Mimicking the reduced, oxidized and azide inhibited form of manganese superoxide dismutase by mononuclear Mn compounds utilizing tridentate ligands

The manganese complexes [Mn^II(Hbmimpm)₂(NO₃)](NO₃) · Et₂O (1), [Mn^III(bmimpm)₂(OAc)] · 2CH₂Cl₂(2), and [Mn^III(bmiapm)₂(OAc)] · MeOH · H₂O · CH₂Cl₂(3) containing the new ligands Bis(1-methylimidazol-2-yl)-(4-methoxyphen-1-yl)methanol (Hbmimpm) and Bis[(1-methylimidazol-2-yl)](2-aminophenyl)methanol (Hbmiapm) were synthesized. They are good structural models for the reduced (1) and oxidized (2, 3) form of manganese superoxide dismutase. All complexes were characterized by spectroscopic methods and X-ray structure analysis. Compounds 1 and 2 crystallize in the monoclinic space group P2₁/c whereas complex 3 crystallizes in the monoclinic space group P2₁/n. The coordination sphere around the manganese cores is distorted octahedral with two corresponding tridentate ligands representing the protein ligands and one nitrate (1) or acetate (2, 3) ion occupying two cis positions. Similar to the enzyme the Mn(III) complex 2 reacts with sodium azide. The obtained microcrystalline azide adduct was characterized by UV-Vis and IR spectroscopy.     

Temperature effect on the conversions of phthalato and maleato manganese(II) complexes with diamine ligands

1,10-Phenanthroline hydrogen phthalato manganese(II) dimer [Mn₂(Hphth)₂(phen)₄] · 2Hphth · 6H₂O (1), monomeric phenanthroline phthalato manganese(II) monomer [Mn(phth)(phen)₂(H₂O)] · 2.5H₂O (2), 2,2′-bipyridine phthalato manganese(II) polymer [Mn(phth)(bpy)(H₂O)₂]_n (3) and 1,10-phenanthroline maleato polymer [Mn(male)(phen)(H₂O)₂]_n · 2nH₂O (4) (H₂phth = o-phthalic acid, male = maleic acid, phen = 1,10-phenanthroline and bpy = 2,2′-bipyridine) have been synthesized and characterized spectroscopically and structurally. Each Mn(II) atom in dimeric 1 is octahedrally coordinated by two oxygen atoms of phthalate anions and by two cis-phenanthroline ligands. The hydrogen phthalato anion bridges the Mn(II) ions through the deprotonated carboxyl groups, while the carboxylic acid group remains free. In the monomeric 2, the Mn(II) ion is octahedrally surrounded by four nitrogen atoms from two cis-phen ligands, one carboxyl oxygen from a monodentate phth ion, and one coordinated water molecule. The dimeric phthalato complex 1 can be cleaved into monomer 2 under heating with deprotonation, and the course of the reaction can be qualitatively traced by IR spectra. The phthalate group in the complex 3 binds to two manganese atoms through the vicinal carboxyl-oxygen atoms in syn-syn bridging mode. The Mn(II) atoms are linked by the phthalate group to yield a one-dimensional chain running along the a-axis. The coordination polymer 3 can be obtained from the reaction of dichloro dibipyridine manganese with phthalate under heating. In polymer 4, the manganese atom is six-coordinated by two nitrogen atoms from phen, two oxygen atoms from the coordinated water molecules and two oxygen atoms from two different maleate dianions. Each maleato unit links two neighboring manganese atoms to yield one-dimensional chain along b-axis in bis-monodentate mode. The single-chain polymer 4 prepared at low temperature can be converted to double-chain coordination polymer [Mn(male)(phen)]_n · nH₂O (5) with dehydration in warm solution.     

