Imidazolate-bridged dicopper(II) and copper(II)–zinc(II) complexes of macrocyclic ligand with methylimidazol pendants: Model study of copper(II)–zinc(II) superoxide dismutase

Two new homo- and hetero-dinuclear complexes, [Cu₂L(im)](ClO₄)₃4H₂O (1) and [CuZnL(im)](ClO₄)₃4H₂O (2) (where Im=1H-1midazole and L = 3, 6, 9, 16, 19, 22-hexaaza-6, 19-bis(1H-imidazol-4-ylmethyl)tricycle[22, 2, 2, 2^11,14]triaconta-1, 11, 13, 24, 27, 29-hexaene) were synthesized and characterized as model compounds for the active site of copper(II)–zinc(II) superoxide dismutase (Cu₂Zn₂–SOD). X-ray crystal structure analysis revealed that the metal centers in both complexes exhibit distorted trigonal-bipyramid coordination geometry and the CuCu and CuZn distances are both 6.02 Å. Magnetic and ESR spectral measurements of 1 showed antiferromagnetic exchange interactions between the imidazolate-bridged Cu(II) ions. The ESR spectrum of 2 displays typical signals of mononuclear Cu(II) complex, demonstrating the formation of heterodinuclear complex 2 rather than a mixture of homodinuclear Cu(II)/Zn(II) complexes. pH-dependent ESR and UV–visible spectral measurements manifest that the imidazolate exists as a bridging ligand from pH 6 to 11 for both complexes. The IC₅₀ values of 1.96 and 1.57 μM [per Cu(II) ion] for 1 and 2 suggest that they are good models for the Cu₂Zn₂–SOD.     

Synthesis and structure of iron (III) and iron (II) complexes in S4P2 environment created by diethyldithiocarbamate and 1,2-bis(diphenylphosphino)ethane chelation: Investigation of the electronic structure of the complexes by Mössbauer and magnetic studies

Iron (II) and iron (III) complexes, [Fe^II(DEDTC)₂(dppe)] · CH₂Cl₂ (1), [Fe^II(ETXANT)₂(dppe)] (2) (DEDTC = diethyldithiocarbamate, ETXANT = ethyl xanthate, dppe = 1,2-bis (diphenylphosphino) ethane), and [Fe^III(DEDTC)₂(dppe)] [Fe^IIICl₄] (3) have been synthesized and characterized. Since 3 contains two magnetic centers, an anion metathesis reaction has been conducted to replace the tetrahedral FeCl₄⁻ by a non-magnetic BPh₄⁻ ion producing [Fe^III(DEDTC)₂(dppe)]BPh₄ (4) for the sake of unequivocal understanding of the magnetic behavior of the cation of 3. With the similar end in view, the well-known FeCl₄⁻ ion, the counter anion of 3, is trapped as PPh₄[Fe^IIICl₄] (5) and its magnetic property from 298 to 2 K has been studied. Besides the spectroscopic (IR, UV-Vis, NMR, EPR, Mass and XPS) characterization of the appropriate compounds, especially 2, others viz. 1, 3 and 4 have been structurally characterized by X-ray crystallography. While Fe^II complexes, 1 and 2, are diamagnetic, the Fe^III systems, namely the cations of 3, and 4 behave as low-spin (S = 1/2) paramagnetic species from 298 to 50 K. Below 50 K 3 shows gradual increase of χ_MT up to 2 K suggesting ferromagnetic behavior while 4 exhibits gradual decrease of magnetic moment from 60 to 2 K, indicating the occurrence of weak antiferromagnetic interaction. These conclusions are supported by the Mössbauer studies of 3 and 4. The Mössbauer pattern of 1 exhibits a doublet site for diamagnetic (2-400 K) Fe^II. The compounds 1, 2 and 4 encompass interesting cyclic voltammetric responses involving Fe^II, Fe^III and Fe^IV.     

