Quantitative study of the structure-stability relationship of Tc complexes

A Computational and Conceptual Density Functional Theory Study of the Properties of Re and Tc Tricarbonyl Complexes

A computational and conceptual density functional study has been performed on metal tricarbonyl complexes (MTC) of both Re(I) and Tc(I). The fully optimized complexes of fac-[Tc(OH(2))(CO(3))](+) and mer-[Tc(OH(2))(CO(3))](+) show geometries that compare favorably with the X-ray data. These structures were used as a starting point to investigate the relative stability of MTC complexes with various ligands containing combinations of N, O, and S as chelating atoms and to evaluate the stabilizing/destabilizing influence of these ligands. Both for Tc and for Re complexes the nitrogen content turns out to be decisive in the stability of the metaltricarbonyl complexes, the finer details being determined by the hardness sequence N > O > S. As the core of the complexes, [(M(CO)(3)(+)], is hard, the main ordering parameter is changed as compared to our previous studies on Tc(V) [3+1] complexes where the number of sulfur atoms was decisive in accordance with the much softer character of the MOCl core. All results are successfully interpreted in terms of the hard and soft acids and bases principle (HSAB) at the local level.

Relative Stability of Mixed [3 + 1] Tc and Re Complexes: a Computational and Conceptual DFT Study

A computational and conceptual density-functional study has been performed on various [3 + 1] complexes of both Re(V) and Tc(V). The fully optimized complexes chloro(3-thiapentane-1,5-dithiolato)oxorhenium(V) and chloro(3-thiapentane-1,5-dithiolato)oxotechnetium(V) show geometries that compare favorably with the X-ray data. These structures were used as a starting point to investigate the relative stability of Tc(V) and Re(V) complexes with various ligands containing combinations of N, O, and S as chelating atoms and to evaluate the stabilizing/destabilizing influence of these N, O, and S combinations. For both Tc and Re complexes, the S content (number and position of S atoms) together with the presence of an oxygen as the central chelating atom turns out to be decisive in the stability of the tridentate complexes, the latter factor being strongly destabilizing and the former stabilizing. The stabilization sequences for both Tc and Re are shown to be identical in the gas phase and in aqueous solutions treated in a polarizable continuum model. The Re(V) complexes are found to be more stable than their Tc(V) analogues. All of the results are successfully interpreted in terms of the hard and soft acids and bases principle, applied at the local level. For this purpose, a softness value for Tc is obtained by interpolating softness trends in neighboring elements of rows 5 and 6 in the periodic table.

Quantitative study of the structure-stability relationship of TcvO(III) complexes

This paper describes the quantitative structure-stability relationship of TcvON2S2 compounds using a stability indicator based on the solid angle factor sum (SAS) for predicting the in vitro stability. The SAS values of six TcvON2S2 and one TcvON4 (D,L-HMPAO) complexes were calculated from their x-ray crystallography data. The rank order of in vitro stability of these compounds, as measured by ligand exchange reaction, is directly related to that of the SAS values. The SAS values are potentially useful for predicting stability and designing new 99mTc radiopharmaceuticals.