A series of the copper(II) complexes with tripodal tetradentate tris(pyridyl 2-methyl)amine-based ligands possessing the hydrogen-bonding 6-aminopyridine units (tapa, three amino groups; bapa, two amino groups; mapa, one amino group) have been synthesized, and their copper(II) complexes with a small molecule such as dioxygen and azide have been studied spectroscopically and structurally. The reaction of their Cu(II) complexes with NaN(3) have given the mononuclear copper complexes with azide in an end-on mode, [Cu(tapa)(N(3))]ClO(4) (1a), [Cu(bapa)(N(3))]ClO(4) (2a), [Cu(mapa)(N(3))]ClO(4) (3a), and [Cu(tpa)(N(3))]ClO(4) (4a) (tpa, no amino group). The crystal structures have revealed that the coordination geometries around the metal centers are almost a trigonal-bipyramidal rather than a square-planar except for 1a with an intermediate between them. The UV-vis and ESR spectral data indicate that the increase of NH(2) groups of ligands causes the structural change from trigonal-bipyramidal to square-pyramidal geometry, which is regulated by a combination of steric repulsion and hydrogen bond. The steric repulsion of amino groups with the azide nitrogen gives rise to elongation of the Cu-N(py) bonds, which leads to the positive shift of the redox potentials of the complexes. The hydrogen bonds between the coordinated azide and amino nitrogens (2.84-3.05 A) contribute clearly to the fixation of azide. The Cu(I) complexes with bapa and mapa ligands have been obtained as a precipitate, although that with tapa was not isolated. The reactions of the Cu(I) complexes with dioxygen in MeOH at -75 degrees C have given the trans-micro-1,2 peroxo dinuclear Cu(II) complexes formulated as [((tapa)Cu)(2)(O(2))](2+) (1c), [((bapa)Cu)(2)(O(2))](2+) (2c), and [((mapa)Cu)(2)(O(2))](2+) (3c), whose characterizations were confirmed by UV-vis, ESR, and resonance Raman spectroscopies. UV-vis spectra of 1c, 2c, and 3c exhibited intense bands assignable to pi(O(2)(2)(-))-to-d(Cu) charge transfer (CT) transitions at lambda(max)/nm (epsilon/M(-1)cm(-1)) = 449 (4620), 474 (6860), and 500 (9680), respectively. The series of the peroxo adducts generated was ESR silent. The resonance Raman spectra exhibited the enhanced features assignable to two stretching vibrations nu((16)O-(16)O/(18)O-(18)O)/cm(-1) and nu(Cu-(16)O/Cu-(18)O)/cm(-1) at 853/807 (1c), 858/812 (2c), 847/800 (3c), and at 547/522 (2c), 544/518 (3c), respectively. The thermal stability of the peroxo-copper species has increased with increase in the number of the hydrogen-bonding interactions between the peroxide and amino groups.
Three new complexes with FeIII2(μ-O)(μ-OH) core surrounded with one, two, and three amino groups, that is, (6-amino-2-pyridylmethyl)bis(pyridylmethyl)amine (MAPA), bis(6-amino-2-pyridylmethyl)(pyridylmethyl)amine (BAPA), and tris(6-amino-2-pyridylmethyl)amine (TAPA), which act as hydrogen-bonding sites, were synthesized and characterized by electronic absorption spectroscopy and X-ray diffraction analysis. Their structural bond parameters, Fe–N(pyridine), Fe–N(amine), and Fe–μ-O(H) bonds, Fe···Fe distance, and Fe–O–Fe angle, could be explained in terms of a combination of two conflicting interactions between NH2 and μ-O(H) groups, that is, a steric repulsion and a hydrogen-bonding interactions. The LMCT bands of μ-O to iron(III) may be affected by hydrogen-bonding interactions between NH and μ-O(H) groups, which are discussed in connection with the formation processes of compound Q and compound X in sMMO and RNR-R2, respectively.
Organic chemistry Z 0200 Complexes with (µ-O)(µ-OH) Core Surrounded by Hydrogen-BondingInteraction -[about 42 refs.]. -(HONDA, Y.; ARII, H.; OKUMURA, T.; WADA, A.; FUNAHASHI, Y.; OZAWA, T.; JITSUKAWA, K.; MASUDA*, H.; Bull. Chem.
With a view to understanding the reactivity of the μ-peroxo diiron(III) complexes in biological oxidation enzymes, such as soluble methane monooxygenase (sMMO) and ribonucleotide reductase (RNR), cis-μ-1,2- and trans-μ-1,2-peroxo diiron complexes were theroretically treated by the use of DFT calculation. Full-optimizations of the structures were carried out using the initial structures of (μ-O2-)(μ-CH3COO-)(μ-O2 2-)[FeIII(A3CY)]2 + and (μ-O2 2- )[FeIII(A3CY)Cl2]2 (A3CY = cis,cis-1,3,5-tris-amino-cyclohexane) for cis- and trans-forms, respectively, by minimizing their total energies. The O-O stretching vibrations were estimated for both isomers; the 16O-16O stretching frequencies for peroxo diiron complexes with cis- and transforms were 840 and 769 cm-1, respectively, which showed an isotope shift to 791 and 724 cm-1, respectively, by the use of 18O2 2- in the place of 16O2 2-. The structure/function relationship for them was discussed.
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