Transition metal complexes with pyrazole derivatives as ligands

Degradation reactions of scorpionates were observed in the presence of transition metal salts MX₂ to give complexes of transition metal and pyrazole derivatives. Otherwise, pyrazolato complexes of transition metals and weakly coordinating anions such as nitrates have been synthesized from transition metal nitrates and 3-phenyl- and 4-phenyldiazo-pyrazole. A number of complexes with pyrazole derivatives as ligands, [Zn(3-tBupzH)₂Cl₂], [Fe₂(3-Phpz)₆Cl₄], [Cu(pzH)₄Br₂], [Ni(py)₂(pzH)₂Cl₂], [Li(THF)₄][Ti₂(μ-pz)₃Cl₄(NMe₂)₂], [Zn₂(μ-3-Phpz)₂(3-PhpzH)₂][(NO₃)₂], [M(3-PhpzH)₄(NO₃)₂] (M = Co, Ni, Cu, Zn, Cd), [Zn(3-PhpzH)₂(NO₃)₂], [Zn(4-PhNNpzH)₂(NO₃)₂](H₂O), and [Cd(4-PhNNpzH)₂(NO₃)₂(H₂O)₂], have been crystallized and characterized by single-crystal X-ray diffraction.     

Molecular and electronic structures of new iron complexes containing N,S-coordinated o-iminothionebenzosemiquinonate(1-) π radical ligands: An experimental and density functional theoretical study

Two new o-aminothiophenol type ligands have been synthesized, namely 1,3-propanediamine-N,N′-bis(benzenethiol), H₄(¹L), and 1,2-bis(2-mercapto-3,5-di-tert-butylaniline)ethane, H₄(²L). The reactions of these ligands with FeBr₂ in dry acetonitrile in the presence and absence of air (and other oxidants such as iodine) afforded seven new complexes which were characterized by single-crystal X-ray crystallography and Mössbauer spectroscopy (as well as EPR- and UV-Vis spectroscopies). Their magnetochemistry has been studied and their electronic structures have been established and verified by broken symmetry (BS) density functional theoretical (DFT) calculations using the B3LYP functional. The ligands are redox-active and the o-iminothiophenolate(2-)-o-iminothiobenzosemiquinonate(1-) oxidation levels are chemically readily accessible. The complexes characterized comprise the dimers [Fe^III(¹L)]₂ (S_T = 0) (1); [Fe^III(²L)]₂ (S_T = 0) (2), and the mononuclear, five coordinate species: [Fe^III(¹L)I] (S_T = ¹/₂) (3); [Fe^III(²L)I] (S_T = ¹/₂) (4); [Fe^II(¹L){P(CH₃)₃}] (S_T = 0) (5); [Fe^II(²L){P(C₆H₅)₃}] (S_T = 0) (6), and [Fe^III(²)(^tpy)] (S_T = 1) (7). (^tBupy) represents 4-tert-butylpyridine and (²)³⁻ is the π radical trianion of the one-electron reduced (²L_gma)²⁻ which in turn is the oxidized form of (²L)⁴⁻ (−4H⁺, −2e).     

Insertion reactions of organic anhydrides and the Cu(I) alkoxide [CuOBu]

The synthesis and structural characterization of the copper salts [Cu₈(benzoate)₈(THF)₆] (1), [Cu₂{(CO₂)₂C₆H₂(Boc)₂}dppm₂]₂ (2) and [Cu₂{(CO₂)₂C₁₀H₄(Boc)₂}dppm₂]₂ (3) [Boc = tert-butoxycarbonyl, dppm = 1,2-bis(diphenylphosphino)methane] prove that cyclic organic anhydrides and dianhydrides readily insert into the Cu-O bond of [CuO^tBu] forming carboxylate ligands with ester functionalities in the ligand periphery. [Mn₃(o-Boc-benzoate)₆(DME)₂] (4) (DME = 1,2-dimethoxyethane) was synthesized by the metathesis reaction of [Cu(I)(o-Boc-benzoate)] with MnCl₂.     

