Driving forces in substitution reactions of octahedral complexes: The influence of the competitive effect

The reaction of cis-[RuCl(2)(P-P)(N-N)] type complexes (P-P = 1,4-bis(diphenylphosphino)butane or (1,1`-diphenylphosphino)ferrocene; N-N = 2,2`-bipyridine or 1,10-phenantroline) with monodentate ligands (L), such as 4-methylpyridine, 4-phenylpyridine and benzonitrile forms [RuCl(L)(P-P)(N-N)](+) species Upon characterization of the isolated compounds by elemental analysis, (31)P{(1)H} NMR and X-ray crystallography it was found out that the type of the L ligand determines its position in relation to the phosphorus atom. While pyridine derivatives like 4-methylpyridine and 4-phenylpyridine coordinate trans to the phosphorus atom, the benzonitrile ligand (bzCN), a good pi acceptor, coordinates trans to the nitrogen atom. A (31)P{(1)H} NMR experiment following the reaction of the precursor cis-[RuCl(2)(dppb)(phen)] with the benzonitrile ligand shows that the final position of the entering ligand in the complex is better defined as a consequence of the competitive effect between the phosphorus atom and the cyano-group from the benzonitrile moiety and not by the trans effect. In this case, the benzonitrile group is stabilized trans to one of the nitrogen atoms of the N-N ligand. A differential pulse voltammetry experiment confirms this statement. In both experiments the [RuCl(bzCN)(dppb)(phen)]PF(6) species with the bzCN ligand positioned trans to a phosphorus atom of the dppb ligand was detected as an intermediate complex. (c) 2009 Elsevier Ltd. All rights reserved.

Synthesis and complexes of the sexidentate macrocycle 15-methyl-1,4,7,10,13-pentaazacyclohexadecan-15-amine

The potentially sexidentate polyamine macrocycle 15-methyl-1,4,7,10,13-pentaazacyclohexadecan-15-amine (1) was prepared via a copper(II)-templated route from 3,6,9-triazaundecan-1,ll-diamine, formaldehyde and nitroethane which first formed the copper(II) complex of the macrocycle 15-methyl-15-nitro-1,4,7,10,13-pentaazacyclohexadecane (2), reduced subsequently with zinc and aqueous acid to yield 1. The hexaamine 1, with five secondary amine groups in the macrocyclic ring and one pendant primary amine group, forms inert sexidentate octahedral complexes with cobalt(III), chromium(III) and iron(III). An X-ray structure of [Co(1)](ClO4)(3) defines the distorted octahedron of the complex cation and shows it is a symmetrical isomer with all nitrogens bound and the central aza group trans to the pendant primary amine group. The [M(1)](3+) ions are all stable indefinitely in aqueous solution and exhibit spectra consistent with MN6 d(3) (Cr), low-spin d(5) (Fe) and low-spin d(6) (Co) electronic ground states. For each complex, a reversible M(III/II) redox couple is observed. (C) 2000 Elsevier Science S.A. All rights reserved.

Cytotoxic iron chelators: Characterization of the structure, solution chemistry and redox activity of ligands and iron complexes of the di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) analogues

