Redox-active on-surface polymerization of single-site divalent cations from pure metals by a ketone-functionalized phenanthroline

Abstract

Metallic iron, chromium, or platinum mixing with a ketone-functionalized phenanthroline ligand on a single crystal gold surface demonstrates redox activity to a well-defined oxidation state and assembly into thermally stable, one dimensional, polymeric chains. The diverging ligand geometry incorporates redox-active sub-units and bi-dentate binding sites. The gold surface provides a stable adsorption environment and directs growth of the polymeric chains, but is inert with regard to the redox chemistry. These systems are characterized by scanning tunnelling microscopy, non-contact atomic force microscopy, and X-ray photoelectron spectroscopy under ultra-high vacuum conditions. The relative propensity of the metals to interact with the ketone group is examined, and it is found that Fe and Cr more readily complex the ligand than Pt. The formation and stabilization of well-defined transition metal single-sites at surfaces may open new routes to achieve higher selectivity in heterogeneous catalysts.

Two‐Dimensional Ketone‐Driven Metal–Organic Coordination on Cu(111)

“…The calculated Fe‐Fe distance along the bonding axis is 10.21 Å. At odds with the PTO−Cu coordination, all Fe‐carbonyl interactions are equivalent, so that the four carbonyl termini sandwiching the Fe atom are arranged in a square geometry (the O‐Fe bond length is approximately 1.92 Å, close to values reported in other MOS and 3D Fe‐carboxylates metal–organic frameworks). This geometry also determines a different angle between the molecular axis and the chain direction (90° for PTO−Fe and 94.6° for PTO−Cu).…”

“…Ketone moieties are known to bind to metallic centres and are particularly interesting, owing to their high electron affinity and consequent potential usefulness in organic optoelectronic devices . Surprisingly, ketone groups have not been extensively used in this context with, to our knowledge, only one very recent example of their application in surface 2D MOS . In this respect, pyrene‐4,5,9,10‐tetraone (PTO) (Figure ) is an ideal molecular candidate for 2D MOS formation, since its equatorial bidentate ketone moieties provide the oxidative potential necessary to stabilise defined oxidation states of the coordination metals.…”

Redox Isomeric Surface Structures Are Preferred over Odd‐Electron Pt1+

“…It fitted to aP t4 f 7/2 position of 73.2 eV,m atching well with previousl iteraturef or Pt II , [20] including studies performed on the same Au(100) surface. [15,21] This is well below the binding energy of 75.7-76.0 eV reportedf or Pt 4 + complexes. [22] We note that the Pt 4f 7/2 positionf or as ub-monolayer quantity of Pt (no ligand present) on the Au(100) surface (70.6 eV) [18] was used as ar eference point for Pt 0 herea st his shows as light shift from the BE for bulk Pt (71.2 eV) [23] due to final state effects in proximity to the Au surface.…”

“…XPS results indicatea2:1 Pt:BMTZ ratio, which would point to coordinationatm ost pyrimidinyl units.Aremarkable feature of this redox isomeric system is the structural irregularity required to accommodate both oxidation states, while related metal-ligand systemso n metal surfaces tend toward ah ighly ordered flat-lying ligand configuration. [15,21,29,32] In the present case, the redox isomers should require significant distortion in the chain geometrya nd molecular orientation with respectt ot he surface. This agrees with the different apparent heights in the STM images (Figure S4), as well as coexistence of two Pt oxidation states within ac hain.…”

“…The result differs from other metalligand redox reactions we have studied, which allow complete metal oxidation under milder conditions. [21,29] Thea pparent tendency of the system to form the observed structure of Pt 2 BMTZ more readily than 1:1P t II -BMTZ chains could indicate at hermodynamically favorable mixed valence system. The persistence of the mixed metal species( 2:1s toichiometry) after annealing fora sl ong as 15 hours could indicate at hermodynamic preference and that any 1:1p roduct is significantly reactive towards additional Pt 0 .…”