Molecular structures bispidine complexes

The synthesis of the 2,4-bisphenol derivative of the standard tetradentate ligand 14 is quite tedious and so far has not been optimized (204). Apart from the fact that the noninnocent phenolate donors may lead to interesting ligand systems and metal complexes, it is the six-membered chelate rings involving the in-plane phenolate donors that lead to structural properties quite different from those of the other bispidine ligands [shown in Fig. 2(e) is a plot of a preliminary X-ray molecular structure of one of the possible conformers (meso form) of a copper(II) complex]. 

The aim of the present communication is to discuss possible reasons for these and other distortions and to describe models with which one can predict the corresponding structures. The correlation of the ensuing structures with molecular properties is also discussed, and answers are sought to the question whether an accurate structural prediction might help to understand specific distortions. In addition, some fascinating properties and applications of bispidine complexes are presented and models are discussed, which assist their thorough understanding. 

First transition metal coordination compounds with bidentate bispidine ligands were described in 1957 (30). The initial report with metal complexes of tetradentate bispidine ligands dates back to 1969 (31). Following these early reports, there have been a number of studies on the complexation properties of several bipidine derivatives (32-35). However, extensive, broad, and thorough studies of the bispidine coordination chemistry began only <10 years ago. These studies will be reviewed here. They include structural and theoretical work, spectroscopy, electron-transfer studies, metal ion selective complexation, and applications in biomimetic chemistry, catalysis, and molecular magnetism. 

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