Microwave spectrum, structure, and dipole moment of 2,3,4,5-tetracarbahexaborane(6)

The structure of 2,3,4,5-tetracarbahexaborane (C4B2H6) has been determined from the microwave spectra of 10 isotopic species. The pentagonal pyramidal geometry of the molecule has been confirmed. The four carbon atoms lie in the pentagonal base; the short C–C bond lengths (1.43 Å) suggest pi-bonding character. A molecular dipole moment of 2.26 ± 0.06 D was determined from the observed Stark effect.