Reversible synthesis of sub-10 nm spherical and icosahedral gold nanoparticles from a covalent Au(CN)2(-) precursor and recycling of cyanide to form ferric ferrocyanide for cell staining

A solution approach based on Au(CN)(2)(-) chemistry is reported for the formation of nanoparticles. The covalent character of the Au(CN)(2)(-) precursor was exploited in the formation of sub-10?nm nanospheres (≈2.4?nm) and highly monodisperse icosahedral Au nanoparticles (≈8?nm) at room temperature in a one-pot aqueous synthesis. The respective spherical and icosahedral Au morphologies can be controlled by either the absence or presence of the polymer polyvinylpyrrolidone (PVP). Using Au(CN)(2)(-) as a metal ion source, our findings suggest that the addition of citrate ions is necessary to enhance the particle formation rate as well as to generate a more homogeneous colloidal dispersion. Because of the presence of oxygen and the operation of a CN(-) etching process associated with Au(CN)(2)(-) complex formation, an interesting reversible formation-dissolution process was observed, which allowed us to repeatedly prepare spherical and icosahedral Au nanoparticles. Time-dependent TEM images and UV/Vis spectra were carefully acquired to study the reversibility of this formation-dissolution process. In view of the accompanying generation of toxic cyanide anions, we have developed a protocol to recycle cyanide in the presence of citrate ions through ferric ferrocyanide formation. After completion of particle formation, the residual solutions containing citrate ions and cyanide ions were processed to stain iron oxide nanoparticles endocytosized in cells. Additionally, the as-prepared 8?nm Au icosahedra could be isolated and grown to larger 57?nm-sized icosahedra using the seed-mediated growth approach.     

Facile Synthesis of Gold Icosahedra in an Aqueous Solution by Reacting HAuCl4 with N‐Vinyl Pyrrolidone

Herein we describe a protocol that generates Au icosahedra in high yields by simply mixing aqueous solutions of HAuCl₄ and N‐vinyl pyrrolidone. Our mechanistic study reveals that water plays an important role in this synthesis: as a nucleophile, it attacks the gold–vinyl complex, leading to the production of an alcohol‐based Au^I intermediate. This intermediate then undergoes a redox reaction in which Au^I is reduced to Au⁰, leading to the formation of Au atoms and then Au icosahedra of about 18 nm in size at a yield of 94 %, together with a carboxylic acid in the final product. This new protocol has also been employed to prepare multiply twinned nanoparticles of Ag (15–20 nm in size), spherical aggregates (25–30 nm in size) of Pd nanoparticles, and very small nanoparticles of Pt (2 nm in size). Since no organic solvent, surfactant, or polymer stabilizer is needed for all these syntheses, this protocol may provide a simple, versatile, and environmentally benign route to noble‐metal nanoparticles having various compositions and morphologies.     

Salts of HCN‐Cyanide Aggregates: [CN(HCN)2]− and [CN(HCN)3]−

Although pure hydrogen cyanide can spontaneously polymerize or even explode, when initiated by small amounts of bases (e.g. CN^?), the reaction of liquid HCN with [WCC]CN (WCC=weakly coordinating cation=Ph₄P, Ph₃PNPPh₃=PNP) was investigated. Depending on the cation, it was possible to extract salts containing the formal dihydrogen tricyanide [CN(HCN)₂]^? and trihydrogen tetracyanide ions [CN(HCN)₃]^? from liquid HCN when a fast crystallization was carried out at low temperatures. X‐ray structure elucidation revealed hydrogen‐bridged linear [CN(HCN)₂]^? and Y‐shaped [CN(HCN)₃]^? molecular ions in the crystal. Both anions can be considered members of highly labile cyanide‐HCN solvates of the type [CN(HCN)_n]^? (n=1, 2, 3 …) as well as formal polypseudohalide ions.     

