Bond length relationships in diazo and diazonium compounds

Geometrical data for 52 instances of the C-N=N substructure have been retrieved from the Cambridge Structural Database. A scatterplot of the N=N bond length (range 1.078-1.146 A) versus the C-N bond length (range 1.278-1.450 A) shows a strong negative correlation (linear correlation coefficient= -0.846) : a decrease in N=N triple-bond character is directly correlated with increasing double-bond character of C-N. Three discrete chemical subgroups can be identified in the dataset : benzenediazonium compounds, diazoketones and diazoalkanes with mean N=N/C-N bond lengths of 1.093 (2)/1.394(6), 1.115(3)/1.328(5) and 1.133(3) /1.301(8)A, respectively.