Adsorption phenomena of cubane-type tetranuclear Ni(II) complexes with neutral, thioether-functionalized ligands on Au(111)

The controlled and intact deposition of molecules with specific properties onto surfaces is an emergent field impacting a wide range of applications including catalysis, molecular electronics, and quantum information processing. One strategy is to introduce grafting groups functionalized to anchor to a specific surface. While thiols and disulfides have proven to be quite effective in combination with gold surfaces, other S-containing groups have received much less attention.

Here, we investigate the surface anchoring and organizing capabilities of novel charge-neutral heterocyclic thioether groups as ligands of polynuclear nickel(II) complexes. We report on the deposition of a cubane-type {Ni4} (=[Ni(μ3-Cl)Cl(HL·S)]4) single-molecule magnet from dichloromethane solution on a Au(111) surface, investigated by scanning tunneling microscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction, both immediately after deposition and after subsequent postannealing.
The results provide strong evidence for partial decomposition of the coordination complex upon deposition on the Au(111) surface that, however, leaves the magnetic {Ni4Cl4n} (n = 1 or 2) core intact. Only post-annealing above 480 K induces further decomposition and fragmentation of the {Ni4Cl4n} core.

The detailed insight into the chemisorption-induced decomposition pathway not only provides guidelines for the deposition of thioether-functionalized Ni(II) complexes on metallic surfaces but also reveals opportunities to use multidentate organic ligands decorated with thioether groups as transporters for highly unstable inorganic structures onto conducting surfaces, where they are stabilized retaining appealing electronic and magnetic propertie

Figure: Normalized XPS S 2p spectra after deposition of (a) bare HL·S ligands on Au(111), (b–d) {Ni4} complexes on Au(111), and (e) the {Ni4} bulk reference sample. Postannealing temperatures for (c) and (d) are indicated. Red crosses represent experimental data and solid lines in (a-d) the decomposition of the spectra into individual doublets at 161.1 eV (green), 161.6 eV (cyan), 162.1 eV (blue), and 163.1 eV (pink) according to Table 1 (see original publication) . Black lines are the fitted total spectra. The background was subtracted with a Shirley algorithm. All S 2p doublets were fitted with a fixed 2p3/2:2p1/2 intensity ratio of 2 and a fixed energy splitting of 1.19 eV by Doniach–Sunjic functions with an asymmetry of−0.1 and a peakwidth of 0.32 eV. Experiments are carried out for (a–d) at BL 5 at DELTA with a photon energy of 375.6 eV and for (e) with a stand-alone spectrometer using monochromatized Al Kα radiation.

Figure: High-resolution STM image and LEED pattern after {Ni4} deposition on Au(111) and post-annealing at 680 K for 1 h. The LEED pattern taken at 82 eV confirms that the local structure observed in the STM image (a) coherently covers large areas on the sample surface. STM image parameters: 40 Å Å~ 40 Å, VBias = −1 V, IT = 1 nA, 5 K.

V. Hess, F. Matthes, D.E. Bürgler, K. Yu. Monakhov, C. Besson, P. Kögerler, A. Ghisolfi, P. Braunstein, C.M Schneider
Adsorption phenomena of cubane-type tetranuclear Ni(II) complexes with neutral, thioether-functionalized ligands on Au(111)
Surface Science 641:210–215 (2015).