127I NQR and crystal structure studies of [N(CH3)4]2CdI4

The temperature dependence of I-127 NQR and DSC as well as the crystal structure at room temperature of the title compound were determined. This compound shows a first-order phase transition of an order-disorder type at 245 K. Eight I-127(nu(1): m = +/-1/2 <-> +/-3/2) NQR lines of 79.57, 81.86, 82.56, 83.36, 84.68, 87.72, 88.34, and 88.86 MHz, and corresponding eight I-127(nu(2): M = +/- 3/2 <-> 5/2) NQR lines were observed at liquid nitrogen temperature. Three I-127(nu(1)) NQR lines with an intensity ratio of 1:1:2 in the order of decreasing frequency were observed just above the transition point and two NQR lines except for the middle-frequency line disappeared around room temperature. This temperature behavior of NQR lines is very similar to that observed in [N(CH3)(4)](2)HgI4. Another first-order phase transition takes place at 527 K. The structure of the room-temperature phase was redetermined: orthorhombic, Pnma, Z = 4, a = 1342.8(3), b = 975.7(2), c = 1696.5(3) pm. The NQR result of three lines with an intensity ratio of 1:1:2 is in agreement with this structure. The thermal displacement parameters of atoms in both cations and anions are large.