Controlled Synthesis of Heterotrimetallic Single‐Chain Magnets from Anisotropic High‐Spin 3 d–4 f Nodes and Paramagnetic Spacers

By using the node‐and‐spacer approach in suitable solvents, four new heterotrimetallic 1D chain‐like compounds (that is, containing 3d–3d′–4f metal ions), {[Ni(L)Ln(NO₃)₂(H₂O)Fe(Tp*)(CN)₃] ? 2 CH₃CN ? CH₃OH}_n (H₂L=N,N′‐bis(3‐methoxysalicylidene)‐1,3‐diaminopropane, Tp*=hydridotris(3,5‐dimethylpyrazol‐1‐yl)borate; Ln=Gd ( 1 ), Dy ( 2 ), Tb ( 3 ), Nd ( 4 )), have been synthesized and structurally characterized. All of these compounds are made up of a neutral cyanide‐ and phenolate‐bridged heterotrimetallic chain, with a {? Fe? C?N? Ni(? O? Ln)? N?C? }_n repeat unit. Within these chains, each [(Tp*)Fe(CN)₃]^? entity binds to the Ni^II ion of the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ motif through two of its three cyanide groups in a cis mode, whereas each [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit is linked to two [(Tp*)Fe(CN)₃]^? ions through the Ni^II ion in a trans mode. In the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit, the Ni^II and Ln^III ions are bridged to one other through two phenolic oxygen atoms of the ligand (L). Compounds 1 – 4 are rare examples of 1D cyanide‐ and phenolate‐bridged 3d–3d′–4f helical chain compounds. As expected, strong ferromagnetic interactions are observed between neighboring Fe^III and Ni^II ions through a cyanide bridge and between neighboring Ni^II and Ln^III (except for Nd^III) ions through two phenolate bridges. Further magnetic studies show that all of these compounds exhibit single‐chain magnetic behavior. Compound 2 exhibits the highest effective energy barrier (58.2 K) for the reversal of magnetization in 3d/4d/5d–4f heterotrimetallic single‐chain magnets.     

Magnetic Anisotropy of Cyanide‐Bridged Core and Core–Shell Coordination Nanoparticles Probed by X‐ray Magnetic Circular Dichroism

The local symmetry and local magnetic properties of 6 nm‐sized, bimetallic, cyanide‐bridged CsNiCr(CN)₆ coordination nanoparticles 1 and 8 nm‐sized, trimetallic, CsNiCr(CN)₆@CsCoCr(CN)₆ core–shell nanoparticles 2 were studied by X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD). The measurements were performed at the Ni^II, Co^II, and Cr^III L_2,3 edges. This study revealed the presence of distorted Ni^II sites located on the particle surface of 1 that account for the uniaxial magnetic anisotropy observed by SQUID measurements. For the core–shell particles, a combination of the exchange anisotropy between the core and the shell and the pronounced anisotropy of the Co^II ions is the origin of the large increase in coercive field from 120 to 890 Oe on going from 1 to 2 . In addition, XMCD allows the relative orientation of the magnetic moments throughout the core–shell particles to be determined. While for the bimetallic particles of 1 , alignment of the magnetic moments of Cr^III ions with those of Ni^II ions leads to uniform magnetization, in the core–shell particles 2 the magnetic moments of the isotropic Cr^III follow those of Co^II ions in the shell and those of Ni^II ions in the core, and this leads to nonuniform magnetization in the whole nanoobject, mainly due to the large difference in local anisotropy between the Co^II ions belonging to the surface and the Ni^II ions in the core.     

Three Dicyanidometallate(I)‐based Complexes Incorporating Hydrogen‐bonding, π–π Packing and d10–d10 Interactions with Auxiliary 2,2′‐Bipyridyl‐like Ligands