Synthesis, crystal structure and magnetic properties of a chain coordination polymer {[Cu4L2(H2O)] · H2O}n

A chain coordination polymer with the chemical formula {[Cu₄L₂(H₂O)] · H₂O}_n, has been synthesized by the assembly reaction of K₂CuL · 1.5H₂O and Cu(OAC)₂ · H₂O with a 1:1 mole ratio in methanol, where H₄L = 2-hydroxy-3-[(E)-({2-[(2-hydroxybenzoyl)imino]ethyl}imino)methyl] benzoic acid, OAC⁻ = CH₃COO⁻. The crystal structure was determined by single-crystal X-ray diffraction analysis, the compound has chain molecular structure formed by dissymmetrical tetranuclear units. The magnetic measurements showed that Cu-Cu of the complex exhibit antiferromagnetic interactions, and satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a binuclear system, and further using molecular field approximation to deal with magnetic exchange interactions between binuclear systems.     

Spectroscopic characterization of a Ni-organic radical intermediate in the aerobic oxidation of methanol catalyzed by a Ni(II)(polyoximate) complex

In the aerobic oxidation of methanol catalyzed by a Ni(II)(TRISOX) complex [H₃TRISOX = tris(1-propan-2-onyl oxime)amine], an intermediate is observed spectroscopically. The intensities of both the UV-Vis absorption and electron paramagnetic resonance (EPR) spectra associated with this intermediate maximize during the time period of maximum formaldehyde production, and decrease as the methanol oxidation activity decreases. The UV-Vis spectrum has prominent features at 350, 420, and 535 nm. The EPR spectrum is centered at g = 2.00 and shows splittings of 28 ± 5 G. Both of these spectra are consistent with characterization of the intermediate as including one or more iminoxyl radicals derived from the oximate groups of the TRISOX ligand. Spectroscopic features very similar to those in the air-oxidized intermediate are observed in electrochemically oxidized samples, suggesting that the electrochemically generated complex will be a useful model for the intermediate observed during catalytic turnover. The crystal structure of a Ni(II) complex with an intermediate protonation state of the ligand, [Ni(II)₂(H₂TRISOX)₂(μ₂:η¹-ONO₂)](NO₃) · (CH₃CN) · 5(H₂O), 4, has been structurally characterized. Comparison to the previously reported [Ni(II)(H₂TRISOX)(CH₃CN)]₂(ClO₄)₂, 3, shows that bis(μ-oximate) dimers can form either with or without an additional bridging ligand. Addition of the nitrato bridge decreases the Ni-Ni distance from 3.5752(13) Å in 3 to 3.2014(4) Å in 4. It is intriguing to note that the reactions catalyzed by the Ni(II)(TRISOX) complex, the net transfer of two hydrogen atoms from an alcohol or amine substrate to O₂, are the same reactions catalyzed by several different metalloenzymes that also incorporate both a redox active metal and a redox active organic component in their active sites.     

Voltammetry of half-sandwich manganese group complexes of η-PhC3B7H9 and η-C60Bn2PhH2, two ligands that are cyclopentadienyl mimicks

The potentials of a series of one-electron oxidation and reduction reactions have been determined for manganese group half-sandwich complexes of the tricarbadecaboranyl ligand PhC₃B₇H₉ and the penta-organo fullerene ligand C₆₀Bn₂PhH₂ (Bn = benzyl). The anodic processes were studied in CH₂Cl₂ and the cathodic processes were studied in both CH₂Cl₂ and THF, the supporting electrolyte being [NBu₄][B(C₆F₅)₄]. The manganese complex Mn(CO)₂(PMe₃)(PhC₃B₇H₉) (1) is a member of a three-electron transfer series which includes oxidation to 1⁺ (0.51 V versus ferrocene) and successive reductions to 1⁻ (−1.66 V) and 1²⁻ (−1.77 V). Both the oxidation and reduction of the closely-related complex Mn(CO)₂(PPh₃)(PhC₃B₇H₉) (2) are chemically irreversible under slow-scan cyclic voltammetry conditions. The rhenium complex Re(CO)₂(PPh₃)(PhC₃B₇H₉) (3) oxidizes (E_1/2 = 0.82 V versus ferrocene) to a radical cation which, unlike its cyclopentadienyl analogue, shows no evidence of dimerization. Oxidation of the fullerene-based complex Re(CO)₃(C₆₀Bn₂PhH₂) is more facile than that of its cyclopentadienyl analogue, in contrast to previous findings in this class of metal-fullerene derivatives. An electrochemical ligand factor, E_L, of 0.63 is calculated for the PhC₃B₇H₉ ligand in manganese group half-sandwich complexes.     