Copper(II) complexes of bidentate ligands containing nitrogen and sulfur donors: Synthesis, structures, electrochemistry and catalytic properties

Two nitrogen and sulfur containing ligands, 1-methyl-4-((4-methylimidazol-5-yl)methylthio)benzene (NS-mim) (1) and 1-methyl-4-(2-pyridylmethylthio)benzene (NS-mpy) (2) were synthesized and a series of their Cu(II) complexes, 3-10, prepared. The imidazole-containing complexes (3-6) have the form [Cu(NS-mim)₂(solvent)₂](X)₂ where X = ClO₄, BF₄and [Cu(NS-mim)₂(Y)₂] where Y = Cl or Br and the pyridine-containing complexes (7-10) have the form [Cu(NS-mpy)₂]X₂ (where X = ClO₄, BF₄) and [Cu₂(NS-mpy)₂Y₄] (where Y = Cl or Br). These complexes were characterized by a combination of elemental analysis, FAB-MS and electrochemistry. The X-ray structure of the imidazole-containing [Cu(NS-mim)₂(DMF)₂](ClO₄)₂ (3) was determined and it showed the copper(II) coordinated only by the nitrogen donors while the sulfurs remain uncoordinated. In comparison, the X-ray structure of the pyridine-containing [Cu₂(NS-mpy)₂(Cl)₄] (9) shows a dinuclear copper(II) complex with the nitrogens and the sulfurs coordinated along with a terminal chloride and two μ-chloro atoms bridging the coppers. Cyclic voltammetry studies indicated that the complexes undergo quasi-reversible one-electron reductions in acetonitrile at potentials between 0.31 and 0.51 V versus SCE. The complexes were found to be active for the oxidation of di-tert-butyl catechol (DTBC) with the rate dependent on the ligand and the counterion present.     

2D and 3D sulfate-water supramolecular networks templated via triazole-nickel(II) complexes

Tuning the substituents of triazoles, we obtained di- and tri-nuclearic triazole-nickel complexes [Ni₂(deatrz)₄(H₂O)₅](SO₄)₂ · 7H₂O (1) and [Ni₃(dmtrz)₆(H₂O)₆](SO₄)₃ · 21H₂O (2) (deatrz = 3,5-diethanyl-4-amino-1,2,4-triazole; dmtrz = 3,5-dimethanyl-1,2,4-triazole). The X-ray single-crystal diffraction results reveal that sulfate anions and water clusters form supramolecular networks in both complexes. In 1, a supramolecular two-dimensional structure was fabricated by nano-sized grid with novel tetramer water rings templated via binuclear-nickel(II) cations, while in 2, water molecules and sulfate anions construct the first sulfate-water three-dimensional supramolecular network as host to encapsulate trinuclear-nickel guests.     

Insertion reactions of organic anhydrides into the M-O bond of CuOBu and Sb(OMe)3

The synthesis and structural characterization of the copper salts [Cu₂(2-Boc-benzoate)₄(dme)₂] (1), [Cu(2-Boc-benzoate)₂(tmeda)] (2), [Cu₂(2-Boc-benzoate)₂(dppm)] (3), [Cu(2-Boc-nicotinate)(PPh₃)₂] (4), [Cu₂{2-Boc-5,6-anhydride-naphthylcarboxylate}₂(dppm)₂] (5) [dme = 1,2-dimethoxyethane, dppm = bis(diphenylphosphino)methane, tmeda = N,N′-tetramethylethylenediamine, Boc = tert-butoxycarbonyl] prove that cyclic organic anhydrides and dianhydrides readily insert into the Cu-O bond of [CuO^tBu] forming carboxylate ligands with ester functionalities in the ligand periphery. [Sb(CO₂Ph-o-CO₂Me)₂(OMe)(tmeda)] (6) was synthesised by insertion reaction of Sb(OMe)₃ with phthalic anhydride.     

