Structure and conformation of bis(acetylacetonato)oxovanadium(IV) and bis(maltolato)oxovanadium(IV) in solution determined by electron nuclear double resonance spectroscopy

The structure and conformation of bis(acetylacetonato)oxovanadium(IV) [VO(acac)(2)] and bis(maltolato)oxovanadium(IV) [VO(malto)(2)] in frozen methanol have been determined by application of electron nuclear double resonance (ENDOR) spectroscopy. The positions of inner- and outer-sphere-coordinated solvent were assigned by ENDOR through use of selectively deuterated analogues of methanol. Similarly, the methyl and methylinyl proton resonance features of VO(acac)(2) were identified by site-selective deuteration. For VO(acac)(2), the ENDOR-determined metal-proton distances were best accounted for by a complex of tetragonal-pyramidal geometry, essentially identical to that determined by X-ray crystallography [Dodge, R. P.; Templeton, D. H.; Zalkin, A. J. Chem. Phys. 1961, 35, 55] but with an inner-sphere solvent molecule coordinated trans to the vanadyl oxygen and an axially positioned solvent molecule hydrogen-bonded to the vanadyl oxygen. In contrast to its trans conformation in crystals [Caravan, P.; et al. J. Am. Chem. Soc. 1995, 117, 12759], the VO(malto)(2) complex was found in a cis conformation whereby the donor oxygen atoms of one maltolato ligand occupied equatorial coordination sites. One of the donor oxygen atoms of the second maltolato ligand occupied the axial coordination site opposite the vanadyl oxygen atom, and the other an equatorial position. An inner-sphere-coordinated methanol molecule in the equatorial plane and a solvent molecule hydrogen-bonded to the vanadyl oxygen were also identified. No evidence for the trans isomer was observed.     

Multi-electron transfer process of vanadyl complexes for oxidative polymerization of diphenyl disulfide

Oligo(p-phenylene sulfide) is synthesized by oxidative polymerization of diphenyl disulfide with oxygen catalyzed by vanadyl acetylacetonate under strongly acidic conditions. The mechanistic studies reveal that the redox cycles of the vanadyl complexes give rise to catalysis through a two-electron transfer between diphenyl disulfide and molecular oxygen. The VO catalysts act as an excellent electron mediator to bridge a 1.0 V potential gap between the oxidation potential of disulfides and the reduction potential of oxygen. The VO-catalyzed oxygen-oxidative polymerization provides pure oligo(pphenylene sulfide)s containing an S–S bond. The polymeric product is of low molecular weight due to the insolubility under these conditions. (N,N′-ethylenebis(salicylideneaminato))oxovanadium-(IV), VO(salen), was used as an inert model compound to elucidate the redox chemistry of the vanadium complex. VO(salen) reacts with trifluoromethanesulfonic acid (CF₃SO₃H) or triphenylmethyl tetrafluoroborate (?₃C(BF₄)) to form a deoxygenated complex, V^IV(salen)²⁺, and a μ-oxodinuclear complex, [(salen)VOV(salen)]X₂, (X = CF₃SO₃^? or BF₄^?). The dimerization of VO(salen) is initiated by deoxygenation to produce V(salen)²⁺ which enters into an equilibrium with a second VO(salen) complex to produce the μ-oxo dimer. The two-electron transfer of the μ-oxo dinuclear vanadium complex is elucidated.     

Kinetics of oxidation of vanadyl acetylacetonate by oxygen in methanolic solution

The kinetics of oxidation of vanadyl acetylacetonate to VO(OH)(OMe)(acac) by molecular O2 in MeOH have been studied spectrophotometrically. The reaction, which is pseudo first-order with respect to [VO(acac)2] and [O2], is inhibited by Hacac and a vanadium(V) complex. The rate data were used to calculate the thermodynamic activation parameters. A mechanism for the reaction is discussed.     