Di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) and a range of its analogues comprise a series of monobasic acids that are capable of binding iron (Fe) as tridentate (N,N,O) ligands. Recently, we have shown that these chelators are highly cytotoxic, but show selective activity against cancer cells. Particularly interesting was the fact that cytotoxicity of the HPKIH analogues is maintained even after complexation with Fe. To understand the potent anti-tumor activity of these compounds, we have fully characterized their chemical properties. This included examination of the solution chemistry and X-ray crystal structures of both the ligands and Fe complexes from this class and the ability of these complexes to mediate redox reactions. Potentiometric titrations demonstrated that all chelators are present predominantly in their charge-neutral form at physiological pH (7.4), allowing access across biological membranes. Keto-enol tautomerism of the ligands was identified, with the tautomers exhibiting distinctly different protonation constants. Interestingly, the chelators form low-spin (diamagnetic) divalent Fe complexes in solution. The chelators form distorted octahedral complexes with Fe-II, with two tridentate ligands arranged in a meridional fashion. Electrochemistry of the Fe complexes in both aqueous and non-aqueous solutions revealed that the complexes are oxidized to their ferric form at relatively high potentials, but this oxidation is coupled to a rapid reaction with water to form a hydrated (carbinolamine) derivative, leading to irreversible electrochemistry. The Fe complexes of the HPKIH analogues caused marked DNA degradation in the presence of hydrogen peroxide. This observation confirms that Fe complexes from the HPKIH series mediate Fenton chemistry and do not repel DNA. Collectively, studies on the solution chemistry and structure of these HPKIH analogues indicate that they can bind cellular Fe and enhance its redox activity, resulting in oxidative damage to vital biomolecules.

Isomers of 1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate characterized as cobalt(III) complexes

The major trans (1) and minor cis (2) isomers of 1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate have been characterized as the complexes [Co(1)](ClO4) and [Co(H-2)(OH2)]Cl(ClO4).H2O. The former crystallized in the C-2/c space group and the latter in the P2(1)/c space group, with cell parameters a 16.258(7), b 9.050(3), c 15.413(6) Angstrom, beta133.29(3)degrees, and a 9.694(4), b 16.135(1), c 12.973(5) Angstrom, beta 93.00(2)degrees, respectively. Their characterization completes identification of the respective trans and cis isomers for the series of C-pendant macrocycles also including 1,4,8,11-tetraazacyclotetradecane-6-amine-13-carboxylate ((3), (4)) and 1,4,8,11-tetraazacyclotetradecane-6,13-diamine ((5), (6)). The complexes show limited distortion from octahedral geometry with the strain in the presence of the coordinated C-pendant carboxylate significantly reduced compared with that for the C-pendant amine in analogues, a consequence mainly of six-membered as opposed to five-membered chelate rings involving the pendant donor. A comparison of the physical properties for the trans isomers of the octahedral complexes of (1), (3), and (5), which reflect progressively increasing strain, is presented.

Synthesis of new zirconium complexes

L'étude suivante décrit la synthèse des ligands nacnacxylH, nacnacBnH, nacnacR,RH et nacnacCyH en utilisant une méthode générale qui implique des rendements élevés et des coûts raisonnables, la complexation de ces ligands au Zr, la caractérisation de ces complexes et l’investigation de leurs réactivités. Les complexes de zirconium ont été obtenus en utilisant deux méthodes synthétiques principales : la première consiste en traitement du sel de lithium du ligand avec le ZrCl4. La seconde est la réaction du ligand neutre avec les complexes d’alkyl-zirconium(IV) par protonation de l'alkyle coordonné. Le ligand adopte deux modes de coordination avec le Zr. Une coordination 2 est observée dans les complexes octaèdriques contenant un ou deux ligands nacnac. En présence d'un autre ligand ayant une coordonnation 5, par exemple Cp ou Ind, le ligand nacnac se trouve en coordination x avec le centre métallique de zirconium. En solution, les complexes obtenus de (nacnac)2ZrX2 montrent un comportement dynamique via un « Bailar-twist » et les paramètres d'activation de cette isomérisation ont été obtenus. Le complexe octaèdrique (nacnacBn)2ZrCl2, 2c, n'a pas montré de réactivité dans la carbozirconation et son alkylation n'était pas possible par l’échange des chlorures avec les alkyles. L’analogue dimethylé (nacnacBn)2ZrMe2, 2d, peut être préparé par alkylation du ZrCl4 avant la complexation du ligand. Ce dernier a été prouvé aussi de ne pas être réactif dans la carbozirconation.

