Temperature Dependence Studies of 3 CI NQR Frequencies in Magnesium and Nickel Hexachlorotellurate(IV) Hexahydrates and Nickel Hexachloroiridate(IV) Hexahydrate*

The C1 NQR frequencies in MgTeCl6 • 6 H 2 0 , NiTeCl6 • 6 H 2 0 , and NiIrCl6 • 6 H 2 0 have been determined at various temperatures. These compounds form rhombohedral crystals with the space group R3, showing a single resonance line. The C1 NQR frequencies of the Te(IV) complexes exhibit an unusual positive temperature coefficient. The deuterated analogs of the Te(IV) complexes show a small frequency shift at 77 K. These results are interpreted by the presene of O H • • • CI type weak H-bonds. The resonance frequency of the Ir(IV) complex versus temperature curve shows a minimum and a maximum. This unusual temperature dependence is mainly explained by the same type of the H-bond as existing in the Te(IV) complexes. The 7r-bond formation between Ir and CI atoms is also partly responsible for the unusual temperature dependence.