Synthesis, characterization and bioactivity of a novel 18-metallacrown-6: [Mn(pcshz)(CH3OH)]6 · 4CH3OH · 4H2O

The reaction of N-propionyl-5-chlorosalicylhydrazide (H₃pcshz) with Mn(OAc)₂ · 4H₂O in methanol solution gives a novel 18-metallacrown-6 [Mn(pcshz)(CH₃OH)]₆ · 4CH₃OH · 4H₂O (1). The structure of 1 has been determined by X-ray diffraction and it crystallizes in the monoclinic system and space group P2(1)/n. The ring of the metallacrown is consisted of six interlink [Mn-N-N] repeated units through hydrazide N-N group bridging the ring manganese ions. And the ligand enforces the metal ions to form the stereochemistry as a propeller configuration with alternation Λ/Δ form. The largest diameters of the disc-shaped hexanuclear ring are about 8.82 Å at entrance, 9.83 Å at the central of the cavity, respectively. The solution integrity and stability of the metallacrown was studied by electrospray ionization (ESI)-MS and UV-Vis spectroscopy. The results show it is soluble and stable in methanol. Antibacterial screening data indicate the forming of the complex weakens dramatically the antibacterial activity of the ligand H₃pcshz except for Eschericha coli.     

Two forms of a copper(II) complex of 3-phenyl-5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole: a six-coordinate monomer versus a five-coordinate polymer

The reaction of the new bidirectional ligand 3-phenyl-5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazole (pyppt) with Cu(ClO₄)₂ · 6H₂O in a 2:1 molar ratio in EtOH affords the complex [Cu^II(pyppt)₂(ClO₄)₂] · H₂O (1) as a microcrystalline turquoise solid. Recrystallisation of complex 1 from MeCN by vapour diffusion of Et₂O gives blue crystals of the monomeric octahedral complex [Cu^II(pyppt)₂(ClO₄)₂] · MeCN (2). In contrast, addition of EtOH to a solution of complex 1 in MeCN followed by slow evaporation yields blue crystals of the five-coordinate polymeric complex {[Cu^II(pyppt)₂](ClO₄)₂ · EtOH}_∞ (3). The structures of both complexes have been determined by single crystal X-ray diffraction.     

Monomeric versus dimeric structures in ternary complexes of manganese(II) with derivatives of benzoic acid and nitrogenous bases: structural details and spectral properties

Adducts formed by [Mn(2,6-dmb)₂(H₂O)₃]_n · nH₂O, 2,6-dmb=2,6-dimethoxybenzoate(1-), Mn(2,4-dhb)₂ · 8H₂O, Mn(2,5-dhb)₂ · 4H₂O or Mn(2,6-dhb)₂ · 8H₂O, dhb=dihydroxybenzoate(1-), and 2,2^′-bipyridine (bpy), 4,4^′-dimethyl-2,2^′-bipyridine (Me₂bpy) or 4,7-dimethyl-1,10-phenanthroline (Me₂phen) were isolated in the solid state and characterised by IR, EPR and thermogravimetry. Two of them, [Mn(2,6-dhb)₂(bpy)₂] (1) and [Mn₂(2,6-dmb)₄(Me₂Phen)₂(H₂O)₂] · 2EtOH (2), were studied by single crystal X-ray diffraction. The adduct 1 is mononuclear and consists of hexa-co-ordinate manganese(II) ions bound to two bipyridine and two 2,6-dihydroxybenzoate ligands in a cis-octahedral arrangement. The complex 2 exhibits a dinuclear structure in which two manganese(II) ions share two carboxylate groups adopting a rather uncommon single-atom bridging mode. The results allow us to conclude that weak, e.g., hydrogen bonding and stacking interactions govern the type of structure, monomeric or dimeric. The spectral features of the complexes are discussed. In particular, the solid-state EPR features of the complexes are interpreted in terms of D, E and H_max, the high-field resonance. For the monomeric species, the higher is the D value, the higher is H_max.     

