The Shape of Germanium Clusters To Come

A different drummer : The existence of endohedral germanium clusters was predicted earlier by gas‐phase experiments. The [Co@Ge₁₀]^3? anion now synthesized is surprising, as it breaks with a long line of exclusively deltahedral structures found in the past. Instead, it has a regular pentagonal‐prismatic structure (see picture; Co gray, Ge red).

     

Development of Gelatin Hydrogel Pads as Antibacterial Wound Dressings

Gelatin hydrogel pads have been prepared from a 10 wt.‐% gelatin solution that contained 2.5 wt.‐% AgNO₃ in 70% v/v acetic acid by a solvent‐casting technique. The AgNO₃‐containing gelatin solution was aged under mechanical stirring for various time intervals to allow for the formation of silver nanoparticles (nAgs). The formation of nAgs was monitored by a UV‐vis spectrophotometer. The morphology and size of the nAgs were characterized by transmission electron microscopy (TEM). To improve the water resistance of the hydrogels, various contents of glutaraldehyde (GTA) were added to the AgNO₃‐containing gelatin solution to cross‐link the obtained gelatin hydrogels. These hydrogels were tested for their water retention and weight loss behavior, release characteristics of the as‐loaded silver, and antibacterial activity against Gram‐negative Escherichia coli and Gram‐positive Staphylococcus aureus. The AgNO₃‐containing gelatin solution that had been aged for 5 d showed the greatest number of nAgs formed. The size of these particles, based on TEM results, was 10–11 nm. With an increase in the GTA content used to cross‐link the hydrogels, the water retention, the weight loss, and the cumulative amount of silver released were found to decrease. Finally, all of the nAg‐loaded gelatin hydrogels could inhibit the growth of the tested pathogens, which confirmed their applicability as antibacterial wound dressings.

     

Role of anions in the polymerization of 2,5‐dimethoxyaniline in the presence of poly(styrene sulfonic acid)

Poly(2,5‐dimethoxyaniline) (PDMA)–Ag composites were successfully obtained through the oxidative polymerization of 2,5‐dimethoxyaniline in poly(styrene sulfonic acid) with CH₃SO₃Ag and AgNO₃ as oxidants. In situ ultraviolet–visible spectroscopy results showed that the growth rate of PDMA was strongly affected by CH₃SO and NO. The coupling reaction of PDMA and NO was proposed to explain the lower growth rate of PDMA with AgNO₃ as the oxidant in comparison with CH₃SO₃Ag. X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to validate the proposed coupling reaction through the monitoring of the side products and oxidized state of PDMA. The results showed that there were more side products and lower oxidized states for the composite structure in the presence of NO than in the presence of CH₃SO, and this agreed with the proposal. Transmission electron microscopy showed that the Ag nanoparticles had almost the same size, regardless of the anions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6624–6632, 2006     

A spirocyclic P-S cage cation: synthesis and formation of P7S6I2+

Upon ionization of the P4S3I2 molecule with Ag[Al(OR)4], a highly reactive sulfonium cation P4S3I+ is generated (NMR simulated and assigned). At -80 degrees C this cation reacts with additional P4S3I2 to give either an iodophosphonium P4S3I3+ cation (NMR simulated and assigned) and P4S3 or to give several isomers of a metastable compound that is probably P8S3I3+. This mixture decomposes at 0 degrees C to give only three isomers of the spirocyclic P7S6I2+ cage cation (31P NMR simulated and assigned, X-ray of one isomer, IR assigned). The oxidation of the [Ag(P4S3)2]+ complex by I2 also resulted in the formation of P7S6I2+, but with more by-products. The spirocyclic 15-atom cage of P7S6I2+ has no precedent and contains the first phosphonium center bonded only to P and S atoms. This structural element gives the first experimental clue as to how formal charge-bearing elements in the still unknown class of binary P-Ch (Ch = chalcogen) or homopolyatomic P cations may be constructed.     

