Search

The structure of aqueous potassium borate solutions is studied by neutron diffraction with H/D isotopic substitution. Key hydration modes of the borate ions are highlighted by a combination of empirical potential structure refinement and DFT.

Choline possesses a gauche configuration in choline chloride-carboxylic acid DESs. DESs are stabilized by hydrogen bonds and carbon–hydrogen bonds. Cl− plays an important role in maintaining the structural stability of DESs.

The structure of aqueous magnesium nitrate solution is gaining significant interest among researchers, especially whether contact ion pairs exist in concentrated solutions. Here, combining X-ray diffraction experiments, quantum chemical calculations and

The local environment of rubidium ion in aqueous rubidium tetraborate solutions was investigated using extended X-ray absorption fine structure. The Rb–O distance and coordination number in the first hydration shell of rubidium ion are 2.92 A and 8.0, respectively. The distribution map of borate anions was calculated using the Newton iteration method, and further verified using nuclear magnetic resonance spectroscopy (NMR). This shows that the dominant species are $${\text{B}}_{4} {\text{O}}_{5} \left( {{\text{OH}}} \right)_{4}^{2 - }$$ and $${\text{B}}_{3} {\text{O}}_{3} \left( {{\text{OH}}} \right)_{4}^{ - }$$ in aqueous rubidium tetraborate solutions at 298.15 K. The dominant species change to $${\text{B}}_{3} {\text{O}}_{3} \left( {{\text{OH}}} \right)_{4}^{ - }$$ and B(OH)3 at 333.15 K. Hydrolysis and polymerization coexist in aqueous rubidium tetraborate solutions with the changes of concentration and temperature.

The solubility isotherms of the ternary systems LiCl–MgCl2–H2O and Li2SO4–MgSO4–H2O were elaborately redetermined at 348.15 K using an isothermal equilibrium method. The compositions of solid phase...

The structure of aq. sodium acetate solution (CH3COONa, NaOAc) was studied by X-ray scattering and density function theory (DFT). For the first hydrated layer of Na+, coordination number (CN) between Na+ and O(W, I) decreases from 5.02 ± 0.85 at 0.976 mol/L to 3.62 ± 1.21 at 4.453 mol/L. The hydration of carbonyl oxygen (OC) and hydroxyl oxygen (OOC) of CH3COO− were investigated separately and the OC shows a stronger hydration bonds comparing with OOC. With concentrations increasing, the hydration shell structures of CH3COO− are not affected by the presence of large number of ions, each CH3COO− group binds about 6.23 ± 2.01 to 7.35 ± 1.73 water molecules, which indicates a relatively strong interaction between CH3COO− and water molecules. The larger uncertainty of the CN of Na+ and OC(OOC) reflects the relative looseness of Na-OC and Na-OOC ion pairs in aq. NaOAc solutions, even at the highest concentration (4.453 mol/L), suggesting the lack of contact ion pair (CIP) formation. In aq. NaOAc solutions, the so called “structure breaking” property of Na+ and CH3COO− become effective only for the second hydration sphere of bulk water. The DFT calculations of CH3COONa (H2O)n=5–7 clusters suggest that the solvent-shared ion pair (SIP) structures appear at n = 6 and become dominant at n = 7, which is well consistent with the result from X-ray scattering.

Raman spectroscopy combined with component analysis and molecular dynamics simulation were used to study chemical species and their transformation in aqueous sodium solutions. Study shows that the characteristic vibrational frequency of nitrate ions (ν

Neutron diffraction, X-ray diffraction, and empirical potential structure refinement modeling were employed to study the structure of alkaline aqueous NaBD4 solutions at different NaBD4 concentrati...