Double complex salts of Pt and Pd ammines with Zn and Ni oxalates - promising precursors of nanosized alloys

Double complex salts [M(NH₃)₄][M′(Ox)₂(H₂O)₂] · 2H₂O (M = Pd, Pt, M′ = Ni, Zn) were synthesized by combination of solutions containing corresponding cations [M(NH₃)₄]²⁺ and anions [M′(Ox)₂(H₂O)₂]²⁻. The salts obtained were characterized by IR spectroscopy, thermal analysis, powder and single crystal X-ray diffraction. The prepared compounds are isostructural and crystallize in the orthorhombic crystal system (space group I222, Z = 2). Thermal decomposition of the salts in helium or hydrogen atmosphere at 200-400 °C results in formation of nano-sized bimetallic powders. Depending on the phase diagram of the respective bimetallic system and temperature conditions, they can be single phase or multiphase products. In particular, thermal decomposition of double complex salts [M(NH₃)₄][Zn(Ox)₂(H₂O)₂] · 2H₂O (M = Pd, Pt) results in formation of PdZn and PtZn intermetallic compounds, correspondingly. Decomposition of [Pd(NH₃)₄][Ni(Ox)₂(H₂O)₂] · 2H₂O affords a disordered solid solution Pd_0.5Ni_0.5. Disordered Pt_0.5Ni_0.5 was obtained from [Pt(NH₃)₄][Ni(Ox)₂(H₂O)₂] · 2H₂O in helium atmosphere, while in hydrogen atmosphere - a two-phase mixture of disordered Pt_0.5Ni_0.5 and ordered PtNi. In all cases crystallite sizes of bimetallic particles varied within 50-250 Å.     

A dimanganese(II) complex with bridging chlorides: Synthesis, electrochemistry, magnetic behavior, structure and bonding

The synthesis of dimeric [Mn₂Cl₂(μ-Cl)₂(dipa)₂]·MeOH (3) (dipa = dipyridylmethylamine) from [MnCl₂(H₂O)₄] (1) and dipa (2) and its structural characterization is reported. In the solid state complex 3 is dimeric and possesses crystallographically imposed C₂ symmetry, which differs from similar dimanganese(II) complexes showing an inversion symmetry for the central Mn(μ-Cl)₂Mn arrangement. Each manganese atom is thereby bound by three nitrogen atoms from a facially coordinated dipa ligand, and three chlorides (1 terminal and 2 μ-bridging) in an octahedrally distorted fashion.The cylovoltammogram of 3 displays that the two manganese(II) ions can independently be oxidized. The magnetic properties of 3 were determined by susceptibility measurements versus temperature. The intramolecular J parameter was determined to a value of J = (−5.2 ± 0.5) cm⁻¹.     

