The thermodynamic solvate difference rule: solvation parameters and their use in interpretation of the role of bound solvent in condensed-phase solvates.
Our earlier-established thermodynamic solvate difference rule encompasses thermodynamic relationships for the quantities P=DeltafH degrees, DeltafG degrees, DeltafS degrees, S degrees, Vm, and UPOT for pairs of condensed-phase solvates (including hydrates) having n and m moles, respectively, of bound solvent (including water, i.e., L=H2O), and can be written as P{MpXq.nL,p} approximately P{MpXq.mL,p}+(n-m).thetaP{L,p-p} (with m=0 for the corresponding thermodynamic quantity of the condensed-phase unsolvated parent, P{MpXq,p}), where thetaP{L,p-p} is the incremental contribution per mole of the bound solvent, L, to the property, P, of the solvate in condensed phase, p (where p=solid or liquid). We find that this rule can be extended to supercooled NaOH (and, probably, even more generally). Once established, the parameter thetaP{L,p-p} provides approximate values of the thermodynamic property, P, for the remaining solvates (hydrates) for which data are unknown. The difference rule is here further extended to heat-capacity data, Cp, for both hydrates and other solvates. For solid-phase hydrates, thetaCp{H2O,s-s} is determined to be 42.8 J K(-1) mol(-1). Further, the method is shown to apply also to the organic solvates, DMSO and DMF (the latter is based on a single example), leading to the (tentative) values thetaCp{DMSO,s-s} approximately 105 J K(-1) mol(-1) (at 255 K); approximately 161 J K(-1) mol(-1) (at 350 K), illustrating typical temperature dependence of the thetaCp values. thetaCp{DMF,s-s} approximately 84 J K(-1) mol(-1). For supercooled NaOH, thetaCp{NaOH,l-l}=77 J K(-1) mol(-1). The values of the solvate difference rule parameters provide us with insight into the bonding condition of the solvent molecule, leading to the conclusion that bound solvent water in an ionic environment is ice-like. The situation is more complex within zeolites because water may enter the solvate in a variety of ways. These latter considerations are also briefly discussed with respect to fullerenes.
Glasser
Leslie
L
Nanochemistry Research Institute, Department of Applied Chemistry, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia. l.glasser@curtin.edu.au
Jenkins
H Donald Brooke
HD