Syntheses, characterization and X-ray crystal structures of Ni(II) complexes of tridentate monocondensed and tetradentate dicondensed Schiff bases

Two octahedral complexes [Ni(HL1)(2)](ClO4)(2) (1) and [Ni(HL2)(2)](ClO4)(2) (2) and a square planar complex [Ni(HL3)]ClO4 (3) have been prepared, where [HL1 = 3-(2-amino-ethylimino)-butan-2-one oxime, HL2 = 3-(2-amino-propylimino)butan-2-one oxime] and H2L3 = 3-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-1-methyl-ethylimino]-buta n-2-one oxime. All the complexes have been characterized by elemental analyses, spectral studies and room temperature magnetic moment measurements. The molecular structures of all three compounds were elucidated on the basis of X-ray crystallography: complexes 1 and 2 are seen to be the met isomers. (C) 2008 Elsevier Ltd. All rights reserved.

Manganese(II) complexes with thiosemicarbazones as potential anti-Mycobacterium tuberculosis agents

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Espectros eletrônicos de alguns complexos de geometria octaédrica de Ni2+: uma introdução prática à teoria do campo cristalino no curso de graduação

The experiment introduces the undergraduate students to the crystal field theory. The electronic spectra of the octahedral complexes of [Ni(L)n]2+ (L = H2O, dmso, NH3 and en) obtained in the experiment are used to calculate 10Dq and B parameters. The experiment shows how the parameters can be calculated and correlated with the nature of the ligands and the field intensities produced.

Synthesis and Crystal Structures of Octahedral Sn(IV) Complexes Prepared from SnCl(2)center dot 2H(2)O and 2-Hydroxyacetophenone (S-benzydithiocarbazate) Ligand (H(2)L)

Two coordination octahedral Sn(IV) complexes [Sn(L)(2)] and cis-[SnCl(2)(L)(dmso)], where H(2)L is 2-hydroxyacetophenone (S-benzydithiocarbazate), were prepared and characterized by elemental analysis, IR, NMR ((1)H, (13)C), (119)Sn Mossbauer spectroscopies and X-ray diffraction techniques to investigate their structural properties. Both crystallize in the Monoclinic system, with parameters: a = 8.1905(3), b = 30.8811(15), c = 12.8959(7) angstrom, beta = 94.465(3)degrees and Z = 4 for [Sn(L)(2)] and a = 8.5247(2), b = 21.5445(7), c = 12.3706(3) angstrom, beta = 96.932(2)degrees and Z = 4 for cis-[SnCl(2)(L)(dmso)]. In both complexes, the Sn(IV) central atom is coordinated in a distorted octahedral geometry with the thiolate ligand (L(2-)) coordinated via O, N and S atoms. The (119)Sn Mossbauer spectroscopy of the complexes were studied and the results revealed that both complexes posses isomer shift (delta) and quadrupole splitting (Delta), which are almost the same.

First- and second-row transition metal oxa-aza macrocyclic complexes: a DFT study of an octahedral conformation

A theoretical study of structures of the 1,7,1 l,17-tetraoxa-2,6,12,16-tetraaza-cycloeicosane ligand ([20]AneN(4)O(4)) coordinated to Fe2+, Co2+, Ni2+, Ru2+, Rh2+, and Pd2+ transition metals ions was carried out with the DFT/B3LYP method. Complexes were fully optimized in C-s symmetry with the metal ions coordinated either to nitrogen (1a) or oxygen atoms (1b). For all the cases performed in this work, 1a was always more stable than 1b. Considering each row it is possible to see that the binding energy increases with the atomic number. The M2+ cation binding energies increase in the following order: Fe2+ < Ru2+ < Co2+ < Ni2+ < Rh2+ < Pd2+. In addition, it was observed the preference of Pd2+ and Rh2+ complexes for a tetrahedral arrangement, while Fe2+, Ru2+, Co2+, Ni2+ complexes had a preference for the octahedral arrangement. From the orbital representation results, it was seen that 1b unsymmetrical orbitals may influence the susceptibility over metal ions orientation toward heteroatoms orbitals.