Nickel(II) complexes of tripodal 4N ligands as catalysts for alkane oxidation using m-CPBA as oxidant: ligand stereoelectronic effects on catalysis

Several mononuclear Ni(II) complexes of the type [Ni(L)(CH(3)CN)(2)](BPh(4))(2) 1-7, where L is a tetradentate tripodal 4N ligand such as N,N-dimethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L1), N,N-diethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L2), N,N-dimethyl-N'-(1-methyl-1H-imidazol-2-ylmethyl)-N'-(pyrid-2-ylmethyl)ethane-1,2-diamine (L3), N,N-dimethyl-N',N'-bis(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L4), N,N-dimethyl-N',N'-bis(quinolin-2-ylmethyl)ethane-1,2-diamine (L5), tris(benzimidazol-2-ylmethyl)amine (L6) and tris(pyrid-2-ylmethyl)amine (L7), have been isolated and characterized using CHN analysis, UV-Visible spectroscopy and mass spectrometry. The single-crystal X-ray structures of the complexes [Ni(L1)(CH(3)CN)(H(2)O)](ClO(4))(2) 1a, [Ni(L2)(CH(3)CN)(2)](BPh(4))(2) 2, [Ni(L3)(CH(3)CN)(2)](BPh(4))(2) 3 and [Ni(L4)(CH(3)CN)(2)](BPh(4))(2) 4 have been determined. All these complexes possess a distorted octahedral coordination geometry in which Ni(II) is coordinated to four nitrogen atoms of the tetradentate ligands and two CH(3)CN (2, 3, 4) or one H(2)O and one CH(3)CN (1a) are located in cis positions. The Ni-N(py) bond distances (2.054(2)-2.078(3) ?) in 1a, 2 and 3 are shorter than the Ni-N(amine) bonds (2.127(2)-2.196(3) ?) because of sp(2) and sp(3) hybridizations of the pyridyl and tertiary amine nitrogens respectively. In 3 the Ni-N(im) bond (2.040(5) ?) is shorter than the Ni-N(py) bond (2.074(4) ?) due to the stronger coordination of imidazole compared with the pyridine donor. In dichloromethane/acetonitrile solvent mixture, all the Ni(ii) complexes possess an octahedral coordination geometry, as revealed by the characteristic ligand field bands in the visible region. They efficiently catalyze the hydroxylation of alkanes when m-CPBA is used as oxidant with turnover number (TON) in the range of 340-620 and good alcohol selectivity for cyclohexane (A/K, 5-9). By replacing one of the pyridyl donors in TPA by a weakly coordinating -NMe(2) or -NEt(2) donor nitrogen atom the catalytic activity decreases slightly with no change in the selectivity. In contrast, upon replacing the pyridyl nitrogen donor by the strongly σ-bonding imidazolyl or sterically demanding quinolyl/benzimidazolyl nitrogen donor, both the catalytic activity and selectivity decrease, possibly due to destabilization of the intermediate [(4N)(CH(3)CN)Ni-O˙](+) radical species. Adamantane is selectively (3°/2°, 12-17) oxidized to 1-adamantanol, 2-adamantanol and 2-adamantanone while cumene is selectively oxidized to 2-phenyl-2-propanol. In contrast to cyclohexane oxidation, the incorporation of sterically hindering quinolyl/benzimidazolyl donors around Ni(ii) leads to a high 3°/2° bond selectivity for adamantane oxidation. A linear correlation between the metal-ligand covalency parameter (β) and the turnover number has been observed.     

New porphyrinoids: vanadyl(IV) complexes of meso-aryl-substituted corrphycene and 10-oxocorrole ligands

Rare vanadyl corrphycene and vanadyl 10-oxocorrole complexes were obtained via an oxidative macrocyclization process by the treatment of 6,6'-di-p-tolyl-2,2'-bidipyrrin with VO(acac)2 in a hot dioxygen atmosphere. The geometric and electronic structures of the new porpyhrinoids were determined and showed the dependency of the spectral pattern from the aromaticity of the macrocyclic ligand.     

