Structural and magnetic phase transitions in (Chloroanilinium)2CuX4 (X = Cl, Br)

Abstract

Successive structural phase transitions of (4-ClC6H4NH3)2CuCl4, which occur in a very narrow temperature range were reinvestigated by Fourier transform nuclear quadrupole resonance (FT NQR) measurements. The phase transitions at 275.5 and 277.0 K were confirmed. The effect of the deuteration of the ammonium end on these transitions was studied. The35Cl NQR frequencies of organic cation were observed to decrease by about 4 kHz and the phase transition temperatures to decrease by about 2 K by the deuteration, suggesting that the −NH3+ … Cl hydrogen bond is weakened by the deuteration. The magnetic phase transition temperature of 8.6 K showed no remarkable change within experimental error by the deuteration. It was found that the magnetically ordered state is broken by the radio-frequency magnetic field of about 15–35 Oe usually employed in pulsed NQR. However, in the deuterated compound (4-ClC6H4ND3)2CuCl4, the ordered state was found to be stabler for the usual radiofrequency power. By combining with the NQR data of (4-ClC6H4NH3)2CuBr4 and (3,5-Cl2C6H3NH3)2CuCl4, the possibility is discussed of tuning the interlayer interaction between the organic cation layer and the inorganic complex anion layer by the halogen substitution in the organic cation as well as by the halogen replacement in the inorganic complex anion.