Pseudohalides, resonance stabilized

As shown in the introduction, the DNM anion can be regarded as a resonance stabilized, nonlinear planar pseudohalide, which forms an insoluble, highly explosive brownish silver salt upon addition of silver nitrate to an aqueous solution of 7. The DNM anion is related to the linear fulminate ion (CNO ) and can formally be regarded as the addition product of NO to fulminic acid (HCNO). Starting from CH4, NO containing nonlinear pseudohalides can be derived by successive substitution of H by NO, e.g. H3C(NO)/H2C(NO), H2C(N0)2/HC(N0)2 and HC(NO)3/C(NO)3, whereas the linear pseudohalide CNO is formally formed by replacing three H atoms by one NO unit and deprotonation. 

Carbanions of the type [HjCR ], [HCR R ] and [CR R R ] (R = NO and R R = CN, NO, NO2) can be considered to be resonance-stabilized, nonlinear pseudohalides. All experimentally known resonance-stabilized methanides are reported to be planar or nearly planar (Table 1). While the parent ion, the methanide anion HsC, adopts a pyramidal structure [Afipianar-pyramidai = 9.8 kJmol rf(CH) = 1.099 A, <(HCH) = 109.7° cf. rf(CH) = 1.093 A, <(HCH) = 109.6°] due to the lack of delocalization (no resonance for the p-AO-type lone pair possible) , substitution of one H atom by NO results in a planar anion since the empty jr -orbitals of the NO group are perfectly suitable to delocalize the carbon lone pair. Further substitution of the second H atom again results in planar anions, and the same holds for the third substitution in case of R = CN. In case of R = NO and NO2, the third substitution leads either to a propeller-type structure with only a small distortion from planarity or one NO2 group is twisted by 90°, nevertheless leaving the central carbon in an almost trigonal planar environment . ... 

H. Brand, J. F. Liebman, A. Schulz, P. Mayer, A. Villinger, Eur. J. Inorg. Chem. 2006,4294-4308. Nonhnear, resonance-stabilized pseudohalides From alkali methanides to ionic liquids of methanides. 

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