Ferromagnetically Coupled S = 1 Chains in Crystals of Verdazyl‐Nitronyl Nitroxide Diradicals
Thermally stable organic diradicals with a triplet ground state along with large singlet‐triplet energy gap have significant potential for advanced technological applications. A series of phenylene‐bridged diradicals with oxoverdazyl and nitronyl nitroxide units were synthesized via a palladium‐catalyzed cross‐coupling reaction of the corresponding iodoverdazyls with a nitronyl nitroxide‐2‐ide gold(I) complex with high yields (up to 82%). The synthesized diradicals exhibit high stability and do not decompose in an inert atmosphere up to 180 °C. The magnetic properties of prepared phenylene‐coupled diradicals were investigated and magneto‐structural correlations were established. For the studied diradicals, both substantial antiferromagnetic (D E ST » ‐64 cm –1 ) and ferromagnetic (D E ST ³ 25 and 100 cm –1 ) intramolecular exchange interactions were observed. The sign of the exchange interaction is determined both by the bridging moiety ( para ‐ or meta ‐phenylene) and by the type of oxoverdazyl block ( C ‐linked or N ‐linked). Upon crystallization, diradicals with the triplet ground state form unique one‐dimensional exchange‐coupled chains with strong intra‐ and weak inter‐diradical ferromagnetic coupling.