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.     

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.     

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.     

New one-dimensional uranyl and neptunyl iodates: crystal structures of K3[(UO2)2(IO3)6](IO3)·H2O and K[NpO2(IO3)3]·1.5H2O

The uranyl and neptunyl(VI) iodates, K₃[(UO₂)₂(IO₃)₆](IO₃)·H₂O (1) and K[NpO₂(IO₃)₃]·1.5H₂O (2), have been prepared and crystallized under mild hydrothermal conditions. The structures of 1 and 2 both contain one-dimensional _∞¹[AnO₂(IO₃)₃]¹⁻(An=U,Np) ribbons that consist of approximately linear actinyl(VI) cations bound by iodate anions to yield AnO₇ pentagonal bipyramids. The AnO₇ units are linked by bridging iodate anions to yield chains that are in turn coupled by additional iodate anions to yield ribbons. The edges of the ribbons are terminated by monodentate iodate anions. For 1 and 2, K⁺ cations and water molecules separate the ribbons from one another. In addition, isolated iodate anions are also found between _∞¹[UO₂(IO₃)₃]¹⁻ ribbons in 1. In order to aid in the assignment of oxidation states in neptunyl containing compounds, a bond-valence sum parameter of 2.018 Å for Np(VI) bound exclusively to oxygen has been developed with b=0.37 Å. Crystallographic data (193 K, MoKα, λ=0.71073): 1, triclinic, , a=7.0609(4) Å, b=14.5686(8)  Å, c=14.7047(8)  Å, α=119.547(1)°, β=95.256(1)°, γ=93.206(1)°, Z=2, R(F)=2.49% for 353 parameters with 6414 reflections with I>2σ(I); (203 K, MoKα, λ=0.71073): 2, monoclinic, P2₁/c, a=7.796(4)  Å, b=7.151(3)  Å, c=21.79(1)  Å, β=97.399(7)°, Z=4, R(F)=6.33% for 183 parameters with 2451 reflections with I>2σ(I).     

A molecule based on polyoxometalate acid and crown ether: synthesis and characterization of [(H3O)(C20H24O6)]2[HPMo12O40]·C20H24O6·3MeCN·H2O (C20H24O6=dibenzo-18-crown-6)

The new molecule based on 12-molybdophosphate acid and dibenzo-18-crown-6, [(H₃O)(C₂₀H₂₄O₆)]₂[HPMo₁₂O₄₀]·C₂₀H₂₄O₆·3MeCN·H₂O 1, was synthesized in acetonitrile and characterized by elemental analyses, IR, ¹H NMR, electrospray mass spectra and single crystal X-ray diffraction, indicating that it contains [(H₃O)(dibenzo-18-crown-6)]⁺ cations, where oxonium ions are out of the planes defined by crown ether oxygen atoms, and disordered PMo₁₂O₄₀³⁻ anions with α-Keggin structure where the crystal has high lattice energy so that it is difficult to dissolve it. The crystallographic disorder averages Mo-Mo distances and Mo-O_b/c-Mo angles between the M₃ triplets and within the M₃ triplet. The interactions between crown ether molecules and oxonium ions are hydrogen-bonding with the O(crown ether)-OH₃⁺ distances of 2.510(10)-2.783(7) Å. The interactions between [(H₃O)(dibenzo-18-crown-6)]⁺ cations and PMo₁₂O₄₀³⁻ anions are dominantly electrostatic. The electrical conductivity is <10⁻⁷ S.cm⁻¹.     

A new sodium hydroxygallophosphate containing tetrameric gallium units: Na3[Ga4O(OH)(H2O)(PO4)4]·H2O

A new sodium hydroxygallophosphate, Na₃Ga₄O(OH)(H₂O)(PO₄)₄·H₂O, has been prepared by hydrothermal synthesis. Its structure has been determined from a single-crystal X-ray diffraction study. It crystallizes in the P2₁/c space group with the cell parameters a=9.445(2) Å, b=9.028(1) Å, c=19.209(3) Å, β=102.08(2), V=1603.4(4) Å³. Its three-dimensional framework can be described from PO₄ monophosphate groups sharing their apices with original Ga₄O₁₆(OH)(H₂O) tetrameric building units, which result from the assembly of one GaO₄ tetrahedron, one GaO₅ trigonal bipyramid and two octahedra: GaO₅(OH) and GaO₄(OH)(H₂O). The sodium cations and one water molecule are located in tunnels running along b.     

