[7−7]- versus [5−5]Bitrovacene: How Linkage Isomerism Affects Exchange Coupling and Redox Splitting1

Thermal rearrangement of dicycloheptatriene C 14 H 14 and subsequent reaction with (η 5 -cyclopentadienyl)(tetracarbonyl)vanadium affords [7−7]bitrovacene, μ-η 7:η 7 -C 14 H 12 [(η 5 -C 5 H 5 )V] 2 ( 8 • • ). Sterically induced avoidance of a planar μ-η 7:η 7 -heptafulvalenediyl bridge leads to a complicated packing pattern of varyingly twisted units of 8 • • which generates a huge unit cell ( Z = 72), in stark contrast to the isomer 7 • •, for which Z = 2 applies. The isomers 8 • • and 7 • • also differ with regard to the extent of intervanadium electro- and magnetocommunication. Redox splittings δ E 1/2 of consecutive ET steps are considerably larger for 8 • •, compared to 7 • •, thereby reflecting the higher contribution the larger ring makes to the SOMO. The higher spin density at the C 7 compared to the C 5 carbon atoms, which governs the EPR spectra, effects a pronounced gradation of the exchange coupling parameter determined by magnetic susceptometry: J ( 7 • • ) = −2.8, J ( 8 • • ) = −24.1 cm - 1 .