Marek Fronc

Electronic structure of the nickel(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylprolinamide and glycine

The experimental charge density of the Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylprolinamide and glycine was derived from high-resolution single-crystal X-ray diffraction data (lambda = 0.5604 A) at low temperature (100 K) with synchrotron radiation at the beamline F1 using a CCD area detector. The central Ni atom is pseudo-square-planar coordinated by three N atoms [1.9414 (3), 1.8559 (3) and 1.8533 (3) A] and by one O atom [1.8620 (4) A]. The N(1) atom is 0.359 A above the plane defined by the atoms Ni(1), N(2) and N(3). The d-orbital population analysis reveals an oxidation state for the Ni atom of +2 with the configuration d(8) and a hole mainly in the d(x(2)-y(2)) orbital, located in the plane of the four ligating atoms. The prochiral reaction centre was examined by topological analysis.

Preparation and Spectroscopic, Magnetic, and Electrochemical Studies of Mono-/Biradical TEMPO Derivatives

A comparison set of mono-/biradical TEMPO derivatives was prepared, novel compounds were fully characterized, and their physicochemical properties were determined. Cyclic voltammetry revealed reversible redox behavior for all studied nitroxides. Moreover, the electron-withdrawing substituents increased the oxidation potential of the respective nitroxides in comparison to electron-donating groups. While EPR spectra of monoradicals in dichloromethane at 295 K reveal the expected three-line signal, spectra of biradicals show more complex features. DFT and MP2 calculations indicate that the EPR splitting pattern of dinitroxide 7 could be explained by its interactions with solvent molecules. In the solid state, mononitroxides 4 and 5 behave as a Heisenberg antiferromagnetic chain, whereas dinitroxides 6-8 are almost isolated paramagnetic diradicals coupled in an antiferromagnetic manner.

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism.

Summary Activated enol ethers derived from esters or the dinitrile of malonic acid, or from pentane-2,4-dione were treated with hydrazine hydrate. The structures of the obtained products – pyrazoles 5 – were studied with a focus on tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arrangement of the formally equivalent subunits.

Conformational, spectroscopic, and molecular dynamics DFT study of precursors for new potential antibacterial fluoroquinolone drugs.

Biological activity, functionality, and synthesis of (fluoro)quinolones is closely related to their precursors (for instance 3-fluoroanilinoethylene derivatives) (i.e., their functional groups, conformational behavior, and/or electronic structure). Herein, the theoretical study of 3-fluoroanilinoethylene derivatives is presented. Impact of substituents (acetyl, methyl ester, and ethyl ester) on the conformational analysis and the spectral behavior is investigated. The B3LYP/6-311++G** computational protocol is utilized. It is found that the intramolecular hydrogen bond N-H···O is responsible for the energetic preference of anti (a) conformer (anti position of 3-fluoroanilino group with respect to the C═C double bond). The Boltzmann ratios of the conformers are related to the differences of the particular dipole moments and/or their dependence on the solvent polarity. The studied acetyl, ethyl ester, and methyl ester substituted fluoroquinolone precursors prefer in the solvent either EZa, ZZa, or both conformers equally, respectively. In order to understand the degree of freedom of rotation of the trans ethyl ester group, B3LYP/6-311G** molecular dynamic simulations were carried out. Vibrational frequencies, electron transitions, as well as NMR spectra are analyzed with respect to conformational analysis, including the effect of the substituent. X-ray structures of the precursors are presented and compared with the results of the conformational analysis.

Charge-density study of [CuI/II(bite)]+/2+ (bite = biphenyldiimine dithioether) complexes

For the presented study two analogous coordination compounds of the copper, [Cu(bite)](BF4) and, [Cu(bite)](BF4)2 (bite = biphenyldiimine dithioether, C28H22N2S2) with copper in oxidation state +I and +II were selected [1]. In the originally work both molecules were synthesized as small-molecule analogue to study properties of the active centre of cuproproteins. In this study we would like to present electron density study of these compounds for the data obtained on a new diffractometer in comparison to the results obtained for the same complexes in the past with the use of Oxford Geminy R diffractometer. Experiments were performed by means of Stoe STADIVARI diffractometer equipped with a Dectris Pilatus 3R 300K and a Incoatec IμS Ag High Brilliance microfocus source (Ag-Kα, λ = 0.56083 Å) at 100 K using a nitrogen gas open-flow cooler Cobra Oxford Cryosystems. Data reduction was processed using X-Area [2]. Multipole refinement and the topological analysis were performed using XD program package. Electronic structure and the results of AIM analysis will be discussed. [1] Flanagan, S. et. al. (1997) J. Am. Chem. Soc., 119, 8857-8868. [2] STOE & Cie GmbH (2016). X-Area 1.76, software package for collecting single-crystal data on STOE area-detector diffractometers, for image processing, scaling reflection intensities and for outlier rejection; Darmstadt, Germany.

