[FeIII(tmdta)]--twist-boat/half-chair conformer ratio reliably deduced from DFT-calculated Raman spectra.

The equilibrium between the twist-boat (tb) and half-chair (hc) conformers of the central diamine chelate ring of [Fe(III)(tmdta)]- in solids and aqueous solution has been studied by Raman spectroscopy, supported by calculated Raman spectra using Density Functional Theory.

Structure of sodium bis(N-methyl-iminodiacetato)iron(III): trans-meridional N-coordination in the solid state and in solution.

The results of a detailed solid state and solution structural study of the Fe(III) bis-mida complex [Fe(III)(mida)(2)]- (mida = N-methyl-iminodiacetate) are reported. The structure of the sodium salt Na[Fe(mida)2][NaClO4]2.3H2O (1) was determined by single-crystal X-ray analysis. The complex anion in 1 contains a six-coordinate Fe(III) centre bound to two tridentate mida ligands arranged in the meridional configuration, and the mer Fe(III)N2O4 chromophore shows a high degree of distortion from regular octahedral symmetry. Raman- and UV/VIS/NIR spectroscopic measurements showed that no gross changes take place in the Fe(III) coordination sphere upon redissolution in water. Quantum chemical calculations of all three possible configurations of the [Fe(mida)2]- complex ion in the gas phase support the finding that the mer isomer is more stable than the u-fac (cis) and s-fac (trans) isomers. Redox potential measurements of the Fe(III/II)(mida) couple in dependence of pH led to the following values for the equilibrium contants: log beta(III)(101) = 11.98 +/- 0.05, log beta(III)(102) = 20.49 +/- 0.01, pK(III)(a1 OH) = 7.81; log beta(II)(101) = 6.17 +/- 0.01, log beta(II)(102) = 11.39 +/- 0.01.

Ion mobility spectrometric investigation of aromatic cations in the gas phase.

In this work, ion mobility (IM) spectra of more than 50 aromatic compounds were recorded with a laser-based IM spectrometer at atmospheric pressure. IM spectra of PAH in the laser desorption experiment show a high complexity resulting from the occurrence of monomeric, dimeric, and oligomeric cluster ions. The mobilities of all compounds were determined in helium as drift gas. This allows the calculation of the diffusion cross sections (Omega(calc)) on the basis of the exact hard sphere scattering model and their comparison with the experimentally determined diffusion cross sections (Omega(exp)). Extended Omega(exp)/Omega(calc) and Omega(exp)/mass correlations were performed in order to gain insight into conformational properties of cationic alkyl benzenes and internal rotation of phenyl rings in aromatic ions. This is demonstrated with some examples, such as the evaluation of the dihedral angle of the ions of 9,10-diphenylanthracene, o- and m-terphenyl, and 1,2,3- and 1,3,5-triphenylbenzene. Furthermore, sandwich and T-structures of dimeric PAH cations are discussed. The analysis was extended to oligomeric ions with up to nine monomer units. Experimental evidence is presented suggesting the formation of pi-stacks with a transition toward modified pi-stacks with increasing cluster size. The distance between monomeric units in dimeric and oligomeric ions was obtained.