Studies on intermolecular interactions of metal chelate complexes. Part X. Interactions of metal chelates with ozone

Summary The interactions of more than forty metal chelate complexes, dithiocarbamates, dithiophosphates and acetylacetonates, with ozone are studied in homogeneous phase and the stoichiometry and the rate constants of the reactions estimated. Most powerful ozone deactivators are nickel(II) and copper(II) dithiocarbamate and dithiophosphate complexes interacting with 6.5 moles ozone per mole of the ligand with rate constant >0⁶m · I^–1 · s^–1. The remote ligand substituents do not influence the reaction parameters. Other sulphur-containing complexes of iron(III), cobalt(II), cobalt(III), zinc(II), manganese(III), bismuth(III), antimony(III), arsenic(III), cadmium(II), platinum(II), palladium(II) and chromium(III) deactivate 3–4 moles ozone per mole ligand with rate constants of 10²–10⁴ m · I^–1 · s^–1. Acetylacetonate complexes of copper(II), nickel(II), cobalt(III), iron(III), chromium (III), and oxovanadium(II) deactivate 1–3 moles ozone per mole ligand with a rate constant of 10–10⁴ m · I^–1 · s^–1. Using e.p.r. and electronic spectra, some intermediate products are detected and the mechanism of the reaction is discussed. The reported data are compared with other widely used antiozonants and the metal chelates are shown to have several advantages.     

Studies on the intermolecular interactions of metal chelate complexesVIII: On the interactions of dithiocarbamato-copper(II) and -copper(I) complexes with haloalkanes

The interaction of Cu(II)(dtc)₂ and Cu(I)(dtc) complexes with haloalkanes were studied by the EPR method. It was found that the Cu(II)(dtc)₂ complex reacted with haloalkanes only in the presence of weak Lewis bases which formed adducts with it. The intermediate reaction product is the mixed-ligand complex Cu(II)(dtc)X_n (X = Cl, Br, n = 1 or 2); the final products being CuX₂B_n (B = Lewis bases, n = 1 or 2) and unstable resin-like residue. Cu(I)(dtc) reacted with haloalkanes without any promoters giving the mixed-ligand complex Cu(II)(dtc)X_n as product. Free radicals were detected in the reaction of Cu(I)(dtc) using the method of “radical scavenger” and were not found in the reaction of Cu(II)(dtc)₂. The reported results confirmed one of the two reaction mechanisms proposed in the previous studies. The role of the solvent on the EPR parameters of the mixed-ligand Cu(II)(dtc)X complex is also discussed.     

Studies on intermolecular interactions of metal chelate complexes. V. copper(ii) dithiophosphate complexes: an example of an inner self-redox reaction

Summary Studies of copper dithiophosphate (dtp) complexes by various physical methods, in the solid and the molten state as well as in solution, are reported. In the solid state all the complexes of dithiophosphate (RO)₂PS ₂ ^– [R = C_nH_2n+1 (n=1–4), Ph, orcyclo-C₆H₁₁] are diamagnetic but in the molten state and in solution they are paramagnetic. Interconversions were found to be reversible, and the effect was ascribed to an inner self-redox reaction. Only the bulkyo-tolyl derivative is paramagnetic in the solid and molten states and in solution. It is proposed that the self-redox reaction involves association between two molecules of Cu^II(dtp)2 during crystallization, followed by formation of [Cu^I(dtp)]₂, and (RO)₂P(S)S-S(S)P(OR)₂, and then [Cu^I(dtp)]₄. The molecular structures of complexes with R = isopropyl ando-tolyl confirm these inferences.Part IV of this series: N. D. Yordanov, V. Iliev, and D. Shopov,Inorg. Chim. Acta, 60, 21 (1982).     

Synthesis and spectroscopic studies of europium chelate complexes

The synthesis of the mixed complexes of the europium ion with 2-pyridylcarbinol-N-oxide, and 2,2′-dipyridyl and 1,10-phenanthroline were prepared. The compounds, were characterized by means of chemical analyses, vibrational spectra, molar conductivities, and electronic spectra. The emission of the [EuL₃, phen] complex at 10 K is very intense and an assignment of the point symmetry of the Eu(III) ion has been made.     

