The triphenylphosphine–benzotrifuroxan reaction. Part IV. Crystal and molecular structures of a red compound; the hydroxytriphenylphosphonium salt of 4-imino-8-aci-nitrobenzo[1,2-c:4,5-c′]difurazan

Abstract

The red compound isolated from the reaction of benzotrifuroxan and triphenylphosphine has been shown by three-dimensional X-ray structure analysis to have a crystal and molecular structure which is consistent with its formulation as the hydroxytriphenylphosphonium salt of 4-imino-8-aci-nitrobenzo[1,2-c:4,5-c′] difurazan. The phosphorus-oxygen-bond-length of 1.63 Å is ca. 0.2 Å greater than the expected value for PO, and it therefore appears that this bond is P⁺–OH. In the anion the C₆ ring is not benzenoid and all the carbon–nitrogen bonds have a high π bond-order. The furazan rings have dimensions similar to those found in other members of this series. The CNO₂^–-group is symmetrical and co-planar with the rest of the anion. The carbon–nitrogen bond of 1.36 Å is 0.1 Å shorter than the corresponding bond of an aromatic nitro-group.