To investigate the influence of the non‐covalent interactions, such as hydrogen‐bonding, π–π packing and d¹⁰–d¹⁰ interactions in the supramolecular motifs, three cyanido‐bridged heterobimetallic discrete complexes {Mn(bipy)₂(H₂O)[Ag(CN)₂]}[Ag(CN)₂] ( 1 ), {Mn(phen)₂(H₂O)[Au(CN)₂]}₂[Au(CN)₂]₂ · 4H₂O ( 2 ), and {Cd(bipy)₂(H₂O)[Au(CN)₂]}[Au(CN)₂] ( 3 ) (bipy = 2,2′‐bipyridine, and phen = 1,10‐phenanthroline), which are based on dicyanidometallate(I) groups with 1:2 stoichiometry of metal ions and 2,2′‐bipyridyl‐like co‐ligands were synthesized and structurally characterized. In compound 1 , hydrogen bonding and π–π interactions governed the supramolecular contacts. In compound 2 , the incorporation of aurophilic, hydrogen bonding and π–π interactions result in a 3D supramolecular network. In compound 3 , hydrogen bonding and π–π stacking interactions result in a 2D supramolecular layer. In the three complexes, hydrogen‐bonding, π–π packing and/or d¹⁰–d¹⁰ interactions can play important roles in increasing the dimensionality of supramolecular assemblies.     

Red to Blue High Electrochromic Contrast and Rapid Switching Poly(3,4‐ethylenedioxypyrrole)–Au/Ag Nanocomposite Devices for Smart Windows

Poly(3,4‐ethylenedioxypyrrole) (PEDOP)–Ag and PEDOP–Au nanocomposite films have been synthesized for the first time by electropolymerization of the conducting‐polymer precursor in a waterproof ionic liquid, 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, followed by Ag/Au nanoparticle incorporation. That the Ag/Au nanoparticles are not adventitious entities in the film is confirmed by a) X‐ray photoelectron spectroscopy, which provides evidence of Ag/Au–PEDOP interactions through chemical shifts of the Ag/Au core levels and new signals due to Ag–N(H) and Au–N(H) components, and b) electron microscopy, which reveals Au nanoparticles with a face‐centered‐cubic crystalline structure associated with the amorphous polymer. Spectroelectrochemistry of electrochromic devices based on PEDOP–Au show a large coloring efficiency (η_max=270 cm² C^?1, λ=458 nm) in the visible region, for an orange/red to blue reversible transition, followed by a second, remarkably high η_max of 490 cm² C^?1 (λ=1000 nm) in the near‐infrared region as compared to the much lower values achieved for the neat PEDOP analogue. Electrochemical impedance spectroscopy studies reveal that the metal nanoparticles lower charge‐transfer resistance and facilitate ion intercalation–deintercalation, which manifests in enhanced performance characteristics. In addition, significantly faster color–bleach kinetics (five times of that of neat PEDOP!) and a larger electrochemical ion insertion capacity unambiguously demonstrate the potential such conducting‐polymer nanocomposites have for smart window applications.     

Electrochemical Determination of L‐Lactate Using Phenylboronic Acid Monolayer‐Modified Electrodes

The surface of a gold (Au) disk electrode was modified with a self‐assembled monomolecular layer of dithiobis(4‐butylamino‐m‐phenylboronic acid) (DTBA‐PBA) to prepare L ‐lactate‐sensitive electrodes. The DTBA‐PBA‐modified electrodes exhibited an attenuated cyclic voltammogram (CV) for the Fe(CN)₆^3? ion in the presence of L ‐lactate, as a result of the formation of phenylboronate ester of L ‐lactate accompanied with the addition of OH^? ion to the boron atom. In other words, the negatively charged DTBA‐PBA monolayer blocked the electrode surface from the access of the Fe(CN)₆^3?/4? ions. Thus, the DTBA‐PBA monolayer‐modified Au electrode can be used for determining L ‐lactate on the basis of the change in redox current of Fe(CN)₆^3?/4? ions. The calibration graph useful for determining 1–30 mM L ‐lactate was obtained.     

Amino‐Containing Ultrafine Organosilica‐Nanoparticle‐Modified Au Electrode for the Determination of Cu(II) Ions

Using 3‐Aminopropyltriethoxysilane(APTES) as a single silica source, an amino‐rich ultrafine organosilica‐nanoparticle‐modified Au electrode was fabricated, following the formation of (3‐mercaptopropyl)‐trimethoxysilane (MPTS) monolayer on Au surface (MPTS/Au). With cetyltrimethylammonium bromide as an additive, APTES‐based gel particles on the electrode have a narrow particle size distribution of 4–7 nm and “crystal‐like” structure. AFM and electrochemical characterization confirmed the successful grafting of APTES nanoparticles on MPTS/Au. The APTES/MPTS/Au electrode is highly sensitive for the detection of copper(II) ions with a detection limit as low as 1.6×10^?12 mol L^?1 (S/N>3) by square wave voltammetry. The current is linear to copper(II) concentration between 1.6×10^?12 and 6.25×10^?10 mol L^?1.     

