Crystalline Structures of Alkylamide Monolayers Adsorbed on the Surface of Graphite

Abstract

Synchrotron X-ray and neutron diffraction have been used to determine the two-dimensional crystalline structures of alkylamides adsorbed on graphite at submonolayer coverage. The calculated structures show that the plane of the carbon backbone of the amide molecules is parallel to the graphite substrate. The molecules form hydrogen-bonded dimers, and adjacent dimers form additional hydrogen bonds yielding extended chains. By presenting data from a number of members of the homologous series, we have identified that these chains pack in different arrangements depending on the number of carbons in the amide molecule. The amide monolayers are found to be very stable relative to other closely related alkyl species, a feature which is attributed to the extensive hydrogen bonding present in these systems. The characteristics of the hydrogen bonds have been determined and are found to be in close agreement with those present in the bulk materials.

Characterization of Primary Amine Capped CdSe, ZnSe, and ZnS Quantum Dots by FT-IR: Determination of Surface Bonding Interaction and Identification of Selective Desorption

“…62 It has been shown that optimum hydrogen-bonding distances between alkylamides is about 3 Å between the N and O and 2 Å between H and O in the NÀH 3 3 3 O bond. 63 However, after crashing, desorption of one of the two binding sites took place, and the highly uniform surface was disrupted, resulting in substantial peak broadening. ZnS appears to be the borderline between strong hydrogen bonding with ordered surface of both Zn and S sites occupied and steric interference between neighboring capping ligands on Zn and S sites, where the crystal structure may favor only Zn sites.…”

Monolayer structures of 4,4′ bipyridine on graphite at sub-monolayer coverage

“…Usually such solid monolayers can form at high, multilayer coverages. However, recent evidence has indicated that alkyl amides can form stable solid monolayers at temperatures well above the bulk melting point, even at submonolayer coverages 1 .…”

The monolayer structure of 1,2-bis(4-pyridyl)ethylene physisorbed on a graphite surface

“…This contrasts with many sub-monolayer coverage physisorbed layers, which show melting points lowered by a greater degree relative to the bulk, typically by a factor of approximately 0.75. While some molecules do form solid monolayers close to, or indeed on rare occasions above [5,7,12], the bulk melting point even at sub-monolayer coverages, such layers are normally stabilized by strong intermolecular interactions like hydrogen bonds [5,12].…”

“…The use of synchrotron X-rays to record monolayer diffraction patterns has been detailed elsewhere [12]. In this work diffraction patterns were recorded using Beamline I11 at Diamond Light Source, UK [13] with a wavelength of 1.054700 Å and zero angle offset of 0.05899 � as determined by silicon standard (NIST SRM 640 c).…”