Thermodynamic Studies of Aqueous Solutions of 2,2,2-Cryptand at 298.15 K: Enthalpy–Entropy Compensation, Partial Entropies, and Complexation with K⁺ Ions

Abstract

The osmotic coefficient measurements for binary aqueous solutions of 2,2,2-cryptand (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8] hexacosane) in the concentration range of ~0.009 to ~0.24 mol·kg(-1) and in ternary aqueous solutions containing a fixed concentration of 2,2,2-cryptand of ~0.1 mol·kg(-1) with varying concentration of KBr (~0.06 to ~0.16 mol·kg(-1)) have been reported at 298.15 K. The diamine gets hydrolyzed in aqueous solutions and needs proper approach to obtain meaningful thermodynamic properties. The measured osmotic coefficient values are corrected for hydrolysis and are used to determine the solvent activity and mean ionic activity coefficients of solute as a function of concentration. Strong ion-pair formation is observed, and the ion-pair dissociation constant for the species [CrptH](+)[OH(-)] is reported. The excess and mixing thermodynamic properties (Gibbs free energy, enthalpy, and entropy changes) have been obtained using the activity data from this study and the heat data reported in the literature. Further, the data are utilized to compute the partial molal entropies of solvent and solute at finite as well as infinite dilution of 2,2,2-cryptand in water. The concentration dependent non-linear enthalpy-entropy compensation effect has been observed for the studied system, and the compensation temperature along with entropic parameter are reported. Using solute activity coefficient data in ternary solutions, the transfer Gibbs free energies for transfer of the cryptand from water to aqueous KBr as well as transfer of KBr from water to aqueous cryptand were obtained and utilized to obtain the salting constant (ks) and thermodynamic equilibrium constant (log K) values for the complex (2,2,2-cryptand:K(+)) at 298.15 K. The value of log K = 5.8 ± 0.1 obtained in this work is found to be in good agreement with that reported by Lehn and Sauvage. The standard molar entropy for complexation is also estimated for the 2,2,2-cryptand-KBr complex in aqueous medium.

Hydrogen Bonding in Liquid Water and in the Hydration Shell of Salts

“…[41][42][43][83][84][85] In the case of complexforming systems in which strong noncovalenti nteractions dominated, we found that nonlinear EEC effects existed and nonlinearity resulted due to the contribution of heatcapacity. [86] In the present case, al inear compensation effect is observed ( Figure 6) with ac ompensation temperature (T comp )o f3 08.9 K and an energetic parametero fÀ5.69 kJ mol À1 .F urthermore, the temperature of 316.5 Ki st he equilibrium point or optimum temperature at which the concentration of fully Hbonded species (ñ = 6300 and 6700 cm À1 Gaussian component) is equal to that of the sum of singly H-bonded and NHB water species( ñ = 7082 and 7368 cm À1 Gaussian component). Thus, fully H-bonded species dominate as the temperature decreases www.chemphyschem.org below 316.5 K, whereas singly H-bonded species becomem ore important as the temperature increases above 316.5 K. These observations are in agreement with those reported by Dougherty and Howard [87] that the minimum in the heat capacity (C P ) occurs at 307.6 K, above which temperature square water arrays have significant concentrations,w hereasp entagonal water arrays become insignificant at about 319 K(the temperature of minimum isothermal compressibility).…”

Melting temperatures deduced from molar volumes: a consequence of the combination of enthalpy/entropy compensation with linear cohesive free-energy densities

“…The experimental linear correlations observed between CFED and the associated melting temperatures T m in Fig. 6 provide eqn (11), which interconnects DH m , DS m and V mol within each series (note that…”

“…1c). 13 Since complexation processes occurring in dilute solutions are complicated by unavoidable solvation changes, 11,14 which may induce additional H/S compensation phenomenon, 15 we resorted to the melting of solids into isotropic liquid conducted in absence of solvents or of additives for getting a rough estimation of the strength of the intermolecular interactions occurring in a solid. 16 These processes can be idealized as reversible n th order chemical reactions, in which n identical monomeric units A associate into fully assembled entities A n (eqn (3)).…”

Cobalt, Iron, and Manganese Metallocorroles in Catalytic Oxidation of Water. An Overview of the Synthesis, Selected Redox and Electronic Properties, and Catalytic Activities

“…[13] In recent years, some examples were reported where dipyrromethanes were obtained under solvent-free conditions. These methodologies involved the use of SnCl 2 • 2H 2 O, [14] I 2 , [15] H 2 SO 4 * SiO 2 , [16] sulfated polyborate, [17] imidazole-based zwitterionic-salts [18] or metal nanoparticles [19] as catalysts. However, due to their simplicity, economy and versatility, methods that use mineral acids in water are the first choice in the synthesis of dipyrromethanes as building blocks to obtain corroles.…”

“…Cao et al [55] studied Co(tpfc)Py 2 (10), Mn(tpfc) (11), and several Mn corroles with zero to three meso-4-nitrophenyl substituents (12)(13)(14)(15), as water oxidation catalysts. The authors found that Co(tpfc)Py 2 was the more active catalyst, with a TOF of 0.2 s À 1 at 1.4 V vs. Ag/AgCl in pH = 7 aqueous phosphate buffer.…”