The micro-structure of aqueous boric acid (H3BO3) solutions is of broad interest in earth sciences, geochemistry, material science, as well as chemical engineering. In the present study, the structure of aqueous H3BO3 solutions was studied via neutron scattering with 2H and 11B isotope labelling combined with empirical potential structure refinement (EPSR) modelling. In aqueous H3BO3 solutions, B(OH)3 is the dominant borate species. Density function theory (DFT) calculations show that the boron hydroxyl has a lower electrostatic potential (ESP), which makes B(OH)3 a relatively weakly hydrated, compared with the bulk water. In the 0.95 mol L-1 H3BO3 solution at 298 K (saturated), ∼18 water molecules enter the hydration sphere of B(OH)3 with the hydration distance (B-O(W)) of 3.75 A, while only 4.23 of them hydrate with H3BO3 as the hydrogen bond (H-bond) acceptor or H-bond donor. Both neutron scattering and DFT calculations for 2B(OH)3·6H2O clusters at the ωB97XD/6-311++g(3df,3pd) basis level show that B(OH)3 forms molecular clusters in bidentate contact molecular pairs (BCMP), mono-dentate molecular pairs (MCMP), solvent-shared molecular pairs (SMP), and parallel solvent-shared molecular pairs (PSMP) in aqueous solutions. Their relative contents are both concentration- and temperature-sensitive. BCMP with the B-B distance of ∼4.1 A is the dominant molecular pair in the aqueous solutions. Relatively less content and van der Waals interactions stabilized PSMP, with a B-B distance of ∼3.6 A between the two parallel layers, which is a crucial species for the crystallization of H3BO3 from aqueous solution.

In this study, microstructure such as intra-molecule interaction B O,O O in polyborate anions (B3O3(OH)4-, B4O5(OH)4-) and inter-molecule (B O(W),M(Rb/Cs) O, M(Rb/Cs) B and O O, M-M i.e.) interaction have been taken into consideration by model calculation with the method of X-ray scattering. The models of B3O3(OH)4-, B3O3(OH)52− and B4O5(OH)42− were optimized by DFT (density functional theory) calculation which have a good agreement with the model calculation. During the process of data analyzing, Raman spectrum, pH, density, stoichiometric volume, atomic mass absorption coefficient have also been carried out. The coordination distance and number of Cs O(wI)(∼0.336 nm, ∼7.8), Cs O(wII)(∼0.526 nm, ∼8.4), O O(W)(∼0.278 nm, ∼2.15) and Cs B(∼0.458 nm, ∼0.9) are concerned to Cs2B4O7 solution. For aqueous Rb2B4O7 samples, the structure parameters of Rb O(wI)(∼0.292 nm, ∼7.0), Rb O(wII)(∼0.467 nm, ∼8.0), O O(W)(∼0.278 nm, ∼2.22), Rb B(∼0.377 nm, ∼0.9) are also listed in the discussion part. And also concluded that cesium ion forms bidentate chelate complexes with tetraborate ion in the solution. Moreover, the influence of the samples, concentration on RDFs (radial distribution function curves) and the difference between cesium tetraborate and rubidium tetraborate also illustrated in paper.

In this paper, the factors determining the spectroscopic characteristics of vsym–B(OH)4− band including coupling effect, hydrogen bonding effect, and direct contact effect in Li[B(OH)4] solutions are investigated by using ab initio calculation. The coupling effect between the liberations of water and [B(OH)4−] has a larger effect on vsym–B(OH)4− in solvent-shared ion pair (SIP) and monodentate contact ion pair (MCIP), but the smaller effect in bidentate contact ion pair (BCIP). Water molecule tends to hydrate to the middle position between the first sphere of B(OH)4− and outer–sphere of [Li(H2O)4+] and has a different effect on vsym–B(OH)4− in ion pairs. The direct contact effect and polarization effect lead to 19.7 cm−1 red shift of vsym–B(OH)4− in MCIP, and 0.4 cm−1 blue shift in BCIP. The association process in Li[B(OH)4] solution was also introduced by using Raman spectral evolution of vsym –B(OH)4− in the dehydration process.