Studies on the intermolecular interactions of metal chelate complexesIX: On the interaction of copper(II) dithiocarbamate with some lewis acids

The intermediate products of the reaction between copper(II) dithiocarbamate complex and some Lewis acids (HgI₂, HgBr₂, GeCl₄, AsBr₃, CoCl₂, C(NO₂)₄) as well as some organometallic compounds (SnEt₄ and PbEt₄) were studied using EPR spectroscopy. In non-polar and non-coordinating solvents HgI₂, HgBr₂ and GeCl₄ formed adducts with Cu(dtc)₂, whereas in polar and coordinating solvents the mixed-ligand complexes of the type Cu(dtc)⁺…A^?(A = HgX₃) were obtained with a complex counterion in the second coordination sphere of copper(II). With C(NO₂)₄ the intermediate reaction product in non-polar solvents was assumed to be Cu(dtc)·NO₂ which dissociates to Cu(dtc)⁺…NO₂^? in polar solvents. Similar EPR spectra were obtained with SnEt₄ and PbEt₄. The reaction of Cu(dtc)₂ with CoCl₂, AsBr₃ and SbCl₃ yielded the mixed-ligand complexes of the type Cu(dtc)X_n (n = 1 or 2) exhibiting well resolved superhyperfine splitting from one or two halogen nuclei. The influence of the medium on the above interaction is also discussed.     

Thermal degradation of iron chelate complexes adsorbed on mesoporous silica and alumina

Nanometric Fe₂O₃ particles could be inserted inside the internal pore volume of SBA-15 mesoporous silica and mesoporous alumina supports, when Fe(III) chelates (EDTA, gluconate or citrate) were used as impregnating precursors. The oxidative degradation of the chelating anions was followed by combined TG-DTA. Strong chelate-SiOH interactions (case of bulky EDTA), favored by the mesopore curvature, yield sub-nanometric extremely well dispersed Fe₂O₃ particles preferentially located at the micropore mouths (confinement effect). Fe₂O₃ even more strongly interacts with alumina walls, generating either (Fe,Al)₂O₃ mixed phases or Fe-aluminate micro domains. These iron-based mesoporous alumina composites proved very active catalysts in total oxidation of phenol at ambient conditions, with extremely low iron leaching (0.2%).     

Photo-switchable spin-crossover iron(III) compound based on intermolecular interactions

Iron(III) spin-crossover compounds, [Fe(qnal)₂]CF₃SO₃·MeOH (1·MeOH) and [Fe(qnal)₂]CF₃SO₃·acetone (1·acetone) were prepared and their spin transition properties were characterized by magnetic susceptibility measurement, Mössbauer spectroscopy and single crystal analysis. Two iron(III) compounds exhibited abrupt spin transition with thermal hysteresis loop (T _1/2?? = 115 K and T _1/2?? = 104 K for 1·MeOH, and T _1/2?? = 133 K and T _1/2?? = 130 K for 1·acetone). Single crystal analysis revealed both of the structures in high-spin (HS) and low-spin (LS) states for 1·acetone. The difference of bond length between the HS and LS states for 1·acetone was ~0.10 Å, which was corresponding to that of typical iron(III) SCO compounds. Specially, it showed strong intermolecular interactions by ???C?? stacking formed between the neighbor complexes leading to 2-D sheet. Both 1·MeOH and 1·acetone exhibited LIESST effect when it was illuminated at 1000 nm. We also confirmed that the introduction of strong intermolecular interactions, such as ???C?? stacking, can play an important role in LIESST effect.     

Cyclic voltammetric studies of certain industrially potential iron chelate catalysts

 For the analysis of infrared spectroscopic bands and complex patterns partial cross correlation functions of a sample spectrum with reference spectra are calculated. The chosen ranges of the spectra are based on empirical knowledge of infrared spectrum structure correlations. The normalised maxima of the partial cross correlation functions are interpreted as fuzzy truth values and are combined by fuzzy logical operators. By application of that procedure larger common substructures will be derived from the reference spectra than by a maximum common substructure search based on the complete spectra. Received: 30 October 1996/Revised: 24 February 1997/Accepted: 26 February 1997     

Evidence for the preservation of specific intermolecular interactions in gaseous protein-oligosaccharide complexes

Arrhenius parameters, obtained with the blackbody infrared radiative dissociation technique, are reported for the dissociation of a series of gaseous protonated complexes composed of mutants of a single chain variable fragment (scFv) of the monoclonal antibody Se155-4 and three trisaccharide ligands. Hydrogen bonding between a ligand and a particular amino acid residue is identified from a comparison of activation energies measured for the complex of the unmodified scFv and the corresponding mutant. It is shown that the specific hydrogen bond between His(101H) and Man C-4 OH is preserved in the gaseous complex.     

