Modeling Spin Interactions in a Triangular Cobalt(II) Complex with Triaminoguanidine Ligand Framework: Synthesis, Structure, and Magnetic Properties

The new tritopic triaminoguanidine-based ligand 1,2,3-tris­[(pyridine-2-ylmethylidene)­amino]­guanidine (H₂pytag) was synthesized. The reaction of a mixture of cobalt­(II) chloride and cobalt­(II) perchlorate with the ligand H₂pytag in pyridine solution leads to the formation of the trinuclear cobalt­(II) complex [Co₃(pytag)­(py)₆Cl₃]­ClO₄. Three octahedrally coordinated high-spin cobalt­(II) ions are linked through the bridging triaminoguanidine backbone of the ligand leading to an almost equilateral triangular arrangement. The magnetic properties of the complex were investigated by magnetic measurements, variable-temperature, variable-field magnetic circular dichroism (MCD) spectroscopy, and density functional theory as well as ab initio calculations. A rather strong antiferromagnetic exchange interaction between the cobalt­(II) centers of ca. −12 cm^–1 is determined together with a strong local anisotropy. The single-ion anisotropy of all three cobalt­(II) centers is found to be easy-plane, which coincides with the tritopic ligand plane. MCD measurements and theoretical investigations demonstrate the presence of rhombic distortion of the local Co surrounding

Structural and Magnetic Studies of a New Co(II) Thiocyanato Coordination Polymer Showing Slow Magnetic Relaxations and a Metamagnetic Transition

Reaction of Co­(NCS)₂ with 4-ethylpyridine leads to the formation of three new compounds of composition Co­(NCS)₂(4-ethylpyridine)₄ (<b>1</b>), [(Co­(NCS)₂]₂(4-ethylpyridine)₆ (<b>2</b>), and [Co­(NCS)₂(4-ethylpyridine)₂]_<i>n</i> (<b>3</b>). In all compounds the coordination of the Co­(II) ions is distorted octahedral. <b>1</b> consists of discrete monomeric complexes and in <b>2</b> two Co­(II) cations are linked by pairs of μ-1,3-bridging thiocyanato ligands into dimers. In the crystal structure of <b>3</b> the Co­(II) cations are connected into chains by the same bridge as in <b>2</b>. Magnetic studies show that <b>1</b> and <b>2</b> are paramagnets down to a temperature of 2 K, while compound <b>3</b>, which is the main object of this study, is an antiferromagnet with the Néel temperature <i>T</i>_N = 3.4 K. Its magnetic structure is built from ferromagnetic chains, which are weakly antiferromagnetically coupled. With increasing magnetic field a metamagnetic transition starts at ∼175 Oe, as observed for a polycrystalline sample. Magnetic relaxations, which were observed in the antiferromagnetic state, are retained at the metamagnetic transition. With decreasing field <b>3</b> remains in a state, in which except of the faster magnetic relaxation process in single chains also a slower process coexists resulting in the appearance of a magnetic hysteresis loop

Structural and Magnetic Studies of a New Co(II) Thiocyanato Coordination Polymer Showing Slow Magnetic Relaxations and a Metamagnetic Transition

Reaction of Co­(NCS)₂ with 4-ethylpyridine leads to the formation of three new compounds of composition Co­(NCS)₂(4-ethylpyridine)₄ (<b>1</b>), [(Co­(NCS)₂]₂(4-ethylpyridine)₆ (<b>2</b>), and [Co­(NCS)₂(4-ethylpyridine)₂]_<i>n</i> (<b>3</b>). In all compounds the coordination of the Co­(II) ions is distorted octahedral. <b>1</b> consists of discrete monomeric complexes and in <b>2</b> two Co­(II) cations are linked by pairs of μ-1,3-bridging thiocyanato ligands into dimers. In the crystal structure of <b>3</b> the Co­(II) cations are connected into chains by the same bridge as in <b>2</b>. Magnetic studies show that <b>1</b> and <b>2</b> are paramagnets down to a temperature of 2 K, while compound <b>3</b>, which is the main object of this study, is an antiferromagnet with the Néel temperature <i>T</i>_N = 3.4 K. Its magnetic structure is built from ferromagnetic chains, which are weakly antiferromagnetically coupled. With increasing magnetic field a metamagnetic transition starts at ∼175 Oe, as observed for a polycrystalline sample. Magnetic relaxations, which were observed in the antiferromagnetic state, are retained at the metamagnetic transition. With decreasing field <b>3</b> remains in a state, in which except of the faster magnetic relaxation process in single chains also a slower process coexists resulting in the appearance of a magnetic hysteresis loop

Design of a Dinuclear Nickel(II) Bioinspired Hydrolase to Bind Covalently to Silica Surfaces: Synthesis, Magnetism, and Reactivity Studies

