Crystal structure, DSC and Raman studies in [C6H5(CH2)2NH3]2Cd0.75Hg0.25Br4

The title compound crystallizes in the space group <f>P21/c</f> with the following unit cell dimensions: <f>a=7.885(2)</f> Å, <f>b=25.937(2)</f> Å, <f>c=11.059(5)</f> Å, <f>β=91.067(2)</f>°, <f>Z=4</f>. The examination of the structure shows a layer arrangement perpendicular to the <f>b</f> axis: planes of <f>β</f> phenylethylammonium cations [C6H5(CH2)2NH3]2+ alternate with planes of [Cd0.75Hg0.25Br4]2- tetrahedra. The cohesion of the atomic arrangement is ensured by hydrogen bonding (N&z.sbnd;H…Br) and Van der Waals contacts. DSC and Raman spectroscopy measurements were carried out and reveals a transition at <f>T=347</f> K. This transition display an order–disorder mechanism involving mainly conformational changes of the organic chain [C6H5(CH2)2NH3]2+ coupled with distortion of the (Cd/Hg)Br4 tetrahedra. The transitional behavior and the crystal dynamics will be discussed and compared with those found in the literature for homologous compounds. [Copyright &y& Elsevier]