Structural influence on the photochromic response of a series of ruthenium mononitrosyl complexes

In mononitrosyl complexes of transition metals two long-lived metastable states corresponding to linkage isomers of the nitrosyl ligand can be induced by irradiation with appropriate wavelengths. Upon irradiation, the N-bound nitrosyl ligand (ground state, GS) turns into two different conformations: isonitrosyl O bound for the metastable state 1 (MS1) and a side-on nitrosyl conformation for the metastable state 2 (MS2). Structural and spectroscopic investigations on [RuCl(NO)py(4)](PF(6))(2)·1/2H(2)O (py = pyridine) reveal a nearly 100% conversion from GS to MS1. In order to identify the factors which lead to this outstanding photochromic response we study in this work the influence of counteranions, trans ligands to the NO and equatorial ligands on the conversion efficiency: [RuX(NO)py(4)]Y(2)·nH(2)O (X = Cl and Y = PF(6)(-) (1), BF(4)(-) (2), Br(-)(3), Cl(-) (4); X = Br and Y = PF(6)(-) (5), BF(4)(-) (6), Br(-)(7)) and [RuCl(NO)bpy(2)](PF(6))(2) (8), [RuCl(2)(NO)tpy](PF(6)) (9), and [Ru(H(2)O)(NO)bpy(2)](PF(6))(3) (10) (bpy = 2,2'-bipyridine; tpy = 2,2':6',2"-terpyridine). Structural and infrared spectroscopic investigations show that the shorter the distance between the counterion and the NO ligand the higher the population of the photoinduced metastable linkage isomers. DFT calculations have been performed to confirm the influence of the counterions. Additionally, we found that the lower the donating character of the ligand trans to NO the higher the photoconversion yield.     

Sterically crowded chelate complexes of copper(II) with phenoxazinyl ligands: ESR study

A copper complex with 1-H-1-oxo-2,4,6,8-tetrakis(tert-butyl)phenoxazinyl free radical ligands was synthesized, and its magnetic properties and ESR spectra were measured at 77–290 K. It was shown that a ground electron state with one unpaired electron is typical of this complex at 77–290 K. The magnetoresonance parameters of this complex are characterized by ag-factor value (1.978) that is rather unusual for copper-containing compounds and by hyperfine coupling due to Cu nuclei. The considerable broadening of ESR spectral lines with increasing temperature is probably not due to the formation of a quartet state (S=3/2). A model of electron states of the compound investigated was developed in the framework of ligand field theory, which made it possible to explain the pattern of the ESR spectra, which were untypical of copper complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 894–899, May, 1995.This study was financially supported by the International Science Foundation (Grant NRT 000).     

Theoretical studies on the intra- and intermolecular C-H activation by T-shaped pincer complexes

Three coordinated, T-shaped (PNP)M^I (M = Co, Ru, Rh, Os and Ir) and [(PCP)Pt⁰]⁻, as well as their reactivities for intra- and intermolecular C-H activation have been studied by DFT methods. The experimental observed reactivities were well reproduced. The calculation also generated structural and energetic information which the experimental values were not yet available. We found that the intramolecular C-H activation is in general possible for the low spin (PNP)M^I. Intermolecular C-H activation is not preferred either thermodynamically or kinetically, but could be in competition if the intramolecular activation is reversible. Using model compounds, we found that the intramolecular C-H activation reactivity is not sensitive to steric effects of the bulky ligands. However, the strain of the four-membered ring in the product significantly reduces the reactivity, and the driving force increases by 4.51-12.95 kcal/mol if the strain was largely removed by changing from a four-membered ring to a five-membered ring. The C-H activation step is quite difficult for metals with a d¹⁰ configuration. Part of the reason is that one phosphine ligand dissociates during the reaction because the product has a d⁸ configuration and prefers a square planar structure.     