An increasing amount of research has investigated whether direct contact ion pairs (CIP) exist in magnesium nitrate solutions. In this work, the relationship between the concentration and microstructure, as well as the details of the ion pair structure in magnesium nitrate solutions were studied by Raman spectroscopy, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations. Component analysis showed that solvent-shared ion pairs (SIPs) and free hydrated ions were the dominant species in dilute solution. SIPs gradually transformed into contact ion pairs as the concentration increased. Complex structures and CIPs were the main species when WSR 10, and as the concentration further increased, the CIP content gradually decreased, while the number of complex structures gradually increased. MD simulations and DFT calculations provide a new understanding of the structural units of ion pairs in magnesium nitrate solutions. The SIPs and CIPs were mainly composed of cationic triple ion clusters with two magnesium ions and one nitrate ion. The nitrate ion mainly existed as monodentate ligand to form a CIP with the magnesium ion. As the solution concentration increased, triple ion clusters gradually transformed into more complex chain structures. The structural complexity of magnesium nitrate solutions deserves further attention.

The micro-structure of aqueous boric acid (H3BO3) solutions is of broad interest in earth sciences, geochemistry, material science, as well as chemical engineering. In the present study, the structure of aqueous H3BO3 solutions was studied via neutron scattering with 2H and 11B isotope labelling combined with empirical potential structure refinement (EPSR) modelling. In aqueous H3BO3 solutions, B(OH)3 is the dominant borate species. Density function theory (DFT) calculations show that the boron hydroxyl has a lower electrostatic potential (ESP), which makes B(OH)3 a relatively weakly hydrated, compared with the bulk water. In the 0.95 mol L-1 H3BO3 solution at 298 K (saturated), ∼18 water molecules enter the hydration sphere of B(OH)3 with the hydration distance (B-O(W)) of 3.75 Å, while only 4.23 of them hydrate with H3BO3 as the hydrogen bond (H-bond) acceptor or H-bond donor. Both neutron scattering and DFT calculations for 2B(OH)3·6H2O clusters at the ωB97XD/6-311++g(3df,3pd) basis level show that B(OH)3 forms molecular clusters in bidentate contact molecular pairs (BCMP), mono-dentate molecular pairs (MCMP), solvent-shared molecular pairs (SMP), and parallel solvent-shared molecular pairs (PSMP) in aqueous solutions. Their relative contents are both concentration- and temperature-sensitive. BCMP with the B-B distance of ∼4.1 Å is the dominant molecular pair in the aqueous solutions. Relatively less content and van der Waals interactions stabilized PSMP, with a B-B distance of ∼3.6 Å between the two parallel layers, which is a crucial species for the crystallization of H3BO3 from aqueous solution.

Structure of alkaline aqueous NaBH4 solutions at NaBH4 concentrations of 1.0 to 9.1 mol·dm−3 (almost saturated) as well as a 1.3 mol·dm−3 NaOH solution was studied by X-ray diffraction and Empirical Potential Structure Refinement (EPSR) modelling. In the 1.0 mol dm−3 alkaline NaBH4 solution, Na+ is surrounded by around six water molecules with octahedral geometry. With an increase in NaBH4 concentration, the hydration number of Na+ decreases from 4.8 ± 1.1 at 2.25 mol·dm−3 solution to 2.9 ± 1.3 at 9.1 mol·dm−3 with an almost constant Na+-O (W: H2O) distance of 2.34 A. The decrease in hydration number for Na+ is compensated by the formation of ion pairs between Na+ and BH4− to ensure an octahedral hydrated geometry for Na+. About 6.0 ± 1.6 water molecules are likely to bond to BH4− via tetrahedral edges or tetrahedral corners without a very specific hydration geometry, giving rise to each hydrogen atom of BH4− bound to 2.3 ± 1.0 water molecules through dihydrogen bonds. The hydration number around BH4− decreases with increasing concentration. BH4− tends to form contact ion pairs with Na+ at the Na-B distances of 3.24 A and 2.82 A in tetrahedral-corner-shared and tetrahedral-edge-shared fashions, respectively; the number of Na-B interactions increases from 0.3 ± 0.5 in 1.0 mol·dm−3 (almost negligible) to 2.1 ± 0.9 in 9.0 mol·dm−3. Tetrahedral-edge-shared bidentate ion pair is likely to be the preferred and dominant ion cluster over the wide concentration range. Ion association between the Na+ and BH4− was crosschecked by density function theory (DFT) calculations on [NaBH4(H2O)6] clusters.

