THERMOCHROMIC PHASE-TRANSITIONS IN 2 AROMATIC TETRACHLOROCUPRATES

Bis(para-toluidinium)2 tetrachlorocuprate and bis(para-chloroanilinium)2 tetrachlorocuprate crystallize in a perovskite-related layer structure. The former crystallizes in an orthorhombic unit cell with a = 6.911 angstrom, b = 7.052 angstrom and c = 33.182 angstrom. It undergoes a thermochromic first order phase transition from a yellow low temperature phase to a dark orange high temperature phase at T = 300 +/- 3 K with a 10-degrees thermal hysteresis. The latter compound undergoes two thermochromic transitions expressed by the relation. Orange Phase (I) [GRAPHICS] Yellow Phase (II) [GRAPHICS] Green Phase (III). Both compounds are ferromagnetic at low temperture with exchange interactions J/k = 17.5-degrees and 20-degrees for the two compounds respectively.