KINETIC-PARAMETERS AND CHEMICAL MECHANISM FOR THE SOLID-STATE DEAQUATION ANATION OF SALTS OF CHROMIUM(III) WITH MIXED AMINE LIGANDS

The solid-state dehydration-anation of trans-[CrF(en)(tn)(H2O)]X2and trans-[CrF(chx)(tn)(H2O)]X2(with en = ethylenediamine, tn = 1,3-diaminopropane, and chx = 1,2-diaminocyclohexane; X = Cl-, Br-, I-, and 1/2S2O6 2) has been studied by isothermal thermogravimetric measurements, previous synthesis, and characterization of the new compounds. The dehydration-anation gives in the majority of the cases the cis isomer, [CrFX(aa)(bb)]X. The activation energies for these processes, compared with those reported for the compounds with only one kind of amine, indicate different trends in the en-tn series with regard to the chx-tn series: in the first series the gradation follows the order en > en-tn > tn as could be expected according to the theory of the free space in the lattice; (b) in the second series, the gradation follows the order chx > chx-tn > tn, indicating that the dehydration and isomerization is expected to be via the rupture of the Cr-N(chx) bond, simultaneously with the rupture of the Cr-OH2bond; (c) the I > S2O6 > Br > Cl gradation in the series en-tn agrees with a dissociative mechanism controlled by the magnitude of the cation/anion ratio. This gradation does not take place in the chx-tn series due to the different extent of the Cr-N(chx) bond rupture, which depends on the entering anion. © 1987, American Chemical Society. All rights reserved.