Dinitrogen complexes of iron(II) with chelating agents as ligands

Two new dinitrogen compounds of formulae Na₂[Fe(EDTA)N₂].2H₂O and Na₂[Fe(CDTA)N₂].2H₂O have been synthesized from [Fe(H-EDTA)H₂O] and [Fe(H-CDTA)-H₂O], respectively, and NaN₃. Both complexes have been characterized by IR and electronic spectra. The thermal behaviour has been studied by TG and DTA techniques.     

Highly cytotoxic palladium(ii) complexes with 1,2,4-triazole-derived carbene ligands

Two novel palladium(ii) complexes, trans-[PdBr₂(tz-Mes)₂] and trans-[PdBr₂(tz-Dipp)₂] featuring less explored 1,2,4-triazole-derived N-heterocyclic carbene (tz) have been synthesized. In solution, they exist both as trans-syn and trans-anti rotamers while their syn/anti ratios can be determined by ¹H NMR harnessing the built-in aromatic rings as NMR probes. Complex trans-[PdBr₂(tz-Mes)₂] is highly cytotoxic toward A549, MCF-7, LNCaP and HT-29 cancerous cells.     

Gaseous iron(II) and iron(III) complexes with BINOLate ligands

Electrospray ionization (ESI) of dilute solutions of 1,1'-bi-2-naphthol (BINOL) and iron(II) or iron(III) sulfate in methanol/water allows the generation of monocationic complexes of iron and deprotonated BINOL ligands with additional methanol molecules in the coordination sphere, and the types of complexes formed can be controlled by the valence of the iron precursors used in ESI. Thus, iron(II) sulfate leads to [(BINOLate)Fe(CH3OH)n]+ complexes (n=0-3), whereas usage of iron(III) sulfate allows the generation of [(BINOLdiate)-Fe(CH3OH)n]+ cations (n=0-2); here, BINOLate and BINOLdiate stand for singly and doubly deprotonated BINOL, respectively. Upon collision-induced dissociation, the mass-selected ions with n>0 first lose the methanol ligands and then undergo characteristic fragmentations. Bare [(BINOLdiate)Fe]+, a formal iron(III) species, undergoes decarbonylation, which is known as a typical fragmentation of ionized phenols and phenolates either as free species or as the corresponding metal complexes. The bare [(BINOLate)Fe]+ cation, on the other hand, preferentially loses neutral FeOH to afford an organic C20H12O+* cation radical, which most likely corresponds to ionized 1,1'-dinaphthofurane.     

Three novel trinuclear zinc(II)/nickel(II) complexes with pentadentate ligands N-nitrobenzoylsalicylhydrazidate

Three trinuclear zinc(II)/nickel(II) complexes with two pentadentate ligands, N-p-nitrobenzoylsalicylhydrazidate (H₃-p-nbzshz) and N-o-nitrobenzoylsalicylhydrazidate (H₃-o-nbzshz) have been synthesized and characterized by X-ray crystallography. The complex [Zn₃(p-nbzshz)₂(C₅H₅N)₄]_n (1) molecule exhibits a one-dimensional wave-like chain structure resulting from the linkage of phenolate oxygen donor atoms of the ligands between neighboring motifs. The two nickel(II) complexes, Ni₃(p-nbzshz)₂(C₅H₅N)₄ (2) and Ni₃(o-nbzshz)₂(C₃H₇NO)₂(C₂H₆O)₂ (3) are trinuclear complexes in which three nickel(II) centers exhibit alternating square-planar and octahedral geometries. Complex 2 exhibits a curved Ni₃ metal arrangement with a Ni(1)–Ni(2)–Ni(3) angle of 62.36°, while the three nickel atoms in complex 3 are strictly linear with an angle of 180°.     

Osmium(VI) complexes as a new class of potential anti-cancer agents

A nitridoosmium(VI) complex [Os(VI)(N)(sap)(OH(2))Cl] (H(2)sap = N-salicylidene-2-aminophenol) displays prominent in vitro and in vivo anti-cancer properties, induces S- and G2/M-phase arrest and forms a stable adduct with dianionic 5'-guanosine monophosphate.     

