Characterization of cis- chloroaquobis(2,2′-dipyridyl)chromium(III) cation, and kinetics of primary and secondary aquation of cis-Dichlorobis(2,2′-dipyridyl)chromium(III) Cation

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Aquation of cis-Cr(dipy) 2Cl 2 + in 0.1–0.5 F HCl (μ = 0.1–0.5 M, NaCl) has been studied spectrophotometrically at 50–70°. At 70° μ = 0.5 M) the first-older rate constant is (5.4 ± 0.5) X 10 −5 sec −1, independent of the acid concentration; E a = 23.4 ± 0.8 kcal mole −1 and log PZ(sec −1) = 10.62 ± 0.55. The product is the previously not fully characterized cis-Cr(dipy) 2(OH 2)Cl 2+, with no evidence for concurrent aquation via CrN bond rupture. At 70° in 0.13 F HCl or HNO 3 (μ = 0.13 M) cis-Cr(dipy) 2(OH 2) 2+ appears to aquate concurrently to cis-Cr(dipy) 2(OH 2) 2 3+ and to an unidentified species of charge ⩾4 +, perhaps Cr(dipy)(dipyH)- (OH 2) 3 4+ (via the intermediate Cr(dipy)(dipyH)(OH 2)( 2- Cl 3+), with a total first-order rate constant of (6.9 ± 0.8) X 10 −5 sec −1. The cis-chloroaquo species has been fully characterized, and its visible absorption spectrum is reported. The new pink complex Cr(dipy)(OH 2) 4 3+ has been chromatographically isolated from a 0.1 F HCl solution of cis-Cr(dipy) 2Cl 2 + which had been aged at 70° for 50 days.