Binary Au/MWCNT and Ternary Au/ZnO/MWCNT Nanocomposites: Synthesis,Characterisation and Catalytic Performance

Gold nanoparticles of 10–24 and 5–8 nm in size were obtained by chemical citrate reduction and UV photoreduction, respectively, on acid‐treated multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNT composites. The shape and size of the deposited Au nanoparticles were found to be dependent upon the synthetic method used. Single‐crystalline, hexagonal gold particles were produced in the case of UV photoreduction on ZnO/MWCNT, whereas spherical Au particles were deposited on MWCNT when the chemical citrate reduction method was used. In the UV photoreduction route, n‐doped ZnO serves as the e^? donor, whereas the solvent is the hole trap. All materials were fully characterised by UV/Vis spectroscopy, scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, Raman spectroscopy and BET surface analysis. The catalytic activity of the composites was studied for the selective hydrogenation of α,β‐unsaturated carbonyl compound 3,7‐dimethyl‐2,6‐octadienal (citral). The Au/ZnO/MWCNT composite favours the formation of unsaturated alcohols (selectivity=50 % at a citral conversion of 20 %) due to the presence of single‐crystalline, hexagonal gold particles, whereas saturated aldehyde formation is favoured in the case of the Au/MWCNT nanocomposite that contains spherical gold particles.     

1,2‐Di­cyano‐1,2‐bis­(imidazolidine‐2‐thione)­digold(I) and 2,2‐di­cyano‐1,1‐bis­(di­methyl­thio­urea)­digold(I)

Gold(I) cyanide forms complexes with imidazolidine‐2‐thione (etu) and di­methyl­thio­urea (dmtu) with the formula [Au₂(CN)₂L₂], i.e. the title complexes di­cyano‐1κC,2κC‐bis(imidazolidine‐2‐thione)‐1κS,2κS‐digold(I)(Au—Au), [Au₂(CN)₂(C₃H₆N₂S)₂], and di­cyano‐1κ²C‐bis(N,N′‐di­methyl­thio­urea)‐2κ²S‐digold(I)(Au—Au), [Au₂(CN)₂(C₃H₈N₂S)₂]. In the etu complex, two approximately linear (etu)AuCN groups are held together by a weak homopolar Au—Au bond [3.117 (1) Å], with a torsion angle of 61 (3)° between the two groups. In the dmtu complex, an approximately linear Au(dmtu)₂ group is bound to an approximately linear Au(CN)₂ group by a weak heteropolar Au—Au bond [3.091 (1) Å], with a torsion angle of 83 (5)° between the two groups.     

Transfer Hydrocyanation of α‐ and α,β‐Substituted Styrenes Catalyzed by Boron Lewis Acids

A straightforward gram‐scale preparation of cyclohexa‐1,4‐diene‐based hydrogen cyanide (HCN) surrogates is reported. These are bench‐stable but formally release HCN and rearomatize when treated with Lewis acids. For BCl₃, the formation of the isocyanide adduct [(CN)BCl₃]^? and the corresponding Wheland complex was verified by mass spectrometry. In the presence of 1,1‐di‐ and trisubstituted alkenes, transfer of HCN from the surrogate to the C?C double bond occurs, affording highly substituted nitriles with Markovnikov selectivity. The success of this transfer hydrocyanation depends on the Lewis acid employed; catalytic amounts of BCl₃ and (C₆F₅)₂BCl are shown to be effective while B(C₆F₅)₃ and BF₃?OEt₂ are not.     

