Spectral and structural characterization of amidate-bridged platinum-thallium complexes with strong metal-metal bonds

The reactions of [Pt(NH3)2(NHCOtBu)2] and TlX3 (X = NO3-, Cl-, CF3CO2-) yielded dinuclear [{Pt(ONO2)(NH3)2(NHCOtBu)}Tl(ONO2)2(MeOH)] (2) and trinuclear complexes [{PtX(RNH2)2(NHCOtBu)2}2Tl]+ [X = NO3- (3), Cl- (5), CF3CO2- (6)], which were spectroscopically and structurally characterized. Strong Pt-Tl interaction in the complexes in solutions was indicated by both 195Pt and 205Tl NMR spectra, which exhibit very large one-bond spin-spin coupling constants between the heteronuclei (1J(PtTl)), 146.8 and 88.84 kHz for 2 and 3, respectively. Both the X-ray photoelectron spectra and the 195Pt chemical shifts reveal that the complexes have Pt centers whose oxidation states are close to that of Pt(III). Characterization of these complexes by X-ray diffraction analysis confirms that the Pt and Tl atoms are held together by very short Pt-Tl bonds and are supported by the bridging amidate ligands. The Pt-Tl bonds are shorter than 2.6 Angstrom, indicating a strong metal-metal attraction between these two metals. Compound 2 was found to activate the C-H bond of acetone to yield a platinum(IV) acetonate complex. This reactivity corresponds to the property of Pt(III) complexes. Density functional theory calculations were able to reproduce the large magnitude of the metal-metal spin-spin coupling constants. The couplings are sensitive to the computational model because of a delicate balance of metal 6s contributions in the frontier orbitals. The computational analysis reveals the role of the axial ligands in the magnitude of the coupling constants.     

Quantitative nanotribology by AFM: a novel universal calibration platform

The quantitative determination of friction forces by atomic force microscopy (AFM) in nanotribology requires the conversion of the output voltage signal of the sector area-sensitive photodiode to force using (a) the torsional spring constant of the cantilever and (b) the lateral sensitivity of the photodiode. Many existing methods provide calibration factors with large errors and suffer from poor reproducibility. We report on the fabrication, validation, and application of a new, universally applicable standard specimen that enables one to accurately calibrate all types of AFM cantilevers and tips for quantitative friction force measurements. The Si(100) calibration standard, which exhibits 30 and 50 mum wide notches with tilt angles theta between 20 degrees and 35 degrees with respect to the wafer surface, was fabricated by focused ion beam (FIB) milling. The quantification of friction forces obtained on this universal standard specimen using a direct method (the improved wedge calibration method, as introduced by Ogletree, Carpick, and Salmeron Rev. Sci. Instrum. 1996, 67, 3298-3306), which yields (a) and (b) simultaneously, was critically tested for various types of Si3N4 integrated cantilever-tip assemblies. The error in the calibration factors obtained was found to be ca. 5%, which is a significant improvement compared to errors of 30-50% observed for the often applied two-step calibration procedures of cantilever lateral force constant and photodiode sensitivity. As demonstrated for oxidized Si(100), thin films of poly(methyl methacrylate) (PMMA), and micropatterned self-assembled monolayers (SAMs) on gold, the calibration of various V-shaped and single beam cantilevers based on the application of the new universal standard in conjunction with the direct wedge method proposed allows one to conveniently perform quantitative nanotribological measurements for a wide range of materials and applications.     

A synthetic receptor for phosphocholine esters

A bifunctional Zn-salen modified cavitand, reminiscent of the enzyme phospholipase C, shows high efficiency and synergic effect in the binding of the phospholipid DOPC.     

Dimeric allylpalladium(II) complexes with pyrazolate bridges: Synthesis, characterization, structure and thermal behaviour

