Di([5]trovacenyl)ethyne, di([5]trovacenyl)butadiyne, and di-1,4-([5]trovacenylethynyl)benzene: Electrocommunication and magnetocommunication mediated by -C C-, -C C-C C- and -C C-C6H4-C C- spacers

摘要

The synthesis of dinuclear derivatives of trovacene (eta(7)-C7H7)V(eta(5)-C5H5) (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 deltaE(1/2)(0/ 1-, 1-/2-) is resolved for 6(..) (deltaE1/2 = 150 mV) and indicated for 7(..) (deltaE(1/2) less than or similar to 80 mV). Magnetocommunication leads to exchange coupling of the two electron spins which reside in vanadium centered orbitals. The values J(EPR)(6(..)) = (-)0.92, J(EPR)(7(..)) = (-)0.56, and J(EPR)(8(..)) = (-)0.005 cm(-1) are derived from the V-51 hyperfine patterns. Accordingly, attenuation of exchange interaction by oligoalkyne spacers is weak, corresponding to a factor of 0.6 only per added -CdropC- unit. In the determination of very weak long distance exchange interactions, EPR excels because of the range 5 x 10(-4) less than or similar to 1.5 cm(-1) accessible in the case of V-51 as a reporting magnetic nucleus and because competing intermolecular exchange is quenched in dilute fluid solution. This is demonstrated by the value J(x)(7(..)) = -3.84 cm(-1) obtained from a magnetic susceptibility study, which exceeds J(EPR)(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 pi-perimeter ligand orbitals and weakly overlapping only with the a(1g)(sigma) ring orbitals, creating two bottlenecks for spin-exchange in the spacer-containing ditrovacenes.