Charge-transfer complexes of benzanilides with π-acceptors

Spectrophotometric studies of several substituted benzanilides as electron donors with tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) as electron acceptors have given results that are consistent with an interpretation of 1:1 charge-transfer (CT) complexes. The nature of interaction as well as the substituent effects on the CT complexation are discussed.     

Inclusion complexes of alcohols with α-cyclodextrin

Calorimetric studies of the inclusion complexes of straight and branched alcohols and of diols with alpha-cyclodextrin (-CD) have been carried out in water solvent. The data suggest that straight and branched chain alcohols enter the cavity of -CD alkyl end first. The hydroxyl group hydrogen bonds to the outer oxygen ring of the cyclodextrin. For branched chain alcohols the longer alkyl part of the molecule penetrates the -CD cavity up to the hydroxyl group. Diols form two hydrogen bonds to the outer oxygen ring of the cyclodextrin with some penetration into its interior.     

Molecular complexes of cyclophanes—XIII. Charge-transfer complexes of cyclophanes with fluoranil

The charge-transfer (CT) complexes of some methylated [2.2]para-, multibridged cyclo- and [2.2]indenophanes as π-donors with fluoranil (TFQ) as π-acceptor have been studied spectrophotometrically. The role of the molecular structure of the donors on their Lewis basicities and stability of their CT complexes with TFQ are discussed. Eight pure crystalline complexes were prepared. Their i.r. spectra indicate an increase of the electron density in the TFQ part of the CT complex.     

Molecular complexes of p-benzoquinonechlorimides with aromatic π-donors

The charge transfer spectra of molecular complexes of chloro substituted p-benzoquinone(4)-chlorimides with aromatic π-donors in cyclohexane have been studied. The interaction of 2,6-dichloro p-benzoquinone with the same set of donors has also been studied. The spectroscopic and thermodynamic data indicate that the complexes are very weak in nature. A comparison of the absorption intensities and formation constants for these complexes shows that the contribution of charge transfer forces are not the only dominant stabilising factors.     

CuLn complexes with a single μ-oximato bridge

Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear Cu^IILn^IIICu^II (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H₂L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the Cu^II and Ln^III ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η²: η¹: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a J_CuGd interaction equal to ?1.25 cm^?1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction.     

Ortho-metallation of η-pyrrolylmetal complexes with triosmium clusters

The cluster [O₃(CO)₁₀(MeCN)₂] reacts with (η-cyclopentadienyl)(η-pyrrolyl)iron [azaferrocene, Fe(C₅H₅)(C₄H₄N) under mild conditions to give the oxidative addition product [Os₃H{(C₄H₃N)Fe(C₅H₅)}(CO)₁₀]. The group (C₄H₃N)Fe(C₅H₅) acts as a three-electron donor through the ortho-metallated pyrrolyl ring. An analogous compounds, [Os₃H{(C₄H₃N)Mn(CO)₃}(CO)₁₀], is obtained by the reaction of [Os₃(CO)₁₀(MeCN)₂] with [Mn(η-pyrrolyl)(CO)₃].     

Resolution of β-aminophosphines with chiral cyclopalladated complexes

Resolution of the racemic chiral β-aminophosphines Ph₂PCH₂CH(Ph)NH(Ar) (L¹ for Ar = C₆H₅ and L² for Ar = 2,6-C₆H₃ⁱPr₂) has been investigated by use of different cyclopalladated complexes as chiral agents. The resulting complexes afford diastereomeric adducts in a 1:1 ratio. After successive crystallizations from ethanol, a d.e. of 98% was achieved for one aminophosphine palladium complex, while no significant d.e. was obtained after crystallizations from chlorinated solvents. The X-ray structure analysis has pointed out intermolecular hydrogen interactions N-H?Cl between the P,N ligand and the chloride ion, which are responsible for the formation and stabilization of the diastereomeric adducts. Thus, the use of oxygenated solvents cancels such hydrogen interactions by their stronger donor character and makes the diastereomers separation possible, allowing to isolate the optically pure (R)-Ph₂PCH₂CH(Ph)NH(Ph) L¹ of which the absolute configuration has been determined from the X-ray structure analysis of the related palladium dichloride complex.     

Reactions of chelated η-pentadienyl iron complexes with nucleophiles

Ferracyclic (1-3-η³)pentadienyl complexes with electronically decoupled allyl and vinyl moieties were reacted with various heteroatom and carbon nucleophiles. Primary amines selectively attacked neutral (4-6-η³-pentadienyl)ferralactones 2 on the end of the allyl ligand to give 3-(endo-vinyl)-(4-6-η³-allyl)ferralactams 4 and by a similar reaction of the latter eventually 6-(exo-vinyl)-(4-6-η³-allyl)ferralactams 5. -like attack on the conjugated coplanar vinyl residue of 2 was not observed. The cationic η³-allyl complex 3 was attacked by nucleophiles either on the allylic terminus furnishing free (1Z, 3E)-dienes 8, or on the vinyl residue which is part of an activated Michael system to give η⁴-1,3-diene complexes 9. η⁴-1,3,5-Triene complex 10 was obtained with basic nucleophiles.     

