Conformation of tripod metal templates in CH3C(CH(2)PPh(2))(3)ML(n) (n=2,3): Neural networks in conformational analysis

The conformational space spanned by tripod metal templates CH3C(CH(2)Ph(2))(3)M is analysed on the basis of the solid-state structures of 82 tripodCo templates in compounds tripodCoL(2) and tripodCoL(3). Systematic analysis, including the techniques of conformational space group scatter graphs, principal component analysis, and partial least squares, reveals a series of basic regularities: The torsion of the phenyl groups is strongly linked to the torsional skew of the bicyclooctane-type framework of the chelate cage. For one sense of this skew there are two classes of low-energy conformation that differ by the helicity of the phenyl arrangement and by the degree of torsional skew in the chelate backbone. From the scatter graphs it is evident that a change in helicity may occur by one- or by two-ring flip mechanisms. The basic regularities found by the above methods are also evident from the analysis of the same data by a neural network approach. The fact that these regularities are found for tripodCoL(2) and tripodCoL(3), irrespective of the widely different coligands L and crystal environments, means that the conformation of the tripod metal templates is governed by the forces acting within them and not so much by the forces imposed on them by their individual chemical or crystal environment. It is shown that the classifications, although derived from a data basis only containing Co compounds, are characteristic for tripod metal templates irrespective of the specific metal involved.