Syntheses and crystal structures of two new hydrated borates, Zn8[(BO3)3O2(OH)3] and Pb[B5O8(OH)]·1.5H2O

Two new hydrated borates, Zn₈[(BO₃)₃O₂(OH)₃] and Pb[B₅O₈(OH)]·1.5H₂O, have been prepared by hydrothermal reactions at 170 °C. Single-crystal X-ray structural analyses showed that Zn₈[(BO₃)₃O₂(OH)₃] crystallizes in a non-centrosymmetric space group R32 with a=8.006(2) Å, c=17.751(2) Å, Z=3 and Pb[B₅O₈(OH)]·1.5H₂O in a triclinic space group P1¯ with a=6.656(2) Å, b=6.714(2) Å, c=10.701(2) Å, α=99.07(2)°, β=93.67(2)°, γ=118.87(1)°, Z=2. Zn₈[(BO₃)₃O₂(OH)₃] represents a new structure type in which Zn-centered tetrahedra are connected via common vertices leading to helical ribbons _∞¹[Zn₈O₁₅(OH)₃]¹⁷⁻ that pack side by side and are further condensed through sharing oxygen atoms to form a three-dimensional _∞³[Zn₈O₁₁(OH)₃]⁹⁻ framework. The boron atoms are incorporated into the channels in the framework to complete the final structure. Pb[B₅O₈(OH)]·1.5H₂O is a layered compound containing double ring [B₅O₈(OH)]²⁻ building units that share exocyclic oxygen atoms to form a two-dimensional layer. Symmetry-center-related layers are stacked along the c-axis and held together by interlayer Pb²⁺ ions and water molecules via electrostatic and hydrogen bonding interactions. The IR spectra further confirmed the existence of both triangular BO₃ and OH groups in Zn₈[(BO₃)₃O₂(OH)₃], and BO₃, BO₄, OH groups as well as guest water molecules in Pb[B₅O₈(OH)]·1.5H₂O.     

Bimetallic single-source precursors [M(NH3)4][Co(C2O4)2(H2O)2]·2H2O (M = Pd, Pt) for the one run synthesis of CoPd and CoPt magnetic nanoalloys

All the steps of the proposed technique, from the synthesis of single-source precursors to the preparation of CoPd and CoPt nanoalloys, are described. The double complex salts (DCS) [M(NH₃)₄][Co(C₂O₄)₂(H₂O)₂]·2H₂O (M = Pd, Pt), which were synthesized by mixing solutions containing [M(NH₃)₄]²⁺ cations and [Co(C₂O₄)₂(H₂O)₂]²⁻ anions, have been used as precursors. The salts obtained were characterized by IR spectroscopy, thermal analysis, XRD and single crystal X-ray diffraction. The prepared compounds crystallize in the monoclinic (space group I2/m, M = Pd) and orthorhombic (space group I222, M = Pt) crystal systems. Thermal decomposition of the salts in helium or hydrogen atmosphere at 200-600 °C results in the formation of nanoalloys powders (random solid solution Co_0.50Pd_0.50 and chemically ordered CoPt). The size of the bimetallic particles varied from 5 to 20 nm. Order-disorder structural transformations in Co_0.50Pt_0.50 nanoalloys were studied. The magnetic properties of both chemically disordered Co_0.50Pd_0.50 and ordered CoPt clusters have also been measured.     

