BF forms at 2000° C , condenses at -196° C.
REACTS. In Dr. Timms' apparatus, gaseous BF3 enters at top and reacts with granular boron in the graphite susceptor (center). The high resulting yield of BF condenses as a polymer on the walls of the lower flask
found to have a simple chain of three boron atoms. The yield of B 3 F 5 from BF alone is rarely more than 2% of the original BF 3 . But, as with the B 2 F 4 , cocondensation of a second vapor—in this case, B2F4—with the emerging BF produces much improved quantities. Further addition of boron monofluoride to triboron pentafluoride to form the next higher homolog, B 4 F 6 , has not been observed, Dr. Timms adds. The pentafluoride reacts rapidly with many substances at low tempera tures. For example, it combines im mediately with hydrogen at —70° C. to form B 2 F 4 , HBF 2 , and a solid yel low polymer. And with C 2 F 4 at —100° C , the pentafluoride reacts smoothly to make an apparently new compound, C2B2F6. The hexafluoride's structure ( double-bonded carbons with the cis-BF2 groups) can be assigned from IR and NMR spectra. If the temperature rises while C 2 F 4 and the pentafluoride are in contact, the reaction mixture ex plodes. B 3 F 5 melts with decomposition at - 5 0 ° to - 5 5 ° C. Colorless as a solid,
the pentafluoride quickly turns bright yellow as a liquid. Above —30° C , it breaks down rapidly to BF 3 , B 2 F 4 , and considerable amounts of one of the curiosities of Dr. Timms' research, the B 8 F 1 2 fraction. Pinning down the structure of the yellow, oily B 8 F ] 2 has not yet been completed, Dr. Timms states. The compound cannot be resolved by frac tional distillation at low temperatures. Vapor density measurements and analysis suggest a composition close to B 8 F 1 2 . The B 8 F 1 2 mass spectrum—termed "very confusing" by Dr. Timms be cause of apparent rearrangement re actions—initially indicates a mixture of Β 9 and B 1 0 compounds. However, when an all-glass inlet system is em ployed, a reproducible spectrum re sults. The most abundant ions then observed at low electron voltages are now B7F
