Chapters authored
Structural Diversity in Substituted Pyridinium Halocuprates(II)
The flexible coordination sphere of the Jahn-Teller active Cu(II) ion provides access to a full spectrum of coordination geometries from 4-coordinate (tetrahedral or square planar) to 6-coordinate elongated octahedral. This is further enhanced in anionic halide complexes by the ability of the halide ligand to bridge between Cu(II) centers to generate extended oligomeric or polymeric complexes. Coordination geometry and extended structure of the anionic complex is very sensitive to the nature of the organic counterion. This is especially true for planar substituted pyridinium cations in which minor changes in the nature or position of the substituted group can generate completely different halocuprate(II) structures. Early work focused on reducing ligand-ligand repulsion through strong hydrogen bonding with the organic cation in order to manipulate the Cu(II) coordination sphere. However, many unique structures have been found in which quaternary pyridinium cations were employed-including the remarkable thermochromic compound (1,2,6-trimethylpyridinium)2CuCl4- in which strong hydrogen bonding is absent. More recently aminopyridinium cations, which further increase structural diversity not only through the possibility of having mono- or di-protonated cations but also the ability of monoprotonated cations to coordinate to the Cu(II) center through the amino group, have been investigated.
Part of the book: Exploring Chemistry with Pyridine Derivatives