Synthesis, characterization, and reactivity of mononuclear O,N-chelated vanadium(IV) and -(III) complexes of methyl 2-Aminocyclopent-1-ene-1-dithiocarboxylate based ligand: reporting an example of conformational isomerism in the solid state

Vanadium(IV) and -(III) complexes of a tetradentate N(2)OS Schiff base ligand H(2)L [derived from methyl 2-((beta-aminoethyl)amino)cyclopent-1-ene-1-dithiocarboxylate and salicylaldehyde] are reported. In all the complexes, the ligand acts in a bidentate (N,O) fashion leaving a part containing the N,S donor set uncoordinated. The oxovanadium(IV) complex [VO(HL)(2)] (1) is obtained by the reaction between [VO(acac)(2)] and H(2)L. In the solid state, compound 1 has two conformational isomers 1a and 1b; both have been characterized by X-ray crystallography. Compound 1a has the syn conformation that enforces the donor atoms around the metal center to adopt a distorted tbp structure (tau = 0.55). Isomer 1b on the other hand has an anti conformation with almost a regular square pyramidal geometry (tau = 0.06) around vanadium. In solution, however, 1 prefers to be in the square pyramidal form. A second variety of vanadyl complex [VO(L(cyclic))(2)](I(3))(2) (2) with a new bidentate O,N donor ligand involving isothiazolium moiety has been obtained by a ligand-based oxidation of the precursor complex 1 with iodine. Preliminary X-ray and FAB mass spectroscopic data of 2 have supported the formation of a heterocyclic moiety by a ring closure reaction involving a N-S bond. Vanadium(III) complex [V(acac)(HL)(2)] (3) has been obtained through partial ligand displacement of [V(acac)(3)] with H(2)L. Compound 3 has almost a regular octahedral structure completed by two bidentate HL ligands along with an acetylacetonate molecule. Electronic spectra, magnetism, EPR, and redox properties of these compounds are reported.     

Syntheses of polyfluorophenylcobalt(III) schiff base complexes using organothallium reagents

The complexes RCo(acacen) [R = C₆F₅, p-HC₆F₄, or o-HC₆F₄; H₂acacen = N,N′-ethylenebis(acetylacetonimine)] and RCo(salen) [R = C₆F₅ or p-HC₆F₄; H₂salen = N,N′-ethylenebis(salicylaldimine)] have been prepared by reaction between Co(acacen) or Co(salen) and the appropriate bromobis(polyfluorophenyl)thallium(III) compounds, and have been isolated as pyridinates. Spectroscopic evidence for formation of C₆F₅Co(salophen) [H₂salophen = _N,N′-o-phenylenebis(salicylaldimine)] has also been obtained. The reactivity of the thallium compounds increased in the sequence Ph₂TlBr ? (o-HC₆F₄)2TlBr < (p-HC₆F₄)₂TlBr < (C₆F₅)₂TlBr, and of the cobalt complexes in the sequence Co(salophen) < Co(salen) < Co(acacen). Possible mechanisms are discussed.     

Vanadium(IV) Complexes with Mixed O,S Donor Ligands. Syntheses, Structures, and Properties of the Anions Tris(2-mercapto-4-methylphenolato)vanadate(IV) and Bis(2-mercaptophenolato)oxovanadate(IV)

Reaction of VO(acac)(2) with 2-mercaptophenol (mpH(2)) in the presence of triethylamine gives the mononuclear tris complex (Et(3)NH)(2)[V(mp)(3)] (1), in which the vanadyl oxygen has been displaced. An analogous reaction using 2-mercapto-4-methylphenol (mmpH(2)) afforded (Et(3)NH)(PNP)[V(mmp)(3)] (2), which was structurally characterized. 2 crystallizes in the orthorhombic space group Pna2(1 )with unit cell parameters (at -163 degrees C) a = 23.974(7) ?, b = 9.569(4) ?, c = 25.101(6) ?, and Z = 4. The coordination geometry around the vanadium is between octahedral and trigonal prismatic. Reaction of VO(acac)(2 )with the sodium salt of 2-mercaptophenol produces the vanadyl(IV) complex Na(Ph(4)P)[VO(mp)(2)].Et(2)O (3), which crystallizes in the triclinic space group P&onemacr; with unit cell parameters (at -135 degrees C) a = 12.185(4) ?, b = 12.658(4) ?, c = 14.244(4) ?, alpha = 103.19(2) degrees, beta = 100.84(2) degrees, and gamma = 114.17(2) degrees. The unit cell of 3 contains a pair of symmetry-related [VO(mp)(2)](2)(-) units bridged through vanadyl and ligand oxygen atoms by a pair of sodium ions, in addition to two PPh(4)(+) ions. The coordination geometry around the vanadium is square pyramidal, with a V=O bond length of 1.611(5) ?. 1, 2, and 3 are characterized by IR and UV-vis spectroscopies, magnetic susceptibility, EPR spectroscopy, and cyclic voltammetry. 1 and 2 can be oxidized by I(2, )Cp(2)Fe(+), or O(2) to [V(mp)(3)](-) and [V(mmp)(3)](-), respectively, which in turn can be reduced back to the dianions by oxalate ion. These reversible redox processes can be followed by UV-vis spectroscopy.     

