The electronic structure and spectra of spin-triplet ground state bis(biuretato)cobalt(III) coordination compounds

The planar coordination compounds of cobalt(III) with bis(biuretato) ligands are highly unusual due to their intermediate spin triplet ground state. Density functional theory (DFT) and time-dependent DFT have been applied in a study of the structure and electronic spectroscopy of this type of coordination compounds. The investigations included prediction and spectroscopic measurements of the absorption and circular dichroism (CD), as well as an experimental study of the magnetic CD. The results obtained by TD-DFT were in excellent agreement with the observed spectral features, both regarding the d-d and the charge transfer regions. There was noted a systematic blue-shift of the TD-DFT results compared to experiment, corresponding to an offset of ca. 0.5 microm(-1) and a scaling factor of 1.25 for the transition energies. The DFT results are rationalized in terms of a qualitative MO analysis.     

Crystal structure of bis(2-(2-thiazolylazo)-4-methylphenol)cobalt(III)chloride.

The reaction between CoCl2 x 6H2O and 2-1-(2-thiazolylazo)-p-cresol (TAC) in acetone resulted in six coordinated cobalt(III) complex, [Co(TAC)2]Cl3. Two TAC ligands coordinate with cobalt ion forming four five membered chelate rings. The cobalt ion is octahedrally coordinated by a phenolic oxygen, azo nitrogen and nitrogen in thiazole rings. Three chloride ions are disordered.     

Crystal structure and luminescence of antimony(III) chloride complex with anilinium chloride

Crystal structure of (C₆H₅NH₃)₃[SbCl₅]Cl·H₂O is determined by X-ray analysis (a = 9.4155(13) Å, b = 11.4344(16) Å, c = 13.1584(18) Å, α = 113.483(2)°, β = 90.383(2)°, γ = 97.323(2)°, space group P \(\bar 1\), Z = 2, ρ_calc = 1.642 g/cm³). The crystal structure is based on [SbCl₅]^2? anions, anilinium cations (C₆H₅NH₃)⁺, isolated Cl^? anions, and water molecules. Structural features responsible for spectral and luminescent properties of the complex are discussed.     

Molecular structure and bonding properties of bis(1-methylimidazole)bis(perchlorato)bis(pyridineN-oxide)copper(II)

Summary The crystal and molecular structure of bis(1-methylimidazole)bis(perchlorato)bis(pyridineN-oxide)copper(II) have been determined using three-dimensional x-ray diffraction data. The complex crystallizes in space group P2₁/c with Z=2. The cell dimensions area=9.355(3),b=14.363(4),c=9.698(4) Å, and =106.40(3)^o. Least-squares refinement of the structure has yielded a final R value of 0.049 for 1235 independent reflections. The centrosymmetric structure consists oftrans pairs of 1-methylimidazole and pyridineN-oxide figands forming a square planar geometry with Cu–N and Cu–O bond lengths of 1.963(4) Å and 1.948(4) Å, respectively. The two perchlorate ions are located above and below the square plane with Cu–O distances of 2.590(5) Å. The uv-vis and i.r. spectra and bonding properties of the title compound are discussed with reference to the structure.     

Synthesis of ribonucleosides of 4(5)-cyano-5(4)-methylimidazole and related 4-substituted-5-methylimidazole ribosides

4-Cyano-1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-5-methylimidazole ( 4 ) and its corresponding 5-cyano-4-methyl substituted isomer ( 5 ) have been obtained by ribosylation of 4(5)-cyano-5(4)-methylimidazole ( 3 ) via the mercuric cyanide method or by ribosylation of the trimethylsilyl derivative of 3 . Treatment of 4 with methanolic ammonia, ammonium chloride in liquid ammonia and potassium hydrosulfide provided 4-cyano-1-β-D-ribofuranosyl-5-methylimidazole ( 6 ), 1-β-D-ribofuranosyl-5-methylimidazole-4-carboxamide ( 2 ) and 1-β-D-ribofuranosyl-5-methylimidazole-4-thiocarboxamide ( 11 ) respectively. Reaction of 6 with hydroxylamine afforded the corresponding 4-carboxamidoxime substituted nucleoside ( 13 ) which on catalytic reduction in the presence of ammonium chloride, was transformed into 1-β-D-ribofuranosyl-5-methylimidazole-4-carboxamidine ( 14 ) as hydrochloride salt.     

Synthesis and crystal structure of tris(ethylenediamine)cobalt(III) bis(tetrachloroaurate(III)) chloride

The binary complex salt [Co(N₂C₂H₈)₃][AuCl₄]₂Cl has been synthesized. Its crystal structure has been determined. Crystal data for C₆H₂₄N₆Cl₉AuCo: a = 20.8976(14) Å, b = 14.4773(9) Å, c = 7.9944(5) Å; β = 110.809(2)°; V = 2260.9(3) ų, space group C2/c, Z = 4, d _calc = 2.798 g/cm³. The plane square environment of the gold atom of the complex anion is completed to a tetragonal pyramid by the chlorine atom of the neighboring complex anion (Au…Cl 3.538 Å). The structure is layered. Layers of complex cations and complex anions alternate along the X axis.     

