Infrared spectra and force constants of urea in the gaseous phase

Infrared spectra in the gaseous phase have been recorded for the first time for urea and the isotopomers urea-D₄, urea-¹⁵N₂ and urea-¹³C. On the base of these data a normal coordinate calculation has been performed, resulting in an optimized force field of urea, showing that, due to the very small intermolecular forces, the internal force constants increase by evaporation. This is especially true for the C=O-bond with a force constant increased by 10%.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthday, to whom since 1957 scientific contacts with the second author developed to a good friendship     

Über Münzmetall‐Quecksilber‐Chalkogenidhalogenide. V1) Solvothermalsynthese und Kristallstruktur der Hochtemperatur‐Modifikation von AgHgSI

On Coinage Metal Mercury Chalcogenide Halides. V. Solvothermal Synthesis and Crystal Structure of the High Temperature Modification of AgHgSI The solvothermal reaction of AgI and α‐HgS in diluted HI as solvent yields yellow crystals of α‐AgHgSI. The compound crystallizes in space group type P2₁2₁2₁ with a = 707.47(1), b = 773.18(2), c = 847.53(2) pm and Z = 4. The structure consists of a distorted hexagonal close packed array of sulphur and iodine, in which one fourth of the tetrahedral voids is occupied by silver and a half of the octahedral voids is occupied by mercury. The distortion of the hexagonal structure is caused by the steric demand of the lone pairs of sulphur and iodine. This could be shown by the calculation of the electron localisation function (ELF). The here described modification of AgHgSI can be obtained at 273 °C from the earlier published β‐AgHgSI and is therefore called α‐AgHgSI.     

The development of analytical methods for the determination of ions and acidity in individual raindrops

Summary In this publication the first results of a microanalytical investigation of individual rain droplets are given. Analytical methods for a sampling procedure as well as analysis in the ultra trace level with volumes less than 1 l have been developed. Because of the small volumes chromatographic methods are to be preferred.     

Conformational analysis of mixed oxathia crown ethers and their complexational ability towards Ag(I) and Pd(II)-an experimental solution NMR and theoretical molecular modelling study

Both the conformation and flexibility of four mixed oxathia crown ethers and their Ag(I) and Pd(II) complexes were studied by (1)H NMR (delta, J, NOE, T(1)), (13)C NMR, dynamic (1)H NMR spectroscopy and molecular modelling. The stoichiometry and stability constants of the complexes were determined from corresponding Job's plots in the case of Ag(I) complexes as the interchange between free and complexed states was fast on the NMR timescale; interchange for the Pd(II) complexes was sufficiently slow such that distinct sub-spectra were observable for the free and complexed states. In all cases where complexation was observed, 1 : 1 complexes were formed. Global minima structures determined from the modelling studies were analysed with respect to the barriers to ring interconversion, the flexibility of the species in solution and the preferred complexation of Ag(I) and Pd(II) to the sulfur atoms of the crown ethers.     

Neutral Pentacoordinate Silicon(IV) Complexes with a Tridentate Dianionic O,N,O or N,N,O Ligand,an Anionic PhX Ligand (X = O,S, Se), and a Phenyl Group: Synthesis and Structural Characterization in the Solid State and in Solution

A series of neutral pentacoordinate silicon(IV) complexes with a SiO₃NC, SiO₂SNC, SiO₂SeNC, SiO₂N₂C, SiOSN₂C, or SiOSeN₂C skeleton was synthesized and structurally characterized by multinuclear NMR spectroscopy in the solid state and in solution and by single‐crystal X‐ray diffraction. The compounds studied contain a tridentate dianionic O,N,O or N,N,O ligand, an anionic PhX ligand (X = O, S, Se), and a phenyl group. The structures, NMR spectroscopic parameters, and chemical properties of these silicon(IV) complexes were compared with those of related compounds that contain a tridentate dianionic S,N,O ligand instead of the O,N,O or N,N,O ligand.     

Solution structure of the palladium(II) complex of 1,4,7,10-tetrathiacyclododec-2-ene-2,3-dicarbonitrile

The solution structure of the Pd(II) complex of mn-12-S4 was studied in detail by NMR spectroscopy. The stoichiometry of the complex was determined by 1H NMR titration experiments. 3J(H,H) coupling constants were extracted from the 2D J-resolved NMR spectrum of the complex providing information concerning the S-C-C-S torsional angles. Further conclusions about the conformation of [Pd(mn-12-S4)](BF4)2 were drawn from experimental NOEs. The results of the NMR study were corroborated by molecular modelling.     

Femtosecond dynamics of isolated phenylcarbenes

Understanding the primary photophysical processes in molecules is essential for interpreting their photochemistry, because molecules rarely react from the initially excited electronic state. In this study the ultrafast excited-state dynamics of chlorophenylcarbene (CPC) and trifluoromethylphenylcarbene (TFPC), two species that are considered as models for carbene dynamics, were investigated by femtosecond time-resolved pump probe spectroscopy in the gas phase. Their dynamics was followed in real time by time-resolved photoionization and photoelectron imaging. CPC was excited at 265 nm into the 3 1A' state, corresponding to excitation from a pi-orbital of the aromatic ring into the LUMO. The LUMO contains a contribution of the p-orbital at the carbene center. Three time constants are apparent in the photoelectron images: A fast decay process with tau1 approximately 40 fs, a second time constant of tau2 approximatley 350 fs, and an additional time constant of tau3 approximately 1 ps. The third time constant is only visible in the time-dependence of low kinetic energy electrons. Due to the dense manifold of excited states between 3.9 and 5 eV, known from ab initio calculations, the recorded time-resolved electron images show broad and unstructured bands. A clear population transfer between the states thus can not directly be observed. The fast deactivation process is linked to either a population transfer between the strongly coupled excited states between 3.9 and 5.0 eV or the movement of the produced wave packet out of the Franck-Condon region. Since the third long time constant is only visible for photoelectrons at low kinetic energy, evidence is given that this time constant corresponds to the lifetime of the lowest excited A 1A' state. The remaining time constant reflects a deactivation of the manifold of states in the range 3.9-5.0 eV down to the A 1A' state.     

Surface acoustic wave biosensors: a review

This review presents an overview of 20 years of worldwide development in the field of biosensors based on special types of surface acoustic wave (SAW) devices that permit the highly sensitive detection of biorelevant molecules in liquid media (such as water or aqueous buffer solutions). 1987 saw the first approaches, which used either horizontally polarized shear waves (HPSW) in a delay line configuration on lithium tantalate (LiTaO₃) substrates or SAW resonator structures on quartz or LiTaO₃ with periodic mass gratings. The latter are termed “surface transverse waves” (STW), and they have comparatively low attenuation values when operated in liquids. Later Love wave devices were developed, which used a film resonance effect to significantly reduce attenuation. All of these sensor approaches were accompanied by the development of appropriate sensing films. First attempts used simple layers of adsorbed antibodies. Later approaches used various types of covalently bound layers, for example those utilizing intermediate hydrogel layers. Recent approaches involve SAW biosensor devices inserted into compact systems with integrated fluidics for sample handling. To achieve this, the SAW biosensors can be embedded into micromachined polymer housings. Combining these two features will extend the system to create versatile biosensor arrays for generic lab use or for diagnostic purposes. SAW based biosensor immersed in a sample flow. Analyte molecules binding to the immobilized antibodies on the sensor surface will influence the velocity of the SAW and hence the output signal generated by the driving electronics.