Platinum(IV) Bromo Aqua Complexes. Acid Hydrolysis Equilibria and Kinetics of Bromiide Anation

• The stepwise stabililty constants, Kn for the bromo aqua complexes PtBrn−1(H2O)7−n5−n; n=4, 5, 6, formed in the successive acid hydrolyses of PtBr62−, have been determined to be K6=(.19±0.1) x 103 M−1, K5= (1.0±0.2) x 104 M−1 and K4=(1.1±0.2) x 105 M−1. A bromide assisted mechanism is proposed for the bromide anations of PtBr4(H2O)2 and PtBr5H2O-. Both these reactions are found to be first order with respect to platinum complex. The dependence of the observed rate constant on the bromide concentration can be described by the eqn. kexp=κ′[Br−]+κ″[Br−]2The last term is probably due to a reaction path via a bromide associated outer sphere complex, which might also be involved in the path described by the first term. A spectrophotometric method has been used. To suppress the protolysis of the aqua complexes, 0.50 M perchloric acid was used as the ionic medium. The temperature was 25.0 °C.

• The stepwise stabililty constants, Kn for the bromo aqua complexes PtBrn−1(H2O)7−n5−n; n=4, 5, 6, formed in the successive acid hydrolyses of PtBr62−, have been determined to be K6=(.19±0.1) x 103 M−1, K5= (1.0±0.2) x 104 M−1 and K4=(1.1±0.2) x 105 M−1. A bromide assisted mechanism is proposed for the bromide anations of PtBr4(H2O)2 and PtBr5H2O-. Both these reactions are found to be first order with respect to platinum complex. The dependence of the observed rate constant on the bromide concentration can be described by the eqn. kexp=κ′[Br−]+κ″[Br−]2The last term is probably due to a reaction path via a bromide associated outer sphere complex, which might also be involved in the path described by the first term. A spectrophotometric method has been used. To suppress the protolysis of the aqua complexes, 0.50 M perchloric acid was used as the ionic medium. The temperature was 25.0 °C.

Ämnesord

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

Nyckelord

Platinum(IV)

Bromo-aqua complexes

Stability constants

Bromide anation

Kinetics

Bromide assisted substitution

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