Structure and properties of the thorium vanadyl tellurate, Th(VO2)2(TeO6)(H2O)2

The hydrothermal reaction of Th(NO3)4.xH2O with V2O5 and H6TeO6 at 200 degrees C under autogenously generated pressure results in the formation of Th(VO2)2(TeO6)(H2O)2 as a pure phase. The single-crystal X-ray data indicate that Th(VO2)2(TeO6)(H2O)2 possesses a three-dimensional structure constructed from ThO9 tricapped trigonal prisms, VO5 distorted square pyramids, VO4 distorted tetrahedra, and TeO6 distorted octahedra. Both of the vanadium polyhedra contain VO2+ vanadyl units with two short V=O bond distances. The tellurate octahedron is tetragonally distorted and utilizes all of its oxygen atoms to bond to adjacent metal centers, sharing edges with ThO9 and VO5 units, and corners with two ThO9, one VO5, and two VO4 polyhedra. Crystallographic data: Th(VO2)2(TeO6)(H2O)2, orthorhombic, space group Pbca, a = 12.6921(7), b = 11.5593(7), c = 13.0950(8) A, Z = 8 (T = 193 K). The UV-vis diffuse reflectance spectrum of Th(VO2)2(TeO6)(H2O)2 shows vanadyl-based charge-transfer absorption features. Th(VO2)2(TeO6)(H2O)2 decomposes primarily to Th(VO3)4 when heated at 600 degrees C in air.     

Manganese(III) Schiff base complexes: chemistry relevant to the copolymerization of epoxides and carbon dioxide

Schiff base complexes of the form (acacen)Mn(III)X (acacen = N,N'-bis(acetylacetone)-1,2-ethylenediimine), where X = OAc, Cl, or N(3), have been evaluated for their ability to couple CO(2) and cyclohexene oxide in the presence of a variety of cocatalysts to provide cyclic or polycarbonates. These complexes proved to be ineffective at catalyzing this process; however, valuable information related to the coordination chemistry of these manganese Schiff bases was elucidated. Of importance, mechanistic findings as revealed by comprehensive studies involving structurally related (salen)CrX and (salen)CoX complexes strongly support the requirement of six-coordinate metal species for the effective copolymerization of CO(2) and epoxides. In the case of these Mn(III) complexes, it was determined that in chloroform or toluene solution a five-coordinate species was greatly favored over a six-coordinate species even in the presence of 20 equiv or more of various Lewis bases. Significantly epoxide monomers such as propylene oxide and cyclohexene oxide displayed no tendency to bind to these (acacen)MnX derivatives, even when used as solvents. Only in the case of excessive quantities of heterocyclic amines such as pyridine, DMAP, and DBU was spectral evidence of a six-coordinate Mn derivative observed in solution. X-ray crystal structures are provided for many of the complexes involved in this study, including the one-dimensional polymeric structures of [(acacen)MnOAc x 2H(2)O](n), [(acacen)MnN(3)](n) (mu(1,3)-N(3)), and a rare mixed bridging species [(acacen)MnN(3)](n) (mu(1,3)-N(3)/mu(1,1)-N(3)). In addition, a structure was obtained in which the unit cell contains both a (acacen)MnN(3)(DMAP) and a (acacen)MnN(3) species.     

