Preparation and aquation kinetics of the pentaaquo(2-mercaptoethylammonium-S)chromium(III) ion. Origin of the Ko term in rate laws of the form-d(ln [(H2O)5CrX]n+)/dt = ko+ k1(H+)

Abstract

The [(H20)5CrSCH2CH2NH3]3+ ion has been prepared via chromium(II) reduction of the (V,S-(2-mercaptoethylamine)bis-(ethylenediamine)cobalt(III) ion in aqueous perchloric acid and subsequent ion exchange separation of the product mixture. In aqueous perchloric acid (0.01-1.99 F), this complex aquates according to the rate law -d(ln [CrSR]3+)/df = k0 + ic1(H+). At µ = 2.00 F (LiC10"), 25°, the specific rate constants are k0 = (4.5 ± 0.2) X 10~® sec"1 and k, = (1.31 + 0.02) X 10"4 F"1 sec"1. The corresponding activation parameters are AH0* = 27.6 ± 0.4 and AH,* = 20.6 ± 0.3 kcal/mol, and AS0* = 14.0 ± 1.2 and AS, * = -7.1 ± 0.9 eu. Data are correlated to show that for pentaaquochromium(III) complexes of ligands derived from weak acids, the k0 and k, terms in the title rate law are similarly dependent upon the ability of the coordinated ligand to be protonated. This provides the first positive evidence that the k0 term of these complexes describes separation of HX from [(H20)4(0H)Cr]2+ and not X from [(H20)sCr]3+. It is also shown that the former k0 mechanism operates when the pKa of HX is >2, while the latter k0 mechanism operates when the of HX is <0.

Synthesis, structure, and stereochemistry of some cysteine- and penicillaminecobalt(III) complexes

“…-18(5) 11 (5) 0(2) 3416 ( 5) 5228 ( 6) 10016 ( 10) 29 ( 4) 43( 4) 76 (6) -13(4) -17( 4) 1(4) 0(3) 3251 ( 7) 651 (10) 6910 (18) 61 (7) 110 ( 9) 134 (11) 42 (7) 12 (8) -5 (9) 0( 4) 2103 ( 12) 1139 ( 12) 8449 ( 17) 221 ( 17) 125 ( 11) 105 ( 10) 90 (12) 102( 12)…”

Crystal and molecular structure of bis(methylcyclopentadienyl)oxomolybdenum [(MeCp)2MoO (MeCp = .eta.5-CH3C5H4)]

“…-2 (2) -26 (2) C( 9) 4643 ( 5) 639 ( 6) 1046 (2) 34 (1) 90 ( 3) 33 (1) -2 (2) 5 (1) "7 (2) C( 10) 3404 (5) -512 ( 5) 819 (2) 52 (2) 60 (2) 33 (2) -9 (2) 7 (1) 18 (2)…”

Mechanistic implications of kinetic data for the formation and aquation of acidopentaamminechromium(III) complexes, Cr(NH3)5X2+, X- = isothiocyanate(1-), trichloroacetate(1-), trifluoroacetate(1-), chloride(1-), bromide(1-), and iodide(1-). Evidence for a dissociative mechanism

“…However, greater dependence of aquation rate constants on the nature of the leaving group as compared to Co(NH3)5X2+ complexes has also been suggested by other workers.37,38 The linear relationship reported by Monacelli39 between the rate constants of aquation of the Cr(NH3)sX2+ complexes, X™ = Cl", Br", and I", and p of the strong acids HC1, HBr, and HI has been criticized for its choice of pKa values. 40,41 From the data reported herein, Tables VIII and IX, a linear relation of log kaq against -log KosKis is observed for complexes Cr(NH3)5X2+, X™ = NCS™, CC13C02™, CF3CO2", Cl", and Br™, Figure 9. The slope, 0.91 ± 0.05, of the line obtained for the Cr(NH3)sX2+ series is much larger than the slope, 0.56, observed for the corresponding plot for the Cr-(H20)5X2+ series, where the slope of these lines is believed to be a measure of the degree of bond breaking in the transition state.…”