X-ray photoelectron spectra of novel aromatic polycyano-substituted molecules derived from tetracyanoethylene

A number of polycyano-substituted molecules derived from tetracyanoethylene, previously structurally characterized, have been studied by the XPS technique: L'[(C11N7H2)(-)], the conjugated acid (LH), the bis-chelated metal(II) complexes (ML2) and the monochelated ones (>ML). The broad band arising from the ionization of the nitrogen K shells can be deconvoluted into several components: three in L', four in LH, two in ML2 or >ML. The specific assignment has been based on the corresponding area ratios of the components and on the empirical correlation between the binding energy of the N Is electrons and the electronic charge as influenced by the substituents on this atom. The lowest energy component is the most intense in any compound and is assigned to the nitrile nitrogen atoms. The component due to the iminonitrogen can be discriminated from that due to the bridging nitrogen neither in >ML nor in most ML2's. The resolution of the band into four components in LH allows one to exclude any fast interconversion in the solid state between the two energetically equivalent 3H-pyrrolizine tautomers.