Zaleplon co-ground complexes with natural and polymeric β-cyclodextrin

In this study, we compared the suitability of parent β-cyclodextrin (βCD) and its water soluble polymeric derivative (PβCD) as co-grinding additives aimed to enhance the solubility of zaleplon (ZAL), a hypnotic drug. Equimolar drug/carrier mixtures were co-ground in a high-energy micromill over different time intervals. Data obtained by differential scanning calorimetry, X-ray powder diffractometry and scanning electron microscopy showed a higher affinity of ZAL for the solid state interaction with PβCD, resulting in powders with lower relative drug crystallinity (RDC) compared to that obtained with natural βCD (RDC = 51.10 and 12.5 % for complexes with βCD and PβCD co-grounded for 90 min, respectively). On the other hand, grinding the drug alone did not result in a significant reduction of the drug crystallinity (RDC = 99.87 % for the sample ground for 90 min). Although ¹H-NMR spectroscopy confirmed that both co-ground products were readily converted into inclusion complexes upon dissolution in water, they presented different dissolution properties. The dissolution velocity of co-ground complex with PβCD was 25 % faster compared to that prepared with the parent βCD and almost double compared to that of the drug alone, irrespective of the pH value of the dissolution media. This clearly demonstrated the suitability of co-ground ZAL/PβCD complex in the development of an immediate release oral formulation of ZAL.     

Azobenzene palladium(II) complexes with β-diketones

A procedure has been developed for the synthesis of cyclometalated azobenzene palladium(II) complexes [Pd(O^O)Azb], where Azb^– is deprotonated azobenzene and (O^O)^– is deprotonated β-diketone (acetylacetone, thenoyltrifluoroacetone, benzoylacetone, or dibenzoylmethane). Electronic absorption spectra and electrochemical behavior of the synthesized complexes have been studied. It has been found that the lowest unoccupied molecular orbital of the complexes is contributed most by the π* orbital of azobenzene, and the highest occupied molecular orbital, by the palladium d orbital.     

Transition metal complexes with 2,6-Di-tert-butyl-p-quinone 1′-phthalazinylhydrazone

2,6-Di-tert-butyl-p-quinone 1′-phthalazinylhydrazone (HL) was synthesized. Quantum-chemical calculations of the energy of possible tautomeric forms of the hydrazone were performed. The complexes of Zn(II), Hg(II), Ni(II), and Cu(II) of ML₂ composition were obtained and studied. The structure of the NiL₂ complex was established by XRD. It was shown by DFT-D3 calculations that the cis-structure of the complex is stabilized due to the interligand dispersion interaction.     

Cyclopalladated complexes of 2-phenylbenzothiazole with 4,4′-bipyridyl

Complexes [Pd(bt)(4,4′-bpy)OOCCH₃], [Pd(bt)NO₃]₂(m-4,4′-bpy), [Pd(bt)(m-4,4′-bpy)]₄(NO₃)₄ (bt⁻ is deprotonated form of 2-phenylbenzothiazole, bpy is 4,4′-bipyridyl) are prepared and characterized by ¹H NMR, electron absorption and emission spectroscopy, as well as by voltammetry. The upfield shift of the signal of proton in the ortho-position to the donor carbon atom of the cyclopalladated ligand in the complexes [(Δδ = −(1.1–1.5) ppm] is assigned to the anisotropic effect of the ring current of the pyridine rings of the 4,4′-bipyridyl moiety, which are orthogonal to the coordination plane. Characteristic longwave absorption bands λ = (387±4) nm and the low-temperature phosphorescence bands λ = (512±3) nm in the complexes are assigned to the chromophore {Pd(bt)} metal complex fragment. The reduction waves in the complexes [E _1/2 = −(1.54±0.04) and E _p = −(1.83±0.03) V] are assigned to the ligand-centered processes of the successive electron transfer to the π* orbitals localized predominantly on the coordinated pyridine components of the 4,4′-bipyridyl moiety.     

Heteroleptic europium complexes with β-diketones and trifluoroacetic acid

Europium complexes with β-diketones and trifluoroacetic acid were obtained and characterized using elemental analysis, IR spectroscopy, emission spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetry. The europium complexes are more stable when fluorinated substituents in β-diketones are replaced by alkyl substituents. Both the ligands (β-diketone and trifluoroacetic acid) are coordinated in a bidentate fashion. The Stark splitting of the ⁷ F ₁ levels in the complexes obtained increases with an increase in the negative inductive effect of the substituents in β-diketones, which indicates the partially ionic character of the Eu-ligand bond.     

