THE KINETICS OF THE SEQUENTIAL STEPS IN THE HG2-ASSISTED CHLORIDE RELEASE FROM SOME TRANS-[CRCL2(NH(2)R)(4)](+) COMPLEXES (R=ET,PR,BU) AND THE X-RAY STRUCTURE OF TRANS-[CRCL2(NH(2)ET)(4)]CL()

The structure of trans-[CrCl2(NH(2)Et)(4)]Cl (monoclinic, I2/a, a = 15 .163(5), b = 6.458(2), c = 16.652(4) Angstrom, beta = 92.51(2)degrees, V = 1629.0(8) Angstrom(3), Z = 4) has been determined. The two Cr-Cl bonds are symmetry related (Cr-Cl = 2.323(1) Angstrom) and two of the (cis) EtNH(2) 'arms' are above and two are below the Cr(N)(4) plane. T he Hg2+-assisted chloride release from trans-[CrCl2(NH(2)R)(4)](+) occ urs in two, well separated steps and the second-order rate constants f or these processes, k(Hg)(1), and k(Hg)(2), have been measured spectro photometrically in 50:50 dioxane:HClO4, (I = 0.5 M). Kinetic parameter s at 25 degrees C are R = Et: k(Hg)(1), = 5.11 x 10(-2) M(-1) s(-1), D elta H-not equal = 70.8 kJ mol(-1), Delta S-not equal = -32 J K-1 mol( -1); k(Hg)(2) 2.41 x 10(-3), 80.6, -25; R = Pr: k(Hg)(1) = 4.92 x 10(- 2) 68.8, -39; k(Hg)(2) = 2.91 x 10(-3), 74.2, -44; R = Bu: k(Hg)(1) = 5.40 x 10(-2), 60.1, -67; k(Hg)(2) = 3.39 x 10(-3), 71.5, -52. These d ata are interpreted in terms of an interchange mechanism for the subst itution process.