Sergey Malinkin

Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions

Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.

cyclo-Tetra­kis(μ-3-acetyl-4-methyl-1H-pyrazole-5-carboxyl­ato-κ4N2,O3:N1,O5)tetra­kis[aqua­copper(II)] tetra­deca­hydrate

The title compound, [Cu4(C7H6N2O3)4(H2O)4]·14H2O, a tetranuclear [2 × 2] grid-type complex with S4 symmetry, contains four CuII atoms which are bridged by four pyrazolecarboxylate ligand anions and are additionally bonded to a water molecule. Each CuII atom is coordinated by two O atoms of the carboxylate and acetyl groups, two pyrazole N atoms of doubly deprotonated 3-acetyl-4-methyl-1H-pyrazole-5-carboxylic acid and one O atom of a water molecule. The geometry at each CuII atom is distorted square-pyramidal, with the two N and two O atoms in the equatorial plane and O atoms in the axial positions. O—H⋯O hydrogen-bonding interactions additionally stabilize the structure. One of the uncoordinated water molecules shows half-occupancy.

(μ-3-Acetyl-5-carboxyl­ato-4-methyl­pyrazolido-1:2κ4N2,O3:N1,O5)-μ-chlorido-tetra­pyridine-1κ2N,2κ2N-chlorido-1κCl-dicopper(II) propan-2-ol solvate

The title compound, [Cu2(C7H6N2O3)Cl2(C5H5N)4]·C3H8O, is a binuclear pyrazolate complex, in which the two CuII atoms have different coordination numbers and are connected by a bridging Cl atom. One CuII atom has a distorted square-pyramidal coordination environment formed by two pyridine N atoms, one bridging Cl atom and an N,O-chelating pyrazolate ligand. The other CuII atom adopts an octahedral geometry defined by two pyridine N atoms at the axial positions, two Cl atoms and the coordinated pyrazolate ligand in the equatorial plane. An O—H⋯O hydrogen bond connects the complex molecules and propan-2-ol solvent molecules into pairs. These pairs form columns along the a axis.

(3-Acetyl-4-methyl-1H-pyrazol-1-ide-5-carboxyl-ato)bis-(1,10-phenanthroline)nickel(II) 3.5-hydrate.

The title compound, [Ni(C7H6N2O3)(C12H8N2)2]·3.5H2O, crystallizes as a neutral mononuclear complex with 3.5 solvent water molecules. One of the water molecules lies on an inversion centre, so that its H atoms are disordered over two sites. The coordination environment of NiII has a slightly distorted octahedral geometry, which is formed by one O and five N atoms belonging to the N,O-chelating pyrazol-1-ide-5-carboxylate and two N,N′-chelating phenanthroline molecules. In the crystal, O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds involving the solvent water molecules and pyrazole-5-carboxylate ligands form layers parallel to the ab plane. These layers are linked further via weak π–π interactions between two adjacent phenanthroline molecules, with centroid-to-centroid distances in the range 3.886 (2)–4.018 (1) Å, together with C—H⋯π contacts, forming a three-dimensional network.

1-{3-[1-(Hydroxyimino)ethyl]-4-methyl-1H-pyrazol-5-yl}ethanone.

In the title compound, C8H11N3O2, the oxime and the acetyl groups adopt a transoid conformation, while the pyrazole H atom is localized in the proximity of the acetyl group and is cis with respect to the acetyl O atom. In the crystal, dimers are formed as the result of hydrogen-bonding interactions involving the pyrazole NH group of one molecule and the carbonyl O atom of another. The dimers are associated into sheets via O—H⋯N hydrogen bonds involving the oxime hydroxyl and the unprotonated pyrazole N atom, generating a macrocyclic motif with six molecules.

Crystal structure and DFT study of 2-(pyren-1-yl)-1H-benzimidazole

The title compound was prepared from an equimolar mixuture of o-phenylenediamine and pyrene-1-carboxaldehyde. We report herein on its crystal structure and a density functional theory (DFT) study.

Crystal structure and DFT study of bis{(S)-2-[(2-hydroxybenzyl)amino]-4-methylpentanoato-κ2N,O}(1,10-phenanthroline-κ2N,N′)nickel(II)

The title compound was prepared from an equimolar mixuture of nickel nitrate, phenanthroline and two equivalents of (S)-2-(2-hydroxybenzylamino)-4-methylpentanoic acid. The NiII complex shows a distorted octahedral geometry which is stabilized by intramolecular hydrogen bonds and a weak π–π interaction.

Crystal structure and DFT study of (E)-N-[2-(1H-indol-3-yl)eth­yl]-1-(anthracen-9-yl)methanimine

In the title compound, the indole ring system makes a dihedral angle of 63.56 (8)° with the plane of the anthracene ring. The conformation about the C=N bond of the –CH2–CH2–N=CH– bridge linking the two units is E. In the crystal, the indole H atom is involved in an intermolecular N—H⋯π interaction with the benzene ring of the indole group, leading to the formation of chains along [010].

(3-Acetyl-5-carboxyl­ato-4-methyl-1H-pyrazol-1-ido-κ2N1,O5)aqua­[(pyridin-2-yl)methanamine-κ2N,N′]copper(II)

In the title compound, [Cu(C7H6N2O3)(C6H8N2)(H2O)], the CuII ion is in a distorted square-pyramidal N3O2 environment formed by two bidentate chelating ligands in the equatorial coordination sites and one water molecule in the apical direction. In the crystal, O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds link the complex molecules into a three-dimensional supramolecular network.