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A hydrido platinum(II) complex with a dihydrosilyl ligand, [cis-PtH(SiH2Trip)(PPh3)2] (2) was prepared by oxidative addition of an overcrowded primary silane, TripSiH3 (1, Trip = 9-triptycyl) with [Pt(η2-C2H4)(PPh3)2] in toluene. The ligand-exchange reactions of complex 2 with free phosphine ligands resulted in the formation of a series of (hydrido)(dihydrosilyl) complexes (3-5). Thus, the replacement of two PPh3 ligands in 2 with a bidentate bis(phosphine) ligand such as DPPF [1,2-bis(diphenylphosphino)ferrocene] or DCPE [1,2-bis(dicyclohexylphosphino)ethane] gave the corresponding complexes [PtH(SiH2Trip)(L-L)] (3: L-L = dppf, 4: L-L = dcpe). In contrast, the ligand-exchange reaction of 2 with an excess amount of PMe3 in toluene quantitatively produced [PtH(SiH2Trip)(PMe3)(PPh3)] (5), where the PMe3 ligand is adopting trans to the hydrido ligand. The structures of complexes 2-5 were fully determined on the basis of their NMR and IR spectra, and elemental analyses. Moreover, the low-temperature X-ray crystallography of 2, 3, and 5 revealed that the platinum center has a distorted square planar environment, which is probably due to the steric requirement of the cis-coordinated phosphine ligands and the bulky 9-triptycyl group on the silicon atom. [ABSTRACT FROM AUTHOR]

Tetrakis(ethylmethylamino) hafnium (TEMAH) can be converted into the unsaturated hafnium atom on the hydroxylated Si(1 0 0) surface through the ligand exchanged reactions (LERs) between the adsorbed TEAMH and the surface hydroxyl groups. [Display omitted] • The ALD of HfO 2 on a Si(1 0 0) surface using TEMAH and water as co-reactants was investigated through DFT calculations. • The activity of the surface LERs of TEMAH was enhanced with the increasing concentration of surface hydroxyl groups. • The water pulse during ALD effectively promoted the LERs and prevented the unwanted ligands from remaining on the surface. The atomic layer deposition (ALD) of hafnium oxide (HfO 2) thin film has attracted considerable attention owing to its crucial role in downscaling semiconductor devices. Herein, we theoretically investigated the reaction mechanisms during the ALD of HfO 2 thin film (HfO 2 –ALD) on silicon (Si) surface using tetrakis(ethylmethylamino) hafnium (TEMAH) and water. By using two surface models, fully and partially hydroxylated Si(1 0 0) surfaces, we demonstrated that controlling the concentration of hydroxyl groups on the surface is important to enhance the activity for ligand-exchange reactions (LERs) of TEMAH and thereby effectively promote HfO 2 –ALD. During the precursor pulse, LERs on the fully hydroxylated Si(1 0 0) surface easily convert TEMAH into an unsaturated Hf atom with a low energy barrier of 25.8 kJ/mol, while mono(ethylmethylamino) hafnium (MEMAH) is obtained as the final product on the partially hydroxylated Si(1 0 0) surface with an energy barrier of 61.3 kJ/mol. The remaining ligand of the adsorbed MEMAH can be removed via LER with water during the water pulse. This work not only provides a better understanding of the conversion of TEMAH into a Hf atom on the hydroxylated Si(1 0 0) surface but also offers us more insights into the role of surface hydroxyls in the formation of HfO 2 thin films. [ABSTRACT FROM AUTHOR]

We report on the capillary electrophoretic behavior of citrate-capped gold and silver nanoparticles in aqueous medium when applying a ligand-exchange surface reaction with thiols. Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) of similar size (39 ± 6 and 41 ± 7 nm, respectively) and shape were synthesized, covered with a citrate shell, and characterized by microscopic and spectroscopic techniques. The analysis of these NPs by CE was accomplished by using a buffer solution (pH 9.7; 40 mM SDS, 10 mM CAPS; 0.1 % methanol) containing the anions of thioctic acid or thiomalic acid. These are capable of differently interacting with the surface of the AuNPs and AgNPs and thus introducing additional negative charges. This results in different migration times due to the formation of differently charged nanoparticles. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] Graphene oxide acts as active radical scavenger. [•] Grafting of PEG onto graphene oxide by radical trapping. [•] Grafting of poly(Vf-co-MMA) onto graphene oxide by ligand-exchange reaction. [•] Dispersibility of graphene oxide was remarkably improved by polymer grafting. [ABSTRACT FROM AUTHOR]

