N- cyanamide

Carrau, R., Hernandez, R Suarez, E., Betancor, C. Intramolecular functionalization of N-cyanamide radicals. Synthesis of 1,4- and 1,5-N-cyanoepimino compounds. J. Chem. Soc., Perkin Trans. 1 1987, 937-943. 

This finding is easily rationalized using Pearson s concept of hard and soft acids and bases (see Section 2.14). Whenever NCN is coordinated by chemically hard cations (for example, Ca +, with rj = 19.52 eV, see Table 2.3) there results a considerable amount of ionic bonding between the cation and a symmetrical N=C=N anion. Chemically softer cations such as Pb + (8.46 eV) or Ag+ (6.7 eV) will bond more covalently to one end of the NCN unit, inducing the less symmetrical (N-C=N ) cyanamide shape this species must be chemically softer. Figure 3.41(b) shows the PbNCN structure with a seven-... 

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