Donor–acceptor complexes of organotellurium compounds. Physical studies: tellurium-125 Mössbauer spectroscopy for the measure of charge transfer. Crystal and molecular structure of the complex dibenzotellurophene–7,7,8,8-tetracyano-p-quinodimethane

Abstract

A range of organotellurium(II) compounds, together with two selenium compounds are used as donors to form donor–acceptor complexes with 7,7,8,8-tetracyano-p-quinodimethane (tcnq). Generally, the stoicheiometry is 1 : 1 but two ditellurides provide an exception in giving R₂Te₂·2tcnq (R = Ph or C₆H₄OEt-p). The complexes are electrical insulators although the conductivities vary over several orders of magnitude. The two ditelluride complexes show evidence of semiconducting properties. E.s.r. and i.r. data are discussed and it is concluded that in most cases the degree of charge transfer is small. Exceptions to the rule appear to be the tcnq complex of 1,3-dihydro-2-telluraindene and Ph₂Te₂·2tcnq which do involve significant charge transfer as assessed from a ¹²⁵Te Mössbauer study. A method of assessing the degree of charge transfer for donor–acceptor complexes of organotellurium compounds using Mössbauer spectroscopy is given. The crystal and molecular structure of the tcnq complex of dibenzotellurophene has been determined and molecular parameters compared with the known structures of the component molecules. The structural data confirm conclusions from i.r. and Mössbauer studies that, in this instance, the degree of charge transfer is very small. A novel feature of the structure is that in addition to intermolecular interactions within the mixed stacks, there are significant Te ⋯ N interactions between stacks. As a consequence, two different orientations of tcnq occur in the complex.