Purpose: This paper presents an improved kinetic-spectrophotometric procedure for determining clonazepam (CZP) in pharmaceutical formulations and human serum. Methods: The method is based on ligand-exchange reaction. The reaction was followed spectrophotometrically by measuring the rate of change of absorbance at 425 nm in ethanolic sodium hydroxide solution. Results: The optimum operating conditions for reagent concentrations and temperature were established. Linear calibration curve was obtained in the range of 0.32 - 4.10 µg mL-1. The optimized conditions yielded a theoretical detection limit of 0.24 µg mL-1 based on the 3.3So criterion, where S0 is standard deviation of the calibration line. The interference of certain drugs, foreign ions and amino acids on the reaction rate were studied in order to assess the selectivity of the method. Conclusion: The developed method is sensitive, accurate and reproducible and could be used for routine anlysis of clonazepam in pharmaceutical preparations and serum samples. [ABSTRACT FROM AUTHOR]

Abstract: To improve the dispersibility of nanodiamond (ND) in solvents and polymer matrices, the grafting of copolymers containing vinyl ferrocene (Vf) onto the surface by a ligand-exchange reaction with ferrocene moieties of the copolymer and polycondensed aromatic rings of ND surface was investigated. The copolymer containing Vf was prepared by the radical copolymerization of Vf with vinyl monomers, such as methyl methacrylate (MMA), styrene (St), and N-isopropylacrylamide (NIPAM), using 2, 2′-azobisisobutyronitrile as an initiator. It was found that by heating of ND with poly(Vf-co-MMA), poly(Vf-co-St), and poly(Vf-co-NIPAN) in the presence of AlCl3 and Al powder as catalysts, the corresponding copolymer was successfully grafted onto the surface. On the contrary, in the absence of AlCl3, no grafting of these copolymers was observed. The grafting of polymers onto the ND surface was confirmed by FT-IR. These polymer-grafted NDs were found to give stable dispersions in solvents for the grafted polymer. In addition, the dispersibility of poly(Vf-co-NIPAM)-grafted ND uniformly dispersed in water below 32°C but precipitated above the temperature. Therefore, it was concluded that the dispersibility of ND in water could be controlled by the temperature of water. [Copyright &y& Elsevier]

To improve the dispersibility of carbon microcoil (CMC) in solvents and polymer matrices, the grafting of copolymer containing vinyl ferrocene (VFE) onto surface by ligand-exchange reaction with ferrocene moieties of the copolymer and polycondensed aromatic rings of CMC was investigated. The copolymer containing VFE was prepared by the radical copolymerization of VFE with vinyl monomers, such as methyl methacrylate (MMA) and styrene (St), using 2,2′-azobisisobutyronitrole as an initiator. It was found that by heating of CMC with poly(VFE-co-MMA) and poly(VTE-co-St) in the presence of AlCl3 and A1 powder as catalyst, these copolymers were grafted onto the surface: the percentage of grafting reached to 64.2%. On the contrary, in the absence of AICI3, no grafting of the copolymer was observed. The grafting of polymers onto the CMC surface was confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR), thermal decomposition gas chromatography-mass spectroscopy (GC-MS) and field-emission scanning electron microscope (FE-SEM). Therefore, it is considered that the copolymer was grafted onto CMC surface by ligand-exchange reaction with ferrocene moieties of the copolymer and polycondensed aromatic rings of CMC. The polymer-grafted CMC gave a stable dispersion in solvents for grafted polymer. [ABSTRACT FROM AUTHOR]

Abstract: To improve the dispersibility of vapor grown carbon fiber (VGCF) in solvents, the grafting of copolymer containing vinyl ferrocene (VFE) onto the surface by ligand-exchange reaction between ferrocene moieties of the copolymer and polycondensed aromatic rings of VGCF was investigated. The copolymer containing VFE was prepared by the radical copolymerization of VFE with methyl methacrylate (MMA) using 2, 2′-azobisisobutyronitrole as an initiator. It was found that by heating of VGCF with poly(VFE-co-MMA) in the presence of AlCl3 and Al powder, the copolymer was grafted onto the wall-surface: the percentage of grafting reached to 57.5%. It is considered that the copolymer was grafted onto VGCF surface by ligand-exchange reaction between ferrocene moieties of the copolymer and polycondensed aromatic rings of VGCF. In addition, carboxyl groups were successfully introduced onto VGCF wall-surface by the ligand-exchange reaction of 1,1′-dicarboxyferrocene with VGCF in the presence of AlCl3 and Al powder. The carboxyl groups on VGCF were reacted with hydroxyl-terminated polymers to give the corresponding polymer-grafted VGCF. The polymer-grafted VGCF gave a stable colloidal dispersion in solvents for grafted polymer. The electric properties of composite prepared from polymer-grafted VGCF in solvent vapor were investigated. [Copyright &y& Elsevier]

We have investigated the development of lanthanide-cored supramolecular complexes containing porphyrins to circumvent the solubility problem and improve the optical amplification property. The new synthetic methodology has been developed and accomplished through the ligand-exchange model reaction using ErCl3 to optimize its synthetic condition. First, we designed and synthesized the model compounds to investigate coordination property between the ligand and the lanthanide ion. In addition, with these synthetic results, lanthanide-cored supramolecular complexes based on porphyrins were synthesized and characterized. Highly coordinated lanthanide-cored model complexes (at least 8 to 10 coordination) showed the strong near infrared emission at 1525 nm, corresponding to the characteristic 4I13/2→ 4I15/2 transition of trivalent erbium ions. [Copyright &y& Elsevier]

