Synthesis and Characterization of Homoleptic and Heteroleptic Cobalt, Nickel, Copper, Zinc and Cadmium Compounds with the 2-(Tosylamino)-N-[2-(tosylamino)benzylidene]aniline Ligand

The electrochemical oxidation of anodic metal (cobalt, nickel, copper, zinc and cadmium) in an acetonitrile solution of the Schiff-base ligand 2-(tosylamino)-N-[2-(tosylamino)-benzylidene] aniline (H(2)L) afforded the homoleptic compounds [ML]. The addition of 1,1-diphenylphosphanylmethane (dppm), 2,2`-bipyridine (bipy) or 1,10-phenanthroline (phen) to the electrolytic phase gave the heteroleptic complexes [NiL(dppm)], [ML(bipy)] and [ML(phen)]. The crystal structures of H(2)L (1), [NiL] (2), [CuL] (3), [NiL(dppm)] (4), [CoL(phen)] (5), [CuL(bipy)] (6) and [Zn(Lphen)] (7) were determined by X-ray diffraction. The homoleptic compounds [NiL] and [CuL] are mononuclear with a distorted square planar [MN(3)O] geometry with the Schiff base acting as a dianionic (N(amide)N(amide)N(imine)O(tosyl)) tetradentate ligand. Both compounds exhibit an unusual pi-pi stacking interaction be-tween a six-membered chelate ring containing the metal and a phenylic ring of the ligand. In the heteroleptic complex [NiL(dppm)], the nickel atom is in a distorted tetrahedral [NiN(3)P] environment defined by the imine, two amide nitrogen atoms of the L(2-) dianionic tridentate ligand and one of the phosphorus atoms of the dppm molecule. In the other heteroleptic complexes, [CoL(phen)], [CuL(bipy)] and [ZnL(phen)], the metal atom is in a five-coordinate environment defined by the imine, two amide nitrogen atoms of the dianionic tridentate ligand and the two bipyridine or phenanthroline nitrogen atoms. The compounds were characterized by microanalysis, IR and UV/Vis (Co, Ni and Cu complexes) spectroscopy, FAB mass spectrometry and (1)H NMR ([NiL] and Zn and Cd complexes) and EPR spectroscopy (Cu complexes).

Crystal structures and thermal behavior of alkaline earth tricyanomethanides

The alkaline earth tricyanomethanides Mg(tcm)(2) center dot 2H(2)O, Ca(tcm)(2), Sr(tcm)(2) - H2O and Ba(tcm)(2) center dot 2H(2)O were prepared from aqueous solutions of the respective chlorides and silver tricyanomethanide. Their IR spectra and thermal behavior are described. The crystal structures of Ca(tcm)(2) and Ba(tcm)(2) center dot 2H(2)O were determined by single crystal X-ray diffraction. The structure of Ca(tcm)(2) is of the type found for several transition metal tricyanomethanides [1], containing two independent interpenetrating networks. Ba(tcm)(2) center dot 2H(2)O has a unique crystal structure corresponding to a three-dimensional coordination polymer with nine fold coordinated Ba atoms connected by water molecules and tricyanomethanide anions.

Electronic Structure of the Ground and Low-Lying Electronic States of MoB and MoB(+)

Multiconfigurational second-order perturbation theory (CASSCF//CASPT2) and quadruple-zeta ANO-RCC basis sets were employed to investigate the ground and low-lying electronic states of MoB and MoB(+). Spectroscopic constants, potential energy curves, wavefunctions, Mulliken population analyses, and ionization energies are given. The ground state of MoB is of X(6)Pi symmetry (R(e) = 1.968 angstrom, omega(e) = 664 cm(-1), and mu = 2.7 D), giving rise to a Omega = 7/2 ground state after including spin-orbit coupling. For MoB(+), the ground state is computed to be of X(7)Sigma(+) symmetry (R(e) = 2.224 angstrom, omega(e) = 141 cm(-1), and mu = 1.2 D), with an adiabatic ionization energy of 7.19 eV and a vertical one of 7.53 eV. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 3362-3370, 2011

Characterization of the products of aniline peroxydisulfate oligo/polymerization in media with different pH by resonance Raman spectroscopy at 413.1 and 1064 nm excitation wavelengths

The pH-structure correlation of the products of aniline peroxydisulfate reaction was mainly investigated by resonance Raman spectroscopy. The reactions of aniline and ammonium peroxydisulfate were carried out in aqueous solutions of initial pH ranging from 4.9 to 13.2 and monomer/oxidant molar ratio of 4/1. For an initial pH of 4.9, the spectroscopic techniques showed that the emeraldine salt form of polyaniline (PANI-ES) is the main product, corroborating that the usual head-to-tail coupling mechanism is taking place. The resonance Raman spectra at 1064 nm exciting wavelength were useful to detect the emeraldine salt as a minor product for reactions at an initial pH of 5.3-11.5. The Raman spectra of the main product of the reaction at initial pH of 13.2 excited at 1064 and 413.1 nm showed new spectral features consistent with 1,4-Michael-type adducts of aniline monomers and 1,4-benzoquinone-monoimine unit. These compounds and their products of hydrolysis/oxidation are the predominant species for the reaction media of initial pH from 5.3 to 13.2. In order to get PANI with different nanoscale morphologies, a pH value of more than 0 or 1 was used in the aniline polymerization. The spectroscopic data obtained in this work reveal that head-to-tail coupling does not occur when aniline reacts at media pH higher than about 5. It is suggested that chemical structures of the products of aniline oxidation by an unusual mechanism are the driving force for the development of assorted morphologies. Copyright (C) 2011 John Wiley & Sons, Ltd.

