Table of Contents
Metal-Based Drugs
Volume 2008, Article ID 745989, 9 pages
Research Article

Kinetic and High-Pressure Mechanistic Investigation of the Aqua Substitution in the Trans-Aquaoxotetracyano Complexes of Re(V) and Tc(V): Some Implications for Nuclear Medicine

1Department of Chemistry, University of the Orange Free State, P.O. Box 339, Bloemfontein 9300, South Africa
2Sasol Technology R & D, P.O. Box 1, Sasolburg 1947, South Africa

Received 16 August 2007; Accepted 8 December 2007

Academic Editor: Jannie Swarts

Copyright © 2008 J. Mattheus Botha and Andreas Roodt. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A kinetic study of the aqua substitution in the [TcO(OH2)(CN)4] complex by different thiourea ligands (TU = thiourea, NMTU = N-methyl thiourea, NNDMTU = N, N-dimethylthiourea) yielded second-order formation rate constants (25C) as follows [NNDMTU, NMTU, TU, respectively]: kf = 11.5 ± 0.1, 11.38 ± 0.04, and 7.4 ± 0.1 M1s1, with activation parameters: ΔHkf#:55±2, 42±3, 35±5 kJ mol1; ΔSkf#:40±8, 84±11, 110±17 J K1mol1. A subsequent high-pressure investigation of the aqua substitution in the [ReO(OH2)(CN)4] and [TcO(OH2)(CN4)] complexes by selected entering ligands yielded ΔVkf# values as follows: Re(V): 1.7±0.3(NCS), 22.1±0.9 (TU) and for Tc(V): 3.5±0.3(NCS), 14±1 (NNDMTU), and6.0±0.5 (TU) cm3mol1, respectively. These results point to an interchange associative mechanism for the negative NCS as entering group but even a pure associative mechanism for the neutral thiourea ligands.