A tetragonal core with asymmetric iron environments supported solely by bis(μ-OH){μ-(O-H···O)} bridging and terminal pyridine amide (N, O) coordination: a new member of the tetrairon(III) family

Room-temperature aerobic reaction of [Fe(MeCN)4][ClO4]2 with 1,3-bis(2-pyridinecarboxamido)propane (H2bpp) yields the tetrairon(III) complex [Fe4(H2bpp)4(μ-OH)2(μ-OHO)][ClO4]7·2H2O·xMeCN (1·xMeCN, 0≤x≤3). Crystal structure determination reveals that 1·3MeCN is a new member of the tetrairon(III) family, bridged solely by two hydroxido ligands and a localized {O-H···O}3- bridging unit. The properties of the "tetragonal" core [Fe4(μ-OH)2{μ-(O-H···O)}]7+ have been investigated by variable-temperature magnetic and Mossbauer spectroscopic measurements. Successful modeling of the data has revealed asymmetric iron environments and three types of magnetic exchange interactions [through μ-OH and μ-O/μ-OH of μ-(O-H···O) bridges]. This tetragonal core is a valuable addition to the tetrairon(III) cluster family from inorganic and bioinorganic perspectives

Room temperature Cu(II) radical-triggered alkyne C-H activation

A dimeric Cu(II) complex [Cu(II)2L2(μ2-Cl)Cl] (1) built from an asymmetric tridentate ligand (2-(((2-aminocyclohexyl)imino)methyl) -4,6-di-tert-butylphenol) and weakly coordinating anions has been synthesized and structurally characterized. In dichloromethane solution, 1 exists in a monomeric [Cu(II)LCl] (1′) (85%)–dimeric (1) (15%) equilibrium, and cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) studies indicate structural stability and redox retention. Addition of phenylacetylene to the CH2Cl2 solution populates 1′ and leads to the formation of a transient radical species. Theoretical studies support this notion and show that the radical initiates an alkyne C–H bond activation process via a four-membered ring (Cu(II)–O···H–Calkyne) intermediate. This unusual C–H activation method is applicable for the efficient synthesis of propargylamines, without additives, within 16 h, at low loadings and in noncoordinating solvents including late-stage functionalization of important bioactive molecules. Single-crystal X-ray diffraction studies, postcatalysis, confirmed the framework’s stability and showed that the metal center preserves its oxidation state. The scope and limitations of this unconventional protocol are discussed

Synthesis and characterization of the tetranuclear iron(III) complex of a new asymmetric multidentate ligand. A structural model for purple acid phosphatases

The ligand, 2-((2-hydroxy-5-methyl-3-((pyridin-2-ylmethylamino)methyl)benzyl)(2-hydroxybenzyl)amino)acetic acid (H(3)HPBA), which contains a donor atom set that mimics that of the active site of purple acid phosphatase is described. Reaction of H(3)HPBA with iron(III) or iron(II) salts results in formation of the tetranuclear complex, [Fe-4(HPBA)(2)(OAc)(2)(mu-O)(mu-OH)(OH2)(2)]ClO4 center dot 5H(2)O. X-Ray structural analysis reveals the cation consists of four iron(III) ions, two HPBA(3-) ligands, two bridging acetate ligands, a bridging oxide ion and a bridging hydroxide ion. Each binucleating HPBA(3-) ligand coordinates two structurally distinct hexacoordinate iron(III) ions. The two metal ions coordinated to a HPBA(3-) ligand are linked to the two iron(III) metal ions of a second, similar binuclear unit by intramolecular oxide and hydroxide bridging moieties to form a tetramer. The complex has been further characterised by elemental analysis, mass spectrometry, UV-vis and MCD spectroscopy, X- ray crystallography, magnetic susceptibility measurements and variable-temperature Mossbauer spectroscopy

A general synthetic route for the preparation of high-spin molecules: Replacement of bridging hydroxo ligands in molecular clusters by end-on azido ligands

Abstract A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler

Dynamic versus Static Character of the Magnetic Jahn–Teller Effect: Magnetostructural Studies of [Fe₃O(O₂CPh)₆(py)₃]ClO₄·py

Complex [Fe₃O­(O₂CPh)₆(py)₃]­ClO₄·py (<b>1</b>) crystallizes in the hexagonal <i>P</i>6₃/<i>m</i> space group, and its cation exhibits a crystallographically imposed <i>D</i>_3<i>h</i> symmetry due to a <i>C</i>₃ axis passing through the oxide of its {Fe₃O}⁷⁺ core. Single-crystal unit-cell studies carried out with synchrotron radiation confirmed that this symmetry is retained down to 4.5 K; a full crystal structure determination carried out at 90 K resolved the previously reported disorder of the perchlorate anion. Magnetic susceptibility and electron paramagnetic resonance (EPR) data for complex <b>1</b> were interpreted with a model considering the retention of the threefold crystallographic symmetry while predicting a lowering of the magnetic symmetry. This model considered the effects of atomic vibrations of the central oxide on the magnetic properties of the complex by incorporating these movements into the spin Hamiltonian through angular overlap considerations of the atomic orbitals; no ad hoc magnetic Jahn–Teller effect was considered. The derived magnetostructural correlations achieved an improvement in the interpretation of the magnetic susceptibility data using the same number of free variables. They also improved the simulations of the EPR data, which exhibit a complicated set of at least five axial resonances; improved simulations were achieved using only two spectral components. Due to the thermal effects on the oxide vibrations, the model predicts a temperature dependence of the magnetic coupling <i>J</i>, which should not be viewed as a constant but as a variable

Dynamic versus Static Character of the Magnetic Jahn–Teller Effect: Magnetostructural Studies of [Fe₃O(O₂CPh)₆(py)₃]ClO₄·py

Complex [Fe₃O­(O₂CPh)₆(py)₃]­ClO₄·py (<b>1</b>) crystallizes in the hexagonal <i>P</i>6₃/<i>m</i> space group, and its cation exhibits a crystallographically imposed <i>D</i>_3<i>h</i> symmetry due to a <i>C</i>₃ axis passing through the oxide of its {Fe₃O}⁷⁺ core. Single-crystal unit-cell studies carried out with synchrotron radiation confirmed that this symmetry is retained down to 4.5 K; a full crystal structure determination carried out at 90 K resolved the previously reported disorder of the perchlorate anion. Magnetic susceptibility and electron paramagnetic resonance (EPR) data for complex <b>1</b> were interpreted with a model considering the retention of the threefold crystallographic symmetry while predicting a lowering of the magnetic symmetry. This model considered the effects of atomic vibrations of the central oxide on the magnetic properties of the complex by incorporating these movements into the spin Hamiltonian through angular overlap considerations of the atomic orbitals; no ad hoc magnetic Jahn–Teller effect was considered. The derived magnetostructural correlations achieved an improvement in the interpretation of the magnetic susceptibility data using the same number of free variables. They also improved the simulations of the EPR data, which exhibit a complicated set of at least five axial resonances; improved simulations were achieved using only two spectral components. Due to the thermal effects on the oxide vibrations, the model predicts a temperature dependence of the magnetic coupling <i>J</i>, which should not be viewed as a constant but as a variable