Natasha Trendafilova

Detecting the bonding type of dithiocarbamate ligands in their complexes as inferred from the asymmetric CS mode

Abstract The IR spectra of a number of dithiocarbamate (dtc) complexes (M(R 2 dtc) 2 , n = 2, M = Ni, Cu, Zn, Cd, Pb, Hg, Se, Te; n = 3, M = Cr, Fe, Co, As, Sb, Bi, R = Et, Pr n , Pr i , Bu n , Br i , as well as the laser Raman spectra of a few colourless compounds (M(Et 2 dtc) 2 M = Zn, Cd, Pb, Hg), have been recorded and discussed as to the validity of the Bonati-Ugo (BU) criterion for discerning the dtc bonding type from its ν as (CS) band ( ca. 1000 cm −1 ), By comparing these bands for dtc complexes containing different N-substituted ligands, their splittings can be proved to be due to interligand coupling of the CS ligand modes. Further comparison with X-ray diffraction data shows that the dtc ligands, irrespective of the host complex or the ligand bonding type, are at sites of C 1 symmetry, thus ruling out the possibility to detect the ligand bonding type from the solid state vibrational spectra. New evidence is presented that the RN modes are present in the 1000 cm −1 region, thus making it unsuitable for the determination of the ligand bonding type.

DFT-based molecular modeling and vibrational study of the La(III) complex of 3,3′-(benzylidene)bis(4-hydroxycoumarin)

AbstractMolecular modeling of the La(III) complex of 3,3′-(benzylidene)bis(4-hydroxycoumarin) (PhDC) was performed using density functional theory (DFT) methods at B3LYP/6-31G(d) and BP86/TZP levels. Both Stuttgart-Dresden effective core potential and ZORA approximation were applied to the La(III) center. The electron density distribution and the nucleophilic centers of the deprotonated ligand PhDC2- in a solvent environment were estimated on the basis of Hirshfeld atomic charges, electrostatic potential values at the nuclei, and Nalewajski-Mrozek bond orders. In accordance with the empirical formula La(PhDC)(OH)(H2O), a chain structure of the complex was simulated by means of two types of molecular fragment: (1) two La(III) cations bound to one PhDC2- ligand, and (2) two PhDC2- ligands bound to one La(III) cation. Different orientations of PhDC2-, OH- and H2O ligands in the La(III) complexes were investigated using 20 possible [La(PhDC2-)2(OH)(H2O)]2- fragments. Energy calculations predicted that the prism-like structure based on “tail-head” cis-LML2 type binding and stabilized via HO...HOH intramolecular hydrogen bonds is the most probable structure for the La(III) complex. The calculated vibrational spectrum of the lowest energy La(III) model fragment is in very good agreement with the experimental IR spectrum of the complex, supporting the suggested ligand binding mode to La(III) in a chain structure, namely, every PhDC2- interacts with two La(III) cations through both carbonylic and both hydroxylic oxygens, and every La(III) cation binds four oxygen atoms of two different PhDC2-. FigureLow energy prism-like model fragment, [La(PhDC2-)2(OH)(H2O)]2-, optimized at BP86/TZP level of theory

Intramolecular Charge-Transfer Excited-State Processes in 4-(N,N-Dimethylamino)benzonitrile: The Role of Twisting and the πσ* State.

The structural processes leading to dual fluorescence of 4-(dimethylamino)benzonitrile in the gas phase and in acetonitrile solvent were investigated using a combination of multireference configuration interaction (MRCI) and the second-order algebraic diagrammatic construction (ADC(2)) methods. Solvent effects were included on the basis of the conductor-like screening model. The MRCI method was used for computing the nonadiabatic interaction between the two lowest excited ππ* states (S2(La, CT) and S1(Lb, LE)) and the corresponding minimum on the crossing seam (MXS) whereas the ADC(2) calculations were dedicated to assessing the role of the πσ* state. The MXS structure was found to have a twisting angle of ∼50°. The branching space does not contain the twisting motion of the dimethylamino group and thus is not directly involved in the deactivation process from S2 to S1. Polar solvent effects are not found to have a significant influence on this situation. Applying Cs symmetry restrictions, the ADC(2) calculations show that CCN bending leads to a strong stabilization and to significant charge transfer (CT). Nevertheless, this structure is not a minimum but converts to the local excitation (LE) structure on releasing the symmetry constraint. These findings suggest that the main role in the dynamics is played by the nonadiabatic interaction of the LE and CT states and that the main source for the dual fluorescence is the twisted internal charge-transfer state in addition to the LE state.