Spin-state splittings of iron(II) complexes with trispyrazolyl ligands

We report a computational study at the OPBE/TZP level on the chemical bonding and spin ground-states of mono-nuclear iron(II) complexes with trispyrazolylborate and trispyrazolylmethane ligands. We are in particular interested in how substitution patterns on the pyrazolyl-rings influence the spin-state splittings, and how they can be rationalized in terms of electronic and steric effects. One of the main observations of this study is the large similarity of the covalent metal–ligand interactions for both the borate and methane ligands. Furthermore, we find that the spin-state preference of an individual transition-metal (TM) complex does not always concur with that of an ensemble of TM-complexes in the solid-state. Finally, although the presence of methyl groups at the 3-position of the pyrazolyl groups leads to ligand–ligand repulsion, it is actually the loss of metal–ligand bonding interactions that is mainly responsible for shifts in spin-state preferences.     

Syntheses and crystal structures of a series of palladium(II) and platinum(II) complexes bearing new hydrazine-based bisphosphinite ligands equipped with pyridyl arms

This paper reports the synthesis of the hydrazine-based bisphosphinito ligands (RO)₂PN(Me)N(Me)P(OR)₂ (R = 2-hydroxy-6-methyl-pyridyl or 3-hydroxy-6-methyl-pyridyl) and their palladium and platinum complexes whose structures were unequivocally determined by X-ray crystallography.     

Spectroscopic,structural and magnetic studies of nickel(II) complexes with tetra- and pentadentate ligands

Abstract  Two new nickel(II) complexes, namely [Ni(BPSE)](BF₄) 1, and [Ni (5-BST)CH₃OH]ClO₄ 2 [BPSE = 2-benzoylpyridinesalicylidene ethylenediamine, 5-BST = 5-bromosalicylidene-tris(2-aminoethyl)amine] have been synthesized and characterized using various physico-chemical methods. The magnetic and spectroscopic data indicate a distorted square planar geometry for complex 1, while complex 2 is assigned a distorted octahedral geometry. Complex 1 crystallized in the triclinic space group P-1. Complex 2 adopts an octahedral geometry with space group symmetry P 21/n. The superoxide dismutase activity of these complexes has been measured. Graphical Abstract  This paper describes three new nickel (II) complexes viz; [Ni(BPSE)](BF4) 1, [Ni(BSE)] 2 and [Ni (5-BST) CH3OH] ClO4 3 [BPSE = 2-benzoylpyridine salicyledene-ethylenediamine, BSE = bis(salicylaldehyde) ethylenediamine, 5-BST = 5-bromosalicyledene-tris(2-amino ethyl) amine]. The magnetic and spectroscopic data indicate a distorted square planar geometry for complex 1 and 2, while the comlplex 3 is assigned a distorted octahedral geometry. Superoxide dismutase activity of these complexes have also been measured. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and properties of iron(II) and manganese(II) complexes derived from a topologically constrained pentadentate ligand

The novel bicyclic pentadentate ligand 5-methyl-1,5,9,24,25-pentaazapentacyclo[7.7.7.5.5]pentacosane11,13,15,18(25),20,22-hexene (L1) has been synthesized. Because of its cross-bridged topology it exhibits a relatively rigid preorganized conformation especially appropriate to complex formation, as shown by the crystal structure of the monoprotonated ligand salt, HL1ClH2O [orthorhombic, P212121, a = 9.4405(5) A, b = 13.3617(5) A, c = 16.710(1) A]. The complexes of L1 with both iron(II) and manganese(II) have been characterized, including the crystal structures of [FeL1CH3CN][FeCL4] and [MnL1Cl][PF6] [monoclinic, P21/n, a = 10.0460(5) A, b = 19.237(9) A, c = 15.6254(8) A, beta = 95.97(2)degrees and a = 7.745(2) A, b = 22.786(4) A, c = 14.639(4) A, beta = 105.074(10)degrees respectively]. The manganese complex is high spin with mueff = 5.96 and theta = 2.5 +/- 0.8 cm(-1), indicating weak ferromagnetic interactions. The reactions of the complexes with tert-butyl hydroperoxide and hydrogen peroxide have been shown by ESR spectroscopy to produce the tert-butyl peroxyl and hydroperoxyl radicals, as evidenced by their spin adducts with the spin traps N,N-dimethyl-1-pyrroline-N-oxide and N-tert-butyl-phenyl-nitrone.     

