Electronic structures and photoelectron spectra of zinc(II) bis-β-diketonates

The influence of thio, dithio, and β-substitutions on the electronic structure and photoelectron spectra of zinc(II) acetylacetonate was studied by the DFT (density functional theory) quantum-chemical method and photoelectron (PE) spectroscopy. The geometry of the metallocycles, the energies, the composition of the molecular orbitals, and the effective charges on atoms were determined. The nature of the corresponding PE spectral bands of the Zn bis-β-diketonates was studied. The bands of four complexes were interpreted. The simulation of the PE spectra with allowance for the Koopmans defect was proposed.     

The vibrational spectra and structure of diiminosuccinonitrile and N,N′-dichlorodiiminosuccinonitrile

The i.r. spectra of diiminosuccinonitrile and N,N′-dichlorodiiminosuccinonitrile were recorded as Nujol mulls, as pellets in KBr and polyethylene matrices and as solutions in CH₃CN in the region 4000-30 cm⁻¹. Raman spectra of the pure solids were obtained and polarization data were recorded from saturated solutions in CH₃CN.The mutual exclusion of i.r. and Raman lines revealed that both compounds existed in the trans conformation and no additional conformers (gauche or cis) were detected in solution.The fundamental frequencies for both molecules were assigned on basis of i.r. and Raman activities, Raman polarization data and the results of normal coordinate analyses.     

Vibrational assignments and resonance Raman spectra of N,N′-ethylenebis(salycilideneiminato)copper(II)

The i.r. spectrum of N,N′-ethylenebis(salycilideneiminato)Cu(II) has been recorded from 4000 to 200 cm⁻¹; polarized i.r. spectra of single crystals have also been obtained. The Raman spectra of polycrystalline samples and solutions have been measured and the resonance behaviour of several Raman bands has been investigated. A detailed assignment of most of the fundamentals is proposed on the basis of the i.r. dichroism and Raman spectra. The origin of the resonance enhancement of some Raman lines is also discussed.     

Structural diversity of isothiocyanato Cd(II) and Zn(II) Girard’s T hydrazone complexes in solution and solid state: effect of H-bonding on coordination number and supramolecular assembly of Cd(II) complex in solid state

The isothiocyanato Zn(II) complex (1) and mixed isothiocyanato/thiocyanato Cd(II) complex (2) with the condensation product of 2-acetylpyridine and trimethylammoniumacetohydrazide chloride (Girard’s T reagent) (HLCl) were investigated both experimentally and theoretically. The crystal structures of both complexes showed tridentate N₂O coordination of hydrazine ligand. In complex 1 square-pyramidal coordination surrounding of Zn(II) consists of deprotonated hydrazone ligand and two isothiocyanato ligands, while in octahedral Cd(II) complex ligand is coordinated without deprotonation as a positively charged species and coordination geometry is completed with two N-coordinated and one S-coordinated NCS^? anions. NMR spectroscopy and molar conductivity results for Cd(II) and Zn(II) complexes indicated their instability in solution. DFT calculations were performed to explain coordination preference and stability of complexes 1 and 2 in solid state and in solution. The obtained Cd(II) complex is the first reported mononuclear pseudohalide/halide Cd(II) complex with quinoline-/pyridine-based hydrazone ligands possessing octahedral geometry in solid state. In this complex, H-bonding has significant impact on coordination number and supramolecular assembly in solid state.     

Solubilities and solvation of bis-(2,2′-bipyridyl)- and bis-(1,10-phenanthroline)dicyanoiron(II) in alcohols

Summary Solubilities of bis-(2,2-bipyridyl)- and bis-(1,10-phenanthroline)dicyanoiron(II) are reported for a range of primary aliphatic alcohols, from MeOH to 1-decanol. The established trends are compared with those for other solutes, and for the title compounds in H₂O-alcohol solvent mixtures.     

Vibrational spectra of carboxylato complexes—I. Infrared and Raman spectra of beryllium(II) acetate and formate and of zinc(II) acetate and zinc(II) acetate dihydrate

The spectra of the title compounds have been recorded and interpreted. On this basis, the structures of the anhydrous compounds Be(OOCH)₂, Be(OOCMe)₂, Zn(OOCMe)₂ are predicted to have tetrahedral coordination with the carboxylate ions acting as bidentate ligands.     

