Double helical assembly of imino nitroxyl diradicals by silver(I) ions

The co-ordination of imino nitroxyl diradicals to diamagnetic silver(I) ions led to the self-assembled double helical dimer [Ag2(bisimpy)2][PF6]2 1 (diradical bisimpy = 2,6-bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-2-yl 1-oxyl)pyridine). The diradical has two imino nitroxyl groups linked by the pyridine group at its meta positions and acts as a tridentate ligand. In the double helicate two bisimpy bridge two silver(I) ions in a {4 + 2} connectivity, and the silver(I) ions have a very short contact of 2.8943(5) Å. Magnetic susceptibility measurements and crystal structure analysis revealed that the two radical moieties in bisimpy are ferromagnetically coupled (J = 17.4(8) cm–1; H = –2JΣSi·Sj) through the pyridine group, and imino nitroxyl overlaps between adjacent molecules result in an intermolecular antiferromagnetic interaction (–52.3(7) cm–1).