Stereoselectivity in reactions of metal complexes IX Stereoselective formation of cobalt(III) complexes with new linear pentadentate ligands

The synthesis of cobalt(III) complexes with the new linear pentadentate ligands meso- and racemic 2,6-bis(3S)-3-carboxy-4-methyl-2-azapentylpyridine ( 2 ) are described. Only one of the different possible isomers is obtained from each ligand. The structure of the complexes has been assigned on the basis of their ¹H-NMR and CD spectra. The structure of the aqua-cobalt(III)- 1a and the aqua-cobalt(III)- 1b has been confirmed by X-ray analysis. Partial resolution of optical antipodes of the aquacobalt(III)- 1b was achieved by column chromatography and a tentative assignment of their absolute configuration is made.     

High-spin and low-spin iron(II) complexes with facially-coordinated borohydride ligands

Rare examples of monometallic high-spin and low-spin L3Fe(H3BH) complexes have been characterized, where the two L3 ligands are [TpPh2] and [PhBP3] ([TpPh2] = [HB(3,5-Ph2pz)3]- and [PhBP3] = [PhB(CH2PPh2)3]-). The structures are reported wherein the borohydride ligand is facially coordinated to the iron center in each complex. Density functional methods have been employed to explain the bonding in these unusual iron(II) centers. Despite the differences in spin states, short Fe-B distances are observed in both complexes and there is significant theoretical evidence to support a substantial bonding interaction between the iron and boron nuclei. In light of this interaction, we suggest that these complexes can be described as (L3)Fe(eta4-H3BH) complexes.     

High turnover catalysis of water oxidation by Mn(II) complexes of monoanionic pentadentate ligands

Capillary electrophoresis (CE) and electrospray ionisation (ESI) mass spectra of aqueous solutions of manganese(II) complexes of the monoanions of the pentadentate ligands N-methyl-N'-carboxymethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (mcbpen(-)) and N-benzyl-N'-carboxymethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (bcbpen(-)), show the presence of a mixture of closely related Mn(II) species, assigned to the mono, di-, tri- and poly-cationic complexes [Mn(II)(L)(H(2)O)](n)(n+), L = mcbpen(-) or bcbpen(-) with n = 1, 2, 3, etc. In solution, these complexes are reversibly oxidized by tert-butyl hydrogen peroxide (TBHP), (NH(4))(2)[Ce(NO(3))(6)], Ce(ClO(4))(4), oxone and [Ru(bipy)(3)](3+) to form metastable (t(?) = min to h) higher valent (hydr)oxide species, showing a collective maximum absorbance at 430 nm. The same species can be produced by [Ru(bipy)(3)](2+)-mediated photooxidization in the presence of an electron acceptor. TBHP oxidation of the complexes, in large excesses of the TBHP, is concurrent with an O(2) evolution with turnovers of up to 1.5 × 10(4) mol of O(2) per mol of [Mn] and calculated rate constants from two series of experiments of 0.039 and 0.026 mol[O(2)] s(-1) M(-2). A 1:1 reaction of TBHP with [Mn] is rate determining and the resultant species is proposed to be the mononuclear, catalytically competent, [Mn(IV)(O)(mcbpen)](+). At very close m/z values [Mn(III)(OH)(mcbpen)](+), [Mn(2)(III/IV)(O)(2)(mcbpen)(2)](+) and [Mn(IV)(2)(O)(2)(mcbpen)(2)](2+) are detected by ESI MS and CE when the concentration of TBHP is comparable to or lower than that of [Mn]. These are conditions that occur post catalysis and these species are derived from [Mn(IV)(O)(mcbpen)](+) through condensation reactions.     

Copper(II) and nickel(II) complexes of a neutral pentadentate Schiff base

A new pentadentate Schiff base 2,6,10-triaza-1,11-bis(2′-aminophenyl)-undeca-1,10-diene, abaDPT, and its complexes of general formula M(abaDPT)X₂ where M = Cu(II), Ni(II), X = Cl, Br, I, NO₃ and ClO₄, have been prepared. The complexes have been characterized by electronic and IR spectra, EPR, magnetic moments, molar conductances, and elemental analysis. IR data show an interaction between halide anion of the outer coordination sphere and the complexed amino group. EPR and spectrophotometric data of most of the copper compounds are consistent with a distorted square pyramidal geometry. Single crystal EPR studies of Cu(abaDPT)(NO₃)₂ and Cu(abaDPT)Br₂ revealed that copper atoms in the former compound occupy two magnetically inequivalent places in the lattice while copper atoms in the latter compound take identical sites. Principal g tensor axes of the two compounds have been determined.     