In this work triangular gold nanoplates (AuNTPs) are prepared by spontaneous conversion of spherical-like gold precursors induced by the shape-directing properties of the diacetylene N,N,N -trimethylpentacosa-10,12-diyn-1-ammonium bromide (PCD_ABr), employed as capping agent. In detail, thin AuNTPs with edge length below 200 nm are obtained by incubating premade isotropic gold nanoparticles protected with chitosan (Chit@AuNPs) in PCD_ABr solutions through a standard ligand-exchange reaction (LER) carried out in water at room temperature. Control of the AuNTPs size as well as the reaction shape-yield up to 65% is achieved by simply varying the reagents ratio in the incubation mixture. Because of the high anisotropy of the flat nanoparticles, the AuNTPs-containing hydrosols show intense, well-defined absorptions in the NIR spectral region, which make them excellent candidates as biosensors also for in vivo assays with biological tissues and fluids. When subjected to UV light, both triangular and nearly spherical PCD_ABr-coated gold nanoparticles exhibit fluorescent properties and Raman features typical of disordered, sp2-based carbon nanostructures. The photogeneration of graphite-like moieties within the diacetylene shell instead of expected polydiacetylene skeleton is most likely due to poor alignment of the monomer chains on the gold surfaces and seems to be favored on isotropic nanoparticles. Image 1 • Triangular Au nanoplates coated with the cationic diacetylene PCD_ABr are prepared. • The synthesis occurs through PCD_ABr-induced reshaping of isotropic precursors. • The triangular nanoplates show high absorptions in the NIR due to their anisotropy. • UV light induces the formation of graphite-like moieties in the PCD_ABr shell. • Photogeneration of sp2-phase provides fluorescence properties to the nanostructures. [ABSTRACT FROM AUTHOR]

The design of electrode with high volumetric performance in energy storages still remains as a significant challenge because it simultaneously requires a high packing density of active materials for high energy density and a conductive porous structure for facile charge transfer. Here, a novel assembly process is introduced for thin‐film anodes for Li‐ion battery with a high volumetric energy density and rate performance by systematically controlling the interfacial structure between metal‐oxide nanoparticles and/or metal clusters. For this study, oleic‐acid‐stabilized Fe3O4 nanoparticles are layer‐by‐layer assembled with small organic molecules through a ligand exchange reaction, which enable a high packing density. During layer‐by‐layer deposition, periodic Pt‐sputtering onto multilayers significantly reduces the internal resistance of the electrodes but maintains the nanopores formed among the nanoparticles. The resulting anode exhibits an extremely high volumetric capacity of ≈3195 mA h cm−3 and rate performance, which are far superior to that reported for Li‐ion battery anodes. Additionally, all components in the electrodes have a stable covalent bond network between the metal atom and the amine group of organic molecule linker, allowing good cycle retention. This approach can be widely applied to the fabrication of various nanoparticle‐based electrodes, enabling maximum charge storage performance in confined volumes. Scalable energy storage electrodes with high volumetric and rate performance are realized by combining ligand‐exchange‐induced layer‐by‐layer assembly and metal sputtering. [ABSTRACT FROM AUTHOR]

Thiolate-protected gold clusters (Aun(SR)m) have attracted considerable attention as functional nanomaterials in a wide range of fields. A ligand-exchange reaction has long been used to functionalize these clusters. In this study, we separated products from a ligand-exchange reaction of phenylethanethiolate-protected Au24Pd clusters (Au24Pd(SC2H4Ph)18), in which Au25(SR)18 is doped with palladium, into each coordination isomer with high resolution by reversed-phase high-performance liquid chromatography. This success has enabled isomer distributions of the products to be quantitatively evaluated. We evaluated quantitatively the isomer distributions of products obtained by the reaction of Au24Pd(SC2H4Ph)18 with thiol, disulfide, or diselenide. The results revealed that the exchange reaction starts to occur preferentially at thiolates that are bound directly to the metal core (thiolates of a core site) in all reactions. Further study on the isomer-separated Au24Pd(SC2H4Ph)17(SC12H25) revealed that clusters vary the coordination isomer distribution in solution by the ligand-exchange reaction between clusters and that control of the coordination isomer distribution of the starting clusters enables control of the coordination isomer distribution of the products generated by ligand-exchange reactions between clusters. Au24Pd(SC2H4Ph)18 used in this study has a similar framework structure to Au25(SR)18, which is one of the most studied compounds in the Aun(SR)m clusters. Knowledge gained in this study is expected to enable further understanding of ligand-exchange reactions on Au25(SR)18 and other Aun(SR)m clusters.