White Light Emissive DyIII Single‐Molecule Magnets Sensitized by Diamagnetic [CoIII(CN)6]3− Linkers

The self‐assembly of Dy^III–3‐hydroxypyridine (3‐OHpy) complexes with hexacyanidocobaltate(III) anions in water produces cyanido‐bridged {[Dy^III(3‐OHpy)₂(H₂O)₄] [Co^III(CN)₆]}?H₂O ( 1 ) chains. They reveal a single‐molecule magnet (SMM) behavior with a large zero direct current (dc) field energy barrier, ΔE=266(12) cm^?1 (≈385 K), originating from the single‐ion property of eight‐coordinated Dy^III of an elongated dodecahedral geometry, which are embedded with diamagnetic [Co^III(CN)₆]^3? ions into zig‐zag coordination chains. The SMM character is enhanced by the external dc magnetic field, which results in the ΔE of 320(23) cm^?1 (≈460 K) at H_dc=1 kOe, and the opening of a butterfly hysteresis loop below 6 K. Complex 1 exhibits white Dy^III‐based emission realized by energy transfer from Co^III and 3‐OHpy to Dy^III. Low temperature emission spectra were correlated with SMM property giving the estimation of the zero field ΔE. 1 is a unique example of bifunctional magneto‐luminescent material combining white emission and slow magnetic relaxation with a large energy barrier, both controlled by rich structural and electronic interplay between Dy^III, 3‐OHpy, and [Co^III(CN)₆]^3?.     

Cyanation of Aryl Bromides with K4[Fe(CN)6] Catalyzed by Dichloro[bis{1‐(dicyclohexylphosphanyl)piperidine}]palladium,a Molecular Source of Nanoparticles,and the Reactions Involved in the Catalyst‐Deactivation Processes

Dichloro[bis{1‐(dicyclohexylphosphanyl)piperidine}]palladium [(P{(NC₅H₁₀)(C₆H₁₁)₂})₂PdCl₂] ( 1 ) is a highly active and generally applicable C? C cross‐coupling catalyst. Apart from its high catalytic activity in Suzuki, Heck, and Negishi reactions, compound 1 also efficiently converted various electronically activated, nonactivated, and deactivated aryl bromides, which may contain fluoride atoms, trifluoromethane groups, nitriles, acetals, ketones, aldehydes, ethers, esters, amides, as well as heterocyclic aryl bromides, such as pyridines and their derivatives, or thiophenes into their respective aromatic nitriles with K₄[Fe(CN)₆] as a cyanating agent within 24 h in NMP at 140 °C in the presence of only 0.05 mol % catalyst. Catalyst‐deactivation processes showed that excess cyanide efficiently affected the molecular mechanisms as well as inhibited the catalysis when nanoparticles were involved, owing to the formation of inactive cyanide complexes, such as [Pd(CN)₄]^2?, [(CN)₃Pd(H)]^2?, and [(CN)₃Pd(Ar)]^2?. Thus, the choice of cyanating agent is crucial for the success of the reaction because there is a sharp balance between the rate of cyanide production, efficient product formation, and catalyst poisoning. For example, whereas no product formation was obtained when cyanation reactions were examined with Zn(CN)₂ as the cyanating agent, aromatic nitriles were smoothly formed when hexacyanoferrate(II) was used instead. The reason for this striking difference in reactivity was due to the higher stability of hexacyanoferrate(II), which led to a lower rate of cyanide production, and hence, prevented catalyst‐deactivation processes. This pathway was confirmed by the colorimetric detection of cyanides: whereas the conversion of β‐solvato‐α‐cyanocobyrinic acid heptamethyl ester into dicyanocobyrinic acid heptamethyl ester indicated that the cyanide production of Zn(CN)₂ proceeded at 25 °C in NMP, reaction temperatures of >100 °C were required for cyanide production with K₄[Fe(CN)₆]. Mechanistic investigations demonstrate that palladium nanoparticles were the catalytically active form of compound 1 .     

