Thermally Stable Intermolecular Proton Bonds in Polyaromatic Aldehyde Crystals

Abstract

We have synthesized self-assembled red-colored proton complexes of the aldehyde derivatives of polyaromatic hydrocarbon with strong intermolecular hydrogen bonding. These intermolecularly proton-bonded polyaromatic aldehydes formed as 1-pyrenecarbaldehyde (Py-CHO) reacted with HAuCl(4) to produce [(Py-CHO)(2)H][AuCl(4)] under dry conditions. The formation of [(Py-CHO)(2)H][AuCl(4)] was confirmed by single-crystal structure determination and IR spectral analysis at various temperatures. The compounds are distinctively hydrophobic in nature and are soluble only in a few organic polar solvents. The proton bonds are clearly observed from both the electron density in X-ray analysis and the characteristic IR frequency signature. The proton complex units have an O-H(+)-O distance of the typical Zundel-like cationic hydrogen bond (in which two O atoms share a proton-like H in the midpoint of the short O-O distance of ≈2.4 Å). The proton bonds are thermally stable, even over 100 °C, because the complexes are stabilized in layered structures with π-π intermolecular interactions of the polyaromatic hydrocarbon ligands. The IR signatures at around 900, 1200, and 1700 cm(-1) for the Zundel-like proton bond are clearly characterized.