Two‐ and Three‐Dimensional Molecular Organization of Schiff‐Base Derivatives

Abstract

We have designed and synthesized a series of Schiff base derivatives, and studied their structural features in two-dimensional (2D) and three-dimensional (3D) states by combining scanning tunneling microscopy (STM) and X-ray diffraction experiments. The Schiff-base derivatives with short alkyl chains crystallize easily, which allows a detailed structural analysis by X-ray diffraction. Due to the strong adsorbate-substrate interactions, those bases with long alkyl chains easily form 2D assemblies on highly oriented pyrolytic graphite (HOPG). The STM images indicate also that the introduction of two methoxy groups into the molecule can change the structure of these 2D assemblies as a result of the increased steric hindrances, for example: the Schiff-base derivative, bearing both methoxy groups and C16H33 tails, forms 2D Moiré patterns, and an alignment of pairing Schiff-base molecules may be easily resolved. Conversely, the Schiff base derivative, bearing solely C16H33 tails, forms 2D non-Moiré patterns. It is demonstrated that the 3D structural features result from the compromise of intermolecular interactions of different molecular moieties. However, there is one more factor, which also governs the 2D structure: the adsorbate-substrate interaction. The 3D crystal structure may thus help to understand many factors involved in the formation of 2D structures, and would be helpful for designing new molecular assemblies with tailoring functions.

Molecular chirality at fluid/solid interfaces: expression of asymmetry in self-organised monolayers

“…Among various classes of molecules examined, [22][23][24] one of the first and most widely studied are azobenzene-based liquid crystals, 25 and in particular 4-(n-alkyl)-4 0 -cyanobiphenyl (nCB) mesogenic (Fig. 4a).…”

Self-assembled monolayers as two-dimensional crystals: relationship to three-dimensional crystals

“…9 The combination of three-dimensional, single crystal X-ray structure determinations with STM investigations of two-dimensional monolayers, or a comparison of results from independent studies, is one means of developing an understanding of the processes that control self-assembly in the bulk crystal and self-organisation on surfaces. [10][11][12][13][14][15][16][17][18][19][20][21][22] Where a threedimensional structure is composed of layers, it is reasonable to anticipate that the lamellar motifs may be replicated on a surface. However, the epitaxial effect of the substrate may induce a different lamella-ordering (for example, alkyl-tailed dodecathiophene) 17 dependent upon the relative strengths of the substratem-adsorbate or adsorbate-adsorbate interactions.…”

Two- and three-dimensional packing diagrams of M(salophen) complexes

“…However, our previous studies have shown that 7 does not form an ordered structure at liquid-HOPG interface, presumably due to its too low surface affinity caused by the non-planar molecular geometry. 16 In the literature comparisons for the 2D and 3D structures are mostly provided for organic compounds 20,[24][25][26][27][28][29][30][31][32][33][34][35] and only a very limited number of metal complexes, namely ferrocenes, diferrocenes and a Zn salophen complex with a coordinated pyridine, 17,36,37 have been studied in this context. In many cases the physisorbed monolayers could be derived from the 3D crystal packings when certain structural differences were considered, 17,20,[24][25][26][27]30,32,33,[35][36][37] but several opposing cases also exist.…”

“…In many cases the physisorbed monolayers could be derived from the 3D crystal packings when certain structural differences were considered, 17,20,[24][25][26][27]30,32,33,[35][36][37] but several opposing cases also exist. [27][28][29]31,34…”

“…Therefore, depending on the compound, it would be very convenient if the 2D patterns could be derived from the 3D structures or vice versa. On the contrary to organic compounds, 20,[24][25][26][27][28][29][30][31][32][33][34][35] studies combining the 2D and 3D structures of metal complexes are rare and only the studies of Wedeking et al 36,37 and Elemans et al 17 are available for comparing the 3D structures of complexes with their 2D assemblies on HOPG.…”