Electronic ground state and the d-d transitions in bis(biuretato)cobaltate(III) ions

The electronic structure of a class of compounds based on the bis(biuretato)cobaltate(III) ion has been investigated by spectroscopic methods (UV-vis, CD, MCD), magnetic susceptibility, and ligand field theory. The concept of molecules in molecules has been introduced to account for the conjugated pi system of the whole ligand entity and its perturbation of the metal ion 3d orbitals. The Slater-Condon-Racah scheme was fully exploited; in particular, differences in occupation numbers of the spin orbitals have been used in the spectral assignments of the d-d transitions. The energy calculations used one sigma parameter, two pi parameters, and two Racah parameters. The pi parameters, which were derived from Orgel orbitals of chi and psi type, were found to be positive. The observed charge-transfer transitions are metal <-- ligand. The results of our calculations are in agreement with available experimental data, including the spin triplet ground state and the position of the lower d-d transitions. The approach is general and, for example, applicable to heme iron(II).     

Crystal structure and cytotoxic activities of a bis(pyrrolyl-imine) gold(III) complex

A gold(III) complex with N,N′-ethylenebis(pyrrol-2-yl-methyleneamine) (H₂pyren) was synthesized and characterized by physicochemical and spectroscopic measurements. Density functional theory (DFT) studies and cytotoxic assays were performed. Infrared, mass spectrometry, and ¹H, ¹³C, and {¹⁵N,¹H} nuclear magnetic resonance analyses indicate that pyren is deprotonated and gold(III) is four coordinate in a square planar environment, with the pyrrole and imine nitrogens as donors. The structure was confirmed by powder X-ray diffraction and confirmed as a minimum of the potential energy surface by DFT. Cytotoxic activity of [Au(pyren)]⁺ was active against three tumorigenic cell lines with IC₅₀ values of 35 μM. Interaction studies with CT-DNA by fluorescence and competition with ethidium bromide (EB) showed a quenching of the emission band of DNA with a Stern–Volmer quenching constant value of (3.0 ± 0.1) × 10⁴ M^?1 and a decrease in fluorescence quenching of EB-DNA system, respectively, confirming that DNA is a possible target for the complex via an intercalative binding, which was confirmed by DNA conformational changes observed with circular dichroism spectroscopy.     

Crystal structure and infrared spectra of dicesium trans-tetraaquadichlorochromium(III) chloride

The crystal structure of dicesium trans-tetraaquadichlorochromium(III) chloride Cs₂Cr^IIICl₅·4H₂O with trans-[M^IIIX₂(H₂O)₄]⁺ complex ions (space group C2/c, Z=4, a=1915.3(4) pm, b=614.1(1) pm, c=1392.0(3) pm, and β=118.24(3)°, final R1=0.0246 for 2100 unique reflections) was redetermined by single-crystal X-ray diffraction studies. It was found to crystallize in a 2c super structure of the structure reported previously (Inorg. Chem. 20 (1981) 1566; Inorg. Chem. 36 (1997) 2248). The obtained structure data now agree with the results of infrared spectroscopic studies, which has been confirmed in this work, namely that there are two different hydrate H₂O molecules in the structure. Phase transitions, static or dynamic disorder of the hydrate H₂O molecules, and space group C2/m proposed in the literature were ruled out. The coordinates of the four hydrogen positions derived from the X-ray data have been improved via the O–H distances derived from the wave numbers of the OD stretching modes of matrix isolated HDO molecules (2426, 2323, and 2306 cm⁻¹, 263 K) by using the ν_OD versus r_O–H correlation curve reported in the literature (J. Mol. Struct. 404 (1997) 63). The ν_OD versus r_HCl correlation curve reported by Mikenda (J. Mol. Struct. 147 (1986) 1) should be improved, especially for strong hydrogen bonds. The two hydrate H₂O molecules of the title compound are strongly distorted with a weak and a relatively strong O–HCl hydrogen bond each thus intramolecular coupling of the two OH stretching vibrations to coupled ones is largely reduced and, hence, the wavenumbers of the OH and OD stretching modes of the HDO molecules mainly resemble those of the H₂O and D₂O molecules. The strength of the hydrogen bonds is in accordance with the predictions of the competitive and synergetic effects. Chloro ligands are weaker hydrogen bond acceptor groups than chloride ions.     

Crystal structure of EuCuGa and related compounds

The crystal structure of the equiatomic compounds EuPdGa and EuPt Ga is TiNiSi type, oP12, and the crystal structure of EuAgGa and EuAuGa is CeCu₂ type, OI12. EuCuGa probably has CeCu₂-type structure. The Eu atom is divalent in the five compounds, as shown by comparison of the unit cell volume with that of other lanthanide ternary compounds.