Self‐assembly of p‐Aminothiophenol on Gold Surface: Application for Impedimetric and Potentiometric Sensing of Cobalt (II) Ions – A Comparative Study

Cobalt, despite an essential biological element, imposes threat to humans when exposed to high concentration or even to low concentration for long term which demands the development of highly sensitive and selective analytical methods for its trace analysis. In the present work, self‐assembly of p‐aminothiophenol (p‐ATP) on gold surface (Au?ATP SAM) was carried out and for the first time, applied as a platform for impedimetric and potentiometric sensing of Co²⁺. Au?ATP SAM was characterized using electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), in the presence of two redox probes: [Fe(CN)₆]^3?/4? and [Ru(NH₃)₆]^2+/3+ to evaluate associated passivating behaviour. Au?ATP SAM completely blocked [Fe(CN)₆]^3?/4? as compared to [Ru(NH₃)₆]^2+/3+ which may be attributed to inner‐sphere and outer‐sphere ET mechanisms, respectively. Au?ATP SAM was found to exhibit excellent sensitivity towards Co²⁺ in a wider concentration range from 1.0×10^?12 M to 1.0×10^?5 M (r²=0.963) at pH 5.5 with a detection limit of 6.0×10^?13 M and superior selectivity. Further, carbon paste electrode (CPE) was prepared by incorporating p‐ATP bound gold nanoparticles and explored for potentiometric sensing of Co²⁺ which exhibited Nernstian slope of 29.2±0.2 mV/dec in linear concentration range of 1.0×10^?6 M–1.0×10^?1 M (r²=0.971) with a detection limit of 8.0×10^?7 M. The proposed sensors were successfully applied for estimation of Co²⁺ content in water samples.     

Study of mechanistic features of tetrahedral-octahedral interconversion of tetracyanozincate (II) to bis(4-(2hyphen;Pyridylazo)hyphen;resorcinol)zincate(II) by stopped-flow technique

The present study examines the kinetics and mechanism of the formation of [Zn(CN)₄]^2? from ZnR₂^2? (R represents 4-(2-Pyridylazo)resorcinol, short named as Par) and vice versa. The reactions have been followed at 494 nm (λ_max of [Zn(Par)₂]^2?, ε = 7.8 × 10⁴ M^?1 cm^?1) using stopped-flow spectrophotometer in presence of excess of incoming ligand. The data show that the formation of [Zn(CN)₄]^2? complex is first order in [ZnR₂^2?] and the order with respect to [CN^?] varies from one at higher cyanide concentration to zero at low [CN^?]. These observations suggest a slow dissociation of [ZnR₂]^2? to ZnR and R^2? and a cyanide assisted rapid dissociation of [ZnR₂]^2? to [ZnR(CN)_x]^x? followed by their rapid conversion to [Zn(CN)₄]^2?. The reaction of Zn(Par) with cyanide ions also follow first order kinetics at higher as well as lower cyanide concentrations. The reverse reaction exhibits first order dependence each in [Zn(CN)₄^2?] and [Par^2?], but an inverse first order dependence in [CN^?] at low Par concentrations. However, at higher Par concentration the reaction rate tends to be independent of [Par^2?]. On the basis of forward and reverse rate studies, a five step mechanism consistent with these results has been proposed. The activation parameters and the effect of ionic strength have been used in further support to the proposed mechanism. The effect of pH on the rates of forward and reverse reaction has also been investigated.     

K2Au(IO3)5 and β‐KAu(IO3)4: Polar Materials with Strong SHG Responses Originating from Synergistic Effect of AuO4 and IO3 Units

Two new polar potassium gold iodates, namely, K₂Au(IO₃)₅ (Cmc2₁) and β‐KAu(IO₃)₄ (C2), have been synthesized and structurally characterized. Both compounds feature zero‐dimensional polar [Au(IO₃)₄]^? units composed of an AuO₄ square‐planar unit coordinated by four IO₃^? ions in a monodentate fashion. In β‐KAu(IO₃)₄, isolated [Au(IO₃)₄]^? ions are separated by K⁺ ions, whereas in K₂Au(IO₃)₅, isolated [Au(IO₃)₄]^? ions and non‐coordinated IO₃^? units are separated by K⁺ ions. Both compounds are thermally stable up to 400 °C and exhibit high transmittance in the NIR region (λ=800–2500 nm) with measured optical band gaps of 2.65 eV for K₂Au(IO₃)₅ and 2.75 eV for β‐KAu(IO₃)₄. Powder second‐harmonic generation measurements by using λ=2.05 μm laser radiation indicate that K₂Au(IO₃)₅ and β‐KAu(IO₃)₄ are both phase‐matchable materials with strong SHG responses of approximately 1.0 and 1.3 times that of KTiOPO₄, respectively. Theoretical calculations based on DFT methods confirm that such strong SHG responses originate from a synergistic effect of the AuO₄ and IO₃ units.     

