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The paramagnetic boronic acid (η⁷-C7H7)V[η⁵-C5H4B(OH)2] (3^•) has been prepared and characterized structurally, emphasis being placed on hydrogen bonding motives present in the crystal. EPR spectroscopy reveals that association of 3^• is absent in fluid solution. Tri([5]trovacenyl)boroxine, 4^•••, the cyclic anhydride of 3^•, engages in antiferromagnetic exchange; magnetic susceptometry provides the value J(4^•••) = −1.04 cm^-1. Accordingly, the EPR spectrum of 4^••• in fluid solution points to 22 ⁵¹V hyperfine components separated by one-third of the coupling constant of mononuclear trovacene derivatives. Redox splittings δE1/2 between consecutive oxidation steps of 4^••• are not resolved, i.e., δE1/2 ≤ 60 mV.

Thermal rearrangement of dicycloheptatriene C14H14 and subsequent reaction with (η⁵-cyclopentadienyl)(tetracarbonyl)vanadium affords [7−7]bitrovacene, μ-η⁷:η⁷-C14H12[(η⁵-C5H5)V]2 (8^••). Sterically induced avoidance of a planar μ-η⁷:η⁷-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 δE1/2 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 C7 compared to the C5 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.

The biradicals 1,8-di([5]trovacenyl)naphthalene (6), 1,5-di([5]trovacenyl)naphthalene (7), and 1,3-di([5]trovacenyl)benzene (8) and the monoradical 1-[5]trovacenylnaphthalene (9) have been prepared and studied by means of single-crystal X-ray diffraction (6, 8, 9), cyclic voltammetry, EPR spectroscopy, and magnetic susceptometry. Comparison of the magnetic properties of 6−9 reveals that π-stacking, as encountered in 6, largely enhances exchange interaction between the two singly occupied V(3dz^{2) orbitals. The effect of π-stacking on the electrochemical properties, as manifested in the redox splitting between consecutive electron transfer steps, is less pronounced. Redox splittings δE1/2 for consecutive reductions exceed those for oxidations of binuclear trovacenes, δE1/2(2+/+, +/0) being apparent for π-stacked 6 only. Because of the orthogonality of the metal-centered redox orbitals V1(dz2) and V2(dz2) and the η5-cyclopentadienyl π-orbitals, electro- and magnetocommunication are indirect processes. Electrocommunication rests on changes of the donor/acceptor properties of V1,V2 caused by oxidation or reduction which govern metal−ligand charge distribution; the latter changes are transmitted via the spacer. Magnetocommunication takes the form of antiferromagnetic coupling, which can be traced to spin polarization of filled π-orbitals of the bridge by orthogonal singly occupied vanadium 3dz2 orbitals.}

Lithiation of trovacene, (η⁷-C7H7)V(η⁵-C5H5), Li/I exchange, and Pd(dppf)Cl2-catalyzed homocoupling affords [5-5]bitrovacene 5^2•. Intermetallic communication manifests itself in typical biradical features of the EPR spectrum and in the resolution of redox splittings of 147 mV for the two subsequent oxidations and 224 mV for the reductions, respectively. 5^2• adopts a trans conformation in the single crystal (X-ray diffraction) as well as in rigid solution (EPR spectroscopy). A magnetic susceptibility study of 5^2• reveals weak antiferromagnetic coupling (J = −2.78 cm^-1) of the two V(d⁵) centers.