F. Michaud et al., ISOMORPHIC RELATIONSHIP BETWEEN 1,2,4,5-TETRACHLOROBENZENE AND 1,2,4,5-TETRABROMOBENZENE, Journal of applied crystallography, 30, 1997, pp. 1152-1155
1,2,4,5-Tetrachlorabenzene (TeCB) exhibits a phase transition alpha-->
beta at 185K whereas 1,2,4,5-tetrabromobenzene (TeBB) exhibits a phase
transition beta-->gamma at 307K, the 'room temperature' form being be
ta for the two compounds. This work establishes which are the isomorph
ous forms. Quenching the molten mixtures into Liquid nitrogen produced
molecular alloys (TeCB)(1-x)(TeBB)(x) at 295 K with any value of x, e
ven in the 0.20 less than or equal to x less than or equal to 0.75 and
0.81 less than or equal to x less than or equal to 0.97 ranges where
these molecular alloys are only metastable because of demixing phenome
na. Powder diffraction analysis on the whale range of molecular alloys
proved that beta TeCB is isomorphous in the strictest sense (i.e. cap
able of giving a continuous series of mixed crystals) with the gamma f
orm of TeBB.