Metal-ion selectivity produced by C-alkyl substituents on the bridges of chelating ligands: the importance of short H-H nonbonded van der Waals contacts in controlling metal-ion selectivity. A thermodynamic, molecular mechanics, and crystallographic study

The effect on metal-ion selectivity of the use of cyclohexenyl bridges in ligands in place of ethylene bridges is examined (selectivity is defined as the difference in log K1 for one metal ion relative to that of another with the same ligand). The syntheses of N,N'-bis(2-hydroxycyclohexyl)ethane-1,2-diamine (Cy2-en), N,N'-bis(2-hydroxycyclohexyl)propane-1,3-diamine (Cy2-tn), and 1,7-bis(2-hydroxycyclohexyl)-1,4,7-triazaheptane (Cy2-dien) are reported. The crystal structures of [Cu(Cy2-tn)(H2O)](ClO4)2 (1) and [Cu(Cy2-dien)](ClO4)2 (2) are reported. Characteristics of 1: monoclinic, Pn space group, a=11.627(2) A, b=7.8950(10) A, c=12.737(8) A, beta=98.15(3) degrees, Z=2, R=0.0524. Characteristics of 2: orthorhombic, Pbca space group, a=21.815(16) A, b=8.525(7) A, c=25.404(14) A, Z=8, R=0.0821. Structure 1 has the Cu(II) atom coordinated in the plane of the ligand to the two N donors and two O donors, with a long bond to an axially coordinated water molecule. 2 has three N donors, and one hydroxyl O donor from the ligand is coordinated in the plane around the Cu(II) atom, with the second hydroxyl O donor of the ligand occupying an axial site with a long Cu-O bond. The salient feature of both structures is the short H-H nonbonded distance between H atoms on the cyclohexenyl bridges and H atoms on the ethylene bridges of the ligand. These short contacts are important in explaining the metal-ion selectivities of these ligands. Formation constants, determined by glass-electrode potentiometry, for the Cy2-en (Cu(II), Ni(II), Zn(II), Cd(II), Pb(II)), Cy2-dien (Cu(II), Zn(II), Cd(II), Pb(II)), and Cy2-tn (Cu(II), Zn(II), Cd(II)) complexes are reported. These all show a strong shift in selectivity toward smaller metal ions compared with the analogous ligands, where ethylene bridges are present in place of the cyclohexenyl bridges of the ligands studied here. Molecular mechanics (MM) calculations are used to analyze these changes in selectivity. These calculations show that the short H-H contacts become shorter with increasing metal-ion size, which is suggested as the cause of the shift in the selectivity of ligands in favor of smaller metal ions when ethylene bridges are replaced with cyclohexenyl bridges. MM calculations are also used to rationalize, in terms of short H-H contacts, the fact that when the chelate ring contains two neutral O donors, more stable complexes result with cis placement of the donor atoms on the cyclohexenyl bridge, but with two N donors, trans placement of the donor atoms results in more stable complexes.     

Ortho-hydroxylation of benzoic acids with hydrogen peroxide at a non-heme iron center

The iron-assisted hydroxylation of benzoic acid to salicylic acid by 1/H2O2 has been achieved in good yield under mild conditions (where is [Fe(II)(BPMEN)(CH3CN)2](ClO4)2 and BPMEN =N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine); the product of this reaction is a novel mononuclear iron(III) complex with a chelating salicylate.     

2D warp-and-woof interwoven networks constructed by helical chains with different chirality

Two unprecedented 2D entangled layers of warp-and-woof threads interwoven by left- and right-handed helical chains, {[Mn(salen)Au(CN)2]4(H2O)}n (salen = N,N'-ethylenebis(salicylideneaminato)) and {Mn(acacen)Ag(CN)2}n (acacen = N,N'-ethylenebis(acetylacetonylideneiminate)) 2, have been synthesized and characterized.     

Studies of the carbon dioxide and epoxide coupling reaction in the presence of fluorinated manganese(III) acacen complexes: kinetics of epoxide ring-opening