The synthesis, characterization and thermal behaviour of some new dimeric allylpalladium (II) complexes bridged by pyrazolate ligands are reported. The complexes ; R = H, R′ = C(CH₃)₃ (1b), R = H, R′ = CF₃ (1c); R = CH₃, R′ = CH(CH₃)₂ (2a); R = CH₃, R′ = C(CH₃)₃ (2b); and R = CH₃, R′ = CF₃ (2c)] have been prepared by the room temperature reaction of [Pd(η³-CH₂C(R)CH₂)(acac)](acac = acetylacetonate) with 3,5-disubstituted pyrazoles in acetonitrile solution. The complexes have been characterized by NMR (¹H, ¹³C{¹H}), FT-IR, and elemental analyses. The structure of a representative complex, viz. 2c, has been established by single-crystal X-ray diffraction. The dinuclear molecule features two formally square planar palladium centres which are bridged by two pyrazole ligands and the coordination of each metal centre is completed by allyl substituents. The molecule has non-crystallographic mirror symmetry. Thermogravimetric studies have been carried out to evaluate the thermal stability of these complexes. Most of the complexes thermally decompose in argon atmosphere to give nanocrystals of palladium, which have been characterized by XRD, SEM and TEM. However, complex 2c can be sublimed in vacuo at 2 mbar without decomposition. The equilibrium vapour pressure of 2c has been measured by the Knudsen effusion technique. The vapour pressure of the complex 2c could be expressed by the relation: ln (p/Pa)(±0.06) = −18047.3/T + 46.85. The enthalpy and entropy of vapourization are found to be 150.0 ± 3 kJ mol⁻¹ and 389.5 ± 8 J K⁻¹ mol⁻¹, respectively.     

Die Kristallstrukturen der Cyanidofluoridoborate K[BFx(CN)4–x], x = 0–4

The crystal structure of K[BF₃(CN)] (Pbcn (Nr. 60) with a = 13.3486(15) b = 6.5239(7) c = 10.0085(11) Å, and eight formula units per unit cell) has been determined and the one of K[BF₂(CN)₂] was confirmed and improved. The different networks in the complete series of borates K[BF_x(CN)_4–x], x = 0–4 are compared and discussed.     

Designer multi-functional comb-polymers for surface engineering of quantum dots on the nanoscale

Synthesis, characterization and cell-biomarker applications for a novel series of comb-copolymers featuring hydrophobic amide side groups, carboxylates and other functionalities such as polymerizable side chains and PEG oligomers are reported. When used as polymer ligand shell for trioctylphosphine oxide (TOPO) coated quantum dots (QDs) these copolymers effectively solubilise CdSe/ZnS QDs in water. A systematic study was carried out to find the relation between the molecular structure of the copolymers, their ability to coat the QDs, and to suspend the nanocrystals in water. To demonstrate potential applications, highly luminescent QD/polymer assemblies were internalized into living and fixed cells.     

Reactions of free gold cluster cations with H2O, CH3Cl, and mixtures thereof

The reactions of the mass-selected gas-phase gold cluster cations Au₃⁺ and Au₅⁺ with H₂O, CH₃Cl, and mixtures of these reactants were studied under well-defined multi-collision conditions in an octopole ion trap. The reaction of CH₃Cl with the gold cations was found to proceed fast at room temperature, leading to the adsorption of one CH₃Cl molecule at each ‘corner’ atom of the cluster ion. This strong adsorption hindered the coadsorption of other reactants like H₂O. However, a considerable reduction of the CH₃Cl partial pressure led to distinct patterns of H₂O/CH₃Cl coadsorption products. Furthermore, the mass spectra indicated the loss of hydrogen after the reaction of CH₃Cl with Au₃⁺.     

Spectroscopic analysis of femtosecond laser plasma filament in air

We report a spectroscopic analysis of a filament generated by a femtosecond laser pulse in air. In the filament spectra, the characteristic Stark broadened atomic oxygen triplet centered at 777.4 nm has been observed. The measured electron impact Stark broadening parameter of the triplet is larger than the theoretical value by Griem [H.R. Griem, Plasma Spectroscopy, McGraw Hill, New York, 1964] by a factor 6.7. Using the experimental value , the plasma densities derived from Stark broadening agree well with those most recently obtained from Théberge et al.’s measurement of the nitrogen fluorescence calibrated by longitudinal diffraction [F. Théberge, W. Liu, P.T. Simard, A. Becker, S. L. Chin, Phys. Rev. E 74 (2006) 036406]. However, the Stark broadening approach is much simpler and can be used to non-invasively measure the filament plasma density distribution in air under different propagation conditions.     

Isotope shift in the dielectronic recombination of three-electron ANd57+

Isotope shifts in dielectronic recombination spectra were studied for Li-like (A)Nd(57+) ions with A=142 and A=150. From the displacement of resonance positions energy shifts deltaE(142 150)(2s-2p(1/2))=40.2(3)(6) meV [(stat)(sys)] and deltaE(142 150)(2s-2p(3/2))=42.3(12)(20) meV of 2s-2p(j) transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of (142 150)deltar(2)=-1.36(1)(3) fm(2). The approach is conceptually new and combines the advantage of a simple atomic structure with high sensitivity to nuclear size.