Synthesis and characterization of a tertiary amine:boric acid (1:1) co-crystal and a neutral zwitterionic diamine pentaboron adduct

Abstract

The syntheses of the 4,4′-trimethylenebis(N-methylpiperidine):boric acid (1:1) co-crystal, 4,4′-(1-MeNC5H9)2(CH2)3.B(OH)3 (1), and a zwitterionic tetrahydroxidohexaoxidopentaboron adduct, [B5O6(OH)4(κN-NH2CH2CH2NHEt2).H2O (2), (NH2CH2CH2NEt2 = deen) from appropriate combinatorial libraries primed with B(OH)3, are reported together with their spectroscopic (NMR, IR) and single-crystal XRD characterization data. Solid-state H-bond interactions are the likely strong drivers for their formation, and these are described in detail. H-bond networks present in co-crystal 1 include C22(16), R22(8), and R66(36) whilst zwitterionic pentaboron derivative 2 has three R22(8) intermolecular H-bond interactions and the Et2NH- group is involved in a S(7) intramolecular H-bond. Thermal (TGA/DSC) data are also reported for 1 which thermally decomposes to B2O3, in a multistage process: dehydration (60–70 °C) and oxidation and further dehydration (90–700 °C).