Cooperative Gold Nanoparticle Stabilization by Acetylenic Phosphaalkenes

Abstract

Acetylenic phosphaalkenes (APAs) are used as an ovel type of ligands for the stabilization of gold nanoparticles (AuNP). As demonstrated by avariety of experimental and analytical methods,both structural features of the APA, that is,t he P = Ca sw ell as the C Cu nits are essential for NP stabilization. The presence of intact APAs on the AuNP is demonstrated by surface-enhanced Raman spectroscopy (SERS), and first principle calculations indicate that bonding occurs most likely at defect sites on the Au surface.A uNPbound APAs are in chemical equilibrium with free APAs in solution, leading to ad ynamic behavior that can be explored for facile place-exchange reactions with other types of anchor groups such as thiols or more weakly binding phosphine ligands.Gold clusters at the nanoscale are generally stabilized by ac oordinating ligand shell.[1] Over the last years,t here has been af ocus on the development of novel anchoring groups for molecule-gold junctions that can overcome the insulating character of thiols which have traditionally been used in the context of molecular electronics.[2] As ageneral theme,these novel anchoring groups bind to the surfaces through ab ond that is orthogonal to aconjugated p-system. Recent examples of this strategy include the grafting of sp-hybridized acetylene termini directly onto AuNPs or flat gold surfaces (type A, Figure 1), [3] or the direct anchoring of phenyl (sp 2 ,type B) and benzyl groups (sp 3 ,t ype C) onto Au substrates,t he latter providing very efficient communication on the basis of ahyperconjugative interaction. [4] Owing to the close relationship between phosphorus and carbon, [5] also phosphorus-based ligands would most likely constitute promising candidates for this type of application, in particular as l 3 s 2 -phosphanes contain al one pair for Au binding,a sw ell as an orthogonal p-system that provides an alternative communication pathway.Stabilization and coating of defined gold clusters (e.g., eleven gold atoms) [6] and small nanoparticles (up to 1.5 nm) have hitherto been mostly limited to saturated l 3 s 3 -phosphanes (e.g., triphenyl phosphine,type D). [7] To the best of our knowledge,t he only example of using unsaturated phosphanes,namely l 3 -phosphinines (type E), as ligands for AuNP stabilization is areport by Le Floch and coworkers.[8] Interestingly,t hese ligands induced as ignificant redshift of the surface plasmon resonance (SPR) compared to thiol-or phosphane-coated AuNPs, [8b] supporting the notion that sizeable communication operates across the AuÀ P phosphinine junction. Structural integrity of the surface-bound phosphinines is however debated in view of as olid-state MAS-NMR spectroscopic study. [9] With our interest to explore low-valent phosphoruscontaining systems for molecular electronics applications, [10] we were intrigued by the possibility to use phosphaalkenes as conducting anchoring groups on Au surfaces.T he inherent instability of phosphaalkenes has presumably kept many researchers from using l 3 s 2 -phosphanes for ...

Negative‐Imaging of Citrate Layers on Gold Nanoparticles by Ligand‐Templated Metal Deposition: Revealing Surface Heterogeneity

“…Given that Au adatoms are present on a gold surface, the binding mode of deprotonated citrate anions (H 2 Cit − , HCit 2− , and Cit 3− ) is more diverse than the previously proposed mode associated with the binding of the two oxygen atoms of the central carboxylate group to the defect‐free metallic surface of AuNPs . To a Au adatom can each oxygen atom of a carboxylate group coordinate through monodentate binding mode to form a AuO bond.…”

“…Oxoanions such as citrate do interact weakly with metallic Au(0), and even water molecules compete with citrate anions in binding on a metallic Au(111) . In general, however, the bond energy of Au(I)‒X is larger than that of Au(0)‒X, and the binding energy of citrate carboxylate to the AuNP surface can be in the range of chemisorption owing to the positively charged low‐coordinated Au adatom . Therefore, it is the Au adatom that causes the strong citrate adsorption on AuNPs, with bond energy of Au‒carboxylate similar to the metal‒oxygen bond energies determined between metal cation and acetate (median energy range: 10‒25 kcal mol −1 ) …”

Cross‐Conjugated π‐Scaffolding with Pendant N‐Heterocyclic Metal‐Binding Sites

“…The Pd-catalysed cross-coupling reactions of the corresponding heterocyclic dibromoolefins and terminal alkynes provide convenient access to the new ligand systems. [20] The path for electron or charge delocalisation can then be influenced by the oxidation state of the metal fragment attached to the coordination site. The coordination of a PdCl 2 fragment to each of the different ligand types along with a comprehensive X-ray crystallographic analysis of the ligands and complexes is reported.…”

“…Although crossconjugation has been a topic of intense research efforts, [5][6][7][8][9][10][11][12][13][14] cross-conjugated systems with N-heterocyclic metal-fragment complexing sites are relatively rare. [20] The path for electron or charge delocalisation can then be influenced by the oxidation state of the metal fragment attached to the coordination site. [20] The path for electron or charge delocalisation can then be influenced by the oxidation state of the metal fragment attached to the coordination site.…”

Organophosphorus Compounds in Organic Electronics

“…These findings are supported by surface‐enhanced Raman spectroscopy (C≡C and P=C stretching vibrations of 2017 and 1207 cm −1 for surface bound and 2131 and 1130 cm −1 for free species). Applications of these 7.9 to 9.8 nm AuNPs through functionalization with other ligand systems was also demonstrated . Over the last years also phosphaalkyne–metal complexes have been investigated due to their potential switch from side‐on to end‐on coordination.…”