Five-coordinate manganese(III) complexes of N, N'-bis(trifluoroacetylacetone)-1,2-ethylenediimine (tfacacen) have been synthesized and structurally characterized by X-ray crystallography. The presence of the electron-withdrawing -CF3 substituents enhances the electrophilicity of the metal center in these (tfacacen)MnX (X=Cl, N3, NCO, NCS) derivatives when compared with their (acacen)MnX (acacen=N, N'-bis(acetylacetone)-1,2-ethylenediimine) analogs. This is demonstrated by the increased propensity of the Mn(III) center in the tfacacen complexes to bind a sixth ligand. Binding studies were performed utilizing the upsilonN3 stretching frequency in (tfacacen)MnN3, which is sensitive to the coordination of a ligand at the vacant axial site. Of importance, cyclohexene oxide was shown to readily bind to (tfacacen)MnN3, thereby providing an opportunity for directly monitoring the dependence of the epoxide ring-opening process on the metal complex concentration. In this instance, as has been amply demonstrated in the (salen)CrX case, the ring opening of cyclohexene oxide was found to be second-order in [(tfacacen)MnN3], with an activation energy of 71.0+/-6.0 kJ/mol. In the presence of strongly coordinating anions or amine bases, the rate of epoxide ring opening by (tfacacen)MnN3 was greatly retarded. The manganese cyanate and thiocyanate complexes were examined in an effort to develop other initiators for epoxide ring opening which provide readily accessible infrared spectroscopic probes. Indeed, the thiocyanate ligand was found to be well-suited for monitoring the epoxide ring-opening reaction by infrared spectroscopy.     

Thorium(IV) complexes with tetradentate Schiff base ligands

Summary Some thorium(IV) complexes were synthesized with the tetradentate Schiff base ligands (N₂O₂ donor set) obtained by the condensation of ethylenediamine with salicylaldehyde (H₂salen) or acetylacetone (H₂ acacen). In all cases the neutral Schiff bases and not their anions are coordinated to the central thorium(IV) atom. The complexes have the general formula: ThL₂Xa (L = H₂ salen; X = Cl, Br, 1, NCS and L = lie acacen; X = Cl, 1, NCS, ClO₄) or ThLX₄ (L = H₂ salen; X = NO₃, ClO₄ and L = H₂ acacen; X = Br, NO₃). The stoichiometry and coordination number of the complexes was determined on the basis of elemental analysis, conductivity measurements, i.r. spectra and t.g.a./d.t.a. data. The coordination number of the complexes is either 12 or 8 for the bisor monocomplexes respectively.     

Dinuclear nickel and palladium complexes with bridging 2,5-diamino-1,4-benzoquinonediimines: synthesis, structures, and catalytic oligomerization of ethylene

Dinuclear, divalent acetylacetonato (acac) complexes of the type [M(acac){mu-C6H2(--NR)4}M(acac)] (M = Ni, Pd) have been prepared by the reaction of the corresponding bis(acac) metal precursor with 2,5-diamino-1,4-benzoquinonediimines C6H2(NHR)2(=NR)2 (4a, R = CH2-t-Bu; 4b, R = CH2Ph; 4c, R = Ph), which are metalated and become bridging ligands, also like in the complex [(C8H11)Pt{mu-C6H2(--NCH2-t-Bu)4}Pt(C8H11)] (6) obtained by the reaction of 4a with [PtCl2(COD)]. The complexes were fully characterized, including by X-ray diffraction for [Ni(acac){mu-C6H2(--NCH2Ph)4}Ni(acac)] (9b) and [Pd(acac){mu-C6H2(--NCH2-t-Bu)4}Pd(acac)] (10a). The coordination geometry around the metal ions is square-planar, and a complete electronic delocalization of the quinonoid pi system occurs between the metal centers over the two N--C--C--C--N halves of the ligand. The nature of the N substituent explains the differences between the supramolecular stacking arrangements found for [Ni(acac){mu-C6H2(--NR)4}Ni(acac)] (9a; R = CH2-t-Bu; 9b, R = CH2Ph). The Ni complexes were evaluated as catalyst precursors for ethylene oligomerization in the presence of AlEtCl(2) or MAO as the cocatalyst, in particular in order to study possible cooperative effects resulting from electronic communication between the metal centers and to examine the influence of the N substituent on the activity and selectivity. These catalysts afforded mostly ethylene dimers and trimers.     

Directed and undirected asymmetric dihydroxylation reactions: application in the synthesis of a C-linked analogue of allolactose

The complex OsO4.(S,S)-1,2-diphenyl-N,N'-bis(2,4,6-trimethylbenzyl)ethane-1,2-diamine is an effective reagent for the desymmetrisation of meso-1,2-bis(3,6-dihydro-2H-pyran-2-yl)ethanes by asymmetric dihydroxylation; this process, whose sense of diastereoselectivity depends on substitution and stereochemistry, has been exploited in the synthesis of a C-linked analogue of allolactose.     