Copper(II) complexes derived from tripodal tris[(2-ethyl-(1-pyrazolyl)]amine

Three mono-nuclear copper(II) complexes [Cu(tepza)X]ClO₄ (X = Cl, 1; X = NCS, 2; X = dca, 3) and two dinuclear bridging complexes [Cu₂(tepza)₂(μ-C₄O₄)](ClO₄)₂·H₂O(4) and [Cu₂(tepza)₂(μ-C₅O₅)](ClO₄)₂(5) where tepza = tris[2-ethyl(1-pyrazolyl)]amine, dca = dicyanamide, C₄O₄²⁻ = 3,4-dihydroxycyclobut-3-ene-1,2-dionate (squarate dianion) and C₅O₅²⁻ = 4,5-dihydroxycyclopent-4-ene-1,2,3-trionate (croconate dianion) were synthesized and structurally characterized by IR and UV-Vis spectroscopy as well as by single X-ray crystallography. In the solid state, the geometry of copper(II) centers in these complexes are as follows: close to SP in 2, distorted TBP in 3, predominant SP in 4, and distorted octahedral in 5, whereas in solution distorted SP geometry was generally found. The squarato and the croconato dianions in complexes 4 and 5 are bridging the two copper(II) centers in cis-bis-monodentate and bis-bidentate bonding modes, respectively. Magnetic susceptibility measurements at variable temperatures (2-300 K) reveal the weak antiferromagnetic coupling in the two bridging dinuclear complexes 4 (J = −24.9 cm⁻¹) and 5 (J = −3.1 cm⁻¹).     

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)] and [Ru(bpy)2(nitatp)]

Two new ruthenium complexes [Ru(bpy)₂(mitatp)](ClO₄)₂1 and [Ru(bpy)₂(nitatp)](ClO₄)₂2 (bpy = 2,2′-bipyridine, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene, nitatp = 5-nitro-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) have been synthesized and characterized by elemental analysis, ¹H NMR, mass spectrometry and cyclic voltammetry. Spectroscopic and viscosity measurements proved that the two Ru(II) complexes intercalate DNA with larger binding constants than that of [Ru(bpy)₂(dppz)]²⁺ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) and possess the excited lifetime of microsecond scale upon binding to DNA. Both complexes can efficiently photocleave pBR322 DNA in vitro under irradiation. Singlet oxygen (¹O₂) was proved to contribute to the DNA photocleavage process, the ¹O₂ quantum yields was determined to be 0.43 and 0.36 for 1 and 2, respectively. Moreover, a photoinduced electron transfer mechanism was also found to be involved in the DNA cleavage process.     

Synthesis, crystal structures and luminescent properties of zinc and manganese complexes from Demko-Sharpless reaction

The synthesis and crystal structure of two new complexes (Zn and Mn) containing tetrazolyl ligands are described. In situ [2+3] cycloaddition reactions of fipronil, (fipronil = (±)-5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazole-3-carbonitrile) with sodium azide in the presence of ZnCl₂ or MnCl₂ as a Lewis acid (Demko-Sharpless tetrazole synthesis method) under hydrothermal (solvothermal) reaction conditions gave [Zn(L)₂](H₂O)₂] · H₂O, 1 and [Mn(L)₂](H₂O)₂] · H₂O, 2, (HL = (±)-5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazole-3-tetrazole). The central metals in both complexes are six coordinated, which connected by two water molecules, two nitrogen atoms from different tetrazolyl groups and two nitrogen atoms from pyrazolyl rings respectively. Photoluminescence studies reveal that both title complexes exhibit strong blue fluorescent emissions at λ_max = 383 nm for 1 and 411 nm for 2 respectively in the solid state at room temperature.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

Novel halogen-bridged bisphosphine nickel(II) complexes

Reaction of [NiCl₂(dtbpe)] (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) with one equivalent of NaBAr^F₄ (BAr^F₄ = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) gives the dinuclear chloro-bridged nickel complex [Ni₂(μ-Cl)₂(dtbpe)₂](BAr^F₄)₂ (1). [Ni(solv)₆](BF₄)₂ reacts with dtbpe to give, depending on the solvent, the fluoro-bridged complex [Ni₂(μ-F)₂(dtbpe)₂](BF₄)₂ (2) (solv = THF) or the mononuclear chelate complex [Ni(MeCN)₂(dtbpe)](BF₄)₂ (3) (solv = MeCN). In 1-3, nickel cations are coordinated in a square-planar fashion according to X-ray crystallography. No Ni-Ni interaction was observed in dinuclear halogen-bridged complexes 1 and 2.     