In this work, the structures of micro-species in [CaCl2(H2O)n = 0–12] were systematically studied by density functional theory. The distances between Ca2+ and the two Cl− ions (rCa–Cl) are all less than 4.2 A when n = 1–4, which shows that the main species is contact ion pair. When n = 5, the main species is solvent separated ion-pair [CaCl−(H2O)5···Cl−] (SIP/s) with one Cl− dissociated from [CaCl2]. When n = 6–9, the main species is changed into solvent separated ion-pair (SIP/d) with two Cl− dissociated from [CaCl2]. Six water molecules are located in the inner shell and other water molecules hydrate in the outer sphere in the form of hydrogen bonding. When n = 10–12, the main structure is still SIP/d. Moreover, the hydration number of calcium with the most stable structure in the first hydration shell is 7. The inner hydration distance remains almost unchanged and the outer water molecules have little effect on the inner ones. The vibrational frequencies of the water molecules in [CaCl2(H2O) n ] were also studied and discussed in detail.

An increasing amount of research has investigated whether direct contact ion pairs (CIP) exist in magnesium nitrate solutions. In this work, the relationship between the concentration and microstructure, as well as the details of the ion pair structure in magnesium nitrate solutions were studied by Raman spectroscopy, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations. Component analysis showed that solvent-shared ion pairs (SIPs) and free hydrated ions were the dominant species in dilute solution. SIPs gradually transformed into contact ion pairs as the concentration increased. Complex structures and CIPs were the main species when WSR

Quantum chemistry calculations were used to study the structure and energy of strontium (Sr) ion hydrated clusters [Sr(H2O)1−25]2+. The saturated hydration number of the first hydration layer of Sr...

In this work, the structural details and Raman spectra of the Ca(NO3)2(H2O) n=0–10 clusters were studied by using ab initio method. The results show that the main species in the cluster is the contact ion pair (CIP) when n = 1–7. When n = 8–10, the main species changes into solvent shared ion pair (SIP) CaNO3(H2O) n …NO3 − in the bidentate form. One of the r Ca–N distances remains unchanged at ~2.95 A, while the other one increases to more than 4.8 A. The hydration distance r Ca–O remains at 2.42 A. The contact between Ca2+ and NO3 leads to a red shift of the v 1–NO3 − band while the polarization of water by Ca2+ leads to a blue shift. The vibrational frequency of water molecules remains unchanged for the same types of water molecules. Hydrogen bonds are the main reason for the red shift of vibrational frequency of water molecules.

Summary The phase transition performance of the CaCl2 · 6H2O–Ca(NO3)2 · 4H2O composite salt system with nucleating and thickening agents was investigated in this paper. The CaCl2 · 6H2O–Ca(NO3)2 · 4H2O composite salt system was prepared by adding Ca(NO3)2 · 4H2O (12 wt%) to CaCl2 · 6H2O. Different nucleating agents including SrCl2 · 6H2O, SrCO3, BaCl2, BaCO3, Na2B4O7 · 10H2O, H3BO3 and NH4Cl were used to address the problems of phase segregation and supercooling phenomena during the phase change process. The results show that the single nucleating agent SrCl2 · 6H2O or the mixture of nucleating agents with 2 wt% SrCl2 · 6H2O, 1 wt% BaCl2 and 0.5 wt% of thickening agent carboxyl methyl cellulose is the most suitable for this system. The latent heat remained constant at about 116 J/g before and after adding the agents. Density functional theory was used to further investigate the microstructure-related reason for the salt–water separation and supercooling phenomena. It can be deduced that the hydrogen bond is the vital factor involved during the phase transition. The aim of adding thickener was to form more hydrogen bonds which encapsulated the hydrated species and made it difficult to lose the hydrated waters. The main purpose of adding nucleating agent was to break the metastable state among microscopic species. The results of this work indicate that the CaCl2 · 6H2O–Ca(NO3)2 · 4H2O salt mixture has potential as a thermal energy storage material. Copyright © 2017 John Wiley & Sons, Ltd.

