Petr Milko

The C-O stretch as an unprecedently large spectral marker for the electron transfer between Copper(II) and a phenolate anion.

An unprecedented red shift of more than 200 cm(-1) in the vibrational frequency of the C-O bond in the [Cu(PhO)Ln]+ complex (PhO = phenoxy), dependent on the number n of additional ligands L, is reported. Upon change of n from 1 to 2, the spin density is shifted from the aromatic ring to the oxygen and copper atoms, which is reflected in the bond order and thus vibrational frequency of the C-O bond.

Comparative study of mono- and dinuclear complexes of late 3d-metal chlorides with N,N-dimethylformamide in the gas phase.

Mono- and binuclear complexes of N,N-dimethylformamide (DMF) with chlorides of the divalent, late 3d metals M = Co, Ni, Cu, and Zn are investigated by means of electrospray ionization (ESI). Specifically, ESI leads to monocations of the type [(DMF)(n)MCl](+) and [(DMF)(n)M(2)Cl(3)](+), of which the species with n = 2 and 3 were selected for in-depth studies. The latter include collision-induced dissociation experiments, gas-phase infrared spectroscopy, and calculations using density functional theory. The mononuclear complexes [(DMF)(n)MCl](+) almost exclusively lose neutral DMF upon collisional activation with the notable exception of the copper complex, for which also a reduction from Cu(II) to Cu(I) concomitant with the release of atomic chlorine is observed. For the dinuclear clusters, there exists a competition between loss of a DMF ligand and cluster degradation via loss of neutral MCl(2) with decreasing cluster stability from cobalt to zinc. For the specific case of [(DMF)(n)ZnCl](+) and [(DMF)(n)Zn(2)Cl(3)](+), ion-mobility mass spectrometry indicates the existence of two isomeric cluster ions in the case of [(DMF)(2)Zn(2)Cl(3)](+) which corroborates parallel theoretical predictions.

Formation of Organoxenon Dications in the Reactions of Xenon with Dications Derived from Toluene

The bimolecular reactivity of xenon with C(7)H(n)(2+) dications (n=6-8), generated by double ionization of toluene using both electrons and synchrotron radiation, is studied by means of a triple-quadrupole mass spectrometer. Under these experimental conditions, the formation of the organoxenon dications C(7)H(6)Xe(2+) and C(7)H(7)Xe(2+) is observed to occur by termolecular collisional stabilization. Detailed experimental and theoretical studies show that the formation of C(7)H(6)Xe(2+)+H(2) from doubly ionized toluene (C(7)H(8)(2+)) and xenon occurs as a slightly endothermic, direct substitution of dihydrogen by the rare gas with an expansion to a seven-membered ring structure as the crucial step. For the most stable isomer of C(7)H(6)Xe(2+), an adduct between the cycloheptatrienyldiene dication and xenon, the computed binding energy of 1.36 eV reaches the strength of (weak) covalent bonds. Accordingly, electrophiles derived from carbenes might be particularly promising candidates in the search for new rare-gas compounds.

Redox processes in the iron(III)/9,10-phenanthraquinone system.

With the use of the model complexes [(PQ)FeCl(CH(3)O)](+), [(phen)FeCl(CH(3)O)](+), and [(PQ)(phen)FeCl(CH(3)O)](+), where PQ is 9,10-phenanthraquinone and phen is 1,10-phenanthroline, the reactivity of phenanthraquinone in complexes with iron(III) is investigated. It is shown that 9,10-phenanthraquinone takes part in redox processes occurring at iron and thereby allows the oxidation of methanolate to formaldehyde. The oxidation is driven by the reduction of iron(III) to iron(II) and 9,10-phenanthraquinone to the semihydroquinone radical or semiquinolate, if the hydrogen atom is transferred from methanolate to chlorine rather than PQ. 1,10-Phenanthroline, on the other hand, acts as an innocent ligand, and the [(phen)FeCl(CH(3)O)](+) complex shows a typical two-state reactivity. The reactivity of [(PQ)(phen)FeCl(CH(3)O)](+) reveals that the hexacoordination of iron energetically facilitates the oxidation of methanolate, and therefore it is proposed that, in the presence of suitable reductants, the mixture of iron(III) and 9,10-phenanthraquinone can lead to the generation of the semihydroquinone radicals, species responsible for the toxicity of PQ. The fragmentation of [(PQ)(phen)FeCl(CH(3)O)](+) also demonstrates a strong binding of phen toward iron(III), which is a reason for using phen as an iron chelator in biochemistry. The structures and reactivities of the complexes are investigated by means of mass spectrometry, infrared multiphoton dissociation spectra, and density functional theory calculations.