Synthesis and structural analysis of some trinitromethanide salts

Two trinitromethanide (TNM) salts containing weakly coordinating cations (tetrabutylammonium and cesium) were synthesized via incomplete nitration of acetic anhydride followed by cation exchange with tetrabutylammonium bromide and cesium fluoride. Their structural characteristics were determined by single crystal X-ray crystallography [J.C. Bryan, M.N. Burnett, A.A. Gakh, Acta Crystallogr., Sect. C (Cr. Str. Comm.) 54 (1998) 1229] followed by comparative analysis with the literature data. In all cases, the TNM anion was found to be a non-planar system. The sum of dihedral angles between the central (C-N₃) plane of the anion and the planes of the individual nitro groups varies from 60 to 100°. C-N and N-O interatomic distances in TNM anion can be correlated with the dihedral angles of the corresponding nitro groups: The ¹³C and ¹⁴N NMR spectra of the TNM anion are very simple (broad singlets), an indication of the equivalence (on the NMR time scale) of the nitro groups in solution. The distribution ratio between organic phase (tributyl phosphate) and water is 5000 times higher for Cs⁺-C(NO₂)₃ compared to Cs⁺NO₃/^-, presumably due to size and/or charge delocalization differences between nitrate and TNM anions. (C) 2000 Elsevier Science B.V.