Synthesis and Thermal Studies of Two Phosphonium Tetrahydroxidohexaoxidopentaborate(1-) Salts: Single-Crystal XRD Characterization of [PrPPh][BO(OH)]·3.5HO and [MePPh][BO(OH)]·B(OH)·0.5HO.

Two substituted phosphonium tetrahydoxidohexaoxidopentaborate(1-) salts, [PrPPh][BO(OH)]·3.5HO () and [MePPh][BO(OH)]·B(OH)·0.5HO (), were prepared by templated self-assembly processes with good yields by crystallization from basic methanolic aqueous solutions primed with B(OH) and the appropriate phosphonium cation. Salts and were characterized by spectroscopic (NMR and IR) and thermal (TGA/DSC) analysis. Salts and were thermally decomposed in air at 800 °C to glassy solids via the anhydrous phosphonium polyborates that are formed at lower temperatures (<300 °C). BET analysis of the anhydrous and pyrolysed materials indicated they were non-porous with surface areas of 0.2-2.75 m/g. Rhe recrystallization of and from aqueous solution afforded crystals suitable for single-crystal XRD analyses. The structure of comprises alternating cationic/anionic layers with the HO/pentaborate(1-) planes held together by H-bonds. The cationic planes have offset face-to-face () and vertex-to-face () aromatic ring interactions with the Pr groups oriented towards the pentaborate(1-)/HO layers. The anionic lattice in is expanded by the inclusion of B(OH) molecules to accommodate the large cations; this results in the formation of a stacked pentaborate(1-)/B(OH) structure with channels occupied by the cations. The cations within the channels have , (edge-to-face), and phenyl embraces. Both H-bonding and phenyl embrace interactions are important in stabilizing these two solid-state structures.