Hydrogen-bonded networks based on manganese(II), nickel(II), copper(II) and zinc(II) complexes of N,N′-dimethylurea

A project related to the crystal engineering of hydrogen-bonded coordination complexes has been initiatied and some of our first results are presented here. The compounds [Mn(DMU)₆](ClO₄)₂ (1), [Ni(DMU)₆](ClO₄)₂ (2), [Cu(OClO₃)₂(DMU)₄] (3) and [Zn(DMU)₆](ClO₄)₂ (4) have all been prepared from the reaction of N,N-dimethylurea (DMU) and the appropriate hydrated metal perchlorate salt. Crystal structure determinations of the four compounds demonstrate the existence of [M(DMU)₆]²⁺ cations and ClO₄ ^– counterions in (1), (2) and (4), whereas in (3) monodentate coordination of the perchlorate groups leads to molecules. The [M(DMU)₆]²⁺ cations and ClO₄ ^– anions self-assemble to form a hydrogen-bonded one-dimensional (1D) architecture in (1) and different 2D hydrogen-bonded networks in (2) and (4). The hydrogen bonding functionalities on the molecules of (3) create a 2D structure. The complexes were also characterised by room-temperature effective magnetic moments and i.r. studies. The data are discussed in terms of the nature of bonding and the known structures.     

The vibrational spectra of complexes with planar monothio-oxamides—I. The Ni(II), Pd(II), Pt(II), Cu(II) and Zn(II) complexes of N,N′-dimethylmonothio-oxamide

The new complexes M(LH)₂ (M = Pd,Pt), ML(M = Pd,Cu) and ML · H₂O (M = Ni,Zn), where LH₂ = N,N′-dimethylmonothio-oxamide, have been prepared. The complexes were characterized by metal analyses, thermal methods and spectral (i.r., Raman, u.v.—vis.) studies. The vibrational analyses of the complexes are given using NH/ND, CH₃/CD₃ and metal isotopic substitutions. The Ni(II), Pd(II), Pt(II) and Cu(II) compounds are square planar. The monoanion LH⁻ shows a chelated bidentate S,O-coordination, while the doubly deprotonated L²⁻ acts as a bridging S,N/N,O-tetradentate ligand giving polymeric structures.     

Solution equilibria of zinc(II) and cadmium(II) complexes with 2,2′-bipyridine in N,N-dimethylacetamide at 25°C

Complexation of zinc(II) and cadmium(II) ions with 2,2-bipyridine (bpy) are studied in N,N-dimethylacetamide (DMA) by calorimetry. Formation constants, enthalpies, and entropies of five mononuclear complexes, [Zn(bpy)_n]²⁺ (n=1–3) and [Cd(bpy)_n]²⁺ (n=1,2), are determined, and compared with the corresponding values in an analogous but less bulky solvent, N,N-dimethylformamide (DMF). The zinc complexes are more stable and the formation is more exothermic in DMA than in DMF, whereas the solvent effect on the cadmium complexes are rather small. A largely positive value of the enthalpy of transfer of Zn²⁺ from DMF to DMA shows that the greater stability of the zinc complexes in DMA is due to the weaker solvation of the metal ion, which is caused by the steric hindrance of DMA molecules. The transfer enthalpies become smaller in the order Zn²⁺>[Zn(bpy)]²⁺>[Zn(bpy)₂]²⁺>[Zn(bpy)₃]²⁺ and dictate gradual relaxation of the steric effect in the complexes. On the other hand, the transfer enthalpies of Cd²⁺ and its complexes are all small, indicating that the hindrance is insignificant in the vicinity of this larger cation.     

Thermochemistry of Cu(II) and Ni(II) complexes with N,N-di-n-butyl-N′-thenoylthiourea and N,N-di-iso-butyl-N′-thenoylthiourea

Two substituted N-acylthioureas and the respective Ni(II) and Cu(II) complexes were synthesized, namely: N,N-di-n-butyl-N′-thenoylthiourea (Hnbtu); N,N-di-iso-butyl-N′-thenoylthiourea (Hibtu); bis[N,N-di-n-butyl-N′-thenoylthioureato]nickel(II), [Ni(nbtu)₂]; bis[N,N-di-n-butyl-N′-thenoylthioureato]copper(II), [Cu(nbtu)₂]; bis[N,N-di-iso-butyl-N′-thenoylthioureato]nickel(II), [Ni(ibtu)₂]; bis[N,N-di-iso-butyl-N′-thenoylthioureato]copper(II), [Cu(ibtu)₂]. The standard (p^° = 0.1 MPa) molar enthalpies of formation and sublimation of the two N-acylthioureas were measured, at T = 298.15 K, by rotating-bomb combustion calorimetry and Calvet microcalorimetry, respectively. The standard (p^° = 0.1 MPa) molar enthalpies of formation of the Ni(II) and Cu(II) complexes were determined, at T = 298.15 K, by high precision solution–reaction calorimetry. From the results obtained, the enthalpies of hypothetical metal–ligand and metal–metal exchange reactions, in the gaseous phase, were derived, thus allowing a discussion of the gaseous phase energetic difference between the complexation of Ni(II) and Cu(II) to 1,3-ligand systems with (S,O) ligator atoms.     