Silver nanocluster redox-couple-promoted nonclassical electron transfer: an efficient electrochemical Wolff rearrangement of alpha-diazoketones

In this work we report the unique electrocatalytic role of benzoic acid protected silver nanoclusters (Ag(n), mean core diameter 2.5 nm) in the Wolff rearrangement (Scheme 1) of alpha-diazoketones. More specifically, the presence of a Ag(n) (0)/Ag(n) (+) redox couple facilitates a nonclassical electron-transfer process, involving chemical reaction(s) interposed between two electron-transfer steps occurring in opposite directions. Consequently, the net electron transfer between the electron mediator (Ag(n)) and alpha-diazoketone is zero. In-situ UV-visible studies using pyridine as a nucleophilic probe indicate the participation of alpha-ketocarbene/ketene as important reaction intermediates. Controlled potential coulometry of alpha-diazoketones using Ag(n) as the anode results in the formation of Wolff rearranged carboxylic acids in excellent yield, without sacrificing the electrocatalyst.     

The transfer of tin and germanium atoms from N-heterocyclic stannylenes and germylenes to diazadienes

New N-heterocyclic stannylenes and germylenes were synthesized by transamination of E[N(SiMe3)2] (E = Ge, Sn) with alpha-amino-aldimines or ethylidene-1,2-diamines and were characterized by spectroscopic methods and in the case of the germylene 10 g by X-ray diffraction. The reactions of several germylenes and stannylenes with diazadienes were studied by using dynamic NMR and computational methods. Experimental and theoretical studies confirmed that metathesis with exchange of the Group 14 atom is feasible for both stannylenes and germylenes, with exchange rates being generally higher for stannylenes. The metathesis of the diazadiene 3 b and the stannylene 1 b follows second-order kinetics and exhibits a sizeable negative entropy of activation. The transfer reaction is inhibited by bulky substituents in both reactants and surprisingly coincides with a suppression of the fragmentation of the stannylene into tin and diazadiene. A connection between oxidative addition and ring fragmentation was also observed in the reaction of 1 f with sulfur. Density functional theory (DFT) calculations suggest that all metathesis reactions proceed via transient spirocyclic [1+4] cycloaddition products, the formation of which is generally endothermic and endergonic. The spirostannanes display a distorted Psi-tbp geometry at the tin atom and their cycloreversion requires low or nearly negligible activation energies; spirogermanes exhibit distorted tetrahedral central atoms and sizeable energy barriers with respect to the same reaction. Complementary studies of cycloadditions of diazadienes to triplet germylenes or stannylenes indicate that these reactions are exothermic. The lowest triplet state in the carbene homologues results from promotion of an electron from an n(N) orbital with pi character rather than the n(C)-sigma orbital as in carbenes, and singlet-triplet excitation energies decrease from carbon to tin. Spirostannanes exhibit a triplet ground-state multiplicity that implies that the energy hypersurfaces for the reactions of singlet and triplet stannylenes with diazadienes intersect; for germylenes, the singlet hypersurface is always lower in energy. A reaction mechanism explaining the different thermal stabilities of N-heterocyclic germylenes and stannylenes, and the coincidence between ring metathesis and thermal decomposition of the latter, is proposed based on the different separation of the singlet and triplet energy hypersurfaces.     

Ruthenium(II), copper(I) and silver(I) complexes of large bite bisphosphinite, bis(2-diphenylphosphinoxynaphthalen-1-yl)methane: Application of Ru(II) complexes towards the hydrogenation of styrene and phenylacetylene