Syntheses, structures and magnetic properties of tetra- and heptanuclear iron(III) clusters incorporating phosphonate ligands

Two iron(III) complexes, [Fe₄OCl(O₂CMe)₃(O₃PC₆H₉)₃(py)₅] (1) and [Fe₇O₂(O₂CPh)₉(O₃PC₆H₉)₄(py)₆] (2), have been prepared through solution reactions of [Fe₃O(O₂CR)₆(H₂O)₃]Cl (R = Me, Ph) with cyclohexenephosphonic acid. Both compounds contain triangular oxo-centered [Fe₃(μ₃-O)]⁷⁺ units. In complex 1, the fourth iron atom is capped on this triangular unit through O-P-O bridges, forming a tetranuclear cluster with a tetrahedral arrangement of iron atoms. In complex 2, two equivalent [Fe₃(μ₃-O)]⁷⁺ units are connected by the fourth iron atom through four phosphonate ligands, forming a heptanuclear cluster. Variable temperature susceptibility measurements were performed for 1 and 2. Both exhibit dominant antiferromagnetic interactions between the Fe(III) centers.     

Long-range superexchanged magnetic interaction observed in heterometallic complex: {[Fe(Tpms)(CN)3][Mn(H2O)2(DMF)2]} · DMF

A new tri-cyanometalate building block for heterometallic complexes, [PPh₄]₂[Fe^II(Tpms)(CN)₃] (2) (PPh₄ = tetraphenylphosphonium; Tpms = tris(pyrazolyl) methanesulfonate), has been prepared. Using it as a building block, a one-dimensional chain compound, {[Fe^II(Tpms)(CN)₃][Mn^II(H₂O)₂( DMF)₂]} · DMF (3), has been synthesized and structurally characterized. The magnetic properties of 3 correspond to a ferromagnetic chain with weak long-range superexchanged magnetic interaction between the high-spin manganese(II) ions.     

Mono- and dinuclear (o-thioetherphenolato)-copper(II) complexes. Structural models for galactose oxidase

Three new o-thioetherphenol ligands have been synthesized: 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)ethane (H₂bse), 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)benzene (H₂bsb), and 4,6-di-tert-butyl-2-phenylsulfanylphenol (Hpsp). Their complexes with copper(II) were prepared and investigated by UV-Vis-, EPR-spectroscopy; their electro- and magnetochemistry have also been studied: [Cu^II(psp)₂] (1), [Cu^II₂(bse)₂] (2), [Cu^II₂(bsb)₂] (3), [Cu^II(bsb)(py)₂] (4). The crystal structures of the ligands H₂bse, H₂bsb, Hpsp and of the complexes 1, 2, 3, 4 have been determined by X-ray crystallography.     

X-ray structure and magnetic properties of dinuclear and polymer iron(II) complexes