Syntheses and characterization of ANi(AsF6)3 (A = H3O, O2, NO, NH4, K, Rb, and Cs) compounds

ANi(AsF₆)₃ (A = O₂⁺, NO⁺, NH₄⁺) compounds could be prepared by reaction between corresponding AAsF₆ salts and Ni(AsF₆)₂. When mixtures of AF (A = Li, Na, K, Rb, Cs) and NiF₂ are dissolved in aHF acidified with an excess of AsF₅ the corresponding AAsF₆ and Ni(AsF₆)₂ were formed in situ. For A = Li and Na only mixtures of AAsF₆ and Ni(AsF₆)₂ were obtained, while for A = K, Rb and Cs, the final products were ANi(AsF₆)₃ (A = K-Cs) compounds contaminated with AAsF₆ (A = K-Cs) and Ni(AsF₆)₂.ANi(AsF₆)₃ (A = H₃O⁺, O₂⁺, NO⁺, NH₄⁺ and K⁺) compounds are structurally related to previously known H₃OCo(AsF₆)₃. The main features of the structure of these compounds are rings of NiF₆ octahedra sharing apexes with AsF₆ octahedra connected into infinite tri-dimensional network. In this arrangement cavities are formed where single charged cations are placed.In O₂Ni(AsF₆)₃ the vibrational band belonging to O₂⁺ vibration is found at 1866 cm⁻¹, which is according to the literature data one of the highest known values, and it is only 10 cm⁻¹ lower than the value for free O₂⁺.     

Thermodynamic representation of the NaCl + Na2SO4 + H2O system with electrolyte NRTL model

A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H₂O binary, the Na₂SO₄ + H₂O binary and the NaCl + Na₂SO₄ + H₂O ternary. The NRTL binary parameters for pairs H₂O-(Na⁺, Cl⁻) and H₂O-(Na⁺, SO₄²⁻), and the aqueous phase infinite dilution heat capacity parameters for ions Cl⁻ and SO₄²⁻ are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H₂O binary and the Na₂SO₄ + H₂O binary with electrolyte concentrations up to saturation and temperature up to 473.15 K. The Gibbs energy of formation, enthalpy of formation and heat capacity parameters for solids NaCl_(s), NaCl·2H₂O_(s), Na₂SO_4(s) and Na₂SO₄·10H₂O_(s) are obtained by fitting experimental data on solubilities of NaCl and Na₂SO₄ in water. The NRTL binary parameters for the (Na⁺, Cl⁻)-(Na⁺, SO₄²⁻) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na₂SO₄ + H₂O ternary.     

Partial exchange of the Li, Na and K alkaline cations in the HNi(PO4)·H2O layered compound

The exchange of the Li⁺(1), Na⁺(2) and K⁺(3) alkaline cations in the layered HNi(PO₄)·H₂O was carried out starting from a methanolic solution containing the Li(OH)·H₂O hydroxide for (1) and the M(OH) (M=Na and K) hydroxides together with the (C₆H₁₃NH₂)_0.75HNiPO₄·H₂O phases for (2) and (3). The compounds are stable until, approximately, 280 °C for (1) and 400 °C for phases (2) and (3), respectively. The IR spectra show the bands belonging to the water molecule and the (PO₄)³⁻ oxoanion. The diffuse reflectance spectra indicate the existence of Ni(II), d⁸, cations in slightly distorted octahedral geometry. The calculated Dq and Racah (B and C) parameters have a mean value of Dq=765, B=905 and , respectively, in accordance with the values obtained habitually for this octahedral Ni(II) cation. The study of the exchange process performed by X-ray powder diffraction indicates that the exchange of the Li⁺ cation in the lamellar HNi(PO₄)·H₂O phase is the minor rapid reaction, whereas the exchange of the Na⁺ and K⁺ cations needs the presence of the intermediate (C₆H₁₃NH₂)_0.75HNiPO₄·H₂O intercalate in order to obtain the required product with the sodium and potassium ions. The Scanning electronic microscopy (SEM) images show a mean size of particle of 5 μm. The Li⁺ exchanged compound exhibits small ionic conductivity (Ω cm⁻¹ is in the 10⁻⁸-10⁻⁹ range) probably restrained by the methanol solvent. Magnetic measurements carried out from 5 K to room temperature indicate antiferromagnetic coupling as the major interaction in the three phases. Notwithstanding the Li and K phases show a weak ferromagnetism at low temperatures.     