Synthesis and crystal structure of one-dimensional zinc(II) polymer constructed by salicylate and trans-1,2-bis(4-pyridyl)ethylene

A new zinc(II) compound, [Zn₂(Hsal)₄(4,4′-bpe)₂] · [Zn(Hsal)₂(4,4′-bpe)(DMF)(H₂O)] · CH₃OH (1) (Hsal = salicylate and 4,4′-bpe = trans-1,2-bis(4-pyridyl)ethylene) has been synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. The crystal structure consists of three independent moieties: [Zn₂(Hsal)₄(4,4′-bpe)₂], [Zn(Hsal)₂(4,4′-bpe)(DMF)(H₂O)], and non-coordinated CH₃OH molecule. In the compound two independent moieties which are connected by 4,4′-bpe to form 1-D chains, respectively, are further expended to accomplish 2-D network through hydrogen-bonding interactions between non-coordinated methanol and coordinated water molecule or carboxylate oxygen atoms of Hsal ligands.     

Synthesis, crystal structures, and characterization of three coordination compounds constructed from 4-sulfophthalic acid ligand

Three new coordination compounds with 4-sulfophthalic acid (H₃SPA) ligand, namely {[Pb₃(4-SPA)₂(H₂O)](H₂O)}_n (1), [Mn(4,4′-bpy)₂(H₂O)₄][Mn₂(4-SPA)₂-(4,4′-bpy)₄(H₂O)₄]·7.5(H₂O) (2) and Cu₂(4-HSPA)₂(2,2′-bpy)₂(H₂O)₂ (3) (4,4′-bpy = 4,4′-bipyridine and 2,2′-bpy = 2,2′-bipyridine), have been synthesized. The structures exhibit different dimensionality depending on the nature of the metal ions and/or the ancillary ligands. Compound 1 has a 2D layered architecture constructed from one-dimensional inorganic lead(II) oxygen chains containing tetranuclear [Pb₄(μ₂-O)₄] cluster. Compound 2 has a dinuclear manganese [Mn₂(4-SPA)₂(4,4′-bpy)₄(H₂O)₄] motif charged with mononuclear [Mn(4,4′-bpy)₂(H₂O)₄]²⁺ cation. Compound 3 is a discrete dinuclear copper(II) structure that linked by extensive hydrogen bonds to form a three-dimensional supramolecular structure. In the solid state, compound 1 exhibits blue photoluminescence with the maximum at 432 nm upon excitation at 350 nm. The temperature-dependent magnetic susceptibility data of 2 have been investigated. The Curie constant C and Weiss constant θ are 3.14 emu K mol⁻¹ and −2.09 K, respectively, revealing antiferromagnetically magnetic interactions between the Mn²⁺ ions. In addition, these compounds are characterized by powder X-ray diffraction, IR, elemental analysis, and thermogravimetric analysis.     

Structural studies on manganese(III) and manganese(IV) complexes of tetrachlorocatechol and the catalytic reduction of dioxygen to hydrogen peroxide

The mononuclear complexes (Bu₄N)[Mn(Cl₄Cat)₂(H₂O)(EtOH)] and (Bu₄N)₂[Mn(Cl₄Cat)₃] (H₂Cat=1,2-dihydroxybenzene) have been synthesised and characterised by X-ray diffraction. This work provides a direct, independent, synthesis of these complexes and an interesting example of how solvent effects can promote the formation of either a manganese(III) or manganese(IV) complex of the same ligand. The characterisation of (Bu₄N)[Mn(Cl₄Cat)₂(H₂O)(EtOH)] supports previous work that manganese(III) is extremely reluctant to form tris (catecholato) complexes due to the short `bite distance' of catecholate oxygen atoms (2.79 Å) which are unable to span the elongated coordination axes of the Jahn-Teller distorted Mn(III) ion and explains the 2:1 and 3:1 tetrachlorocatechol:manganese ratios in the Mn(III) and Mn(IV) complexes, respectively. Hydrogen peroxide production using dioxygen and hydroxylamine as substrates in acetonitrile/water mixtures, under ambient conditions, can be demonstrated with both complexes, suggesting that neither labile coordination sites nor the oxidation state of the manganese are important to the catalytic system. Turn over frequencies (TOF, moles of H₂O₂ per moles of manganese per hour) of ∼10 000 h⁻¹ are obtained and this compares very favourably with the commercial production of hydrogen peroxide by the autoxidation of 2-ethylanthrahydroquinone (AO process).     

