Franz L. Dickert

Molecular recognition of organic solvents and ammonia: shapes and donor properties as sensor effects

Abstract Chemically sensitive layers have been developed to characterize the donor properties and shapes of analytes by resistive and optical means. Macrocyclic nickel(II) complexes show substitution reactions with donor molecules. This behaviour is used as a model system for the detection of ammonia and the formation of mobile anions leads to increased conductivity. A detection limit in the ppm range can be achieved. Furthermore, cholesteric liquid crystals are able to distinguish molecules according to their morphological properties. The incorporation of the analyte leads to a shift of the absorbance maximum. The sensor characteristics reveal that these layers differentiate between homologous molecules, e.g., alcohols and hydrocarbons. Due to their shapes, these compounds give different sensor responses even at the same vapour pressure.

Supramolecular detection of solvent vapours with QMB and SAW devices

Abstract The principles of supramolecular host—guest chemistry can be applied for the design of chemically sensitive layers. Using molecular cavities, such as modified cyclodextrines, surface acoustic wave (SAW) devices yield a detection limit of a few ppm for tetrachloroethylene even with monomolecular films. Para cyclophanes have the advantage that chemical modifications can tune the cavity parameters in a wide range. Thus, systems with a graduated sensitivity for benzene, chloroform and tetrachloroethylene, for esxample, are obtained. The results of molecular modelling simulations provide a suitable basis for predicting the sensitivity of a given system. Channel structures in crystalline solids are also applicable. They strictly exclude too-bulky molecules. The sensitivity depends on the molecular weight and on the vapour pressure of the analyte. Thus, branched and unbranched isomers, e.g., n- and i-octane, can be differentiated.

Tetraazacyclophanes as host molecules for solvent vapours: mass-sensitive detection and force-field calculations

Abstract The principles of host-guest chemistry are applied to the design of chemically sensitive layers. Substituted tetraazacyclophanes are used as coatings for a mass-sensitive quartz microbalance. Thus, a variety of solvent vapours can be detected with a high sensitivity in the ppm range with very small water cross-sensitivities. This procedure is especially suitable for halogenated and aromatic hydrocarbons, such as tetrachloroethylene and benzene. Evidence for the host-guest binding mechanism is given by the satisfying correlation between the sensor response and the complexation energies calculated by force-field methods.

Chemistry of polyfunctional molecules. Part 86. Organoarsenic compounds derived from 1,3-bis(di-iodoarsino)propane with monocyclic, tricyclic, and straight-chain structures; X-ray crystal structure of 2,8,13,14-tetraoxa-1,3,7,9-tetra-arsatricyclo[7.3.1.1]tetradecane

Treatment of (C6H5)3As(CH2)3As(C6H5)2(1) with HI gives under elimination of benzene I2As(CH2)3- AsI2(2). The reduction of (2) with sodium in tetrahydrofuran leads to the heterocyclic compound I[graphic omitted]sI (3). Hydrolysis of (2) yields the new tricyclic compound (CH2)3As4O4(CH2)3(4). The oxidative solvolysis of (2) with H2O2 results in the formation of (HO)2OAs(CH2)3AsO(OH)2(5). All the compounds have been characterized by elemental analysis, i.r., Raman, 1H n.m.r., and mass spectra and by conductivity measurements. The crystal structure of compound (4) has been solved by X-ray diffraction. Crystals are monoclinic, space group P21/c, with a= 6.886(2), b= 14.745(5), c= 11.577(4)A, β= 94.15(3)°, and Z= 4. Data collection yielded 4 183 reflections, of which 2 026 with I 3σ(I) gave R= 0.038. The molecule consists of a tricyclic ring system. The main skeleton is an eight-membered As4O4 ring comparable to the endo–endo structure of N4S4. The As atoms are linked together by two (CH2)3 chains forming an open-envelope conformation. The solid state and a solution of (4) in CS2 show appreciable evidence for the existence of intramolecular C–H ⋯ O–As bonding.

