NQR, NMR, and X-ray crystal structure studies of [4-C2H5-C6H4NH3]2MBr4 (M=Zn, Cd)

The crystal structure of [4-C2H5-C6H4NH3](2)ZnBr4 (1) has been determined at 150(2) K: triclinic, P (1) over bar, a =724 .82(2) , b =1194.20(4), c = 1322.26(4) pm, alpha =74.151(3), beta = 80.887(3), gamma =80.434(3)degrees, and Z=2. There are two crystallographically independent cations in the unit cell of 1: one has its benzene ring perpendicular to the crystallographic a axis of the unit cell and the other one has its benzene ring perpendicular to the c axis. These cations are alternatingly located along the c axis and form organic layers, and the ZnBr4 anions form inorganic layers in between. Zn-Br center dot center dot center dot H-N hydrogen bonds are formed between cations and anions. In accordance with the crystal structure, four nuclear quadrupole resonance (NQR) lines of Br-81 were observed. The temperature dependence of the Br-81 NQR frequencies between 77 and 320 K shows a peculiar feature which is not due to a structural phase transition. The measurement of C-13 nuclear magnetic resonance spectra at around T=340 K indicates a redistribution of cations. The temperature dependence of Br-81 NQR frequencies and differential thermal analysis measurements show that [4-C2H5-C6H4NH3](2)CdBr4 (2) undergoes a structural phase transition at around 190 K.