Potassium tetrahydroxyborate solution is a significant material in the borate solution family, but there is limited knowledge about hydration structures and interactions of K+, [B(OH)4−], and water. In this study, the X-ray diffraction measurements of potassium tetrahydroxyborate solutions have been made. The experimental structure factors are subjected to Empirical Potential Structure Refinement (EPSR) modeling to reveal the details of ion hydration and association in the aqueous solutions. This study shows that the O(W)–O(W) distance of water in the studied solutions ranges from 2.82 to 2.76 A with a coordination number that ranges from 4.7 ± 1.4 to 3.1 ± 1.3 when the value of the water–salt molar ratio (WSR) is decreased from 30 to 6. The addition of ions slightly affects the tetrahedral structure of water even when the concentration of ions is high. The first hydration distance of K+ remained at ∼2.67 A, whereas the value of the coordination number (CN) decreased from 5.4 ± 1.3 to 3.9 ± 1.5 when the concentration of the borate solution was increased. The hydration ability of K+ was weak and almost did not have a fixed local hydration structure. The pair distribution function (PDF) of gB–O(W)(r) shows that [B(OH)4−] has a broad hydration distance from 2.9 to 5.4 A because of the complex interactive relationship between K+, [B(OH)4−] and water. There is a competitive hydration between K+ and [B(OH)4−]. Both the X-ray diffraction and DFT-based calculations confirm that the main species is monodentate contact ion pairs when WSR = 30, bidentate contact ion pairs when WSR = 14, and triple contact ion pairs when WSR = 6. These results will provide a new understanding about potassium tetrahydroxyborate solution.

In this study, microscopic Raman spectroscopy and Ab initio quantum chemical calculation were used to determine the structural details of ion pairs and their transformation in concentrated K[B(OH)

Recognition of the reaction mechanism of hydrogen generation by borohydrides hydrolysis can provide effective help for optimizing the reaction condition and catalyst design. In the present work, the underlying mechanisms of BH 4 − spontaneous hydrolysis under water-deficiency (2 water molecules) and water-rich (4 water molecules) condition were elaborated by the second-order Moller-Plesset perturbation theory (MP2) at MP2/6-311++G(3df, 3pd) level of theory. The present theoretical calculations predicted that dihydrogen bonding plays an extremely important role in the process of BH 4 − hydrolysis, and H2 is formed by a hydridic B-H hydrogen and a protic O H hydrogen. The hydrogen generation mechanism of BH 4 − hydrolysis in water-rich condition may experience BH 4 − → BH 3 ( OH ) − , BH 3 ( OH ) − → BH 2 ( OH ) 2 − , BH 2 ( OH ) 2 − → BH ( OH ) 3 − and BH ( OH ) 3 − → B ( OH ) 4 − four steps. BH 4 − hydrolysis mechanism in water-deficiency condition includes four steps in two possible reaction pathways as the water molecules participate with the reaction in different steps. All those reaction pathways with the same first step ( BH 4 − → BH 3 ( OH ) − ) and it's the Rate Determining Step (RDS) of the whole reaction. BH 4 − spontaneous hydrolysis at neutral or weak alkaline should be in the acid-catalyzed mechanism.

