Structural Induction via Solvent Variation in Assemblies of Triphenylboroxine and Piperazine—Potential Application as Self-Assembly Molecular Sponge

This study examined the direct effect of solvent on the chemical composition and structure of supramolecular assemblies formed from triphenylboroxine ((PhBO)3) and piperazine (ppz) through N→B bonds. Oxygen-containing solvents with a molecular size smaller than 4.1 A produce 1D polymeric structures (1:1 boroxine/piperazine) of compositions {(PhBO)3(ppz)}n·nTHF (1a·THF) and {(PhBO)3(ppz)}n·nAcetone (1a·Acetone), in which the boroxine B3O3 rings are linked through N→B bonded piperazine molecules in a cis-conformation. In both cases, a pseudocavity is generated between two polymer chains, which is occupied by a solvent molecule interacting through bifurcated N–H···O···H–N hydrogen bonds with one of the chains. In contrast, oxygen-based solvents with a size larger than 6.3 A give rise to discrete 2:1 assemblies, {(PhBO)3}2(ppz)·2Ethyl acetate (2·AcOEt) and {(PhBO)3}2(ppz)·2Pentanone (2·Pentanone), with the piperazine molecule bridging two B3O3 rings and interacting with two solvent molecules via N–H···O hydro...