Interaction of vanadyl (VO2+) with ligands containing serine, tyrosine, and threonine

Reaction of vanadyl sulfate with an aldehyde (2-hydroxy-1-naphthaldehyde (nap); 3-methoxysalicylaldehyde = o-vanillin (van)) and an amino acid carrying an OH group (L-tyrosine (L-tyr); L-serine (L-ser), L-threonine (L-thr)) yielded the complexes [VO(nap-D-Tyr)(H2O)] 1a, [VO(van-D,L-Tyr)(H2O)] 1c, [VO(nap-Ser)(H2O)] 2a, [VO(van-D,L-Ser)(H2O)] 2b, [VO(nap-Thr)(H2O)] 3a, and [VO(van-Thr)(H2O)] 3b. [VO(nap-L-tyr(H2O)], 1b, was obtained from the reaction between [VO(nap)(2)] and l-TyrOMe. The crystal and molecular structures of 1a.CH3OH, 1b.CH3OH, 1c.H2O, 2b.2H2O, and the Schiff base nap-D,L-TyrOMe (4) are reported. The ligands coordinate in a tridentate manner through the phenolate component of nap or van, the imine nitrogen, and the carboxylate of the amino acid. Direct coordination of the (deprotonated) OH amino acid functionality is not observed in these complexes. Instead, the OH groups are involved in hydrogen bonding, leading, along with pi-pi stacking, to extended one- and three-dimensional supramolecular networks. The relevance for the interaction between oxovanadium(IV,V) and proteins having serine, threonine, or tyrosine at their reactive sites is addressed.     

New data on the mechanism of hydrogen peroxide decomposition in acetic acid in the presence of vanadyl and cobalt (II) acetylacetonates

The process of catalytic hydrogen peroxide decomposition in acetic acid in the presence of vanadyl and cobalt (II) acetylacetonates was studied using modern spectroscopic and kinetic techniques. The formation of intermediates during the catalytic decomposition of hydrogen peroxide in the presence of VO(acac)₂ was observed using UV—Vis and ESR spectroscopy. The decomposition of H₂O₂ occurs both catalytically and via the radical route.     

A versatile series of nickel(II) complexes derived from tetradentate imine/pyridyl ligands and various pseudohalides: azide and cyanate compared

The chemical reactions of a family of tetradentate pyridyl/imine ligands, L1, L2, and L3 (L1=[ N, N'-bis(2-pyridinylmethylene)]ethane-1,2-diamine; L2=[ N, N'-bis(pyridin-2-yl)benzylidene]ethane-1,2-diamine; L3=[ N, N'-bis(2-pyridinylmethylene)]propane-1,3-diamine), with Ni (II) in the presence of various pseudohalides (N3(-), SCN(-), and NCO(-)) have served to prepare six different complexes, [Ni 2(L1)2(N3)2](ClO4)2.H2O (1), [Ni 2(L2)2(N3)2](ClO4)2 (2), [Ni2(L2)2(NCS)4] (3), [Ni2(L2)2(NCO) 2](ClO4)2 (4), [Ni2(L3)2(NCO)2](ClO4)2 (5), and [Ni(L3)(N 3)2] (6), which have been characterized by X-ray crystallography. Interestingly, four of these complexes are dinuclear and exhibit end-on (EO) pseudohalide bridges (1, 2, 4, and 5), one is dinuclear and bridged exclusively by the tetradentate ligand (3), and one is mononuclear (6). The bulk magnetization of the complexes bridged by EO pseudohalides has been studied, revealing these ligands to mediate ferromagnetic coupling between the Ni(II) ions, with modeled coupling constants, J, of +31.62 (1), +28.42 (2), +2.81 (4), and +1.72 (5) cm(-1) (where the convention H=-2JS1S2 was used). The striking difference in the coupling intensity between N3(-) and NCO(-) has prompted an investigation by means of density functional theory calculations, which has confirmed the experimental results and provided insight into the reasons for this observation.