Abstract
The solid state phase transitions in the perovskite-type layer compound ( n-C 12H 25NH 3 2CuCl 4, have been studied by X-ray diffraction, differential scanning calorimetry and i.r. spectroscopy. Two-step reversible phase transitions are observed at T c 1 = 327.9 K and T c 2 = 335.7 K on heating whereas at T c 1 = 324.4 K and T c 2= 330.1 K on cooling, accompanied with the increase of interlayer distance ( Δ d 1≅ 1.8 A ̊ and Δ d 2≅ 0.85 A ̊ , respectively). In the first transition important melting of the hydrocarbon chains occurs together with the flipping of polar NH 3 groups. Defects of the gt 3 g′ and end gauche forms are found. The weakening of the NH-Cl hydrogen bonds is also observed. Further conformational changes of the hydrocarbon part are dominantly observed in the second phase transition. As the interlayer spacing is increased, only short gtg ' kinks are allowed. The mechanism of conformational transition for this compound can be therefore suggested as follows: gt 9 or tgt 8 → 2g − 2 kink (−gt 3g′−) → 2g −1 kink (−gtg′−) .
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