Ruthenium(II), copper(I) and silver(I) complexes of large bite bisphosphinite Ph₂P{(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)}PPh₂ (1) are described. Reactions of bisphosphinite 1 with [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂ and RuCl₂(PPh₃)₃ afford mono- and bis-chelate complexes [RuCl(η⁶-p-cymene){η²-Ph₂P{(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)}PPh₂-κP,κP}]Cl (2) and trans-[RuCl₂{η²-Ph₂P{(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)}PPh₂-κP,κP}₂] (3), respectively. Treatment of 1 with CuX (X = Cl, Br and I) furnish 10-membered chelate complexes of the type [Cu(X){η²-Ph₂P(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)PPh₂-κP,κP}] (4, X = Cl; 5, X = Br; 6, X = I), whereas [Cu(MeCN)₄]PF₆ affords a bis-chelated cationic complex [Cu{η²-Ph₂P(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)PPh₂-κP,κP}₂][PF₆] (7). Reaction between 1 and AgOTf produce both mono- and bis-chelated complexes [Ag{η²-Ph₂P(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)PPh₂-κP,κP}(SO₃CF₃)] (8) and [Ag{η²-Ph₂P(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)PPh₂-κP,κP}₂][SO₃CF₃] (9), respectively; whereas the similar reaction of 1 with[Ag(OTf)PPh₃] affords chelate complex of the type [Ag{η²-Ph₂P(-OC₁₀H₆)(μ-CH₂)(C₁₀H₆O-)PPh₂-κP,κP}(PPh₃)(SO₃CF₃)] (10). All the complexes were characterized by ¹H NMR, ³¹P NMR, elemental analysis and mass spectrometry, including low-temperature NMR studies in the case of silver complexes. The molecular structures of 4 and 6 are determined by X-ray diffraction studies. Ruthenium complexes 2 and 3 promote catalytic hydrogenation of styrene and phenylacetylene with good turnover numbers.     

Synthesis of New Amphiphilic Comb-Like Copolymers Based on Maleic Anhydride and α-Olefins

Summary: Novel amphiphilic comb-like poly(α-olefin-co-maleic anhydride) with a controlled ratio of hydrophilic (polyoxyethylene) and hydrophobic (polymethylene) side chains have been synthesized and characterized. The comb-like copolymers are soluble in organic and aqueous media and form micelles whose behaviour could be correlated to the chemical structure of polymers. We foresee that amphiphilic properties of the novel comb-like polymers are obviously the basis of new architectures in solution which could be used in a broad range of applications. Using micelles from these copolymers, silver nanoparticles with a narrow particle size distribution have been obtained as stable dispersion in both polar and non-polar media.     

A Series of Novel Organically Templated Germanium Antimony Sulfides

A series of novel organically templated germanium antimony sulfides have been solvothermally synthesized and structurally, thermally, and optically characterized. The compound [Me₂NH₂]₆[(Ge₂Sb₂S₇)(Ge₄S₁₀)] ( 1 ) features two distinct tetranuclear [Ge₂Sb₂S₇]^2? and [Ge₄S₁₀]^4? isolated clusters. The compound [(Me)₂NH₂][DabcoH]₂[Ge₂Sb₃S₁₀] ( 2 ) (Dabco=triethylenediamine) features a 1D‐[Ge₂Sb₃S₁₀]_n^3n? ribbon constructed with two [GeSbS₅]_n^3n? chains bridged by Sb³⁺ ion in ψ‐SbS₄ configuration. Compounds [M(en)₃][GeSb₂S₆] (M=Ni ( 3 ), Co ( 4 ) en=ethylenediamine) feature the unique 2D grid layer structures of [GeSb₂S₆]_n^2n?. The compound [(Me)₂NH₂]₂[GeSb₂S₆] ( 5 ) previously reported by us features a 3D chiral microporous structure with the chiral channels. The optical absorption spectra indicate that all the compounds are wide bandgap semiconductors. Thermal stabilities of these compounds have been investigated by thermogravimetric analyses (TGA).     

Capsules with Silver Nanoparticle Enrichment Subdomains and Their Antimicrobial Properties

The fabrication of polyelectrolyte multilayer capsules with controllable submicron‐sized subdomains and the in situ synthesis of silver nanoparticles are reported. Because poly(acrylic acid) (PAA) is released from the shell of the capsules in the dissolution process of sacrificial cores, the remaining poly(4‐vinylpyridine) (PVP) forms subdomains of spheres with controllable sizes, which can be tuned by the number of PVP/PAA bilayers. This creates capsules with special surface morphology and enables the in situ synthesis of Ag nanoparticles within the PVP subdomains on the shell of capsules. In addition, the in‐situ formed Ag nanoparticles can be mostly released from PVP subdomains of capsules in pH 2.0 solution, whereas they are stable in neutral solution. These specially designed capsules containing Ag nanoparticles can be used as antimicrobial materials and potentially benefit remote drug release by laser activation.