| الوصف: |
Bis(2-picolyl)amine (bpa) ligands are tridentate ligands, with flexible linking arms that allow both meridional (mer) and facial (fac) coordination geometry. The formation of geometrical isomers, as well as the formation of complexes of different stoichiometry and coordination number, can be influenced by a number of effects, for example the coordinating ability of the counterion. Counterions of strong coordinating ability, due to their localized charge, compete with the ligands for binding the metal, and often lead to formation of ML or bridged complexes. In literature, similar complexes were studied as models for multinuclear zinc enzymes for capturing CO2. Large counterions of dispersed charge, such as perchlorate do not interfere with binding of the ligand, enabling formation of ML2 complexes. A similar system was described as a fluorescent Zn(II) indicator. In this work, we studied how different counterions effect the stoichiometry, coordination number and geometry of complexes. Crystal structures of four Zn(II) and four Cu(II) complexes were determined, revealing complexes of a large structural variety: monomeric ML and ML2, bridged dimers, a coordination polymer and a cyclic trimer that binds atmospheric CO2. For Cu(II) complexes, the local magnetic properties were studied by ESR spectroscopy, while NMR spectroscopy was used to study the solution structure of Zn(II) complexes. For the ML2 complex obtained with the perchlorate anion, DFT calculations were used to determine the relative stability of isomers. |
