Confinement of a bioinspired nonheme Fe(II) complex in 2D hexagonal mesoporous silica with metal site isolation.

A mixed amine pyridine polydentate Fe(II) complex was covalently tethered in hexagonal mesoporous silica of the MCM-41 type. Metal site isolation was generated using adsorbed tetramethylammonium cations acting as a patterned silanol protecting mask and trimethylsilylazane as a capping agent. Then, the amine/pyridine ligand bearing a tethering triethoxysilane group was either grafted to such a pretreated silica surface prior to or after complexation to Fe(II). These two synthetic routes, denoted as two-step and one-step, respectively, were also applied to fumed silica for comparison, except that the silanol groups were capped after tethering the metal unit. The coordination of the targeted complex was monitored using UV-visible spectrophotometry and, according to XPS, the best control was achieved inside the channels of the mesoporous silica for the two-step route. For the solid prepared according to the one-step route, tethering of the complex occurred mainly at the entrance of the channel.

Polymorphism in the spin-crossover ferric complexes [(TPA)Fe(III)(TCC)]PF6.

We have identified two polymorphs of the molecular complex [(TPA)Fe((III))(TCC)]PF(6) [TPA = tris(2-pyridylmethyl)amine and TCC = 3,4,5,6-tetrachlorocatecholate dianion]: one is monoclinic and the other is orthorhombic. By lowering the temperature both undergo a thermal spin-crossover between a high-spin (S = 5/2) and a low-spin (S = 1/2) state, which we detected by magnetic, optical and X-ray diffraction measurements. The thermal crossover is only slightly shifted between the polymorphs. Their crystalline structures consist of similar cation layers alternating with PF(6) anion layers, packed differently in the two polymorphs. The magnetic and optical properties of the polymorphs are presented.

Proton-mediated redox control in a nickel(II)-bisimidazolate complex: spectroscopic characterisation and density functional analysis.

The synthesis and characterisation of the pro-ligand LH4, in which L is the o-phenylenebisamide-2-imidazole and its nickel(II) complexes are reported. The X-ray structures of the fully protonated [NiLH2] and deprotonated [NiL] complexes are presented. The effects of the deprotonation of the imidazole functions on the electronic structure of the complexes are analysed by (1)H NMR, UV/Vis and IR spectroscopy and cyclic voltammetry. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations support the analysis based on experimental data. The singly oxidised form of the deprotonated complex [NiL] was generated by preparative electrolysis and its electronic structure was investigated. Spectroelectrochemistry shows the appearance of intense transitions in the region lambda = 600-900 nm with several isosbestic points. X-band EPR spectroscopy presents an isotropic signal at g = 2.03, whereas the Q-band EPR reveals a weak anisotropic signal characteristic of a metalloradical species. DFT and TDDFT data support the description of the species as a nickel(II)-radical form, with a major contribution of the spin density on the phenylene ring and the amidate functions with a negligible participation of the imidazolate groups. This finding is in sharp contrast with those obtained from the one-electron-oxidised form of nickel(II) complexes containing phenolate groups.

Fe(II) mononuclear complexes with a new aminopyridyl ligand bearing a pivaloylamido arm. Preparation and spectroscopic characterizations of a Fe(III)-hydroperoxo complex with oxygen and nitrogen donors.

Two new mononuclear FeII complexes, [(L52aH)FeII](PF6)2 (1-(PF6)2) and [(L52a)FeII]BPh4 (2-(BPh4)) have been synthesized with the new aminopyridyl ligand bearing a pivaloylamido arm L52aH (2,2-dimethyl-N-[6-({[2-(methyl-pyridin-2-ylmethyl-amino)-ethyl]-pyridin-2-ylmethyl-amino}-methyl)-pyridin-2-yl]-propionamide), or its deprotonated form L52a-. The structures of the ferrous complexes have been determined by X-ray analysis. The mononuclear FeII is in a pseudo-octahedral environment in both complexes, the six positions around the metal center being occupied by five nitrogen atoms and one oxygen atom from the ligand. Whatever the protonation state of the amide function, the structures are very similar, the FeII being 6-fold coordinated by the two amines, three pyridines, and the oxygen atom from the ligand. These two complexes exhibit an acid/base equilibrium in solution that has been studied by UV-vis spectroscopy and cyclic voltammetry in acetonitrile. The reactivity of 1-(PF6)2 with H2O2 in methanol affords the formation of a new low-spin FeIII(OOH) intermediate in which the oxygen atom is retained in the coordination sphere of the metal.

Structures of Fe(II) Complexes with N,N,N'-Tris(2-pyridylmethyl)ethane-1,2-diamine Type Ligands. Bleomycin-like DNA Cleavage and Enhancement by an Alkylammonium Substituent on the N' Atom of the Ligand.

The complexes [L(5)Fe(II)Cl]BPh(4) and [L(5)Fe(II)(H(2)O)](BPh(4))(2) (L(5) = N,N,N'-tris(2-pyridylmethyl)-N'-methyl-ethane-1,2-diamine) have been isolated. Bernal et al. (Bernal, J.; et al. J. Chem. Soc., Dalton Trans. 1995, 3667-3675) have prepared this ligand and the corresponding complex [L(5)Fe(II)Cl]PF(6). We obtained the structural data of [L(5)Fe(II)Cl]BPh(4) by X-ray diffraction. It crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 17.645(7) Å, b = 16.077(6) Å, c = 13.934(5) Å, V = 3953(3) Å(3), and Z = 4. It presents Fe(II)-N bond lengths close to 2.2 Å, typical of high-spin Fe(II). In solution the [L(5)Fe(II)(H(2)O)](BPh(4))(2) complex showed a dependence of spin state upon the nature of the solvent. It was high spin in acetone and changed to low spin in acetonitrile. This was detected by UV-vis spectroscopy and by (1)H NMR. Bernal et al. (ibidem) showed that these complexes in the presence of an excess of H(2)O(2) give a purple species, very likely the [L(5)Fe(III)(OOH)](2+) derivative, with spectroscopic signatures analogous to those of "activated bleomycin". The formation of [L(5)Fe(III)(OOH)](2+) is confirmed here by electrospray ionization mass spectrometry. We found that a L(5)/Fe system gave single-strand breaks on plasmid DNA in the presence of either a reducing agent (ascorbate) and air or oxidants (H(2)O(2), KHSO(5), MMPP) at 0.1 &mgr;M concentration. The methyl group in L(5) was substituted by a (CH(2))(5)N(CH(3))(3)(+) group in order to get higher affinity with DNA. The corresponding ligand L(5)(+) was used to prepare the complexes [L(5)(+)Fe(II)Cl]Y(2) (Y = BPh(4)(-), PF(6)(-), ClO(4)(-)) and [L(5)(+)Fe(II)Br](PF(6))(2). The crystal structure of [L(5)(+)Fe(II)Cl](ClO(4))(2) was solved. It crystallizes in the monoclinic space group P2(1)/a with a = 14.691(2) Å, b = 13.545(2) Å, c = 17.430(2) Å, beta = 93.43(1) degrees, V = 3462(1) Å(3), and Z = 4. The Fe(II)-ligand distances are similar to those of [L(5)Fe(II)Cl]BPh(4). At the relatively low concentration of 0.01 &mgr;M, [L(5)(+)Fe(II)Br](2+) promoted DNA breaks. The reaction was not inhibited by hydroxyl radical scavengers. The reaction might involve a nondiffusible oxygen reactive species, either a coordinated hydroperoxide or a high-valent metal-oxo entity.