Charge Density Study of two Ni(III) and Ni(II) complexes

Experimental charge density of two nickel complexes with oxidation state +3 and +2 of composition (CH3(Ph)3P)+[Ni(bdtCl2)2]-, C31H22Cl4S4P1Ni1 [I] and (CH3(Ph)3P)+[Ni(bdtCl2)2]dimethylsulfoxide solvate, C25H20Cl2S2P1Ni0.5; C2H6SO [II], (bdtCl2 = 3,6dichloro-1,2-benzenedithiole ), has been studied. The coordination of Ni central atom by bdtCl2 as a non-innocent ligand gives rise to interesting electronic properties. Compounds I and II crystalize in a monoclinic space groups P 21/c and II in P 21/n, respectively. Their coordination is square-planar with the chromophore [NiS4]. Obvious differences for interatomic distances in metallocycles were found. For I in Ni1-S1-C1-C6-S2-Ni1 there are bond lengths of 2.1534(1), 1.7375(5), 1.4144(8), 1.7327(5), 2.1432(1) Å; and in Ni2-S3C7-C12-S4-Ni2 there are bond lengths of 2.1453(1), 1.7390(5), 1.4133(7), 1.7387(5), 2.1523(1) Å. For II in Ni1-S1-C1-C6-S2-Ni1 there are bond lengths of 2.1776(2), 1.7437(8), 1.4169(11), 1.7431(8), 2.1663(2) Å. Significantly longer distances for II are in good agreement with the lower oxidation state of central atom. Very accurate data for I an II complexes were obtained with Oxford Diffraction CCD GEMINI R diffractometer at 100K. Multipolar refinement and consecutive topological analysis was performed using XD package. Differences in distribution of electron density in both complexes will be disscussed and compared with quantum-chemical calculations at BP86/VTZP level of theory [1]. This work has been supported by Slovak Grant Agency APVV and VEGA (APVV-0202-10 and 1/0679/11).

3-(2-Heteroaryl)-pyrazolotetrazoles – a subunits for losartan-like structures

Abstract A modification of biphenylyltetrazole moiety of Losartan (A) by 3-(2-heteroaryl)-pyrazolotetrazole (B) is described. Ketone semicarbazones react with two moles of phosphorus oxychloride-dimethylformamide with the formation of 3-substituted pyrazol-4-carbaldehydes. The transformations of 3-substituted pyrazole-4- carboxaldehydes to 3-substituted pyrazole-4-nitriles were carried out by reaction of hydroxylamine in DMFA. The prepared cyano pyrazoles were converted to tetrazoles by heating with trimethylsilylazide and dibuthyltinoxide in toluene.

Pseudo‐merohedrally twinned tetra­kis­(1H‐imidazole‐κN3)bis­(N‐nitro­cyanamidato‐κN)copper(II)

Crystals of the title complex, [Cu(CN3O2)2(C3H4N2)4], the structure of which has been determined by single-crystal X-ray diffraction at 304 K, appear to be pseudo-merohedrally twinned. Transformation to a monoclinic C-centred cell was necessary in order to derive the twin law. Twin refinement in a triclinic unit cell significantly reduced the R value. The asymmetric unit of the triclinic cell consists of one molecule in a general position and two half entities with the Cu atom on a centre of inversion. The coordination of the Cu atom is quasi-octahedral, with four imidazole N-atom donors in the equatorial plane and two cyano N atoms from the N-nitrocyanamidate anion in axial positions. Owing to symmetry in the centrosymmetric molecules, the trans imidazole ligands are parallel, while those in the non-centrosymmetric molecule make angles of 22.8 (2) and 77.9 (2) degrees .

Pseudo-merohedrally twinned tetrakis(1H-imidazole-kappaN3)bis(N-nitrocyanamidato-kappaN)copper(II).

Crystals of the title complex, [Cu(CN3O2)2(C3H4N2)4], the structure of which has been determined by single-crystal X-ray diffraction at 304 K, appear to be pseudo-merohedrally twinned. Transformation to a monoclinic C-centred cell was necessary in order to derive the twin law. Twin refinement in a triclinic unit cell significantly reduced the R value. The asymmetric unit of the triclinic cell consists of one molecule in a general position and two half entities with the Cu atom on a centre of inversion. The coordination of the Cu atom is quasi-octahedral, with four imidazole N-atom donors in the equatorial plane and two cyano N atoms from the N-nitrocyanamidate anion in axial positions. Owing to symmetry in the centrosymmetric molecules, the trans imidazole ligands are parallel, while those in the non-centrosymmetric molecule make angles of 22.8 (2) and 77.9 (2) degrees .

Charge density studies of [Cu(bite)](BF4)

Charge density studies of [Cu(bite)](BF4) and [Cu(bite)](BF4)2 [1], (where bite = biphenyldiimino dithioether, C28H22N2S2) is undertaken in order to contribute to the understanding of the oxidationreduction process in “blue-protein” model compounds. Cu(I) in [Cu(bite)](BF 4) is tetrahedrally coordinated by two sulphur and two nitrogen atoms comparing to square-planar or semi-octahedral (Cu-F ≈ 2.546 Å) coordination in the case of Cu(II) in [Cu(bite)](BF 4)2 . The oxidation-reduction process in electron transfer reactions of these compounds is as a gated electron transfer reaction [2,3]. Small structural changes take place in the geometry of “rigid” Cu(I) polyhedron, as “plastic” Cu(II) coordination polyhedron could easily fit the requirements of neighbouring donating atoms. Gating phenomenon is important in two distinguished manners: 1) gating might serve to impede undesirable back-reactions, 2) conformational gating might have a regulatory role to provide absolute control of the rate of electron-transfer reactions.