Mass spectrometric study of the vaporization of N,N′-<Emphasis Type="Italic">o</Emphasis>-phenylene-bis(salicylideniminate) nickel(II), copper(II), and zinc(II) and N,N′-ethylene-bis(salicylaldiminate) zinc(II) complexes

The thermodynamics of vaporization of Ni(saloph), Cu(saloph), Zn(saloph), and Zn(salen) complexes are studied by Knudsen effusion method with mass spectrometric control of the vapor composition. It is noted that in the mass spectra of Zn(saloph) and Zn(salen), there are low-intensity peaks corresponding to ions of dimer. The effect of the nature of a metal and a ligand on the behavior of fragmentation of the complexes during their ionization with electrons is discussed. The enthalpies of sublimation, ΔH _s ^○ (T), are calculated by second law of thermodynamics: Ni(saloph) (502–578 K), 163 ± 1 kJ/mol; Cu(saloph) (475–550 K), 162 ± 1 kJ/mol; Zn(saloph) (571–637 K), 176 ± 4 kJ/mol; Zn(salen) (568–634 K), 169 ± 2 kJ/mol.     

Investigation of complexes of zinc(II) and cadmium(II)DI-n-butyldithiocarbamates with 2,2′-bipyridyl

A new mixed-ligand complex, Cd(S₂CN(C₄H₉)_{2 2})₂(2,2′-Bipy), was synthesized. A polycrystal X-ray diffraction analysis was performed (DRON-3M and DRON-UM1 diffractometers, CuK_α radiation, Ni filter) and the crystal structure was determined [Enraf-Nonius CAD-4 automatic diffractometer, MoK_α radiation, 2440 nonzero independent reflections, 153 refined structural parameters, R is 0.11 for I>2σ(I)]. Crystal data for C₂₈H₄₄CdN₄S₄ : a = 28.716(4), b = 6.848(6), c = 17.188(2) Å, space group Pcca, V-3380.2(7) ų, Z = 4, M = 679.42, dcaU.= 1.335 g/cm3. The structure consists of monomeric molecules in which the cadmium atom has a distorted octahedral environment. The polycrystal diffraction analysis revealed that the complex is isostructural with the defined complex Zn(S₂CN(C₄Hg)₂)₂(2,2′-Bipy). A crystal-chemical search on metal dialkyldithiocarbamates in the Cambridge Structural Database was accomplished and isostructural pairs of Zn and Cd metal complexes were found.     

Role of hydration in determining the structure and vibrational spectra of L-alanine and N-acetyl L-alanine N′-methylamide in aqueous solution: a combined theoretical and experimental approach

In this work we have utilized recent density functional theory Born-Oppenheimer molecular dynamics simulations to determine the first principles locations of the water molecules in the first solvation shell which are responsible for stabilizing the zwitterionic structure of L-alanine. Previous works have used chemical intuition or classical molecular dynamics simulations to position the water molecules. In addition, a complete shell of water molecules was not previously used, only the water molecules which were thought to be strongly interacting (H-bonded) with the zwitterionic species. In a previous work by Tajkhorshid et al. (J Phys Chem B 102:5899) the L-alanine zwitterion was stabilized by 4 water molecules, and a subsequent work by Frimand et al. (Chem Phys 255:165) the number was increased to 9 water molecules. Here we found that 20 water molecules are necessary to fully encapsulate the zwitterionic species when the molecule is embedded within a droplet of water, while 11 water molecules are necessary to encapsulate the polar region with the methyl group exposed to the surface, where it migrates during the MD simulation. Here we present our vibrational absorption, vibrational circular dichroism and Raman and Raman optical activity simulations, which we compare to the previous simulations and experimental results. In addition, we report new VA, VCD, Raman and ROA measurements for L-alanine in aqueous solution with the latest commercially available FTIR VA/VCD instrument (Biotools, Jupiter, FL, USA) and Raman/ROA instrument (Biotools). The signal to noise of the spectra of L-alanine measured with these new instruments is significantly better than the previously reported spectra. Finally we reinvestigate the causes for the stability of the P_π structure of the alanine dipeptide, also called N-acetyl-L-alanine N′-methylamide, in aqueous solution. Previously we utilized the B3LYP/6-31G* + Onsager continuum level of theory to investigate the stability of the NALANMA4WC Han et al. (J Phys Chem B 102:2587) Here we use the B3PW91 and B3LYP hybrid exchange correlation functionals, the aug-cc-pVDZ basis set and the PCM and CPCM (COSMO) continuum solvent models, in addition to the Onsager and no continuum solvent model. Here by the comparison of the VA, VCD, Raman and ROA spectra we can confirm the stability of the NALANMA4WC due to the strong hydrogen bonding between the four water molecules and the peptide polar groups. Hence we advocate the use of explicit water molecules and continuum solvent treatment for all future spectral simulations of amino acids, peptides and proteins in aqueous solution, as even the structure (conformer) present cannot always be found without this level of theory. Festschift in Honor of Philip J. Stephens’ 65th Birthday. During the proof stage of this article a very relevant article has been published by M. Losada and Y. Xu titled “Chirality transfer through hydrogen-bonding: Experimental and ab initio analyses of vibrational circular dichroism spectra of methyl lactate in water” in Phys Chem Chem Phys 2007, 9: 3127–3135. In that work they confirm that the effects of water are seen in the VCD spectra and hence it is fundamental to include explicit water molecules in modeling studies of the vibrational spectra of biomolecules in aqueous solution.     

