RT journal article
T1 The Solution Chemistry of Cu2+–tren Complexes Revisited: Exploring the Role of Species That Are Not Trigonal Bipyramidal
A1 Castillo González, Carmen Esther
A1 García Algarra, Andrés
A1 Máñez Muñoz, María Ángeles
A1 Duboc, Carole
A1 García Basallote, Manuel
A2 Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica
K1 Copper complexes
K1 Kinetics
K1 UV
K1 Vis spectroscopy
K1 Density functional calculations
K1 EPR spectroscopy
AB Potentiometric and spectrophotometric titrations indicate that aqueous solutions that contain equimolar amounts ofCu2+ and tren contain the HCuL3+, CuL2+ and CuL(OH)+ species and that their relative concentrations depend on the pH of the solution. The stability constants and the UV/Vis and EPR spectra of the three species have been determined. The position of the absorption maximum clearly corresponds to a trigonal bipyramidal (tbp) geometry for CuL2+, whereas for HCuL3+ and CuL(OH)+ there are also bands that could correspond to square pyramidal (sp) complexes, but the EPR spectra indicate that only HCuL3+ can be considered to be sp. When any of these species is mixed with an excess of acid, an intermediate is formed within the mixing time of the stopped-flow technique. This intermediate undergoes complete decomposition in a second slower step. Interestingly, the spectrum of this intermediate is typical of sp geometry. Kinetic studies on complex formation in general indicate that complexation occurs in a single step, although under certain conditions an additional step has been observed that probably corresponds to the conversion of CuL2+ to HCuL3+, and the spectral changes indicate that the process involves structural reorganization from tbp to sp geometry. DFT and TDDFT calculations have been carried out for the three stable species, as well as for species in a higher protonation state. The results indicate that CuL2+ exists as a species with tetradentate tren and tbp geometry, although a wide range of distortions between the ideal tbp geometry and a geometry closer to sp is possible with a very modest energy cost. The energy change associated with hydrolysis of one of the Cu– N bonds to give a species with tridentate tren was found to be slightly higher than that previously found for a related ligand, which contains a substituent at one of the terminal amino groups. For CuL(OH)+, the calculations suggest that an equilibrium exists between species with essentially the same energy but different geometries, each one of the species is closer to one of the ideal tbp and sp limits. For HCuL3+, the relevance of the sp geometry was confirmed by the calculations.
PB Willey
YR 2012
FD 2012
LK http://hdl.handle.net/10498/20508
UL http://hdl.handle.net/10498/20508
LA eng
DS Repositorio Institucional de la Universidad de Cádiz
RD 15-nov-2026