Karel G. von Eschwege

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.

Ultrafast photochemistry of dithizonatophenylmercury(II)

The initial photochromic reaction of dithizonatophenylmercury(II) in solution was investigated by femtosecond transient absorption spectroscopy. Ultrafast excitation within less than 100 fs caused a radiationless photoreaction with a time constant of 1.5 ps, which is interpreted as C=N isomerization through a conical intersection. The orthogonally twisted intermediate state was observed through its excited-state absorption. Bifurcation along pathways towards the ground states of the orange cis and blue trans configurations occurs below the funnel of the conical intersection. The photochromism of the title compound in a very polar solvent such as methanol is observed for the first time.

[1,5-Bis(4-fluoro-phen-yl)thio-carbazo-nato-κN,S]phenyl-mercury(II) dichloro-methane hemisolvate.

In the title compound, [Hg(C6H5)(C13H9F2N4S)]·0.5CH2Cl2, the Hg(C6H5) units are twisted out of the planes of the thiocarbazonate ligands by 61.49 (10) and 67.79 (11)° in the two complex molecules comprising the asymmetric unit. Important geometrical parameters include Hg—C = 2.079 (4) and 2.087 (4) Å, Hg—S = 2.3869 (10) and 2.3889 (11) Å, and C—Hg—S = 166.42 (12) and 168.09 (13)°. Weak intramolecular Hg—N bonding interactions of 2.589 (4) and 2.626 (4) Å are observed. In the crystal, C—H⋯Cl, C—H⋯F, C—H⋯N, C—H⋯π and π–π [centroid–centroid distances = 3.648 (3) and 3.641 (3) Å] interactions, create parallel planes along [101].

Synthesis and Kinetics of Sterically Altered Photochromic Dithizonatomercury Complexes

Following a previous study where 12 electronically altered dithizones were synthesized, here we report on attempts to synthesize 26 dithizones. The purpose was to explore the boundaries within which dithizones may be synthesized, explore spectral tuning possibilities, and investigate steric effects on the photochromic reaction of its mercury complexes. Contrary to expectation, large substituents like phenoxy groups increased the rate of the photochromic back-reaction. In the series H-, 2-CH3-, 4-CH3-, 3,4-(CH3)2-, 2-OC6H5-, and 4-OC6H5-dithizonatophenylmercury(II), the lowest rate of 0.0004 s(-1) was measured for the 2-CH3 complex, while the rate for the 2-OC6H5 derivative was 20 times higher. A solvent study revealed a direct relationship between dipole moment and the rate of the back-reaction, while the relationship between temperature and rate is exponential, with t1/2 = 2 min 8 s for the 4-phenoxy complex. The crystal structures of two dithizone precursors, 2-phenoxy- and 4-phenoxynitroformazan, are reported.

1-(2-Meth­oxy­phen­yl)-2-{[2-(2-meth­oxy­phen­yl)hydrazinyl­idene](nitro)­meth­yl}diazene

In the title compound, C15H15N5O4, a nitroformazan derivative, the formazan unit is essentially planar with an r.m.s. deviation of 0.0204 (6) Å and adopts a closed syn,s-cis configuration with an intramolecular N—H⋯N hydrogen bond. The formazan plane makes dihedral angles of 4.32 (5) and 24.35 (5)° with the benzene rings. The dihedral angle between the formazan plane and the nitro group is 12.58 (8)°. In the crystal, C—H⋯O interactions connect the molecules into an inversion dimer.

1,5-Bis(2-methyl-phen-yl)-3-nitro-formazan.

In the title compound, C15H15N5O2, the nitro O atoms are disordered over two sets of sites with an occupancy ratio of 0.75 (4):0.25 (4). Amine–imine tautomerism is observed in the formazan group. This was evident from the similar C—N bond distances in the formazan [1.319 (2) and 1.332 (3) Å], as well as the distribution of the imine proton in the Fourier difference map which refined to a 0.53 (3):0.47 (3) ratio. C—H⋯O and π–π interactions [centroid–centroid distances = 3.4813 (1) and 3.3976 (1) Å] are observed in the crystal packing.

[1,5-Bis(2-meth-oxy-phen-yl)thio-carbazo-nato-κN,S]phenyl-mercury(II).

The title compound, [Hg(C6H5)(C15H15N4O2S)], shows the metal–phenyl moiety coordinated out of plane with the thiocarbazonate ligand by 43.84 (6)°. Important geometrical parameters include Hg—S = 2.3653 (10) Å, Hg—C = 2.058 (4) Å and S—Hg—C = 179.06 (11)°. There is a weak coordination of an N atom of the ligand to Hg [Hg—N = 2.725 (3) Å]. S⋯Hg interactions[3.2928 (10) Å] form chains along [001], stabilizing the crystal structure.

2,3-Bis(3-fluoro-phen-yl)tetra-zolium-5-thiol-ate.

The zwitterionic title compound, C13H8F2N4S, is situated on a twofold rotation axis running along the C—S [1.691 (2) Å] single bond. The phenylene ring is twisted out of the tetrazolium plane by 42.18 (7)°. Relatively short distances [3.7572 (9) and 4.0625 (6) Å] between the centroids of the phenylene and tetrazolium rings of neighbouring molecules suggest π–π interactions. The crystal under investigation was a non-merohedral twin, with a 33% twin component.

Synthesis and structure of dithizonato complexes of antimony(III), copper(II) and tin(IV)

Abstract In view of the important role of dithizone in trace metal analyses, new structural aspects and approaches used to probe metal complexes of dithizone are of interest. Three X-ray diffraction structures are reported, dichloridobis(dithizonato)tin(IV), dichlorido(dithizonato)antimony(III), and bis(dithizonato)copper(II). During synthesis of the tin complex, auto-oxidation of SnIICl2 to SnIV occurred without chloride liberation. The SbIII complex revealed a unique distorted see-saw geometry which is, as for the other complexes, predicted by DFT molecular orbital calculations. The computed products of the lowest energy reactions are in agreement with experimentally obtained reaction products, which, together with molecular orbital renderings serve as a tool toward prediction of modes of coordination in these complexes. The S–M–N bond angle in the five-membered coordination ring shows a linear relationship with the corresponding metal ionic radii.

(1,5-Diphenyl­thio­carbazonato-κS)trimethyl­tin(IV)

In the title compound, [Sn(C13H11N4S)(CH3)3], the SnIV atom is coordinated by an S atom from the 1,5-diphenylthiocarbazonato (L) ligand [Sn—S 2.4710 (6) Å] and by three methyl groups [Sn—C 2.123 (3)–2.130 (2) Å] in a distorted tetrahedral geometry. The aromatic rings of the L ligand form a dihedral angle of 2.1 (1)°.