Gold‐loading magnetic core–shell organic/inorganic nanocomposites: facile preparation and multiple properties

Magnetic composite nanospheres (MCS) were first prepared via mini‐emulsion polymerization. Subsequently, the hybrid core–shell nanospheres were used as carriers to support gold nanoparticles. The as‐prepared gold‐loading magnetic composite nanospheres (Au‐MCS) had a hydrophobic core embed with γ‐Fe₃O₄ and a hydrophilic shell loaded by gold nanoparticles. Both the content of γ‐Fe₃O₄ and the size of gold nanoparticles could be controlled in our experiments, which resulted in fabricating various materials. On one hand, the Au‐MCS could be used as a T₂ contrast agent with a relaxivity coefficient of 362 mg^?1 ml S^?1 for magnetic resonance imaging. On the other hand, the Au‐MCS exhibited tunable optical‐absorption property over a wavelength range from 530 nm to 800 nm, which attributed to a secondary growth of gold nanoparticles. In addition, dynamic light scattering results of particle sizing and Zeta potential measurements revealed that Au‐MCS had a good stability in an aqueous solution, which would be helpful for further applications. Finally, it showed that the Au‐MCS were efficient catalysts for reductions of hydrophobic nitrobenzene and hydrophilic 4‐nitrophenol that could be reused by a magnetic separation process. Copyright © 2014 John Wiley & Sons, Ltd.     

Transformations of [Au(CN)2]− at the contact with activated carbon surface

We have studied the processes occurring when alkaline aqueous solution of Na[Au(CN)₂] is brought in contact with activated carbon surface. It has been shown that the adsorption of the gold cyanide complex occurs via several independent routes, one of them being accompanied with the partial breakdown of the inner sphere of the compound and free cyanide ions release into the solution. The latter process decreases the gold recovery by aqueous NaOH during the high-temperature (150°C) desorption. A prolonged storage of the adsorbent saturated with [Au(CN)₂]^? in air produces a similar result. The reasons of the observed phenomena have been discussed.     

Poly[tetraamminecopper(II) bis[tris(μ2‐cyanido‐κ2C,N)dicuprate(I)]]: a unique CuI–CuII mixed‐valence complex containing anionic cuprous cyanide layers and [Cu(NH3)4]2+ cations

The title compound, {[Cu(NH₃)₄][Cu(CN)₃]₂}_n, features a Cu^I–Cu^II mixed‐valence CuCN framework based on {[Cu₂(CN)₃]⁻}_n anionic layers and [Cu(NH₃)₄]²⁺ cations. The asymmetric unit contains two different Cu^I ions and one Cu^II ion which lies on a centre of inversion. Each Cu^I ion is coordinated to three cyanide ligands with a distorted trigonal–planar geometry, while the Cu^II ion is ligated by four ammine ligands, with a distorted square‐planar coordination geometry. The interlinkage between Cu^I ions and cyanide bridges produces a honeycomb‐like {[Cu₂(CN)₃]⁻}_n anionic layer containing 18‐membered planar [Cu(CN)]₆ metallocycles. A [Cu(NH₃)₄]²⁺ cation fills each metallocyclic cavity within pairs of exactly superimposed {[Cu₂(CN)₃]⁻}_n anionic layers, but there are no cations between the layers of adjacent pairs, which are offset. Pairs of N—H...N hydrogen‐bonding interactions link the N—H groups of the ammine ligands to the N atoms of cyanide ligands.