Tuning of the charge in octahedral ferric complexes based on pyridoxal-N substituted thiosemicarbazone ligands

Four novel mononuclear coordination compounds namely: [Fe(Hthpy)2](SO4)1/2·3.5H2O 1, [Fe(Hthpy)2]NO3·3H2O 2, [Fe(H2mthpy)2](CH3C6H4SO3)3·CH3CH2OH 3 and [Fe(Hethpy)(ethpy)]·8H2O 4, (H2thpy = pyridoxalthiosemicarbazone, H2mthpy = pyridoxal-4-methylthiosemicarbazone, H2ethpy = pyridoxal-4-ethylthiosemicarbazone), were synthesized in the absence or presence of organic base, Et3N and NH3. Compounds 1 and 2 are monocationic, and were prepared using the singly deprotonated form of pyridoxalthiosemicarbazone. Both compounds crystallise in the monoclinic system, C2/c and P21/c space group for 1 and 2, respectively. Complex 3 is tricationic, it is formed with neutral bis(ligand) complex and possesses an interesting 3D channel architecture, the unit cell is triclinic, P1 space group. For complex 4, the pH value plays an important role during its synthesis; 4 is neutral and crystallises with two inequivalent forms of the ligand: the singly and the doubly deprotonated chelate of H2ethpy, the unit cell is monoclinic, C2/c space group. Notably, in 1 and 4, there is an attractive infinite three dimensional hydrogen bonding network in the crystal lattice. Magnetic measurements of 1 and 4 revealed that a rather steep spin transition from the low spin to high spin Fe(III) states occurs above 300 K in the first heating step. This transition is accompanied by the elimination of solvate molecules and thus, stabilizes the high spin form due to the breaking of hydrogen bonding networks; compared to 2 and 3, which keep their low spin state up to 400 K.

Polymerisable octahedral rhenium cluster complexes as precursors for photo/electroluminescent polymers

New polymerisable photoluminescent octahedral rhenium cluster complexes trans-[{Re6Q8}(TBP)4(VB)2] (Q = S or Se; TBP-p-tert-butylpyridine; VB-vinyl benzoate) have been synthesised, characterised and used to construct rhenium cluster-organic polymer hybrid materials. These novel polymer systems are solution-processable and the rhenium clusters retain their photoluminescent properties within the polymer environment. Notably, when the rhenium cluster complexes are incorporated into the matrix of the electroluminescent polymer poly(N-vinylcarbazole), the resultant cluster polymer hybrid combined properties of both components and was used successfully in the construction of a polymer light emitting diode (PLED). These prototype devices are the first PLEDs to incorporate octahedral rhenium clusters and provide the first direct evidence of the electroluminescent properties of rhenium clusters and indeed, to the best of our knowledge, of any member of the family of 24-electron hexanuclear cluster complexes of molybdenum, tungsten or rhenium.

Octahedral molybdenum cluster complexes with aromatic sulfonate ligands

This article describes the synthesis, structures and systematic study of the spectroscopic and redox properties of a series of octahedral molybdenum metal cluster complexes with aromatic sulfonate ligands (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] (where X- is Cl-, Br- or I-; OTs- is p-toluenesulfonate and PhSO3 - is benzenesulfonate). All the complexes demonstrated photoluminescence in the red region and an ability to generate singlet oxygen. Notably, the highest quantum yields (>0.6) and narrowest emission bands were found for complexes with a {Mo6I8}4+ cluster core. Moreover, cyclic voltammetric studies revealed that (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] confer enhanced stability towards electrochemical oxidation relative to corresponding starting complexes (nBu4N)2[{Mo6X8}X6].

