The acid-catalysed hydrolysis of nitrotrichloroplatinate(II) and tetranitro-platinate(II) and -palladate(II) anions

Abstract

The replacement of a nitro-group from the anions [Pt(NO₂)₄]^2–, [Pd(NO₂)₄]^2–, and [PtCl₃NO₂]^2– in aqueous solutions of strong acids has been studied. The kinetics and mechanism of the hydrolysis of the [PtCl₃NO₂]^2– ion have been investigated in detail since it could be studied over a much wider range of acid concentrations than could the hydrolysis of the tetranitro-species. It was found that [Pd(NO₂)₄]^2– reacted 10⁵–10⁶ times more quickly than the platinum analogue and appeared to be a stronger base. For the acid-catalysed hydrolysis of [PtCl₃NO₂]^2– the rate constant first increased with acid concentration, passed through a maximum, and then decreased with further increase in acid concentration. The difference in behaviour of [PtCl₃NO₂]^2– in solutions of sulphuric and perchloric acids is discussed in terms of the species present in the solutions. Experiments with D₂O–D₂SO₄ were performed and the slight acceleration of the rate (ca. 15%) could be attributed to the difference in the protolytic equilibria for the protium and deuterium solutions. Arrhenius parameters have been evaluated and their significance is discussed.

The basic hydrolyses and aquations of the tetranitro-species has also been studied. The palladium complex is hydrolysed 10³–10⁴ times more quickly than the platinum analogue. The rate of hydrolysis is only slightly dependent on the hydroxide ion concentration but was noticeably affected by ionic strength.