The phase change performance of the CH3COONa·3H2O–KCl composites salt system with Al2O3 nanoparticles and carboxyl methyl cellulose (CMC) were investigated in this paper. The CH3COONa·3H2O–KCl composite salt system was prepared by adding KCl (at 2, 4, 6, 8, and 10 wt.%) to CH3COONa·3H2O, respectively. Al2O3 nanoparticles were proposed as the nucleating agent and CMC was selected as a thickening agent for the CH3COONa·3H2O–8 wt.%KCl composites salt system. The results show CH3COONa·3H2O–8 wt.%KCl composites salt system with 1 wt.% Al2O3 nanoparticles and 4 wt.% CMC, in which almost no supercoiling phenomenon occurs. After 50 cycles of the melting–freezing cycle test, aluminum oxide is uniformly dispersed in SAT composites matrix, the latent heat remained constant at about 232.29 J/g. The maximum deviations of latent heat of composites CH3COONa·3H2O–8 wt.%KCl with 1 wt.% Al2O3 nanoparticles and 4 wt.% CMC before and after the fifty-run-recycling test are only 3.6%.

Based on the measured pH data and reported equilibrium constants, the main polyborate species formation existing in solution was investigated using the Newton iteration method at 298 and 333 K, and checked by the method of 11B nuclear magnetic resonance (NMR) spectroscopy. The neighboring structure of rubidium ion was studied at room temperature, which the structural parameters, including the coordination number, interatomic distance of Rb-O and Debye-Waller factor, were determined by the synchrotron radiation extended X-ray absorption fine structure (EXAFS). The results show that the average interatomic distance of Rb-O is 2.93 ± 0.004 A and coordination number is 7.7 ± 0.9 in the first hydration shell around rubidium ion.

The structure of aqueous lithium tetraborate solutions was investigated by species distribution calculation and synchrotron X-ray scattering. It shows that the dominant species in supersaturated solution at 298.15 K is B4O5(OH) 4 2− and the minor species are B3O3(OH) 5 2− , B3O3(OH) 4 − and B(OH)3. The ‘intramolecular’ structural parameters of B4O5(OH) 4 2− , such as bond length and coordination number, were gives out using density function theory calculation. X-ray scattering study shows that the distance Li–O(H2O)I of [Li(H2O)4]+ is about 0.1983 nm with the coordination number(CN) 4 in tetrahedral configuration. The B–O(H2O) distance in hydrated anion B4O5(OH)4(OH2) 8 2− is 0.3662 nm with the CN 12. The Li+–B distance is about 0.3364 nm with a coordination number ~1.0. The temperature effect on solution structure was also discussed.

Molecular dynamics (MD) simulation was employed to explore the structural and thermodynamic characteristics of 18-crown-6 ether selectivity to alkali metal ions in aqueous solution. The radial distribution functions (RDFs), potentials of mean force (PMFs) and binding free energies between Li+, Na+, K+, Rb+, Cs+ and 18-crown-6 ether with SPC/E and TIP4P water models in aqueous solutions at 278.15 K, 298.15 K and 318.15 K were obtained. It shows that K+ is selected over other alkali metal ions by 18-crown-6 ether in aqueous solution at all water models and temperatures we considered, and increasing temperature is beneficial for the binding of 18-crown-6 ether to alkali metal ions. The calculated selective sequence (Li+ ≪ Na+ Rb+ > Cs+) in aqueous solution is close to the experimental results. The gas-phase binding energies of 18-crown-6 to alkali metal ions and the minimum potential energies with corresponding minimum positions of alkali ions complexes were got by density functional theory (DFT). The results reveal that the selectivity of 18-crown-6 to alkali metal ions in gas-phase follows the sequence, Li+ > Na+ > K+ > Rb+ > Cs+, and follows their ionic potentials. The effect of solvent on the selectivity of 18-crown-6 ether to alkali ions is confirmed by comparing the selective sequences in gas-phase and aqueous solution. The noncovalent interactions sites and types between alkali ions and 18-crown-6 ether were determined by electrostatic potential (ESP) and the average reduced density gradient (aRDG), which shows that the interactions between alkali ions and 18-crown-6 are electrostatic dominated.

