Chemical Reactivity of Naphthalenecarboxylate-Protected Ruthenium Nanoparticles: Intraparticle Charge Delocalization Derived from Interfacial Decarboxylation

Abstract

Ruthenium nanoparticles were prepared by thermolytic reduction of RuCl 3 in 1,2-propanediol containing sodium 2-naphthalenecarboxylate. Transmission electron microscopic measurements showed that the average diameter of the resulting 2-naphthalenecarboxylate-protected ruthenium nanoparticles (RuCOONA) was 1.30 ± 0.27 nm. Interestingly, hydrothermal treatment of the nanoparticles at controlled temperatures led to decarboxylation at the metal−ligand interface, and the naphthalenyl moieties became directly bonded to the metal cores, which was confirmed by infrared and X-ray photoelectron spectroscopic measurements. In comparison with the as-produced RuCOONA nanoparticles, the decarboxylated nanoparticles (RuNA) exhibited markedly different optical and electronic properties, as manifested by an apparent red shift of the photoluminescence profiles, which was ascribed to electronic coupling between the particle-bound naphthalene groups. Electrochemical measurements exhibited consistent results where a negative shift was observed of the formal potential of the particle-bound naphthalene moieties. This was attributed to intraparticle charge delocalization that led to extended spilling of nanoparticle core electrons to the naphthalene moieties. ■ INTRODUCTIONOrganically capped metal nanoparticles have been attracting extensive interest because the material properties may be readily controlled by the chemical nature of the metal cores and the organic protecting ligands as well as their interfacial bonding interactions. 1−5 In fact, the bonding linkages at the metal−ligand interface have been observed to impact the nanoparticle dimensions, morphology, and stability; inversely, metal nanoparticles also have influence on the ligand physical and chemical property, reactivity, and configuration. 4,6,7 Of these, ruthenium nanoparticles have been intensively studied due to its stability and affinity to many organic capping ligands, such as mercapto derivatives, alkylamines, diazo, acetylene, nitrene, and carboxylate moieties. 4,7−11 For instance, for ruthenium nanoparticles functionalized by acetylene derivatives, the formation of conjugated metal−ligand π-bonds leads to intraparticle charge delocalization, and hence, the nanoparticles exhibit new optical/electronic characteristics that are analogous to those of diacetylene derivatives. 11−13 These results highlight the significance of interfacial engineering in the manipulation of nanoparticle materials properties.Conjugated metal−ligand interfacial bonds may also be produced by exploiting the unique interfacial reactivity of organic ligands on nanoparticle surfaces. For instance, we recently observed that alkene derivatives might self-assemble onto platinum nanoparticle surfaces, forming platinum−vinylidene or −acetylide bonds as a consequence of platinumcatalyzed dehydrogenation and transformation of the olefin groups. 14 In another study, 15 ruthenium nanoparticles were protected by ferrocenecarboxylates, and galvanic exchange reactions with Pd(II) led to the deposition of a s...

Surface Functionalization of Metal Nanoparticles by Conjugated Metal–Ligand Interfacial Bonds: Impacts on Intraparticle Charge Transfer

“…Interfacial reactivity of other ligands has also been exploited for effective intraparticle charge delocalization. 28,29 This has been demonstrated by nanoparticle-catalyzed decarboxylation at the metal−ligand interface, leading to direct bonding of functional moieties onto the nanoparticle surface.…”

“…Recently a wide variety of metal–ligand bonds have been formed and used to functionalize metal nanoparticles, − beyond the conventional metal–thiolate (M–S) linkages . This is primarily motivated by results from earlier studies of the adsorption of hydrocarbons on transition-metal surfaces. , The bonding interactions are generally believed to involve dπ–pπ interactions between the transition metals and the terminal carbon moieties. − For instance, metal–carbon (M–C) covalent bonds can be readily formed by using aryl diazonium as the precursors which exhibit significantly reduced interfacial resistance, as compared to the M–S counterparts. − Metal–carbene (MC) π bonds are formed by using diazo derivatives as the capping ligands, , and metal–acetylide (M–C)/–vinylidene (MCC−) bonds are produced by the self-assembly of acetylene derivatives onto transition-metal surfaces. ,,,− More recently, it has been found that olefin derivatives may also be exploited as new capping ligands for nanoparticle surface functionalization, as a result of platinum-catalyzed dehydrogenation, such that the produced acetylene moieties self-assemble onto the nanoparticle surfaces. , Of these, the formation of conjugated metal–carbon interfacial bonds is found to endow the nanoparticles with unprecedented optical, electronic and electrochemical properties, due to effective intraparticle charge delocalization among the nanoparticle-bound functional moieties. ,,,,− Importantly, this may be readily manipulated by the electronic properties of the metal cores which serve as part of the chemical bridge for intraparticle charge transfer. , In addition, when multiple functional moieties are incorporated onto the same nanoparticle surface, specific electronic interactions with selective molecules/ions may also be exploited as an effective variable in gating the intraparticle charge transfer, − a platform that has the potential for chemical sensing of specific molecules/ions , and deliberate manipulation of the nanoparticle electrocatalytic activity in fuel cell electrochemistry. ,− ,…”

Photo-Gated Intervalence Charge Transfer of Ethynylferrocene Functionalized Titanium Dioxide Nanoparticles

“…The successful incorporation of the eFc ligands onto the TiO 2 nanoparticle surface was confirmed by 1 H NMR and FTIR spectroscopic measurements. [12,23,24]. The fact that no sharp features were observed, along with the absence of alkynyl (≡CH) protons at 2.7 ppm, suggests that the nanoparticles were spectroscopically clean and free of monomeric eFc ligands [25].…”