Presented herein is the design of a dinuclear Ni^II synthetic hydrolase [Ni₂(HBPPAMFF)­(μ-OAc)₂(H₂O)]­BPh₄ (<b>1</b>) (H₂BPPAMFF = 2-[(<i>N</i>-benzyl-<i>N</i>-2-pyridylmethylamine)]-4-methyl-6-[<i>N</i>-(2-pyridylmethyl)­aminomethyl)])-4-methyl-6-formylphenol) to be covalently attached to silica surfaces, while maintaining its catalytic activity. An aldehyde-containing ligand (H₂BPPAMFF) provides a reactive functional group that can serve as a cross-linking group to bind the complex to an organoalkoxysilane and later to the silica surfaces or directly to amino-modified surfaces. The dinuclear Ni^II complex covalently attached to the silica surfaces was fully characterized by different techniques. The catalytic turnover number (<i>k</i>_cat) of the immobilized Ni^IINi^II catalyst in the hydrolysis of 2,4-bis­(dinitrophenyl)­phosphate is comparable to the homogeneous reaction; however, the catalyst interaction with the support enhanced the substrate to complex association constant, and consequently, the catalytic efficiency (<i>E</i> = <i>k</i>_cat/<i>K</i>_M) and the supported catalyst can be reused for subsequent diester hydrolysis reactions

Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper­(II) complexes, using the unsymmetrical ligands <i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L1</b>) and <i>N</i>′,<i>N</i>′-bis­(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)­(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L2</b>). The structures of the complexes [Cu₂(<b>L1</b>)­(μ-OAc)]­(ClO₄)₂·(CH₃)₂CHOH (<b>1</b>) and [Cu₂(<b>L2</b>)­(μ-OAc)]­(ClO₄)·H₂O·(CH₃)₂CHOH (<b>2</b>) were determined by X-ray crystallography. The complex [Cu₂(<b>L3</b>)­(μ-OAc)]²⁺ [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807–1822). Magnetic data show that the Cu^II centers in <b>1</b> and <b>2</b> are antiferromagnetically coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = −4.3 cm^–1 for <b>1</b> and <i>J</i> = −40.0 cm^–1 for <b>2</b>) is a function of the Cu–O–Cu bridging angle. In addition, <b>1</b> and <b>2</b> were tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu^II-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis­(dinitrophenyl)­phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu^II center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (<i>K</i>_ass. and <i>k</i>_cat.) of <b>1</b> and <b>2</b> in comparison with that found for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity

Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper­(II) complexes, using the unsymmetrical ligands <i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L1</b>) and <i>N</i>′,<i>N</i>′-bis­(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)­(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L2</b>). The structures of the complexes [Cu₂(<b>L1</b>)­(μ-OAc)]­(ClO₄)₂·(CH₃)₂CHOH (<b>1</b>) and [Cu₂(<b>L2</b>)­(μ-OAc)]­(ClO₄)·H₂O·(CH₃)₂CHOH (<b>2</b>) were determined by X-ray crystallography. The complex [Cu₂(<b>L3</b>)­(μ-OAc)]²⁺ [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807–1822). Magnetic data show that the Cu^II centers in <b>1</b> and <b>2</b> are antiferromagnetically coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = −4.3 cm^–1 for <b>1</b> and <i>J</i> = −40.0 cm^–1 for <b>2</b>) is a function of the Cu–O–Cu bridging angle. In addition, <b>1</b> and <b>2</b> were tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu^II-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis­(dinitrophenyl)­phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu^II center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (<i>K</i>_ass. and <i>k</i>_cat.) of <b>1</b> and <b>2</b> in comparison with that found for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity

Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper­(II) complexes, using the unsymmetrical ligands <i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L1</b>) and <i>N</i>′,<i>N</i>′-bis­(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)­(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L2</b>). The structures of the complexes [Cu₂(<b>L1</b>)­(μ-OAc)]­(ClO₄)₂·(CH₃)₂CHOH (<b>1</b>) and [Cu₂(<b>L2</b>)­(μ-OAc)]­(ClO₄)·H₂O·(CH₃)₂CHOH (<b>2</b>) were determined by X-ray crystallography. The complex [Cu₂(<b>L3</b>)­(μ-OAc)]²⁺ [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807–1822). Magnetic data show that the Cu^II centers in <b>1</b> and <b>2</b> are antiferromagnetically coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = −4.3 cm^–1 for <b>1</b> and <i>J</i> = −40.0 cm^–1 for <b>2</b>) is a function of the Cu–O–Cu bridging angle. In addition, <b>1</b> and <b>2</b> were tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu^II-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis­(dinitrophenyl)­phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu^II center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (<i>K</i>_ass. and <i>k</i>_cat.) of <b>1</b> and <b>2</b> in comparison with that found for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity