Polymorphism of [Zn(NH3)(4)](ClO4)(2) and [Zn(NH3)(4)](BF4)(2) studied by differential scanning calorimetry and far infrared spectroscopy

The phase transitions in [Zn(NH3)(4)](ClO4)(2) and [Zn(NH3)(4)](BF4)(2) wer e determined by differential scanning calorimetry (DSC) and the discovered phases were identified by far infrared spectroscopy (Fr-FIR). Four solid ph ases were found for both the compounds. The characteristic changes in the F T-FIR absorption spectra were observed in the particular phases of both the compounds at temperatures predicted by the DSC. Additionally, the FT-FIR s pectra of [Zn(NH3)(4)](ClO4)(2) suggested a new phase at 25 K. The splittin g of the band connected with the nu (d)(ZnN) = nu (3)(F-2) mode in the spec tra of the low temperature phases for both the compounds suggested a struct ural character of the phase transition. The absence of the delta (d)(OClO) = nu (2)(E) band and the presence of the delta (d)(FBF) = nu (2)(E) band in the FT-FIR spectra at 298 K of [Zn(NH3)(4)](ClO4)(2) and [Zn(NH3)(4)](BF4) (2), respectively, indicates that the structure of the room temperature pha ses is different for both the compounds. (C) 2001 Elsevier Science B.V. All rights reserved.