Donor-acceptor interactions between cyclic trinuclear pyridinate gold(i)-complexes and electron-poor guests: nature and energetics of guest-binding and templating on graphite.

Raiko Hahn,Birgit Esser,Stefan Grimme,Stefan Kotte,Stefan-S Jester,Tristan J Keller,Andreas Hansen,Fabian Bohle

doi:10.1039/c7sc05355j

Raiko Hahn, Birgit Esser + Show 6 more

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https://doi.org/10.1039/c7sc05355j

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Abstract

Donor-acceptor-type interactions between π-electron systems are of high relevance in the design of chemical sensors. Due to their electron-rich nature, cyclic trinuclear complexes (CTCs) of gold(i) are ideal receptor sites for electron-deficient aromatic analytes. Scanning tunneling microscopy provided insight into the structures of two-dimensional crystals of pyridinate gold CTCs that form on a graphite template at the solid/liquid interface. One polymorph thereof - in turn - templated the on-top co-adsorption of π-acidic pyrazolate CTCs as electron-poor guests up to a certain threshold. From NMR titration experiments, we quantified free energies of -6.1 to -7.5 kcal mol-1 for the binding between pyridinate gold(i) CTCs and π-acidic pyrazolate CTCs. Quantum chemical calculations revealed that these interactions are largely dominated by London dispersion. These results give a more detailed insight into a rational design of sensitive CNT- or graphene-based sensors for π-acidic analytes, such as electron-deficient aromatics.

Highlights

Non-covalent interactions between p–systems and cations, anions or aromatics are found in biological systems and are important in, among others, host/guest chemistry, selfassembly,[1,2,3] and molecular machines.[4,5,6,7] Donor–acceptor-type interactions between planar arenes[8] play an important role in the design of chemical sensors, for instance for the detection of electron-poor nitroaromatics, such as 1,3,5-trinitrotoluene, TNT, or structurally related explosives.[9]
In order to obtain derivatives of cyclic trinuclear complexes (CTCs) 1 with the ability to form stable 2D self-assemblies on highly-oriented pyrolytic graphite (HOPG) for Scanning tunneling microscopy (STM) studies and with high solubility in organic solvents for NMR titration experiments, one (1b, d) or two (1c, e) alkyl chains of different lengths were attached to each pyridine ring
Pyrazolate CTCs 2a–c were synthesized according to literature procedures[23,36] and were obtained in excellent purity

Summary

Introduction

Non-covalent interactions between p–systems and cations, anions or aromatics are found in biological systems and are important in, among others, host/guest chemistry, selfassembly,[1,2,3] and molecular machines.[4,5,6,7] Donor–acceptor-type interactions between planar arenes[8] play an important role in the design of chemical sensors, for instance for the detection of electron-poor nitroaromatics, such as 1,3,5-trinitrotoluene, TNT, or structurally related explosives.[9]. Cyclic structure and the electron-rich nature of their p-system, cyclic trinuclear complexes (CTCs) of gold(I)[15,16,17] with pyridinate ligands (1, Fig. 1a) are promising candidates for the design of such graphene-based sensors.

Results

Conclusion