Several mixed complexes, such as Fe(phen)2(CN)2are subject to variations in color, according to the acceptor properties of the molecular environment. The charge transfer band is gradually shifted to decreasing wave length of the absorption maximum, as the acceptor number of the solution is increased. Likewise, the charge transfer band of the copper(II)-complex with tetramethyl-ethylenediamine and acetylacetonate as ligands is shifted to greater wave length as the donor number of the solution is increased, thus providing evidence for gradual changes from the planar into octahedral arrangement. All complexes have in common that their coordination centre is hard enough to respond to changes of an essentially hard environment and soft enough to redistribute any changes in charge density over the whole system in such ways that the basic characteristics of the complex molecule under consideration is retained. The charge density pattern around the coordination centre, which is at the same time an integral part of the molecular outer regions, appears to retain locally a nearly invariant charge density. The redistribution of the charge density pattern appears to be subject to the regulating actions around the coordination centre. This is therefore considered as representing the highest hierarchic level, to which the charge densities in all other boundary areas are subordinated. Reorganization of the charge density pattern is performed due to the mobilities of the π-electron systems under control of the said superordinated levels. The lowest hierarchic level seems to be represented by the charge density areas along the structural framework, which provides the static boundary conditions for the more highly developed dynamic properties of the higher levels
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