Relationships between crystal structures and thermodynamic properties of phenylbutazone solvates

The relationships between the crystal structures and the thermodynamic properties of six phenylbutazone solvates were studied. From the crystal structures the free volume available to the solvent molecules, V-asm, the packing density of the solvent in the solvate channels, K-chan, and the lattice energy of each solvate, E-lattice, were calculated and the intermolecular interactions in the solvates were identified. From the measured equilibrium vapor pressure of the solvent above each solvate and above each liquid solvent, the standard free energy, DeltaG(des)(circle minus), enthalpy, DeltaH(des)(circle minus), and entropy, DeltaS(des)(circle minus), of desolvation of each solvate were calculated. Linear correlations between K-chan and DeltaS(des)(circle minus), between E-lattice and DeltaH(des)(circle minus), and between V-asm and both DeltaS(des)(circle minus) and DeltaH(des)(circle minus) suggest that similar crystal structures afford smooth monotonic variations in intermolecular interaction energies.