Kinetics of Aquation and Chloride Anation of Chloroaquobis(ethylenediamine)chromium(III) Cations

The first-order rate constants for production of ionic chloride from cis-[Cr(en)(2)(OH2)Cl](+2) in 0.10 and 1.3 F HNO3 at 35.00 were found by chloride titrations to be k(46) = (9.23 +/- 0.02) x 10(-5) sec(-1) and (22.8 +/- 0.3) x 10(-6) sec(-1), respectively. The stereochemical result of the aquation is similar to 100% cis-[Cr(en)(2)(OH2)(2)](+3). Aquation of trans[Cr(en)(2)(OH2)Cl](+2) +1 in 0.10 F HNO3 at 35.0 degrees was found fro n chloride titrations, spectrophotometry, and chromatography to be complex; a reaction scheme which accounts satisfactorily for the observations is [GRAPHICS] with first-order rate constants (10(5) k, sec.(-1)): k(35) + k(36) = 0.28 +/- 0.14, k(27) = 4.2 +/- 1.4, k(78) = 2.8 +/- 0.6, k(34) < 0.6, k(43) < 2, k(46) = 9.23 +/- 0.02. Pseudo first-order rate constants obtained spectrophotometrically at 35.0 degrees for chloride anation of trans- and cis-[Cr(en)(2)(OH2)Cl](+2) are (10(5)k, sec.(-1)): k(31)(trans) = 17 +/- 5 in 10.2 F HCl, k(12)(cis) = 140 +/- 10 in 10.9 F HCl and 27 +/- 4 in 5.69 F HCl. The trans isomer produces only trans- [Cr(en)(2)Cl-2](+) and the cis isomer only cis-[Cr(en)(2)Cl-2](+) up to the attainment of a quasi-equilibrium, which lies at the following % dichloro complex: similar to 35 (trans in 10.2 F HCI); similar to 84 and similar to 46 (cis in 10.9 and 5.69 F HCl, respectively). All reactions were studied in the absence of light, with initial complex concentrations similar to 1-40 mF.