SYNTHESIS AND KINETICS OF FORMATION AND AQUATION OF CIS-BIS(OXALATO)BIS(DIMETHYLFORMAMIDE)CHROMATE(III)

The isolation by ion-exchange chromatography of cis-Cr(C2O4)2(HCON(CH3)2)2- has been effected. The complex has visible maxima at 418 and 565 nm with molar absorptivities of 87.5 and 96.5 M-1 cm-1, respectively. The aquation of this compound occurred in consecutive first-order reactions with the first step corresponding to the replacement of the first HCON(CH3)2 and the second step corresponding to the replacement of the second HCON(CH3)2. The intermediate was concluded to be cis-Cr(C2O4)2(HCON(CH3)2)(OH2)- The reactions are independent of pH between pH l and 5 with k1 = (6.95 ± 0.28) × 10-4 s-1 and k2 = (3.27 ± 0.18) × 10-4 s-1 at 25 °C and μ = 1.00 M (NaNO3). The activation parameters are ΔH∗ = 14.3 ± 0.4 and 14.2 ± 0.9 kcal/mol and ΔS∗ = -24.9 ± 1.3 and -26.9 ± 3.0 cal/(deg mol) for the first and second steps, respectively. An Ia mechanism was assigned for both steps. The solvolysis reaction of cis-Cr(C2O4)2(OH2)2_ in HCON(CH3)2 is very similar to the aquation reaction. The value of fc_2 (first step) is (1.75 ± 0.04) × 10-3 s-1 and k-1 (second step) is (1.87 ± 0.05) × 10-4 s-1 at 25 °C. The values of the activation parameters are AH∗ = 14.4 ± 0.2 and 14.7 ± 0.3 kcal/mol and ΔS∗ = -22.8 ± 0.7 and -26.1 ± 0.9 cal/(deg mol) for the first and second steps, respectively. The equilibrium behavior was studied at 25 °C, [H+] = 10-3 M, and Xdmf = 0.028-0.90 in aqueous dimethylformamide solutions. The equilibrium quotients are Q1 = 5.55 ± 0.27 and Q2 = 0.437 ± 01069. © 1979, American Chemical Society. All rights reserved.