Elsevier

Polyhedron

Volume 200, 15 May 2021, 115149
Polyhedron

Design and synthesis of novel terpyridine-based ligands with one and two terminal aurophilic moieties and their Rh(III) and Ru(II) complexes for the adsorption on metal surfaces

https://doi.org/10.1016/j.poly.2021.115149Get rights and content

Highlights

  • Novel terpyridine ligands with one and two terminal aurophilic sulfur containing fragments were synthesized.

  • Mononuclear ruthenium(II) and rhodium(III) complex of these ligands were obtained.

  • Complexes with 3,4- and 3,5-position of sulfur-containing substituents adsorb faster on the Au surface than 2,4-substituted analogs.

Abstract

Novel terpyridine ligands with one and two terminal aurophilic sulfur containing fragments, (S)-11-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenoxy)undecyl 5-(1,2-dithiolan-3-yl)pentanoate (7), (S)-((4-([2,2′:6′,2″-terpyridin]-4′-yl)-1,3-phenylene)bis(oxy))bis(undecane-11,1-diyl) bis(5-((S)-1,2-dithiolan-3-yl)pentanoate) (11a), (S)-((4-([2,2′:6′,2″-terpyridin]-4′-yl)-1,2-phenylene)bis(oxy))bis(undecane-11,1-diyl) bis(5-((S)-1,2-dithiolan-3-yl)pentanoate) (11b), (S)-((5-([2,2′:6′,2″-terpyridin]-4′-yl)-1,3-phenylene)bis(oxy))bis(undecane-11,1-diyl) bis(5-((S)-1,2-dithiolan-3-yl)pentanoate) (11c) were synthesized and employed to synthesis of mononuclear ruthenium(II) and rhodium(III) complexes. Electrochemical studies of the obtained ligands and coordination compounds and their ability to chemisorb on gold electrodes surfaces have been carried out. Among the obtained metal complexes, compounds with the minimum time of chemisorption with the formation of Au-S bonds were revealed, which are complexes of 3,4- and 3,5-substituted phenylterpyridines.

Graphical abstract

Novel terpyridine ligands with one and two terminal aurophilic sulfur containing fragments based on lipoic acid and their mononuclear ruthenium(II) and rhodium(III) complexes were synthesized.

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Introduction

The interest in the development of metal-containing aurophilic organic derivatives with one or two terminal sulfur-containing groups in ligand fragments is associated with the promise of such molecules for the creation of single-electron single-molecule transistors or charge-sensitive biosensors [1], [2], [3], [4], [5], [6], [7] and luminescent probes [8], [9]. In particular, the polypyridyl complexes of ruthenium(II) and rhodium(III) are used as luminophores in DNA-based biosensors [10], [11], [12], [13].

The presence of two sulfur-containing groups in the organic ligand, used to obtain the metal complexes, give possibility to such coordination compounds chemosorb on two closely spaced gold electrodes to form strong Au-S covalent bonds. One of the promising using of these compounds may be the single-molecular sequencing based on charge-sensitive sensors. It is proposed to use metal complexes fixed between planar nanoelectrodes as a bridge-molecule in the sensors for detecting the one charge pair separation as a result of DNA/RNA polymerization [14], [15], [16]. The key to the practical implementation of such sequencing is the development of reliable methods for producing organic ligands with three functional groups, while one is able to coordinate a metal atom, and the other two groups can bind to electrodes.

Coordination compounds of ruthenium with bipyridine ligands have been offered as sensors for various amino acid fragments (phenylglycine, valine), as well as phosphate anions [17], [18], [19]. There are works devoted to the creation of single-molecule sensors based on aurophilic nitrogen-containing coordination compounds 4,4′-bipyridine, N′-bis(6-mercaptohexyl)-(4,4′-bipyridine) and N,N′-bis(6-acetoxythio)-(4,4′-bipyridine) [20], [21], [22], as well as S-alkyl- and ruthenium 4-pyridyl substituted terpyridine complexes [23] and complexes of terpyridines with Zn(II) [24], [25].

