Structural chemistry of subvalent oxo- and nitrdiometalates: chemical twinning of ionic and metallic building units

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Subvalent compounds hold a special position within solid state chemistry. Ionic and metallic bonding contributions are realised within them in a unique manner. Structural units which can be regarded as cut-outs from (inter-)metallic phases alternate periodically with motifs from ionic structures and form an ordered crystal lattice. Subvalent compounds thus are solids in which areas with perdominantly metallic bonding coexist with areas in which ionic bonding prevails. According to the two different characters of the structural building units, subvalent compounds combine the typical behaviour of metals and ionic solids. Subvalent compounds show overall good metallic behavour but interaction of the conduction electrons with the local Coulomb potentials from the ionic regions lead to interesting new effects. Unexpected combinations of metallic and ionic properties can prospectively lead to novel materials. The combination of metallic conductivity and e. g. ocalised magnetic transition metal centres could result in matierals of interest for electronic or data storage devices. Modifying the volume fraction of ionic and metallic structural areas could enable the rational design of low-dimensional metallic conductors or even quantum dots of small, not interacting atomic groups of atoms. Also strongly anisotropic optical materials are conceivable.Systematic work on these aspects of the solid state chemistry of subvalent compounds is scarce. The first representatives of this class of substances were the alkali metal suboxides and he subnitrides of the heavy alkaline earth metals. We succeeded in broadening the family of subvalent compounds by synthesising alkali metal suboxometalates and the first alkaline earth subnitridometalates containing complex, tetrahedral oxo- and nitridometalate anions and by characterising new structural families.This project aims at a systematic expansion of the classes of suboxo- and subnitridometalates and the characterisation of the properties of new representatives. By comparing as many individual examples of subvalent metalates as possible a ddeper insight for the interaction of ionic ande metallic structural subunits and its influence on macroscopic properties may be gained. A comprehensive picture of the structure-property relations of subvalent compounds based on measurements of electric conductivity, heat capacity, magnetic suscebility in combination with quantum chemical calculations of the electronic structure is to be established.