Binary systems of C 60 with positional isomers 1,2- and 1,3-C 6 H 4 Br 2 N.V. Avramenko a , E.B. Stukalin a , M.V. Korobov a,* , I.S. Neretin b , Yu.L. Slovokhotov b a Department of Chemistry, Moscow State University, Moscow 119899, Russia b Institute of Organoelement Compounds, RAS, Moscow 117813, Russia Received 23 August 2000; received in revised form 30 September 2000; accepted 23 November 2000 Abstract Thermodynamic properties of binary systems of C 60 with 1,2- and 1,3-dibromobenzenes have been studied by means of differential scanning calorimetry (DSC). Solid solvates with the compositions C 60 3(1,2-C 6 H 4 Br 2 ); C 60 2(1,3-C 6 H 4 Br 2 ) and C 60 0.6(1,3-C 6 H 4 Br 2 ) have been found. The solvates have been characterised by their enthalpies and temperatures of incongruent melting transition and in part by X-ray powder data. It has been shown that positional isomers 1,2- and 1,3- of the substituted benzenes formed two series of ``typical'' phase diagrams. Solubility behaviour of C 60 in positional isomers has been discussed. # 2001 Elsevier Science B.V. All rights reserved. Keywords: DSC; Fullerenes; Solvates; Solubility; Isomers 1. Introduction The solubility of C 60 and other fullerenes is of both practical and theoretical interest. The necessity of dissolving fullerenes in order to extract, purify and modify them chemically is obvious. Being a globular molecule, C 60 is an excellent candidate for checking different models of solute±solvent interactions and solubility [1]. The thermodynamic studies of solubility behaviour of C 60 in the most ef®cient aromatic solvents have shed light on the importance of studying solid solvate formation. The decomposition of these van der Waals complexes causes temperature maximums in solubi- lity measurements [2]. Another intriguing feature of the solution behaviour of C 60 is the large difference in solubility observed for positional isomers, e.g. for 1,2-dichlorobenzene, the room temperature solubility of C 60 is about 10 times higher, than for 1,3-dichlorobenzene, 24.6 and 2.4 mg/ ml, respectively [3]. The chemical properties and solvent parameters [4] of the two isomers are similar. It has been claimed [3], that differences in solubility in positional isomers can be due to the formation of solid solvates, different in structure and stability. The solu- bility is in part determined by the solid phase in equilibrium with the solution. In the case of C 60 and aromatic solvents, this solid phase is usually a solid solvate (not pristine C 60 !) with the geometry of the crystal lattice, controlled by the geometry/space structure of the solvent molecule, which is different in the case of two positional isomers. The effect of the solid phase combined with the similar properties of Thermochimica Acta 370 (2001) 21±28 * Corresponding author. 0040-6031/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0040-6031(00)00757-7