Cationic motions and crystal structures of 1,3,5-trimethylpyridinium hexachlorometallates [(CH3)2C5H3N(CH3)]2MCl6 (M is SN and Te) studied by 1H NMR and X-ray diffraction

Article abstract of DOI:10.1016/S0022-2860(97)00281-0

The crystal structure of 1,3,5-trimethylpyridinium hexachlorometallates [(CH₃)₂C₅H₃N(CH₃)]₂MCl₆ (M is Sn and Te) were determined at 298 K and found to be orthorhombic Pnnm (No. 58) and Z = 2, a = 8.996(2), b = 11.330(2), c = I 1.596(2) A, V = 1182.0(7) A³ for the stannate, and a = 9.072(4), b = 11.399(5), c = 11.63(2) A, V = 1203(3) A³ for the tellurate, by single-crystal X-ray diffraction. No phase transition was detected by DTA from 80 to 573 K. The cationic motions were studied by ¹H NMR and the C₃ reorientation of the CH₃ groups was observed below 273 K, having an activation energy of 3.1 kJ mol^-1 for the stannate and 3.7 kJ mol^-1 for the tellurate. Another cationic motion, with an activation energy of about 20 kJ mol^-1, was observed above 380 K for both salts. This is attributable to the pseudo-C₃ reorientation around the axis perpendicular to the pyridinium ring. The cationic motions and the crystal structure are discussed from the point of view of the hydrogen bonding.