Bisdiazonium dication

Figure 5-2 shows schematically the dependence of the relative concentration of the diazo equilibrium forms on the pH (for the diazoanhydride mentioned in this figure see Sec. 5.2). The relative concentrations of the two major equilibrium forms, the diazonium ion and the diazoate ion, decrease on the right and left sides, respectively, of the pH value corresponding to equal concentrations of these two forms ([ArNj] = [ArN20-]). The gradients correspond to a factor of 100 per pH unit, compared with only 10 per pH unit in the case of dibasic Bronsted acids. The equilibrium concentrations of the diazohydroxide and the diazoanhydride (except for very reactive diazonium ions such as the benzene-1,4-bisdiazonium dication mentioned above) are very small at all pH values, with a maximum at pH = pKm. 

Rasul, Prakash, and Olah442 have attempted to generate bisdiazonium dication 215 by the diazotization of aminodiazonium ion 212 with NO+BF4 (HSC F-SbFs-SO2CIF, -78°C), but no further diazotization was observed. The linear Dxh structure was found to be a minimum on the potential energy surface at various levels of theory 442,502 Bond distances represent bisdiazonium character. 

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