7 research outputs found
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-trisĀ[(pyridine-2-ylmethylidene)Āamino]Āguanidine
(H<sub>2</sub>pytag) was synthesized. The reaction of a mixture of
cobaltĀ(II) chloride and cobaltĀ(II) perchlorate with the ligand H<sub>2</sub>pytag in pyridine solution leads to the formation of the trinuclear
cobaltĀ(II) complex [Co<sub>3</sub>(pytag)Ā(py)<sub>6</sub>Cl<sub>3</sub>]ĀClO<sub>4</sub>. Three octahedrally coordinated high-spin cobaltĀ(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 cobaltĀ(II) centers of ca. ā12 cm<sup>ā1</sup> is determined together with a strong local anisotropy.
The single-ion anisotropy of all three cobaltĀ(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 CoĀ(NCS)<sub>2</sub> with 4-ethylpyridine leads to the formation
of three new compounds of composition CoĀ(NCS)<sub>2</sub>(4-ethylpyridine)<sub>4</sub> (<b>1</b>), [(CoĀ(NCS)<sub>2</sub>]<sub>2</sub>(4-ethylpyridine)<sub>6</sub> (<b>2</b>), and [CoĀ(NCS)<sub>2</sub>(4-ethylpyridine)<sub>2</sub>]<sub><i>n</i></sub> (<b>3</b>). In all compounds
the coordination of the CoĀ(II) ions is distorted octahedral. <b>1</b> consists of discrete monomeric complexes and in <b>2</b> two CoĀ(II) cations are linked by pairs of Ī¼-1,3-bridging thiocyanato
ligands into dimers. In the crystal structure of <b>3</b> the
CoĀ(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 NeĢel temperature <i>T</i><sub>N</sub> =
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 ā¼175 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 CoĀ(NCS)<sub>2</sub> with 4-ethylpyridine leads to the formation
of three new compounds of composition CoĀ(NCS)<sub>2</sub>(4-ethylpyridine)<sub>4</sub> (<b>1</b>), [(CoĀ(NCS)<sub>2</sub>]<sub>2</sub>(4-ethylpyridine)<sub>6</sub> (<b>2</b>), and [CoĀ(NCS)<sub>2</sub>(4-ethylpyridine)<sub>2</sub>]<sub><i>n</i></sub> (<b>3</b>). In all compounds
the coordination of the CoĀ(II) ions is distorted octahedral. <b>1</b> consists of discrete monomeric complexes and in <b>2</b> two CoĀ(II) cations are linked by pairs of Ī¼-1,3-bridging thiocyanato
ligands into dimers. In the crystal structure of <b>3</b> the
CoĀ(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 NeĢel temperature <i>T</i><sub>N</sub> =
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 ā¼175 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<sup>II</sup> synthetic
hydrolase [Ni<sub>2</sub>(HBPPAMFF)Ā(Ī¼-OAc)<sub>2</sub>(H<sub>2</sub>O)]ĀBPh<sub>4</sub> (<b>1</b>) (H<sub>2</sub>BPPAMFF
= 2-[(<i>N</i>-benzyl-<i>N</i>-2-pyridylmethylamine)]-4-methyl-6-[<i>N</i>-(2-pyridylmethyl)Āaminomethyl)])-4-methyl-6-formylphenol)
to be covalently attached to silica surfaces, while maintaining its
catalytic activity. An aldehyde-containing ligand (H<sub>2</sub>BPPAMFF)
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<sup>II</sup> complex covalently attached to the silica surfaces
was fully characterized by different techniques. The catalytic turnover
number (<i>k</i><sub>cat</sub>) of the immobilized Ni<sup>II</sup>Ni<sup>II</sup> catalyst in the hydrolysis of 2,4-bisĀ(dinitrophenyl)Āphosphate
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><sub>cat</sub>/<i>K</i><sub>M</sub>) 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 copperĀ(II) complexes, using the unsymmetrical ligands <i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(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>ā²,<i>N</i>ā²-bisĀ(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)Ā(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L2</b>). The structures of the complexes [Cu<sub>2</sub>(<b>L1</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>1</b>) and [Cu<sub>2</sub>(<b>L2</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)Ā·H<sub>2</sub>OĀ·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>2</b>) were determined by X-ray
crystallography. The complex [Cu<sub>2</sub>(<b>L3</b>)Ā(Ī¼-OAc)]<sup>2+</sup> [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(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>, 1807ā1822). Magnetic data show that the Cu<sup>II</sup> 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> = ā4.3 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> = ā40.0
cm<sup>ā1</sup> for <b>2</b>) is a function of the CuāOāCu
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<sup>II</sup>-bound hydroxo group, their
activity toward hydrolysis of the model substrate 2,4-bisĀ(dinitrophenyl)Āphosphate
and DNA was also investigated. Double electrophilic activation of
the phosphodiester by monodentate coordination to the Cu<sup>II</sup> 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><sub>ass.</sub> and <i>k</i><sub>cat.</sub>) 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 copperĀ(II) complexes, using the unsymmetrical ligands <i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(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>ā²,<i>N</i>ā²-bisĀ(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)Ā(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L2</b>). The structures of the complexes [Cu<sub>2</sub>(<b>L1</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>1</b>) and [Cu<sub>2</sub>(<b>L2</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)Ā·H<sub>2</sub>OĀ·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>2</b>) were determined by X-ray
crystallography. The complex [Cu<sub>2</sub>(<b>L3</b>)Ā(Ī¼-OAc)]<sup>2+</sup> [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(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>, 1807ā1822). Magnetic data show that the Cu<sup>II</sup> 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> = ā4.3 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> = ā40.0
cm<sup>ā1</sup> for <b>2</b>) is a function of the CuāOāCu
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<sup>II</sup>-bound hydroxo group, their
activity toward hydrolysis of the model substrate 2,4-bisĀ(dinitrophenyl)Āphosphate
and DNA was also investigated. Double electrophilic activation of
the phosphodiester by monodentate coordination to the Cu<sup>II</sup> 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><sub>ass.</sub> and <i>k</i><sub>cat.</sub>) 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 copperĀ(II) complexes, using the unsymmetrical ligands <i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(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>ā²,<i>N</i>ā²-bisĀ(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)Ā(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L2</b>). The structures of the complexes [Cu<sub>2</sub>(<b>L1</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>1</b>) and [Cu<sub>2</sub>(<b>L2</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)Ā·H<sub>2</sub>OĀ·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>2</b>) were determined by X-ray
crystallography. The complex [Cu<sub>2</sub>(<b>L3</b>)Ā(Ī¼-OAc)]<sup>2+</sup> [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(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>, 1807ā1822). Magnetic data show that the Cu<sup>II</sup> 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> = ā4.3 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> = ā40.0
cm<sup>ā1</sup> for <b>2</b>) is a function of the CuāOāCu
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<sup>II</sup>-bound hydroxo group, their
activity toward hydrolysis of the model substrate 2,4-bisĀ(dinitrophenyl)Āphosphate
and DNA was also investigated. Double electrophilic activation of
the phosphodiester by monodentate coordination to the Cu<sup>II</sup> 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><sub>ass.</sub> and <i>k</i><sub>cat.</sub>) 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