Electrolytic formation of technetium complexes with π-acceptor ligands

Electrolytic reduction of pertechnetate was performed in aqueous solution containing -acceptor ligands. Cyanide and 1,10-phenanthroline were the selected ligands. In both cases, electrolyses produced a cathodic TcO₂ deposit and soluble Tc complexes. When cyanide was the ligand, the complexes formed were [Tc (CN)₆]^5– and [TcO₂ (CN)₄]^3–. When working with the amine, [Tc (phen)₃]²⁺ and another positively charged species were found after reaction. Results are compared with previous studies with amines, and the usefulness of the electrolytic route to obtain Tc complexes is evaluated.     

New rhenium(III) complexes with fluorinated β-diketones

Five new rhenium(III) complexes of the general formula ReCl₂(R_FCOCHCOR_F)(PPh₃)(OPPh₃), where R_F = CF₃ (I), C₂F₅ (II), C₃F₇ (III), C₄F₉ (IV), and CF₃CFOC₃F₇ (V), were synthesized. The known rhenium(V) complex ReOCl₂(OC₂H₅)(PPh₃)₂, which can readily be obtained from metallic rhenium, was used as a precursor. Two polymorphous modifications of compound I were found and studied by X-ray diffraction analysis. The thermal properties of the synthesized complexes were characterized by the DTA-TG method.     

Inclusion complexes of β-cyclodextrin with dihydroxyphenols of various nature

The ways for the practical preparation of stable inclusion complexes of β-cyclodextrin with dihydroxyphenols of various nature are developed. Mutual orientation of hydroxy groups and the nature of the bridge in the bisphenols are shown to affect considerably their ability to the complex formation.     

Binuclear complexes with uranyl ions in non-equivalent coordination environments: synthesis and electrochemistry of complexes with binucleating aroyl hydrazones and 2,2′-bipyridine

The binuclear complexes [(UO₂bipy)₂L^1–3]NO₃, (1–3), {H₃L^1–3=1-(2-hydroxybenzoyl)-2-(2-hydroxy-benzal/3-methoxybenzal/naphthal)hydrazine}, and [(UO₂bipy)₂L^4–5](AcO)₂, (4–5), [H₂L^4–5 = 1-(2-aminobenzoyl)-2-(2-hydroxy-benzal/naphthal)hydrazine], have been synthesised. Complexes (4–5) possess longer O=U=O bonds than those in the complexes (1–3) as the strong -donating phenolate is replaced by the amino group. The spectral data and electrochemical behaviour confirm the electronic nonequivalence of the coordination environments around the two uranyl ions in these complexes.     

Synthesis and structure of cobalt α-dioximate complexes with isonicotinamide

New cobalt trans-dioximate complexes with isoniconinamide have been synthesized: [Co^II(DmgH)₂(Inia)₂] (I), [Co^III(DmgH)₂(Inia)₂][PF₆] · 1.5H₂O (II), [Co^III(NioxH)₂ (Inia)₂][PF₆] · H₂O · CH₃OH (III), and [CoIIICl(DmgH)₂(Inia)] · H₂O (IV), where DmgH⁻ and NioxH⁻ are the dimeth-ylglyoxime and 1,2-cyclohexanedionedioxime monoanions, respectively; Inia is the isonicotinamide molecule. The structures of compounds I–IV have been determined by X-ray crystallography. In I–IV, Co(II) or Co(III) has an octahedral environment with the pseudomacrocyclic (DioxH⁻)₂ moiety (DioxH⁻ is the dioximate monoanion) in the equatorial plane. The latter is stabilized by O-H…O hydrogen bonds. The isonicotinamide molecules in all four complexes are monodentately bound to the metal ion through the heterocyclic nitrogen atom.     

Coordination field analysis of rare earth complexes with triangular symmetry

The calculation of the complex matrixes in odd triangular symmetry was accomplished.The configurations of the coordination unit with various triangular symmetries and different ligand numbers were discussed.On the basis of the double-sphere coordination point-charge (DSCPCF) model,the detailed forms of the DSCPCF parameters Bmk and the expressions of the perturbation matrix elements in triangular field (D3,D3h,D3d) were derived.Thereby,the calculation scheme of coordination field perturbation energy of the rare earth complexes with triangular symmetry was constructed After the calculation scheme was programmed,the Stark energies of the crystalline TbAl3(BO3)4 were calculated The results were considerably close to the experimental values