Directing Boron-Phosphorus Bonds in Crystalline Solid: Oxidative Polymerization of P═B═P Monomers into 1D Chains

Over 20 years after the last inorganic ternary B-P compound was reported, Na₂BP₂, a new compound containing one-dimensional B-P polyanionic chains has been synthesized. Common high-temperature synthetic methods required for the direct reaction of boron and phosphorus negate the possible formation of metastable or low temperature phases. In this study, oxidative elimination was used to successfully condense 0D BP₂^3- anionic monomers found in a Na₃BP₂ precursor into unique 1D BP₂^2- chains consisting of five-member B₂P₃ rings connected by bridging P atoms in the crystal structure of Na₂BP₂. The synthesis was guided by in situ X-ray powder diffraction studies, which revealed the metastable nature of the products of oxidative elimination reactions. Na₂BP₂ is predicted to be an electron balanced semiconductor which was confirmed by UV-vis spectroscopy with the experimentally determined band gap of 1.1 eV.