Coordination compounds of Fe, Co, Cr, Ru with ligands based on substituted aurophilic terpyridines showed higher conductivity compared to 4,4′-bipyridine and its analogues. These results have evidenced the terpyridine coordination compounds are highly perspective for using in single-molecule devices as an island [26], [27]. Earlier, we proposed the method of single-molecule nanotransistors producing based on gold electrodes located at the 4 nm distance. The gap between electrodes is occupied by the chemically-formed symmetric aurophilic coordination compound of Rh(III) with (S)-4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl 5-(1,2-dithiolan-3-yl)pentanoate. It is shown that in the obtained molecular nanotransistors the electrons tunneling was carried out through the rhodium atom was the only intramolecular charge center [28].

The development of the above-mentioned single-molecule devices requires the developing a convenient synthetic procedure for the preparation of suitable organic ligands and their bis-ligand coordination compounds that can be chemisorbed on two gold electrodes located at a distance of several nm. It was previously proved that when such a pair of electrodes is immersed in a solution of a bis-(S-containing ligand) coordination compound with the distances between two terminal sulfur-containing groups no less than the interelectrode gap, some of the molecules of the symmetric aurophilic coordination compound can be adsorbed with Au-S bonds formation on two different electrodes, connecting them among themselves [28].

In this article, novel terpyridine ligands with one and two terminal aurophilic fragments was designed to provide the following criteria: (1) the ligand possibility to bound second-row transition metal ions, in particular rhodium and ruthenium, forming mononuclear coordination compounds [29], [30]; (2) the presence of the stable disulfide fragment, which at the same time provides the possibility of rapid chemosorption on gold electrodes surface with the formation of Au-S bonds; (3) the distance between the sulfur-containing fragments is about 4 nm, which corresponds to the achievable interelectrode gap in the nanoelectrode device [28]. The target ligands (L) were synthesized and employed to synthesize of ruthenium(II) and rhodium(III) complexes with the Ru(L)DMSOCl2 or RhM(L)Cl3 composition. The possibility of the resulting complexes adsorption on the gold electrodes surface was demonstrated.

Section snippets

Materials and methods

All starting materials were obtained from commercial sources and used without additional purification. 1H and 13C NMR spectra were obtained on a Bruker Avance spectrometer (400 and 100 MHz respectively) instrument, internal standard was HMDS (δ 0.05 ppm).

Preparative chromatographic separation of the reaction mixtures was carried out using the INTERCHIM puriFlash 430 chromatograph.

High resolution mass spectra were recorded on the Orbitrap Elite high resolution mass spectrometer. Solutions of

Ligands synthesis

The structure of the organic ligands 7, 11a-c synthesized in this work is shown in Scheme 1, Scheme 2. Compounds 7, 11a-c contain the terpyridine fragment for metal ion coordination, and two disulfide groups in the lipoic acid fragment, which allow adsorption on gold electrodes. The length of linker fragment between the two disulfide groups was selected in such way as to ensure a distance between them about 4 nm, corresponding to the achievable inter electrode gap in the nanoelectrode device

Conclusion

Thus, we have developed a convenient methods for the preparation of aurophilic terpyridine ligands with one or two terminal disulfide groups. On their basis, mononuclear coordination compounds with Rh(III) and Ru(II) were synthesized for the subsequent study of the possibility of their adsorption on the metal surfaces. Among the obtained metal complexes, compounds with the minimum time of chemisorption on the surface of gold electrodes with the formation of Au-S bonds were revealed, which are

CRediT authorship contribution statement

Irina O. Salimova: Methodology, Formal analysis, Visualization, Writing - original draft. Anna V. Berezina: Validation. Ilona A. Shikholina: Investigation. Nikolai V. Zyk: Data curation, Supervision. Elena K. Beloglazkina: Conceptualization, Writing - review & editing, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful to the Russian Science Foundation (Project 19-73-00193) and Russian Foundation of Basic Research (Project 19-33-90146) for the financial support of this work. This work in part of NMR study was supported by the M.V. Lomonosov Moscow State University Program of Development.

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