Five new octahedral iron(II) complexes [FeL2(4-dpa)]_n(EtOH) (1), [FeL2(bipy)]_n(DMF) (2), [FeL1(bpee)]_n (3), [Fe₂L3(1-meim)₄](1-meim)₄ (4) and [FeL1(DMAP)₂] (5), with L1 and L2 being tetradentate coordinating Schiff base like ligands (L1 = (E,E)-[{diethyl-2,2′-[1,2-phenylenebis(iminomethylidyne)]bis[3-oxobutanato](2-)-N,N′,O³,O³′}, L2 = (3,3′)-[{1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentane-dionato)(2-)-N,N′,O²,O²′}) and L3 being a octadentate dinucleating coordinating Schiff base like ligand ({tetraethyl-(E,E,E,E)-2,2′,2′′,2′′′-[1,2,4,5-phenylentetra(iminomethylidine)]tetra[3-oxobutanoato](2-)-N,N′,N′′,N′′′,O³,O³′,O³′′,O³′′′}); 4-dpa = di(4-picolyl)-amine, bipy = 4,4′-bipyridine, bpee = trans-1,2-bis(4-pyridyl)ethylene, 1-meim = 1-methylimidazole and DMAP = 4-dimethylaminopyridine, have been synthesized and characterised using X-ray structure analysis and T-dependent susceptibility measurements. Both methods indicate that all iron(II) centres are in the paramagnetic high-spin state over the whole temperature range investigated. The O-Fe-O angle, the so called bit of the equatorial ligand, is with an average of 111° in the region typical for high-spin iron(II) complexes of this ligand type. In the case of compound 1 an infinite two-dimensional hydrogen bond network can be found, for the compounds 2-4 no hydrogen bond interactions are observed between the complex molecules. A comparison of the curve progression obtained from the magnetic measurements of the mononuclear complex 5 and the polymeric complexes 1-3 leads to the conclusion that no magnetic interactions are mediated over the bridging axial ligands. For the dinuclear complex 4 weak antiferromagnetic interactions between the two iron centres are found.     

Hybrid scorpionate/cyclopentadienyl titanium and zirconium complexes with alkoxide and imido ligands

The reactivity of hybrid scorpionate/cyclopentadienyl ligand-containing trichloride zirconium complexes [ZrCl₃(bpzcp)] (1) [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl] and [ZrCl₃(bpztcp)] (2) [bpztcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl] toward several lithium alkoxides has been carried out. Thus, alkoxide-containing complexes [ZrCl₂(OR)(bpzcp)] (R = Me, 3; Et, 4; ⁱPr, 5; (R)-2-Bu, 6), [ZrCl₂(OR)(bpztcp)] (R = Me, 7; Et, 8; ⁱPr, 9; (R)-2-Bu, 10) and [Zr(OR)₃(bpztcp)] (R = Et, 11; ⁱPr, 12) were prepared by deprotonation of the appropriate alcohol group with BuⁿLi followed by reaction with 1 or 2. In addition, the imido-complex [Ti(N^tBu)Cl(bpztcp)(py)] (13) were also prepared. The structures of these complexes have been proposed on basis of spectroscopic and DFT methods.     

Characterization of an Fe<Superscript>III</Superscript>-OOH species and its decomposition product in a bleomycin model system

To model the mononuclear Fe^III-OOH species identified in the catalytic cycle of the anticancer drug bleomycin, the iron chemistry of the pentadentate ligand N-[bis(2-pyridylmethyl)aminoethyl]pyridine-2-carboxamide (H-PaPy₃) has been investigated. The complex [Fe^III(PaPy₃)OCH₃](ClO₄) was reacted with H₂O₂ to form a red species (_max=480 nm, =1800 M^–1 cm^–1) with an S=1/2 EPR signal at g=2.25, 2.17, and 1.95. This species has been identified by electrospray ionization mass spectrometry as [Fe^III(PaPy₃)OOH](ClO₄) and further characterized by resonance Raman and EXAFS analysis. The decomposition of this intermediate leads to the modification of the ligand, as revealed by ¹H NMR. One hydrogen atom is substituted by a solvent-derived methoxy group. The substitution at this site is a result of the two-electron oxidation of the ligand following the heterolytic cleavage of the O–O bond of the Fe^III-OOH species. This is a plausible mechanism to rationalize related ligand modifications that have been proposed in the decay of activated bleomycin.Abbreviations ABLM activated bleomycin - BLM bleomycin - ESI-MS electrospray ionization mass spectrometry - EXAFS extended X-ray absorption fine structure - H-PaPy₃ N-[bis(2-pyridylmethyl)aminoethyl]pyridine-2-carboxamide