Iron(III) and iron(II) complexes of 1-thia-4,7-diazacyclononane ([9]aneN(2)S) and 1,4-dithia-7-azacyclononane ([9]aneNS(2)). X-Ray structural analyses, magnetic susceptibility, Mossbauer, EPR and electronic spectroscopy

The complexes [Fe([9]aneN(2)S)(2)][ClO4](2), [Fe([9]aneN(2)S)(2)][ClO4](3) and [Fe([9]aneNS(2))(2)][ClO4](2) ([9]aneN(2)S = 1-thia-4. 7-diazacyclononane and [9]aneNS(2) = 1,4-dithia-7-azacyclononane) have been prepared and the latter two characterised by X-ray crystallography. The Mossbauer spectra (isomer shift/mm s(-1), quadrupole splitting/mm s(-1), 4.2 K) for [Fe([9]aneN(2)S)(2)][ClO4](2) (0.52, 0.57), [Fe([9]aneN(2)S)(2)][ClO4](3) (0.25, 2.72) and [Fe([9]aneNS(2))(2)][ClO4](2) (0.43, 0.28) are typical for iron(II) and iron(III) complexes. Variable-temperature susceptibility measurements for [Fe([9]aneN(2)S)(2)][ClO4](2) (2-300 K) revealed temperature-dependent behaviour in both the solid state [2.95 mu(B) (300 K)-0.5 mu(B) (4.2 K)] and solution (Delta H degrees 20-22 kJ mol(-1), Delta S degrees 53-60 J mol(-1) K-1). For [Fe([9]aneN(2)S)(2)][ClO4](3) in the solid state [2.3 mu(B) (300 K)-1.9 mu(B) (4.2 K)] the magnetic data were fit to a simple model (H = -lambda L . S + mu L-z) to give the spin-orbit coupling constant (lambda) of -260 +/- 10 cm(-1). The solid-state X-band EPR spectrum of [Fe([9]aneN(2)S)(2)][ClO4](3) revealed axial symmetry (g(perpendicular to) = 2.607, g(parallel to) = 1.599). Resolution of g(perpendicular to) into two components at Q-band frequencies indicated a rhombic distortion. The low-temperature single-crystal absorption spectra of [Fe([9]aneN(2)S)(2)][ClO4](2) and [Fe([9]aneNS(2))(2)][ClO4](2) exhibited additional bands which resembled pseudotetragonal low-symmetry splitting of the parent octahedral (1)A(1g) --> T-1(2g) and (1)A(1g) ---> T-1(1g) transitions. However, the magnitude of these splittings was too large, requiring 10Dq for the thioether donors to be significantly larger than for the amine donors. Instead, these bands were tentatively assigned to weak, low-energy S --> Fe-II charge-transfer transitions. Above 200 K, thermal occupation of the high-spin T-5(2g) ground state resulted in observation of the T-5(2g) --> E-5(g) transition in the crystal spectrum of [Fe([9]aneN(2)S)(2)][ClO4](2). From a temperature-dependence study, the separation of the low-spin (1)A(1g) and high-spin T-5(2g) ground states was approximately 1700 cm(-1). The spectrum of the iron(III) complex [Fe([9]aneN(2)S)(2)][ClO4](3) is consistent with a low-spin d(5) configuration.

Ni-II and Zn-II complexes of the hexadentate macrocyclic ligand cis-6,13-dimethyl-1,4,8,11-tetraazacyclotetra- decane-6,13-diamine

The title pendent-arm macrocyclic hexaamine ligand binds stereospecifically in a hexadentate manner, and we report here its isomorphous Ni-II and Zn-II complexes (both as perchlorate salts), namely (cis-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine-kappa(6)N)nickel(II) diperchlorate, [Ni(C12H30N6)](ClO4)(2), and (cis-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine-kappa(6)N)zinc(II) diperchlorate, [Zn(C-12 H30N6)](ClO4)(2). Distortion of the N-M-N valence angles from their ideal octahedral values becomes more pronounced with increasing metal-ion size and the present results are compared with other structures of this ligand.