 kJ² mol⁻², mean free energy E = 8.74 ± 0.12 kJ mol⁻¹, Freundlich sorption capacity K_F = 0.24 ± 0.11 mol g⁻¹, 1/n = 0.90 ± 0.04 and of Langmuir constant K_L = 6800 ± 600 dm³ mol⁻¹ and C_m = 120 ± 18 μmol g⁻¹. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol⁻¹, ΔS = −64.0 ± 2.7 J mol⁻¹ K⁻¹ and ΔG_298k = −4.04 ± 0.09 kJ mol⁻¹. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.     

Hydrothermal synthesis, characterization and thermochemistry of Ca2[B2O4(OH)2]·0.5H2O

A pure calcium borate Ca₂[B₂O₄(OH)₂]·0.5H₂O has been synthesized under hydrothermal condition and characterized by XRD, FT-IR and TG as well as by chemical analysis. The molar enthalpy of solution of Ca₂[B₂O₄(OH)₂]·0.5H₂O in HC1·54.582H₂O was determined. From a combination of this result with measured enthalpies of solution of H₃BO₃ in HC1·54.561H₂O and of CaO in (HCl + H₃BO₃) solution, together with the standard molar enthalpies of formation of CaO(s), H₃BO₃(s) and H₂O(l), the standard molar enthalpy of formation of −(3172.5 ± 2.5) kJ mol⁻¹ of Ca₂[B₂O₄(OH)₂]·0.5H₂O was obtained.     

Heat capacity and thermodynamic properties of crystalline ornidazole (C7H10ClN3O3)

The molar heat capacities of 1-(2-hydroxy-3-chloropropyl)-2-methyl-5-nitroimidazole (Ornidazole) (C₇H₁₀ClN₃O₃) with purity of 99.72 mol% were measured with an adiabatic calorimeter in the temperature range between 79 and 380 K. The melting-point temperature, molar enthalpy, Δ_fusH_m, and entropy, Δ_fusS_m, of fusion of this compound were determined to be 358.59±0.04 K, 21.38±0.02 kJ mol⁻¹ and 59.61±0.05 J K⁻¹ mol⁻¹, respectively, from fractional melting experiments. The thermodynamic function data relative to the reference temperature (298.15 K) were calculated based on the heat capacities measurements in the temperature range from 80 to 380 K. The thermal stability of the compound was further investigated by DSC and TG. From the DSC curve an intensive exothermic peak assigned to the thermal decomposition of the compound was observed in the range of 445-590 K with the peak temperature of 505 K. Subsequently, a slow exothermic effect appears when the temperature is higher than 590 K, which is probably due to the further decomposition of the compound. The TG curve indicates the mass loss of the sample starts at about 440 K, which corresponds to the decomposition of the sample.     

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.     

Study of the in vitro degradation of poly(ethyl glyoxylate)

In vitro degradation of poly(ethyl glyoxylate) (PEtG), a functionalised polyacetal, was investigated. First, the thermodynamic polymerization parameters and the ceiling temperature (T_c) were determined (ΔH_p = 28 ± 3 kJ mol⁻¹, ΔS_p = 98 ± 7 J mol⁻¹ K⁻¹, T_c = 310 ± 4 K). Secondly, PEtG hydrolysis was investigated using potentiometry, weight loss measurements, SEC and ¹H NMR. The results show that PEtG is stable for at least 7 days in aqueous media. Then degradation occurs and releases ethanol and glyoxylic acid hydrate as final products. A scheme for the degradation mechanism involving chain scission and ester hydrolysis is proposed.     

Synthesis and thermochemistry of SrB2O4·4H2O and SrB2O4

Two pure strontium borates SrB₂O₄·4H₂O and SrB₂O₄ have been synthesized and characterized by means of chemical analysis and XRD, FT-IR, DTA-TG techniques. The molar enthalpies of solution of SrB₂O₄·4H₂O and SrB₂O₄ in 1 mol dm⁻³ HCl(aq) were measured to be −(9.92 ± 0.20) kJ mol⁻¹ and −(81.27 ± 0.30) kJ mol⁻¹, respectively. The molar enthalpy of solution of Sr(OH)₂·8H₂O in (HCl + H₃BO₃)(aq) were determined to be −(51.69 ± 0.15) kJ mol⁻¹. With the use of the enthalpy of solution of H₃BO₃ in 1 mol dm⁻³ HCl(aq), and the standard molar enthalpies of formation for Sr(OH)₂·8H₂O(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(3253.1 ± 1.7) kJ mol⁻¹ for SrB₂O₄·4H₂O, and of −(2038.4 ± 1.7) kJ mol⁻¹ for SrB₂O₄ were obtained.     

Synthesis and thermochemistry of MgO·3B2O3·3.5H2O

A new magnesium borate MgO·3B₂O₃·3.5H₂O has been synthesized by the method of phase transformation of double salt and characterized by XRD, IR and Raman spectroscopy as well as by TG. The structural formula of this compound was Mg[B₆O₉(OH)₂]·2.5H₂O. The enthalpy of solution of MgO·3B₂O₃·3.5H₂O in approximately 1 mol dm⁻³ HCl was determined. With the incorporation of the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5595.02±4.85) kJ mol⁻¹ of MgO·3B₂O₃3.5H₂O was obtained. Thermodynamic properties of this compound was also calculated by group contribution method.