Di([5]trovacenyl)ethyne, Dl([5]trovacenyl)butadiyne, and Di-1,4-([5]trovacenylethynyl)benzene: Electrocommunication and magnetocommunication mediatedby -C≡C-, -C≡C-C≡C- and -C≡C-C6H4-C≡C- spacers

The synthesis of dinuclear derivatives of trovacene (η 7 -C 7 H 7 )V(η 5 -C 5 H 5 ) (1') is reported, in which ethynyl (6..), butadiynyl (7..), and 1,4-di(ethynyl)phenyl (8..) groups serve as spacers between paramagnetic (S = 1 / 2 ) [5]trovacenyl units. The mononuclear precursors [5]trovacenylcarbaldehyde (2.) and [5]trovacenylacetylene (4.) are also described. Structural characterization by X-ray diffraction has been performed for 4., 6.., 7.., and 8... Electronic communication as gleaned from cyclic voltammetry only manifests itself in the reduction processes where redox splitting δE 1 / 2 (0/ 1-, 1-/2-) is resolved for 6.. (δE 1 / 2 = 150 mV) and indicated for 7.. (δE 1 / 2 ≤ 80 mV). Magnetocommunication leads to exchange coupling of the two electron spins which reside in vanadium centered orbitals. The values J E P R (6..) = (-)0.92, J E P R (7..) = (-)0.56, and J E P R (8..) = (-)0.005 cm - 1 are derived from the 5 1 V hyperfine patterns. Accordingly, attenuation of exchange interaction by oligoalkyne spacers is weak, corresponding to a factor of 0.6 only per added -C≡C- unit. In the determination of very weak long distance exchange interactions, EPR excels because of the range 5 x 10 - 4 ≤ J ≤ 1.5 cm - 1 accessible in the case of 5 1 V as a reporting magnetic nucleus and because competing intermolecular exchange is quenched in dilute fluid solution. This is demonstrated by the value J Χ (7..) = -3.84 cm - 1 obtained from a magnetic susceptibility study, which exceeds J E P R (7..) by a factor of 7. The small magnitude of spin exchange interaction between trovacene units reflects the fact that the spin bearing V3d z 2 orbital is virtually orthogonal to the π-perimeter ligand orbitals and weakly overlapping only with the a 1 g (σ) ring orbitals, creating two bottlenecks for spin-exchange in the spacer-containing ditrovacenes.