Molecular structure and spectroscopic studies on novel complexes of coumarin-3-carboxylic acid with Ni(II), Co(II), Zn(II) and Mn(II) ions based on density functional theory.

Novel Ni(II), Co(II), Zn(II) and Mn(II) complexes of coumarin-3-carboxylic acid (HCCA) were studied at experimental and theoretical levels. The complexes were characterised by elemental analyses, FT-IR, (1)H NMR, (13)C NMR and UV-Vis spectroscopy and by magnetic susceptibility measurements. The binding modes of the ligand and the spin states of the metal complexes were established by means of molecular modelling of the complexes studied and calculation of their IR, NMR and absorption spectra at DFT(TDDFT)/B3LYP level. The experimental and calculated data verified high spin Ni(II), Co(II) and Mn(II) complexes and a bidentate binding through the carboxylic oxygen atoms (CCA2). The model calculations predicted pseudo octahedral trans-[M(CCA2)(2)(H(2)O)(2)] structures for the Zn(II), Ni(II) and Co(II) complexes and a binuclear [Mn(2)(CCA2)(4)(H(2)O)(2)] structure. Experimental and calculated (1)H, (13)C NMR, IR and UV-Vis data were used to distinguish the two possible bidentate binding modes (CCA1 and CCA2) as well as mononuclear and binuclear structures of the metal complexes.

Solvatochromic and ionochromic effects of Iron(II)bis(1,10-phenanthroline)dicyano: a theoretical study.

Solvatochromic and ionochromic effects of the iron(II)bis(1,10-phenanthroline)dicyano (Fe(phen)(2)(CN)(2)) complex were investigated by means of combined DFT/TDDFT calculations using the PBE and B3LYP functionals. Extended solvation models of Fe(phen)(2)(CN)(2) in acetonitrile and aqueous solution, as well as including interaction with Mg(2+), were constructed. The calculated vertical excitation energies reproduce well the observed solvatochromism in acetonitrile and aqueous solutions, the ionochromism in acetonitrile in the presence of Mg(2+), and the absence of ionochromic effect in aqueous solution. The vertical excitation energies and the nature of the transitions were reliably predicted after inclusion of geometry relaxation upon aqueous micro- and global solvation and solvent polarization effect in the TDDFT calculations. The two intense UV-vis absorption bands occurring for all systems studied are interpreted as transitions from a hybrid Fe(II)(d)/cyano N(p) orbital to a phenanthroline pi* orbital rather than a pure metal-to-ligand-charge transfer (MLCT). The solvatochromic and ionochromic blue band shifts of Fe(phen)(2)(CN)(2) were explained with preferential stabilization of the highest occupied Fe(II)(d)/cyano N(p) orbitals as a result of specific interactions with water solvent molecules or Mg(2+) ions in solution. Such interactions occur through the CN(-) groups in the complex, and they have a decisive role for the observed blue shifts of UV-vis absorption bands.

Lanthanide and transition metal complexes of bioactive coumarins: Molecular modeling and spectroscopic studies

The present paper summarizes theoretical and spectroscopic investigations on a series of active coumarins and their lanthanide and transition metal complexes with application in medicine and pharmacy. Molecular modeling as well as IR, Raman, NMR and electronic spectral simulations at different levels of theory were performed to obtain important molecular descriptors: total energy, formation energy, binding energy, stability, conformations, structural parameters, electron density distribution, molecular electrostatic potential, Fukui functions, atomic charges, and reactive indexes. The computations are performed both in gas phase and in solution with consideration of the solvent effect on the molecular structural and energetic parameters. The investigations have shown that the advanced computational methods are reliable for prediction of the metal-coumarin binding mode, electron density distribution, thermodynamic properties as well as the strength and nature of the metal-coumarin interaction (not experimentally accessible) and correctly interpret the experimental spectroscopic data. Known results from biological tests for cytotoxic, antimicrobial, anti-fungal, spasmolytic and anti-HIV activities on the studied metal complexes are reported and discussed.

