Ab initio and density functional force field studies on the IR spectra and structure of diazonium dicyanomethylide (diazodicyanomethane)

The structure of diazonium dicyanomethylide (diazodicyanomethane) þN2–C(CN)2 2 $ N2yC(CN)2 has been studied on the basis of ab initio HF, MP2 and DFT BLYP force field calculations, as well as of literature IR spectra and X-ray diffraction structural data. The results have been compared with those obtained for a series of chemical relatives of the title compound, i.e. molecules, push-pull molecules, anions and zwitterions, containing a-dicyano or diazo fragments, and especially substituted ammonium dicyanomethylides and diazomethane þN2–CH2 2 $ N2yCH2. It has been found on the basis of spectral, bond length, bond order and electric charge analyses that the diazonium (or carbanionic, left) canonical form is much more important for the title zwitterion, than the corresponding one for diazomethane. So, the title compound can be named (and considered as) both diazonium dicyanomethylide and dicyanodiazomethane. q 2004 Elsevier B.V. All rights reserved.