Fac vs Mer Selection in Octahedral Complexes of the N-Benzyl-Substituted Triazolylpyridine Diad with Labile Metal Ions (Zinc(II), Iron(II), and Nickel(II))

Pseudo-octahedral complexes built on chelating ligands offer valuable isomeric properties such as the formation of fac vs mer isomers, and Λ vs Δ enantiomers. This article discusses factors guiding the fac vs mer selection of complexes built from the triazolyl-pyridine platform bearing a benzyl substituent, in conjunction with labile metal ions such as zinc(II), iron(II), and nickel(II). Critical parameters that are explored include the geometrical flexibility of the individual metal ion, and the nature of the counteranion. In essence, it was observed that ions which can withstand significant distortions in their first coordination sphere, such as zinc(II), generally prefer forming the mer isomer irrespective of the counteranion, whereas ions with more restricted geometry, such as iron(II), are directed either to a fac arrangement by small, tetrahedral anions such as tetrafluoroborate or perchlorate or to a mer organization by counteranions of lower symmetry, such as triflate. The molecular interactions o...