Synthesis, Solution and Solid State Structure of Titanium-Maltol Complex

The reaction of Cp₂TiCl₂ with two equivalents of maltol (3-hydroxy-2-methyl-4-pyrone) in water, at room temperature and pH of 5.4, leads to a complete replacement of Cp and chloride ligands affording, Ti(maltolato)₂(OH)₂. The complex has been characterized by IR, NMR and ESI-MS spectroscopic and cyclic voltammetry methods. In DMSO-d₆ solution, the complex shows two isomers in a ratio of 4:1, in which one OH signal can be identified per isomer. This suggests that in solution the complex is monomeric, most likely a chiral cis-Ti(maltolato)₂(OH)₂ and trans-Ti(maltolato)₂(OH)₂. The monomeric nature of the complex (in water/methanol 1:1) was verified by ESI-MS spectroscopy, showing a parent peak at 329 m/z. Electrochemical behavior of Ti(maltolato)₂(OH)₂using cyclic voltammetry experiments showed the complex undergoes irreversible reduction in aprotic solvents. In D₂O solution, at pH of 8.4, the ¹H NMR spectrum of the complex shows a mixture of monomer and tetramer Ti(IV)-maltol complexes in a ratio of 1:1. The crystallization of Ti(maltolato)₂(OH)₂ at pH of 8.4 leads to the formation of [Ti₄(maltolato)₈(μ-O₄)] · 18H₂O. A single crystal of [Ti₄(maltolato)₈(μ-O₄)] · 18H₂O was analyzed by X-ray diffraction methods. Solid state structure determination of the Ti-maltol complex showed to be tetrameric, containing two bridging oxides (in cis position) and two bidentate maltol ligands per titanium in a pseudo-octahedral coordination geometry.     

Structure and characterization of a μ-phenoxo-bis μ-acetato dinuclear Mn(II,II) complex [Mn2(LO)(μ-OAc)2](ClO4) (LOH = 2,6-bis{bis(2-(2-pyridyl)ethyl)aminomethyl}-4-methylphenol): Substituent effects

The synthesis, structure and characterization of the dinuclear Mn(II) complex [Mn₂(LO)(μ-OAc)₂](ClO₄) (1) where LOH = 2,6-bis{bis(2-(2-pyridyl)ethyl)aminomethyl)}-4-methylphenol are reported. The reaction of Mn(ClO₄)₂ · 6H₂O with the dinucleating ligand LOH and H₃CCOONa in the presence of NEt₃ in dry, degassed methanol and under an argon atmosphere, yields 1 as a colorless powder. The crystal structure of 1, determined by X-ray diffraction methods, shows a dinuclear Mn(II) complex in which two Mn(II) ions, each in six-coordinate approximate octahedral coordination, are bridged by the phenolate oxygen of LO⁻ and by two acetate ions in a syn,syn-1,3-bridging mode. The Mn-Mn distance is 3.557(1) Å and Mn-O_phenolate-Mn angle is 112.50(9)°. Cyclic voltammetry of 1 in acetonitrile solution shows a quasi-reversible wave at E_1/2 = 0.65 V, for the Mn₂(II,II)/Mn₂(II,III) redox process, and an irreversible oxidation peak at E_p,c = 1.22 V versus Ag/AgCl for the Mn₂(II,III) to Mn₂(III,III) oxidation process. Controlled potential electrolysis of 1 in acetonitrile solution at 0.85 V (versus Ag/AgCl) takes up 1 F of charge per mole of 1 to yield a brown solution of the Mn₂(II,III) state of the complex, which, however, is unstable and reverts back to the Mn₂(II,II) state in solution at room temperature. Least square fitting of the variable temperature magnetic susceptibility measurements on powdered sample of 1 is obtained with g = 1.888, J = −2.75 cm⁻¹, Par = 0.008, TIP = 0. The low −J value and the room temperature calculated magnetic moment of the complex (5.30 BM per Mn(II)), which is less than the spin-only moment of Mn(II), show that the two Mn(II) ions are weakly antiferromagnetically coupled.     