Complexes of N-aroyl-N′-thiobenzohydrazide with cobalt(II), nickel(II) and zinc(II)

Summary New potential tetradentate ligands, N-benzoyl-N-thiobenzohydrazide (H₂BTBH) and N-salicyl-N-thiobenzohydrazide (H₂SBTH) have been prepared and characterized. Their complexes with Co^II, Ni^II and Zn^II have been prepared and characterized on the basis of elemental analyses, magnetic susceptibility measurements, and u.v.-vis., i.r. and ¹H-n.m.r. spectral studies. The bonding and stereochemistries of the complexes are discussed. H₂BTBH, H₂SBTH and the complexes have been screened towards a number of bacteria.     

The infrared spectra of ethylenediamine complexes—II. Tris-, bis- and mono(ethylenediamine) complexes of metal(II) halides

The i.r. spectra of the complexes M(en)₃X₂ (M = Mn, Fe, Co, Ni, Cu, Zn), trans-Cu(en)₂X₂, Ni(en)₂X₂ and M(en)X₂ (M = Ni, Cu, Zn; X = Cl, Br, I) have been studied. Assignments are proposed for the tris(ethylenediamine) complexes on the basis of ¹⁵N-, N₂D₄- and C₂D₄-labelling of en and the effects of metal ion substitution in relation to our earlier study of [M(en)₃]SO₄ complexes. Assignments for the bis(ethylenediamine) complexes are based on our observations of halogen-sensitivity and earlier studies on metal isotope labelling and ligand deuteration of the halide complexes and a normal coordinate analysis of the [Cu(en)₂]²⁺ species. The spectra of the halide complexes have been extended below 200 cm⁻¹ for the first time. Finally, the spectra of the mono(ethylenediamine) complexes are discussed in relation to their known or probable structures.     

Cobalt(III), nickel(II) and copper(II) complexes of N,N′-didodecildithiooxamide

The complexes of N,N′-didodecildithiooxamide (L): CoL₃(ClO₄)₃, NiL₂X₂ (X = Cl, Br, I, ClO₄, HSO₄), CuL₂X₂ (X = ClO₄, HSO₄) and CuLX₂ (X = Cl, Br) were prepared. The cobalt and nickel complexes are diamagnetic, with octahedral and planar coordination respectively. The copper complexes are paramagnetic with normal magnetic moments corresponding to a tetragonal coordination. The i.r. and far i.r. spectra are discussed.     

Structure,spectral and thermal characteristics of zinc(II) halide complexes with N,N-dimethyl-N′,N′-dimethylthiocarbamoyl sulfenamide

We have studied the spectral (IR, PMR, EAS) and thermal properties of new ZnX₂ complexes (X = Cl, Br, I) with N,N-dimethyl-NN,NN-dimethylthiocarbamoyl sulfenamide (L). We have established that the {[ZnLX₂]}₂ compounds obtained are dimers with Zn—X bridging bonds and monodentate coordination of L through the thione sulfur atom.     

Copper(II) and palladium(II) complexes of N,N′-bis(2-hydroxyethyl)stilbenediamine

A new 1,2-diamine ligand, N,N-bis(2-hydroxyethyl)stilbenediamine (L), has been prepared by reduction of the condensation product of benzaldehyde with 2-aminoethanol with Al amalgam. Mononuclear complexes of the [CuL(H₂O)]X₂ type where X=Cl^– or AcO^– with Cu^II and PdLCl₂ with palladium(II) have been prepared and characterized by elemental analysis and i.r., u.v.–vis. or ¹H-n.m.r. spectroscopy.     

Synthesis of N,N′-bis(isopropylaminoethyl)-1,10-phenanthroli ne- 2,9-dimethanamine and N,N′-bis(diethylaminoethyl)-1,10-phenanthroline -2,9-dimethanamine and potentiometric determination of the formation constants of their complexes with manganese(II), cobalt(II), copper(II) and zinc(II)

Two hexadentate compounds incorporating 1,10-phenanthroline and four alkylamino donors have been prepared. The protonation constants and the formation constants of dipositive ion (Mn2+, Co2+, Cu2+ and Zn2+) complexes have been determined in aqueous solution by pH titration at 25 ± 0.1 °C and I = 0.1 mol·dm–3 NaNO3.