Structure of uranyl complexes with acetylenedicarboxylic acid, K(H5O2)[UO2(OOCC≡CCOO)2 · H2O] · 2H2O and Cs2[UO2(OOCC≡CCOO)2 · H2O] · 2H2O

Uranyl complexes with acetylenedicarboxylic acid, K(H₅O₂)[UO₂L₂H₂O] · 2H₂O (I) and Cs₂[UO₂L₂H₂O] · 2H₂O (II), L²⁻ = C₄O ₄ ²⁻ were prepared for the first time. The composition and structure of the complexes were determined by X-ray diffraction. The crystal data are as follows: a = 16.254(12) ?, b = 13.508(8) ?, c = 7.683(6) ?, β = 90.91(7)°, space group C2/c, V = 1687(2) ?³ (I); a = 7.0745(10), b = 18.4246(10), c = 13.1383(10) ?, space group Abm2, V = 1712.5(3) ?³ (II). The structures of I and II are based on [UO₂L₂H₂O] _n ²⁻ anionic chains stretched along the [101] direction (I) or [010] direction (II). In I and II, the uranium coordination polyhedron is a pentagonal bipyramid in which the equatorial environment of the uranyl ions is formed by the oxygen atoms of the four L²⁻ anions and the water molecule. The L²⁻ anions in I and II are bidentate bridging ligands connecting two uranium atoms that are next to each other in the anionic chain; their coordination capacity is equal to 2. In I, the K⁺ and H₅O ₂ ⁺ cations are outer-sphere species. The latter form hydrogen bonds combining the anionic chains shifted by translation b with respect to each other. The [UO₂L₂H₂O] _n ²⁻ chains in I are surrounded by the potassium and oxonium cations; in II, these are combined by hydrogen bonds into anionic layers between which Cs⁺ cations are arranged. The IR spectrum of compound II was measured and interpreted. Original Russian Text ? I.A. Charushnikova, A.M. Fedoseev, N.A. Budantseva, I.N. Polyakova, Ph. Moisy, 2007, published in Koordinatsionnaya Khimiya, 2007, Vol. 33, No. 1, pp. 63–69.     

Synthesis and crystal structure of KNa3[Fe3O(CH3COO)6(H2O)2]3 [α-P2W17Fe(H2O)O61]·32.5H2O

A complex of the composition KNa₃[Fe₃O(CH₃COO)₆(H₂O)₃]₃ [α-P₂W₁₇Fe(H₂O)O₆₁]·32.5H₂O (I) was obtained by interaction of FeCl₃·6H₂O and phosphotungstate K₁₀[α₂-P₂W₁₇O₆₁]·20H₂O in an acetate buffer with a yield of 52%. Compound I was characterized by single crystal X-ray phase analysis and IR spectroscopy. In the crystal structure, the Na and K cations bind [Fe₃O(CH₃COO)₆(H₂O)₃]⁺ trinuclear cations and [α-P₂W₁₇Fe(H₂O)O₆₁]⁷⁻ heteropolytungstate anions into infinite zigzag chains. Original Russian Text Copyright ? 2005 by N. V. Izarova, M. N. Sokolov, A. V. Virovets, H. G. Platas, and V. P. Fedin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 1, pp. 149–155, January–February, 2005.     

Crystal structure of a new phosphate compound, Mg2KNa(PO4)2·14H2O

A new phosphate compound, Mg₂KNa(PO₄)₂·14H₂O, formed in the laboratory by cyanobacteria, has been identified and its crystal structure studied with single-crystal X-ray diffraction and infrared spectroscopy. The crystal is orthorhombic with the space group Pnma and unit-cell parameters a=25.1754(18) Å, b=6.9316(5) Å, c=11.2189(10) Å, V=1957.8(3) Å³. Its structure can be viewed as stacking of three types of layers along the a-axis in a sequence ABCBABCB…, where layer A is composed of Mg1(H₂O)₆ octahedra and Na(H₂O)₆ trigonal prisms, layer B of two crystallographically distinct PO₄³⁻ tetrahedra (designated as P1 and P2), and layer C of Mg2(H₂O)₆ octahedra and highly irregular K-polyhedra formed by five H₂O molecules and one O²⁻ from the P2 tetrahedron. The linkage between layers is principally achieved through hydrogen bonding, except for the K-O5 bond between layers B and C. The structure of Mg₂KNa(PO₄)₂·14H₂O has many features similar to those for the struvite analogs of MgK(PO₄)·6H₂O (Acta Crystallogr. B 35 (1979) 11) or MgNa(PO₄)·7H₂O (Acta Crystallogr. B 38 (1982) 40) and represents the first struvite-type phosphate compound that contains both K and Na as univalent cations.     

