Formation and Surface Behavior of Pt and Pd Complexes with Ligand Systems Derived from Nitrile‐functionalized Ionic Liquids Studied by XPS

Abstract

We studied the formation and surface behavior of Pt(II) and Pd(II) complexes with ligand systems derived from two nitrilefunctionalized ionic liquids (ILs) in solution using angle-resolved X-ray photoelectron spectroscopy (ARXPS). These ligand systems enabled a high solubility of the metal complexes in IL solution. The complexes were prepared by simple ligand substitution under vacuum conditions in defined excess of the coordinating ILs, [C 3 CNC 1 Im][Tf 2 N] and [C 1 CNC 1 Pip][Tf 2 N], to immediately yield solutions of the final products. The ILs differ in the cationic head group and the chain length of the functionalized substituent. Our XPS measurements on the neat ILs gave insights in the electronic properties of the coordinating substituents revealing differences in donation capability and stability of the complexes. Investigations on the composition of the outermost surface layers using ARXPS revealed no surface affinity of the nitrile-functionalized chains in the neat ILs. Solutions of the formed complexes in the nitrile ILs showed homogeneous distribution of the solute at the surface with the heterocyclic moieties preferentially orientated towards the vacuum, while the metal centers are rather located further away from the IL/vacuum interface.

The Buoy Effect: Surface Enrichment of a Pt Complex in IL Solution by Ligand Design

“…The small N CNcoord peak at 401.3 eV corresponds to the CN group coordinated to the metal center. [20] The absence of the signal from uncoordinated CN groups at ∼400 eV (Figure 1 ) confirms the quantitative formation of 1 in [C 4 C 1 Im][PF 6 ]. The C 1s region shows the complex‐specific C CF3 and C CF2 signals, and the broad peak at ∼287 eV.…”

“…This is also true for the N Im signal. The small N CNcoord peak at 401.3 eV corresponds to the CN group coordinated to the metal center [20] . The absence of the signal from uncoordinated CN groups at ∼400 eV (Figure 1) confirms the quantitative formation of 1 in [C 4 C 1 Im][PF 6 ].…”

“…[17]. Measurement parameters were reported previously [20] . All XP spectra were normalized to the overall intensity detected from the 0° emission region scans of the 5 % mol solution of 1 in [C 4 C 1 Im][PF 6 ].…”

“…Measurement parameters were reported previously. [20] All XP spectra were normalized to the overall intensity detected from the 0° emission region scans of the 5 % mol solution of 1 in [C 4 C 1 Im][PF 6 ]. Procedures for peak fitting of the recorded spectra are outlined in the Supporting Information.…”

The Buoy Effect: Surface Enrichment of a Pt Complex in IL Solution by Ligand Design

“…Compound 1 was prepared directly in [C 4 C 1 Im][PF 6 ] (for details see experimental section) similar to a procedure reported previously. [20] To exemplify the buoy-effect, we also prepared an equivalent solution of [PtCl 2 (C 3 CNC 1 Im) 2 ][PF 6 ] 2 (2), which does not contain fluorinated side chains.…”