Electronic structure and chemical bonding in W(2) molecule

The electronic structure of the lowest-lying electronic states of W(2) were investigated at the CASPT2 level. The ground state is a X(1)Sigma(+)(g) state, followed by the a(3)Delta(u), b(3)Sigma(+)(u) and A(1)Delta(u) electronic states. Seven low-lying Omega-states were computed: (1)0(g)(+), (2)3(u), (3)2(u), (4)1(u), (5)0(u)(-), (6)1(u), and (7)2(u), with the ground state corresponding to the (1)0(g)(+)(X(1)Sigma(+)(g)) state. Comparison with the other VIB transition metal group dimers indicates a common pattern of electronic structure and spectroscopic properties. (C) 2010 Elsevier B.V. All rights reserved.

Solvatochromic and lonochromic 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.

Identification of species formed after pyridine adsorption on iron, cobalt, nickel and silver electrodes by SERS and theoretical calculations

The adsorption of pyridine (py) on Fe, Co, Ni and Ag electrodes was studied using surface-enhanced Raman scattering (SERS) to gain insight into the nature of the adsorbed species. The wavenumber values and relative intensities of the SERS bands were compared to the normal Raman spectrum of the chemically prepared transition metal complexes. Raman spectra of model clusters M(4)(py) (four metal atoms bonded to one py moiety) and M(4)(alpha-pyridil) where M = Ag, Fe, Co or Ni were calculated by density functional theory (DFT) and used to interpret the experimental SERS results. The similarity of the calculated M(4)(py) spectra with the experimental SERS spectra confirm the molecular adsorption of py on the surface of the metallic electrodes. All these results exclude the formation of adsorbed alpha-pyridil species, as suggested previously. Copyright (C) 2009 John Wiley & Sons, Ltd.

Electronic Structure and Chemical Bonding in the Lowest Electronic States of TcN

Multiconfiguration second-order perturbation theory, with the inclusion of relativistic effects and spin-orbit Coupling, was employed to investigate the nature of the ground and low-lying Lambda-S and Omega states of the TcN molecule. Spectroscopic constants, effective bond order, and potential energy curves for 13 low-lying Lambda-S states and 5 Omega states are given, The computed ground state of TcN is of Omega = 3 symmetry (R(e) = 1.605 angstrom and omega(e) = 1085 cm(-1)), originating mainly from the (3)Delta Lambda-S ground state. This result is contrasted with the nature of the ground state for other VIIB transtion-metal mononitrides, including X(3)Sigma(-) symmetry for MnN and Omega = 0(+) symmetry for ReN, derived also from a X(3)Sigma(-) state.

Electronic structure and chemical bonding in the ground states of Tc(2) and Re(2)

Multiconfiguration second-order perturbation theory, including relativistic effects and spin-orbit coupling, has been employed to investigate the nature of the chemical bonding in the ground state of Tc(2) and Re(2). The Tc(2) ground state is found to be a 0(g)(+) state, with an effective bond order (EBO) of 4.4, and a dissociation energy of 3.25 eV. The Re(2) ground state is a 1(g) state, with EBO = 4.3. Almost degenerate to it, is a 0(g)(+) state (T(e) = 77 cm(-1)), with EBO = 4.1. Experimental evidence also indicates that the ground state is of 1(g) nature. The dissociation energy is computed to be 5.0 eV in agreement with an experimental estimate of 4 +/- 1 eV.

New Relativistic Atomic Natural Orbital Basis Sets for Lanthanide Atoms with Applications to the Ce Diatom and LuF3

New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are inluded as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.

Comparison of SERS performances of Co and Ni ultrathin films over silver to electrochemically activated Co and Ni electrodes

In this work, the surface-enhanced Raman scattering (SERS) spectra of pyridine (py) on thin films of Co and Ni electrodeposited on an Ag electrode activated by oxidation-reduction cycles (ORC) are presented. The SERS spectra from the thin films were compared to those of py on activated bare transition metal electrodes. It was verified that the SERS spectra of py on 3 monolayers (ML)-thick films of Ni and Co presented only bands assignable to the py adsorbed on transition metal surfaces. It was also observed that even for 50 ML-thick transition metal films, the py SERS intensity was ca. 40% of the intensity from the 3 ML-thick films. The relative intensities of the SERS bands depended on the thickness of the films, and for films thicker than 7 ML for Co and 9 ML for Ni they were very similar to those of the bare transition metal electrodes. The transition metal thin films over Ag activated electrodes presented SERS intensities 3 orders of magnitude higher than the ones from bare transition metal electrodes. These films are more suitable to study the adsorption of low Raman cross-section molecules than are ORC-activated transition metal electrodes.