Molecular mechanical and quantum chemical study on the species involved in the hydrolysis of cis-diamminedichloroplatinum(II) and substituted bis(ethylenediamine)dichloroplatinum(II) complexes Part I. Reactants and products

Cisplatin and its substituted ethylenediamine derivatives, cis-PtCl2(R2en) (en=ethylenediamine, R=H, Ph (phenyl), 2-, 3- and 4-PhOH) have been studied with respect to the first step of their hydrolysis reaction. The geometry of the reactants and products was determined by molecular mechanics (MM). The MM optimized structures were used to calculate by the extended Huckel method the charge distribution and relative electronic energies. The MM and EH calculations were carried out with different ligand conformations. Due to increased non-bonded repulsion, with increasing ligand buikiness, the square planar arrangement is the preferred geometry also by the MM results. This additional (to the electronic) stabilization of the square planar arrangement around Pt(II) is unfavorable for the aquation process. The thermodynamic stabilities correlate with the rate of hydrolysis of meso-, (+)- and (−)-[1,2-bis(2-hydroxyphenyl)ethylenediamine]dichloroplatinum(II) (3-PtCl2). The slower rate of hydrolysis of the meso diastereoisomer as compared with that of the d, l species of 3-PtCl2 is explained by the presence of a 5th Pt-O contact in the meso diastereoisomer which hinders the entrance of the water molecule and makes the hydrolysis slower.

Molecular structures and infrared spectra of five-coordinate copper(II) complexes including one tridentate diethylenetriamine ligand

Abstract The molecular structures of five-coordinate Cu(dien)L2 (dien = diethylenetriamine; LNO3−, Br−, Cl−, ClO4−) have been examined by molecular mechanics (MM2). All compounds have dien in the meridional (mer) position and k,k′ (symmetric) conformation. The dien position, however, differs from the rigorous mer form as to the NCuN (N-terminal) being less than the expected 180°. The IR bands of these compounds in the 50–4000 cm−1 range have been recorded in the solid state and assigned on the basis of normal coordinate analysis (potential energy distribution) of the dien molecule. The experimental IR spectra of the studied compounds were compared with frequencies calculated by the MOPAC 6.0 package assuming dien to be coordinated in fac and mer positions. The comparison shows that in fact the dien ligand in the studied compounds should be midway between the fac and mer positions.

DFT study of hydrogen-bonded dimers and tetramer of glyoxilic acid oxime

Abstract DFT study of hydrogen-bonded dimers and tetramer of glyoxilic acid oxime (GAO) has been performed at B3LYP/6-31G* and B3LYP/6-31++G** levels of the theory. The N⋯HO and O⋯HO hydrogen bondings in the self-assembling structures studied have been estimated from intermolecular distances, enthalpy of stabilization, hydrogen-bonding energies and AIM electron density at the hydrogen bond critical points. The calculated hydrogen-bonding energies of various GAO dimers suggested a cooperative interaction in the cyclic dimers and tetramer. The comparative study of chain aggregate with both head-to-head and tail-to-tail bondings and chain aggregate only with head-to-tail bondings, showed that the latter is enthalpically preferred in agreement with the crystal structure of GAO. Harmonic frequencies for the monomer, five dimers and tetramer have been calculated and discussed as to the changes in the most sensitive to the complexation vibrations and as to the strengths of the O⋯HO and N⋯HO hydrogen bondings. Vibrational analysis at B3LYP/6-31G* level confirmed the suggestion for a cooperativity in the cyclic H-bonded complexes. Natural population analysis was performed to predict electrostatic interactions in the cyclic H-bonded complexes. The π-delocalization was estimated on the basis of the calculated AIM ellipticity.

IR and Raman study of Pt(II) and Pd(II) complexes of amino substituted phosphine oxides: Normal coordinate analysis

Abstract IR and Raman spectra of Pt(dapo) 2 Cl 2 and Pd(dapo) 2 Cl 2 (dapo=dimethyl(aminomethyl)phosphine oxide) have been measured in the 200–4000 cm −1 frequency range. Both the IR and Raman spectra show that dimethyl(aminomethyl)phosphine oxide ligands are monodentate coordinate. The results from the normal coordinate analysis calculations confirm the monodentate coordination of the ligands in agreement with some literature data. For Pd(dapo) 2 Cl 2 complex the possibility for bidentate coordination of one dapo ligand is also considered.