Anion-templated self-assembly of highly stable Fe(II) pentagonal metallacycles with short anion-π contacts.

The crystal structures of the self-assembled metallapentacycles [{Fe(5)(bptz)(5)(CH(3)CN)(10)} ⊂ 2SbF(6)][SbF(6)](8) (1) and [{Fe(5)(bmtz)(5)(CH(3)CN)(10)} ⊂ SbF(6)][SbF(6)](9) (2) with the π-acidic ligands bptz (3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) and bmtz (3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine), respectively, revealed cationic pentagons templated by [SbF(6)](-) ions. The short anion-π contacts established between the anions and the tetrazine rings play an important role in the stability of the pentagons.