Synthesis and electrochemical studies of heterobinuclear zinc and molybdenum mononitrosyl complexes linked by Schiff base ligands

The reaction of 1 mol equivalent of MoCl₂(NO)T^* _p [T^* _p = tris(3,5 dimethylpyrazolyl)borate] with one mole equivalent of the zinc Schiff base complexes obtained from the condensation of 2,5-dihydroxybenzaldehyde, salicylaldehyde and a series of , diamines [NH₂(CH₂) _n NH₂, n = 2–4] is described, together with the i.r.; u.v.–vis. and ¹H-n.m.r. spectroscopic properties of these products. Cyclic voltammetric data in CH₂Cl₂ reveal that the binuclear complex products undergo reversible one-electron reductions associated with the MoCl(NO)T^* _p centre. No zinc-based redox processes in the new complexes could be detected on the cyclic voltammetry timescale. The behaviour of the MoCl(NO)T^* _p centre in DMSO indicates that the complexes undergo irreversible reductions at anodically shifted potentials (in comparison with the reduction of binuclear complexes in CH₂Cl₂), indicating that reductions of the binuclear complexes are solvent dependent.     

Computational studies of the intermolecular interactions in dimers of the bowl-shaped sumanene molecule

Sumanene, C₂₁H₁₂, the second smallest “buckybowl,” is a bowl-shaped fragment of buckminsterfullerene, C₆₀. It can be described as a slice of buckminsterfullerene with 21 carbon atoms with all vacant valences terminated by hydrogens. A computational study of dimers of the sumanene molecule has been carried out. The concave–convex surface arrangement is the most favorable arrangement, and the binding energy and the equilibrium distance for the most stable conformation of the sumanene dimer are predicted to be 19.3 kcal/mol and 3.7 Å, respectively. The most stable geometry was the staggered stacked concave–convex motif, where one monomer was rotated by 60° from the eclipsed conformation. The binding energy of the eclipsed concave–convex dimer is predicted to be 16.7 kcal/mol with an equilibrium distance between the monomer units of 3.8 Å. At the MP2 level, the basis set superposition errors are quite large, 3–5 kcal/mol at the equilibrium distance depending on the basis set. The basis set superposition errors are smaller for dispersion-corrected density functional methods.     

Studies on the interactions of copper(II) chelate complexes with SO2

The reaction of bis (acetylacetonato) copper(II) with SO₂ yields CuSo₄ as a final product. Using e.p.r. technique mixed-ligand complexes of the type Cu(acac) (acacSO₂) have been detected at 100 K. The e.p.r. spectrum of the latter complex disappeared under passing argon through the sample. Lewis bases accelerated the reaction. No interaction of SO₂ with other complexes containing CuO₂N₂, CuN₂S₂, CuS₄ chromophores has been detected. In a common solution of Cu(acac)₂ and Cu(dtc)₂ the reaction proceeded only with Cu(acac)₂ though a mixed-ligand complex Cu(acac) (dtc) was formed. The addition of bases accelerated the reaction, all spectra disappeared and only Cu^I(dtc) has been found as a final product.     

Chemistry of iron complexes—III. X-ray diffraction,ESR and other spectral studies of new iron(II) and iron(III) complexes with tri-p-tolylarsine oxide

Reactions of iron(II) and iron(III) salts with tri-p-tolylarsine oxide(L) in suitable organic solvents yield complexes of formulas: (i) [FeL₂Cl₂(OH₂)₂] [FeCl₄].2H₂O, [FeL₂Br₂] [FeBr₄].2H₂O; (ii) [Fe(NCS)₃L₂].H₂O; (iii) [FeL(O₂ClO₂)₂(OH₂)] (ClO₄).0.25C₆H₆; (iv) [FeL₃I] [FeI₃].H₂O and (v) [Fe(CO)₃LI]I. Characterization has been done through elemental analyses, IR, far IR, ESR, and reflectance spectra, molar conductance, magnetic moments, t.g.a. and X-ray diffraction (powder) data. The species [FeL₂Cl₂(OH₂)₂]⁺, [FeL₂Br₂]⁺, [Fe(NCS)₃L₂], [FeL(O₂ClO₂)₂OH₂]⁺, [FeL₃I]⁺ and [Fe(CO)₃LI]⁺ have been assigned trans-octahedral, trans-square planar, trans-trigonal bipyramid, trans-octahedral, tetrahedral and cis-trigonal bipyramid structures respectively.