| Abstract
| - The paramagnetic boronic acid (η7-C7H7)V[η5-C5H4B(OH)2] (3•) has been prepared andcharacterized structurally, emphasis being placed on hydrogen bonding motives present inthe 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 EPRspectrum 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 δE1/2between consecutive oxidation steps of 4••• are not resolved, i.e., δE1/2 ≤ 60 mV.
- The paramagnetic organometallic boronic acid 3• has been prepared and characterized, including structural studies of the solvates 3•·Et2O and 3•·H2O. The latter differ because of the disparate hydrogen-bonding abilities of Et2O and H2O. EPR spectroscopy fails to provide evidence for an equilibration 2 3• ⇌ (3•)2 in fluid solution. The cyclic anhydride 4••• forms readily and exhibits antiferromagnetic exchange, as demonstrated by EPR and magnetic susceptometry. The relatively small value of the exchange coupling constant, J = −1.04 cm-1, points to spin frustration in 4•••.
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