An oxamato bridged trinuclear copper(II) complex: Synthesis, crystal structure, reactivity, DNA binding study and magnetic properties

A linear tri-nuclear oxamato bridged copper(II) complex [Cu₃(pba)(dpa)₂(H₂O)(ClO₄)](ClO₄)·H₂O (1) (pbaH₄ = 1,3-propanediylbis(oxamic acid), dpa = 2,2′-dipyridylamine) was isolated from the reaction mixture of Na₂[Cu(pba)]·3H₂O, copper perchlorate hexahydrate and dipyridylamine in methanol. On reaction with dpa or DMF in basic medium (KOH) at ambient temperature complex 1 changed to dinuclear oxalate bridged copper(II) derivatives, [Cu₂(μ-C₂O₄)(dpa)₄](ClO₄)₂ (2) and [Cu₂(μ-C₂O₄)(dpa)₂(DMF)₂](ClO₄)₂ (3), respectively. The complexes 1, 2 and 3 have been characterized by physicochemical and spectroscopic tools, and also by the X-ray single crystal analysis. The hydrolysis of 1 in basic medium and thermo-gravimetric analysis has been studied. Absorption and emission spectral studies showed that complex 1 interacts with calf thymus-DNA (CT-DNA) with a binding constant (K_b) of 4.01 × 10⁴ M⁻¹ and linear Stern-Volmer quenching constant (K_sv) of 6.9 × 10⁴. A strong anti-ferromagnetic interaction with a coupling constant J_CuCu of 320.0 ± 0.3 cm⁻¹ was observed from the study of magnetic behavior of complex 1 in the temperature range of 2-300 K. Electrochemical equivalency of three copper(II) ions in 1 was identified by getting only one quasi reversible cyclic voltammogram.     

Trinuclear copper(II) complexes of bis(acylhydrazone) ligands. Structural analysis and magnetic properties of a sulfato-bridged hexanuclear dimer

The synthesis and spectroscopic characterization of the new symmetric, ligand bis(salicylaldehyde)methyliminodiacetylhydrazone (H₄MeImds) is reported. The reactions of H₄ MeImds with copper(II) chloride, nitrate and sulfate give trinuclear metal complexes of formula Cu₃(MeImds)Cl₂ · CHCl₃ · H₂O, Cu₃(MeImds)(NO₃)₂ · 2H₂O and Cu₃(MeImds)(SO₄) · 8H₂O; the trinuclear species are obtained in spite of the used metal:ligand molar ratio. The X-ray crystal structure of [Cu₃(MeImds)(SO₄)(H₂O)₃] · 5H₂O is determined; it consists of linear units, with the nonadentate ligand bound to three copper ions. The trimetallic units are bridged via sulfate anions to give hexanuclear dimers with an imposed centre of symmetry. The magnetic properties of [Cu₃(MeImds)(SO₄)(H₂O)₃] · 5H₂O are characterized by a significant antiferromagnetic coupling within the trimetallic units and by a weak antiferromagnetic coupling between them. The analogous trinuclear copper(II) complexes Cu₃(HImds)Cl₂ · H₂O and Cu₃(HImds)(SO₄) · 4H₂O (H₅Imds, bis(salicylaldehyde)iminodiacetylhydrazone) were also prepared and spectroscopically characterized.     