Chromium(III), manganese(II), iron(III), cobalt(II), nickel(II) and copper(II) complexes with a pentadentate, 15-membered new macrocyclic ligand

Complexes of Cr^III, Mn^II, Fe^III, Co^II, Ni^II and Cu^II containing a macrocyclic pentadentate nitrogen–sulphur donor ligand have been prepared via reaction of a pentadentate ligand (N₃S₂) with transition metal ions. The N₃S₂ ligand was prepared by [1 + 1] condensation of 2,6-diacetylpyridine with 1,2-di(o-aminophenylthio(ethane. The structures of the complexes have been elucidated by elemental analyses, molar conductance, magnetic susceptibility measurements, i.r., electronic and e.p.r. spectral studies. The complexes are of the high spin type and are six-coordinate.     

Binding of pi-acceptor ligands to (triamine)iron(II) complexes

A series of (Me3TACN)FeII derivatives with soft coligands have been investigated, where Me3TACN is N,N',N"-trimethyl-1,4,7-triazacyclononane. Treatment of Me3TACN with FeCl2 afforded a compound with the empirical formula (Me3TACN)FeCl2 (1). Compound 1, which is a versatile precursor reagent, was shown by single-crystal X-ray diffraction to be the salt [(Me3TACN)2Fe2Cl3][(Me3TACN)FeCl3], containing isolated [(Me3TACN)2Fe2Cl3]+ and [(Me3TACN)FeCl3]- subunits. Treatment of 1 with NaBPh4 gave the known [(Me3TACN)2Fe2Cl3]BPh4, while the addition of Me3TACN to FeCl4(2-) gave [(Me3TACN)FeCl3]-. Oxygenation of 1 afforded [(Me3TACN)FeCl2]2(mu-O), which was shown crystallographically to be centrosymmetric with a pair of distorted octahedral Fe centers. The Fe-N bond trans to the Fe-O bond is elongated by 02 A relative to the other Fe-N distances. Solutions of 1 and thiolates absorb CO to give [(Me3TACN)Fe(SPh)(CO)2]BPh4 and (Me3TACN)Fe(S2C2H4)(CO) (nu CO = 1896 cm-1). Treatment of 1 with excess CN- afforded [(Me3TACN)Fe(CN)3]-, isolated as its PPh4+ salt 5. Crystallographic and spectroscopic studies show that 5 is low spin with a C3v structure; its Fe-N distances contracted by 023 A relative to those in [(Me3TACN)FeCl3]-. Aqueous solutions of 1 bind CO upon the addition of CN- to produce (Me3TACN)Fe(CN)2(CO) (6) Analogous to 6 is (Me3TACN)Fe(CN)2(CNMe), prepared by methylation of 5. The metastable dicarbonyl [(Me3TACN)FeI(CO)2]I was prepared by treatment of FeI2(CO)4 with Me3TACN and was crystallographically characterized as its BPh4- salt. Values of E1/2 for [(Me3TACN)FeCl3]-, 5, and 6 are -0409, -0640, and 0533 V vs Fc/Fc+, respectively.     

Nitrosubstituted hydroxamate ligands in new triphenyltin(IV) complexes as prospective antimicrobial agents

New triphenyltin(IV) hydroxamate complexes, [Ph₃Sn(4-NO₂CnH)] and [Ph₃Sn(4-NO₂BzH)] have been synthesized by the reactions of Ph₃SnCl with potassium 4-nitrocinnamo hydroxamate [4-NO₂C₆H₄CHCHCONHOK] (KHL¹) and potassium 4-nitro benzohydroxamate [4-NO₂C₆H4CONHOK] (KHL²). The complexes were synthesized in 1:1 molar ratio in MeOH?+?C₆H₆ and characterized by physicochemical and IR, ¹H NMR, and mass spectrometry. The bidentate hydroxamate involving bonding through carbonyl and hydroxamic oxygen (O, O coordination) has been inferred from IR spectra. The electrochemical behavior of complexes has been analyzed. Quasi-irreversible two electron metal-centered cathodic process of type Sn^IV/Sn^II redox couple was indicated by cyclic voltammetric technique. The thermal behavior of 1 and 2 studied by TGA has shown continuous decomposition to yield Sn + 0.5SnO₂ and SnO₂ as final residues. The in vitro antimicrobial activity assays of 1 and 2 against pathogenic Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus), Gram-negative bacteria (Salmonella typhi and Pseudomonas aeruginosa), and fungi (Aspergillus fumigatus and Alternaria alternata) were done by MIC method. The complexes have exhibited appreciable antimicrobial activity relative to the respective standard Gentamycin and Nystatin drugs.     