Hydrothermal synthesis and characterization of layered vanadium phosphite: [HN(C2H4)3N][(VO)2(HPO3)2(OH)(H2O)]·H2O

A novel compound, [HN(C₂H₄)₃N][(VO)₂(HPO₃)₂(OH)(H₂O)]·H₂O, was hydrothermally synthesized and characterized by single crystal X-ray diffraction. This compound crystallizes in the monoclinic system with the space group C2/c and cell parameters a=11.0753(3) Å, b=17.8265(6) Å, c=16.5229(5) Å, and β=92.362(2)°. The structure of the compound consists of vanadium phosphite layers which are built up from the infinite one-dimensional chains of [(VO)(H₂O)(HPO₃)₂]²⁻ of octahedral VO₅(H₂O) and pseudo pyramidal [HPO₃], and bridging binuclear fragments of [VO(OH)]₂. Thermogravimetric analysis and magnetic susceptibility data for this compound are given.     

Selective anion-exchange intercalation of isomeric benzoate anions into the layered double hydroxide [LiAl2(OH)6]Cl·H2O

All the geometric isomers of the benzoate derivatives, XC₆H₄CO₂⁻ (X=F, Cl, Br, OH, OCH₃, NO₂, CO₂CH₃, NH₂, N(CH₃)₂) can be intercalated into the layered double hydroxide [LiAl₂(OH)₆]Cl·H₂O in 50% (v/v) water/ethanol solution at 80 °C to give fully anion-exchanged first stage intercalation compounds [LiAl₂(OH)₆]G·yH₂O (G=a substituted benzoate). The observed interlayer separations of the intercalates vary from 14.3 Å for [LiAl₂(OH)₆](4-nitrobenzoate)·2H₂O to 20.6 Å for [LiAl₂(OH)₆](3-dimethylaminobenzoate)·3H₂O. Competitive intercalation studies using mixtures of isomeric benzoates showed that the 4-isomers and 2-isomers are the most and the least preferred anions, respectively. Comparing the calculated dipole moments of the anions with the observed isomeric intercalation preferences suggests that dipole moment may be a good general index for the preference; however, it should be remembered that the bulkiness and electronegativity of the other substituent could be very important factors that affect the preferential intercalation.     

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.     

Synthesis, characterization and thermochemistry of K2B5O8(OH)·2H2O

A pure hydrated potassium borate K₂B₅O₈(OH)·2H₂O has been synthesized under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, XRD, FT-IR, Raman spectra and DTA-TG. The crystal structure consists of two K-O polyhedra and [B₅O₈(OH)]²⁻ polyborate anion. The enthalpy of formation was determined to be −4772.6 ± 4.0 kJ mol⁻¹ by solution calorimetry.     

A rare multi-coordinate tellurite, NH4ATe4O9·2H2O (ARb or Cs): The occurrence of TeO3, TeO4, and TeO5 Polyhedra in the same material

Two new tellurites, NH₄RbTe₄O₉·2H₂O and NH₄CsTe₄O₉·2H₂O have been synthesized and characterized. The compounds were synthesized hydrothermally, in near quantitative yields, using the alkali metal halide, TeO₂, and NH₄OH as reagents. The iso-structural materials exhibit layered, two-dimensional structural topologies consisting of TeO_x (x=3, 4, or 5) polyhedra separated by NH₄⁺, H₂O, Rb⁺ or Cs⁺ cations. Unique to these materials is the presence of TeO₃, TeO₄, and TeO₅ polyhedra. Thermogravimetric and infrared spectroscopic data are also presented. Crystal data: NH₄RbTe₄O₉·2H₂O: Monoclinic I2/a (no. 15), a=18.917(3) Å, b=6.7002(11) Å, c=21.106(5) Å, β=101.813(2)°, V=2618.5(9) Å³, Z=8; NH₄CsTe₄O₉·2H₂O: Monoclinic I2/a (no. 15), a=18.9880(12) Å, b=6.7633(4) Å, c=21.476(2) Å, β=102.3460(10)°, V=2694.2(3) Å³, Z=8.     

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.