Annemarie Kuhn

Dithizone and its oxidation products: a DFT, spectroscopic, and X-ray structural study.

Air oxidation of ortho-fluorodithizone resulted in the first X-ray resolved structure of a disulfide of dithizone, validating the last outstanding X-ray structure in the oxidation of dithizone, H(2)Dz, which proceeds via the disulfide, (HDz)(2), to the deprotonated dehydrodithizone tetrazolium salt, Dz. Density functional theory calculations established the energetically favored tautomers along the entire pathway; in gas phase and in polar as well as nonpolar solvent environments. DFT calculations using the classic pure OLYP and PW91, or the newer B3LYP hybrid functional, as well as MP2 calculations, yielded the lowest energy structures in agreement with corresponding experimental X-ray crystallographic results. Atomic charge distribution patterns confirmed the cyclization reaction pathway and crystal packing of Dz. Time dependent DFT for the first time gave satisfactory explanation for the solvatochromic properties of dithizone, pointing to different tautomers that give rise to the observed orange color in methanol and green in dichloromethane. Concentratochromism of H(2)Dz was observed in methanol. Computed orbitals and oscillators are in close agreement with UV-visible spectroscopic experimental results.

Low-temperature redetermination of 1,3-bis-(penta-fluoro-phen-yl)triazene.

The crystal structure of the title compound, (C6F5)2N3H, is stabilized by N—H⋯N hydrogen bonding, forming centrosymmetric dimers organized in a herringbone motif. Important geometrical parameters are N—N = 1.272 (2) and 1.330 (2) Å and N—N—N = 112.56 (15)°. The dihedral angle between C6F5 groups is 21.22 (9)°. The room temperature structure was reported by Leman et al. (1993). Inorg. Chem. 32, 4324–4336]. In the current determination, the data were collected to a higher θ angle, resulting in higher precision for the C—C bond lengths(0.001–0.005 versus 0.003 Å).

Orbital control over the metal vs. ligand reduction in a series of neutral and cationic bis(cyclopentadienyl) Ti(IV) complexes

Quantum chemistry calculations showed that the first reduction, as experimentally observed by cyclic voltammetry for a series of neutral and cationic functionalised bis(cyclopentadienyl) titanium(IV) derivatives, is metal based, involving the chemically and electrochemically reversible TiIV/TiIII redox couple. The second reduction peak observed is chemically and electrochemically irreversible. For the neutral [Cp2TiIV(ligand)n] (n = 1 or 2) complexes (Cp = cyclopentadienyl), the second irreversible reduction peak is metal-based, while for the cationic [Cp2TiIV(ligand)]+ complexes, the second irreversible reduction peak involves ligand reduction, leading to a TiIII species coupled to a ligand radical. The electronic properties of the substituents directly influence electron density at the reduction centre when π-interactions between the electro-active centre and the substituent groups exist in the lowest unoccupied molecular orbital (LUMO) of the complexes. In this case, a number of relationships between the electronic properties of the substituents and the reduction potentials have been affirmed, yielding linear relationship between experimentally measured reduction potentials and DFT calculated energies (energy of the LUMO, electron affinity, Mulliken electronegativity and global electrophilicity index). However, the substituent effect is ill defined when the LUMO is highly localised without π-interaction between the electro-active centre and the substituents.