Half-Crystal Energy and Enthalpy of Sublimation of Diuron: 3-(3,4-Dichlorophenyl)-1,1-dimethylurea

• Published in: Journal of applied crystallography 1997-10, Vol.30 (5-1), p.527-531
• Main Authors: Pfefer, G., Sabbah, R., Boistelle, R.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Crystal binding; cohesive energy; Crystalline state (including molecular motions in solids); Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Heat capacities of solids; Physics; Solid-vapor transitions; Specific phase transitions; Structure of solids and liquids; crystallography; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties
• ISSN: 1600-5767; 0021-8898; 1600-5767
• DOI: 10.1107/S0021889896014501

The enthalpy of sublimation of diuron, 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea, C9H10ON2Cl2, was measured at 393 K using a Tian–Calvet calorimeter. The corrected experimental value ΔsubHmο (298K) = 133.87 (74) kJ mol−1 was then compared to the half‐crystal energy Ek. This energy was calculated from structural data using the `consistent valence force field', which consists of a 6–12 Lennard–Jones potential and a Coulomb term. The disagreement between ΔsubHmο (298K) and Ek = 152.6 kJmol−1 is about 14%. It can be partially attributed to the inaccuracy of the atomic coordinates of the crystal structure and to the charges of the force field. For simple molecules such as normal octadecane (n‐C18H38), hexanedioic acid (C6H10O4), diphenylmethanone (C13H10O) and anthracene (C14H10), the agreement is very good, about 3%.