Kinetic studies using Co(III) and Cr(III) complexes of 1,4,7,11-tetraazaundecane (2,2,3-tet) and the crystal structure of trans-[CrCl2(2,2,3-tetH)(OH2)]Cl center dot ClO4

摘要

The rate of loss of the first chloro ligand from trans-(R,S)(S,R)-[MCl2(2,2,3-tet)](+) (M = Co, Cr) to give trans-(R, S)(S,R)-[MCl(2,2,3-tet) (OH2)](2+) has been measured spectrophotometrically. Kinetic parameters (25.0 degrees C) are: M = Co (0.01 M HCl) k(H) = 2.03 x 10(-3) s(-1) Delta H-not equal = 102 +/- 4 kJ mol(-1), Delta S-not equal = +45 +/- 8 J K-1 mol(-1); M = Cr (0.1 M HNO3) k(H) = 7.66 x 10(-6) s(-1), Delta H-not equal = 99.0 +/- 2, Delta S-not equal = -11 +/- 4. For Co(III), the loss of the second chloro ligand (k(H)(2)) is accompanied by trans --> cis-beta isomerisation with k(H)(2) (0.01 M HCl; 25.0 degrees C) = 8.78 x 10(-5) s(-1), Delta H-not equal = 100, Delta S-not equal = +14 while for Cr(III), the second step is complicated by Cr-N bond rupture. The ring opened complex trans-[CrCl2(2,2,3-tetH)(OH2)]Cl . ClO4 (1) has been characterised by a single crystal X-ray structure (monoclinic, P2(1), a = 6.284(2), b = 28,633(7), c = 9.700(2) Angstrom, beta = 96.25(2)degrees, V = 1734.9(8) Angstrom 3, Z = 4) and the terminal five-membered ring, originally coordinated in trans-[MCl2(2,2,3-tet)](+), is dechelated. Attempted thermal aquation of this ring-opened complex resulted in further Cr-N bond rupture, but the Hg2+-assisted chloride release reaction gave k(Hg) (25.0 degrees C, I = 1.0 M HNO3) = 8.03 x 10(-3) M-1 s(-1), Delta H-not equal = 84.4 +/- 2.3, Delta S-not equal = - 2 +/- 5. Addition of Hg2+ to trans-[CoCl2(2,2,3-tet)](+) results in the rapid formation of trans-[Co(2,2,3-tet)(OH2)(2)](3+) and this then isomerises to cis-beta-[Co(2,2,3-tet) (OH2)(2)](3+), independent of [Hg2+]. k(tsom) (25.0 degrees C, I = 1.0 M HNO3) = 28.7 x 10(-4) s(-1), Delta H-not equal = 86.5 +/- 1.8, Delta S-not equal = -3 +/- 5. spontaneous (k(H)) and Hg2+-assisted (k(Hg)) chloride release reaction rates have also been measured for trans-(R,S)(S,R)- [CoCl(2,2,3-tet) (NH3)](2+) with k(H) (25 degrees C, I = 0.1 M HNO3) = 1.08 x 10(-6), Delta H-not equal = 119 +/- 1, Delta S-not equal = +40 +/- 3; k(Hg) = (25 degrees C, I = 1.0 M HNO3) = 57.5 M-1 s(-1), Delta H-not equal = 64.1 +/- 1.3, Delta S-not equal = -54 +/- 4. (C) 1998 Elsevier Science S.A. All rights reserved. [References: 38]