A Sterically Hindered Derivative of 2,1,3‐Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium–Nitrogen Radical Anion

Abstract

Abstract Interaction of the tetradentate redox‐active 6,6′‐[1,2‐phenylenebis(azanediyl)]bis(2,4‐di‐ tert ‐butylphenol) (H 4 L) with TeCl 4 leads to neutral diamagnetic compound TeL ( 1 ) in high yield. The molecule of 1 has a nearly planar TeN 2 O 2 fragment, which suggests the formulation of 1 as Te II L 2− , in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp 2 ] leads to quantitative formation of the paramagnetic salt [CoCp 2 ] + [ 1 ] .− , which was characterised by single‐crystal XRD. The solution EPR spectrum of [CoCp 2 ] + [ 1 ] .− at room temperature features a quintet due to splitting on two equivalent 14 N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the 125 Te nucleus. Two‐component relativistic DFT calculations perfectly reproduce the a ( 14 N) HFI constants and A ∥ ( 125 Te) value responsible for the low‐temperature satellite splitting. Calculations predict that the additional electron in 1 .− is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1 .− can be regarded as the first example of a structurally characterised monomeric tellurium–nitrogen radical anion.