Electronic Structure and Chemical Bonding in the Ground and Low-Lying Electronic States of Ta(2)

The electronic structure and chemical bonding of the ground and low-lying Lambda - S and Omega states of Ta(2) were investigated at the multiconfiguration second-order perturbation theory (CASSCF//CASPT2) level. The ground state of Ta(2) is computed to be a X(3)Sigma(-)(g) state (R(e) = 2.120 angstrom, omega(e) = 323 cm(-1), and D(e) = 4.65 eV), with two low-lying singlet states close to it (a(1) Sigma(+)(g) : T(e) = 409 cm(-1), R(e) = 2.131 angstrom, and omega(e) = 313 cm(-1); b(1) Gamma(g): T(e) = 1, 038 cm(-1), R(e) = 2.127 angstrom, and omega(e) = 316 cm(-1)). These electronic states are derived from the same electronic configuration: vertical bar 13 sigma(2)(g)14 sigma(2)(g)7 delta(2)(g)13 pi(4)(u)>. The effective bond order of the X(3) Sigma(-)(g) state is 4.52, which indicates that the Ta atoms are bound by a quintuple chemical bond. The a(1) Sigma(+)(g) state interacts strongly with the X(3)Sigma(-)(g) g ground state by a second-order spin-orbit interaction, giving rise to the (1)0(g)(+) (ground state) (dominated by the X(3)Sigma(-)(g) Lambda - S ground state) and (9)0(g)(+) (dominated by the a(1) Sigma(+)(g) Lambda - S state) Omega states. These results are in line with those reported for the group 5B homonuclear transition metal diatomics. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1306-1315, 2011

Triangular ruthenium acetate clusters containing the bis(pyridyl)propane ligand and their inclusion chemistry with beta-cyclodextrin

The triruthenium carboxylate cluster [Ru(3)O(OAc)(6)(py)(2)(bpp)](+) (OAc = acetate) containing the bridging 1,3-bis(4-pyridyl)propane (bpp) ligand, and its dimeric species [{Ru(3)O(OAc)(6)(py(2))}(2)(mu-bpp)](2+) were synthesized in order to investigate their inclusion compounds with beta-cyclodextrin (beta-CD). Characterization of the complexes was carried out based on spectroscopic, electrochemical and spectroelectrochemical techniques, while the formation of inclusion complexes was evaluated using (1)H NMR/NOESY spectroscopy. Since bpp is a flexible ligand, a DFT study was carried out in order to characterize its conformational isomers and their possible role in the host-guest chemistry with beta-CD. Instead of observing the formation of inclusion compounds with different stoichiometries, we observed the formation of 1:1 bpp/beta-CD compounds in which the bpp ligand assumes different conformations. The assembly of polymetallic rotaxane species was successfully demonstrated by monitoring the (1)H NMR spectra of the monomeric cluster species in the presence of aquapentacyanoferrate(II) ions and beta-CD.

A theoretical study of the binding and electronic spectrum of the Mo-2 molecule

Multiconfigurational SCF and second-order perturbation theory have been employed to study seven low-lying singlet and triplet electronic states of the Mo-2 molecule. The bond order of the ground state has been analyzed based on the effective bond order (EBO), indicating that a fully developed sextuple bond is formed between the two Mo atoms. The experimentally observed excited states a(3)Sigma(+)(u) and A(1)Sigma(+)(u) have been determined and the so-called (3)Lambda excited state identified as the b(3)Sigma(+)(u) state, in agreement with experimental expectations. (C) 2007 Elsevier B.V. All rights reserved.

Synthesis, spectroscopic characterization and radiosensitizing properties of acetato-bridged copper(II) complexes with 5-nitroimidazole drugs

Three novel acetato-bridged dinuclear copper(II) complexes with 5-nitroimidazoles (CuAcNtrim) and the known copper-acetato-metronidazole have been prepared by an environment-friendly route and spectroscopically characterized. The CuAcNtrim compounds of formula [Cu(2)(mu-O(2)CCH(3))(4)Ntrim(2)], where Ntrim = metronidazole (1), secnidazole (2), tinidazole (3) or nimorazole (4), exhibit dimeric copper-acetato paddle-wheel structures with Ntrim axial ligands coordinated to copper(II) ions through the N(3) atoms of the imidazole rings. EPR data indicate antiferromagnetic behavior for this novel series of copper complexes. The constant coupling has been found to decrease along with the increasing of basicity of the Ntrim axial ligand. The CuAcNtrim complexes and the correspondent Ntrim parent drugs have shown radiosensitizer properties for Hep2 (human larynx cancer) cell line in vitro. The best enhancement of radiosensitizer activity upon coordination of the Ntrim drug to copper(II) has been found for the nimorazole compound which has the strongest Cu-Ntrim bond and exhibits the highest lipophilicity within the series of CuAcNtrim complexes. (C) 2010 Elsevier B.V. All rights reserved.