Synthesis, characterization, and crystal structure of a quadruply bonded dimolybdenum(II) complex containing the water-soluble phosphine 1,3,5-triaza-7-phosphaadamantane (PTA)

The quadruply bonded molybdenum(II)-molybdenum(II) complex, tetrachlorotetrakis(1,3,5-triaza-7-phosphaadamantane) dimolybdenum(II), Mo₂Cl₄(PTA)₄, was synthesized by reaction of 1,3,5-triaza-7-phosphaadamantane (PTA) with K₄[Mo₂Cl₈] in refluxing methanol. The complex was characterized using ¹H and ³¹P NMR, and UV-Vis spectroscopy, X-ray crystallography, and cyclic voltammetry. The Mo-Mo separation in the solid state structure is 2.13 Å, with the PTA and chloride ligands in an eclipsed arrangement with a P-Mo-Mo-Cl twist angle of 1.75(3)°. The ³¹P NMR spectrum contains a single peak at −62.8 ppm, and the ¹H NMR spectrum exhibits two singlets of equal height at 4.60 and 4.33 ppm. The UV-Vis spectrum contains three absorbance features at 615, 363, and 231 nm, with the absorbance at 615 nm due to the δ → δ* transition. The one electron oxidation of Mo₂Cl₄(PTA)₄ is reported at E_1/2 = 0.91 V relative to Ag/Ag⁺ in CH₂Cl₂. Also discussed is the reactivity of the molybdenum complex with CN⁻, H₂O, and HCl.     

New Nanomedicine Approaches Using Gold-thioguanine Nanoconjugates as Metallo-ligands

Reactions of [MCl₂(tmeda)] (M = Cd or Hg; tmeda = N,N,N′,N′-tetramethylethylenediamine) with M′SeC₅H₃(R-3)N (R = H or Me) gave selenolate complexes of the general formula [M{SeC₅H₃(R-3)N}₂(tmeda)_n] (M/R/n = Cd/H/1 (1); Cd/Me/1 (2); Hg/H/1 (3) and Hg/Me/0 (4)). The complexes were characterized by elemental analysis, UV-Vis and NMR (¹H, ¹³C, ⁷⁷Se, ¹¹³Cd and ¹⁹⁹Hg) spectroscopy. The crystal structures of {SeC₅H₃(Me-3)N}₂, [M(SeC₅H₄N)₂(tmeda)] (M = Cd or Hg) and [Hg{SeC₅H₃(Me-3)N}₂] were established by single crystal X-ray diffraction. The complex, [Cd(SeC₅H₄N)₂(tmeda)] comprises of an octahedral cadmium atom containing three chelating, two SeC₅H₄N and one tmeda, ligands. The corresponding mercury complex adopts a severely distorted tetrahedral configuration defined by the two-monodentate selenolate and chelating tmeda. The complex, [Hg{SeC₅H₃(Me-3)N}₂] has a linear structure with monodentate selenolate ligand. The cadmium complexes undergo a two-step decomposition (TGA) leading to the formation of CdSe. Thermolysis of [Cd{SeC₅H₃(R-3)N}₂(tmeda)_n] in hexadecylamine (HDA)/tri-n-octylphosphineoxide (TOPO) yields CdSe nanoparticles, which were characterized by UV-Vis, XRD, SEM and TEM (in part).     

Europium (III) complexes derived from carboxylic-substituted polychlorotriphenylmethyl radicals

Two europium (III) complexes (3 and 4) have been obtained reacting europium (III) nitrate and two polychlorotriphenylmethyl radicals properly functionalized with one (PTMMC⁻, 1) and six (PTMHC⁶⁻, 2) carboxylate groups, respectively. While complex 3 reveals a lamellar polar-apolar separated ion pair structure alternating PTM-based bilayers with nonaaquaeuropium cations ([Eu(H₂O)₉](PTMMC)₃(PTMMCH)₃ · 7H₂O · 6EtOH), complex 4 shows a one-dimensional chain-like structure with formula [Eu₂(PTMHC)(H₂O)₁₃] · 16H₂O · EtOH. Magnetic properties of both complexes were studied in the 2-300 K range, and show the presence of weak inter-radical antiferromagnetic interactions below 5 K.