Crystal Structure of H3BO3∙2Ph3PO

The crystal molecular structure of the co-crystal of boric acid (BA) with triphenylphosphine oxide (TPO) 1:2, H3BO3∙2Ph3PO, was determined by single-crystal X-ray diffraction. In the crystal, pairs of the boric acid molecules are connected to each other by hydrogen bonds, and each acid molecule forms two hydrogen bonds with the oxygen atoms of two triphenylphosphine oxide molecules. The crystal packing of the new complex was compared with the crystal packings of the known 1:1 complex of boric acid and triphenylphosphine oxide, and boric acid and triphenylphosphine oxide themselves. Also, the energetic preferences and densities of the co-formers (BA and TPO) were compared for their pure forms and co-crystals. It is shown that more tight crystal packing is not necessarily accompanied by higher stability.