Structural and catalytic aspects of copper(II) complexes containing 2,6-bis(imino)pyridyl ligands

The synthesis, structure, and ligand substitution mechanism of a new five-coordinate trigonal-bipyramidal copper(II) complex, [Cu^II(py ^tBuMe₂N₃)Cl₂] (1), with a sterically constrained py ^tBuMe₂N₃ chelate ligand, py ^tBuMe₂N₃?=?2,6-bis-(ketimino)pyridyl, are reported. The kinetics and mechanism of chloride substitution by thiourea, as a function of nucleophile concentration, temperature, and pressure, were studied in detail and compared with an earlier study reported for the analogous complex [Cu^II(py ^tBuN₃)Cl₂] (2) [py ^tBuN₃?=?2,6-bis-(aldimino)pyridyl]. Catalysis of the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone by 1 and 2 was studied. Correlations between the reactivity, chloride substitution behavior, and reduction potentials of both complexes were made. These show that the rate of oxidation is independent of the rate of chloride substitution, indicating that the substitution of chloride by catechol as substrate occurs in a fast step. Spectral data show a non-linear relationship between the ability of the complexes to oxidize 3,5-DTBC and the Lewis acidity of their copper(II) centers. Electrochemical data demonstrate that the most effective complex 1 has a E ⁰ value that approaches the E ⁰ value of the natural tyrosinase enzyme.     

Water exchange on seven-coordinate Mn(II) complexes with macrocyclic pentadentate ligands: insight in the mechanism of Mn(II) SOD mimetics

Seven-coordinate manganese(II) complexes [Mn(L)(H2O)2]2+, where L represents an equatorial pentadentate macrocyclic ligand with five nitrogen donor atoms, were studied with regard to their acid-base properties, water-exchange rate constants, and corresponding activation parameters (DeltaH, DeltaS, and DeltaV). Three of the studied complexes without imine bonds in the macrocyclic ligand are proven superoxide dismutase (SOD) mimetics. Their water-exchange parameters were compared with those of the imino groups containing complex [Mn(L1)(Cl)2] (dichloro-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]-octadeca-1(18),2,12,14,16-pentaenemanganese(II)), which does not show SOD activity. In addition the X-ray crystal structure of a new complex, dichloro-2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]pyridine-manganese(II) [Mn(L2)(Cl)2], which is the acyclic analog of [Mn(L1)(Cl)2], is reported. Stability constants of the complexes and the pKa values of the ligands were measured by potentiometric titration. The titrations of [Mn(L1)(H2O)2]2+ and [Mn(L2)(H2O)2]2+ led to complicated species distribution curves because of their ligands containing imine bonds. Water exchange was measured by temperature- and pressure-dependent 17O NMR techniques. In addition to the measurements on [Mn(EDTA)(H2O)]2- and its derivatives, this is the only study of water exchange on seven-coordinate manganese complexes. The water exchange rate constants vary between 1.6 x 107 s-1 and 5.8 x 107 s-1 at 25 degrees C and are mainly controlled by the pi-acceptor abilities of the ligands. The exchange rate constant of the diaqua-1,4,7,10,13-pentaazacyclopentadecanemanganese(II) [Mn([15]aneN5)(H2O)2]2+ complex seems to be even higher but could not be exactly determined. On the basis of the obtained activation parameters, the exchange mechanism of the studied seven-coordinate manganese(II) complexes follows a dissociative pathway (Id mechanism). DFT calculations (UB3LYP/LANL2DZp) were performed to obtain the energy required for the dissociation of the coordinated water molecule, that is, the energy difference between the starting seven-coordinate complex and a six-coordinate intermediate. The results have been discussed in terms of the catalytic mechanism of the proven SOD mimetics.