In this study, ion pairs in a single sodium tetrahydroxyborate [Na [B(OH)4] droplet were analyzed using an “in-situ strategy” in which a sample-droplet of nanogram mass was deposited on a hydrophobic substrate and droplet was forced to enter into a supersaturated state by decreasing the relative humidity (RH) of the environment. The structure of the solvated [B(OH)4−] ionic moiety with various molar water-to-solute ratios (WSR) was analyzed using Raman spectroscopy. To confirm the structural changes in the droplet, electronic structure calculations were carried out using density functional theory (DFT). The frequencies calculated for the totally symmetric BO stretching vibration (vsym(BO)) of the [B(OH)4−] moiety were compared with those of the fundamental bands observed in the Raman spectra recorded of the droplets. The following results have been obtained: (i) when WSR is reduced from 9 to 0.1, the frequency of the band that corresponds to vsym(BO) shifts from 745 to 746 cm−1, and its full-width at half-maximum value increases from 19.7 to 20.5 cm−1; (ii) when WSR ≥7, the solvent-shared ion pair (SIP) is predominantly present in the solution, whereas in the case of WSR

In this study, microscopic Raman spectroscopy and Ab initio quantum chemical calculation were used to determine the structural details of ion pairs and their transformation in concentrated K[B(OH)4] droplets. The Raman experiment shows that the vsym-B(OH)4− undergoes a downward shift with the decrease of WSR. The contact ion pairs (CIPs) change to solvent shared ion pairs when the molar water-to-solute ratio (WSR) is bigger than 6; CIPs are the dominant species when 1.33

In this paper, the factors determining the spectroscopic characteristics of v

As a Lewis weak acid, the hydration and acid dissociation mechanisms of B(OH) 3 are still unclear. In present letter, we calculated the optimized structure, stability and Raman spectra for micro-hydrated clusters of B(OH) 3 with DFT in both gaseous and aqueous phase at B3LYP/aug-cc-pVDZ level. The stepwise micro-hydration process of B(OH) 3 were described in detailed. The micro-hydration process and Raman spectrum study indicate that the axial hydration is a “trigger” for B(OH) 3 dissociation.

The structure of aqueous potassium pentaborate solution has been confirmed by species distribution calculation, synchrotron X-ray scattering, density function theory calculation. The kinds of species and the transformation relationship were investigated by species distribution calculation. The radial distribution function and the structure parameters were given out by synchrotron X-ray scattering experiment. The hydration distance of K–O(H 2 O) is ∼0.294 nm with a average hydration number of 8.0. The B–O(H 2 O) distance in hydrated anion [B 3 O 3 (OH) 4 (H 2 O) n ] − were determined to be ∼0.37 nm with the hydration number of 4–5. The structure and interaction energy of the first hydration sphere of [K(H 2 O) n ] + and [B 3 O 3 (OH) 4 (H 2 O) n ] − were also studied by density functional theory calculation.

DFT-based calculations show that B5O6(OH)4- forms B5O5(OH)6− intermediate during the first step of hydrolysis. Then, the hydrolysis pathways are divided to principal and secondary reactions. In the principal reaction, hydrolysis occurs at the bridge position between the six-membered ring and branch BO3 units to form B(OH)3 and B3O3(OH)4−. B3O3(OH)4− hydrolyzes in dilute solution to B(OH)3 and B(OH)4−. In the secondary reaction, hydrolysis of B5O5(OH)6− occurs at the bridge position in the ring to form a “network-chain” structure B5O4(OH)8−. Then, hydrolysis occurs at the bridge atoms, each BO3 unit is converted to B(OH)3, and BO4 unit is finally converted to B(OH)4−.

Physicochemical property data, such as density, electrical conductivity, and pH of aqueous solutions of LiB(OH)4, Li2B4O5(OH)4, and LiB5O6(OH)4 have been accurately determined at different temperatures. Density values were given from 288.15 K to 323.15 K, and pH and electrical conductivity from 293.15 K to 323.15 K. The properties were represented by semiempirical equations as functions of concentration. The mole fractions of polyborates were obtained in aqueous lithium borate solutions, and their distribution and relevant mechanism were also suggested.