Komplexbildung und Ligandenfluktuation im System Co (II) / [18] Krone-6 / Complex Formation and Ligand Fluctuation in the System Co(II)/[18]crown-6

The ligand properties of [18]crown-6 towards Co(II) ions were studied by 1H and 13C NMR spectroscopy in nitromethane and nitromethane/methanol. The complexes [Co([18]crown-6)]++ and mer-[Co([18]crown-6)(CH3OH)3]++ which were detected in solution show ligand fluctuations on the NMR time scale. For the mixed complex a crown ether rotation occurs. Additionally, a synchronous process between the movement of the macrocyclic ligand and the dissociation reaction of methanol from the metal ion is observed.

The Effect of Quinolyl Endgroups on Podand Fluctuations-1-DNMR and 2D-EXCSY-NMR of Co(II)-Complexes

Ligand fluctuations in complexes [Co(Kr5)]X2 (Kr 5 = 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane) with X = ClO4-, CF3SO3- can be detected by NMR spectroscopy above room temperature in inert solvents such as nitromethane. This unusually slow ligand movement is due to the strong coordination of the quinolyl end groups to the Co(II) ion as demonstrated through measurements with oligo-ethylene-glycols. In contrast to the 13C spectra, the 1H 2 D EXCSY NMR spectra reveal cross peaks which are due to a magnetisation exchange between the chemically non-equivalent protons in the -CH2- groups of the podand. This process is associated with a movement of the chain segments towards each other.

Sensor materials based on convex and concave chemistry-optical detection and mass sensitive devices

Based on the principles of convex and concave chemistry, sensor materials were developed for the detection of organic solvent vapors and ammonia. Species with pronounced electron donating properties are especially easy to detect with organic and inorganic cations. The resulting convex interactions permit the monitoring of ammonia by means of optical and resistive measurements. Concave chemistry was realized with liquid crystals, molecular holes, and channels. The incorporation of solvent vapors by cholesteric liquid crystals leads to absorbance changes by dichroic effects. Molecular holes and channels show an analogy to enzymes and are able to include guests which can be detected by mass-sensitive devices such as the quartz microbalance and the more sensitive surface-acoustic-wave oscillator.<<ETX>>

Ionic Sensor Layers on Microelectronic Structures for the Detection of Solvent Vapours

Several types of microelectronic devices such as interdigital structures, SAW-resonators, and ChemFETs were used for the development of chemical sensor systems for the detection of organic solvents and ammonia in the air and waste water. The chemically sensitive coatings are based on reversible equilibria in which hydrophobic ions are involved. An incorporation of solvent vapours leads to a change of the ion concentrations. A large variety of pollutants such as alcohols, ketones, esters, and even aromatic and halogenated hydrocarbons can be analyzed in this way.

[M(II)([15]Krone-5)(L)2 ]++ -Komplexe -der Einfluß des Kronenetherhohlraums auf die Mobilität der Liganden L / [M(II)([15]Crown-5)(L)2]++ Complexes - The Influence of the Crown Ether Cavity on the Mobility of the Ligands L

Abstract The mobility of coordinated methanol in the complex [Co(II)(Benzo[15]crown-5)(CH3OH)2]f + was studied in nitromethane. The methanol exchange mechanism tends to an associative nature with an increasing amount of methanol in the solutions as can be deduced from the activation entropy. All activation data can be combined in an isokinetic relationship which is also valid for the respective complex with the unsubstituted [15]crown-5 ether ligand

Konkurrierende Koordination von Kronenethern, Perchloratanionen und Lösungsmittelmolekülen am Co(II)-Ion — Eine Leitfähigkeits-und NMR-Studie in Nitromethan / Competitive Coordination of Crown Ethers, Perchlorate Anions and Solvent Molecules at Co(II)-Ions — A Conductivity and NMR Study on Nitromethane

Abstract The 1:1 complexes between Co(II) and the crown ethers dibenzo[24]crown-8, dibenzo[18]-crown-6 and [18]crown-6 show a molar conductivity in nitromethane which indicates coordination of even perchlorate anions. The substitution of this anion by solvent molecules can be monitored by conductometric titrations. This procedure reveals that dibenzo[24]crown-8 and [18]crown-6 is a potent five dentate ligand whereas dibenzo[18]crown-6 strongly coordinates only via three donor atoms. The mixed complexes with crown ether and methanol show strong outer-sphere associa-tion with the Perchlorate anions, which can be confirmed by investigations with [15]crown-5 complexes.