29 research outputs found
Особливості реалізації графічного конвеєру при візуалізації тривимірних моделей приміщень університету
В більшості систем комп‘ютерної графіки застосовується графічний конвеєр – логічна група послідовно виконуваних обчислень (етапів), які в результаті дають синтезовану сцену на екрані комп‘ютера. Серед основних – етапи геометричних перетворень та візуалізації. Результат виконання кожного з цих етапів впливає на кінцевий вигляд синтезованої сцени, тому їх коректне завершення є необхідною умовою отримання якісного зображення
Structural Studies on a New Family of Chiral BioMOFs
The
use of a family of dinuclear copper(II) complexes, prepared
from enantiopure disubstituted oxamidato ligands derived from the
natural amino acids l-alanine, l-valine, and l-leucine, as metalloligands toward barium(II) cations leads
to the formation of three novel three-dimensional (3D) chiral metal–organic
frameworks (MOFs). They exhibit different architectures, which serve
as playground to study both how the chiral information contained in
the starting enantiopure ligands is ultimately transmitted to the
3D structure and the effect of the size of the aliphatic residue of
the amino acid on the final architecture
Solvent-Dependent Self-Assembly of an Oxalato-Based Three-Dimensional Magnet Exhibiting a Novel Architecture
The
old but evergreen family of bimetallic oxalates still offers innovative
and interesting results. When (Me<sub>4</sub>N)<sub>3</sub>[Cr(ox)<sub>3</sub>]·3H<sub>2</sub>O is reacted with Mn<sup>II</sup> ions
in a nonaqueous solvent, a novel three-dimensional magnet of the formula
[N(CH<sub>3</sub>)<sub>4</sub>]<sub>6</sub>[Mn<sub>3</sub>Cr<sub>4</sub>(ox)<sub>12</sub>]·6CH<sub>3</sub>OH is obtained instead of
the one-dimensional compound obtained in water. This new material
exhibits an unprecedented stoichiometry with a binodal (3,4) net topology
and the highest critical temperature (<i>T</i><sub>C</sub> = 7 K) observed so far in a manganese–chromium oxalate based
magnet
Solvent-Dependent Self-Assembly of an Oxalato-Based Three-Dimensional Magnet Exhibiting a Novel Architecture
The
old but evergreen family of bimetallic oxalates still offers innovative
and interesting results. When (Me<sub>4</sub>N)<sub>3</sub>[Cr(ox)<sub>3</sub>]·3H<sub>2</sub>O is reacted with Mn<sup>II</sup> ions
in a nonaqueous solvent, a novel three-dimensional magnet of the formula
[N(CH<sub>3</sub>)<sub>4</sub>]<sub>6</sub>[Mn<sub>3</sub>Cr<sub>4</sub>(ox)<sub>12</sub>]·6CH<sub>3</sub>OH is obtained instead of
the one-dimensional compound obtained in water. This new material
exhibits an unprecedented stoichiometry with a binodal (3,4) net topology
and the highest critical temperature (<i>T</i><sub>C</sub> = 7 K) observed so far in a manganese–chromium oxalate based
magnet
Rational Synthesis of Chiral Metal–Organic Frameworks from Preformed Rodlike Secondary Building Units
The
lack of rational design methodologies to obtain chiral rod-based MOFs
is a current synthetic limitation that hampers further expansion of
MOF chemistry. Here we report a metalloligand design strategy consisting
of the use, for the first time, of preformed 1D rodlike SBUs (<b>1</b>) for the rational preparation of a chiral 3D MOF (<b>2</b>) exhibiting a rare <b>eta</b> net topology. The encoded
chiral information on the enantiopure ligand is efficiently transmitted
first to the preformed helical 1D building block and, in a second
stage, to the resulting chiral 3D MOF. These results open new routes
for the rational design of chiral rod-based MOFs, expanding the scope
of these unique porous materials
Double Interpenetration in a Chiral Three-Dimensional Magnet with a (10,3)‑a Structure
A unique chiral three-dimensional
magnet with an overall racemic double-interpenetrated (10,3)-a structure
of the formula [(<i>S</i>)-(1-PhEt)Me<sub>3</sub>N]<sub>4</sub>[Mn<sub>4</sub>Cu<sub>6</sub>(Et<sub>2</sub>pma)<sub>12</sub>](DMSO)<sub>3</sub>]·3DMSO·5H<sub>2</sub>O (<b>1</b>; Et<sub>2</sub>pma = <i>N</i>-2,6-diethylphenyloxamate)
has been synthesized by the self-assembly of a mononuclear copper(II)
complex acting as a metalloligand toward Mn<sup>II</sup> ions in the
presence of a chiral cationic auxiliary, constituting the first oxamato-based
chiral coordination polymer exhibiting long-range magnetic ordering
Selective Guest Inclusion in Oxalate-Based Iron(III) Magnetic Coordination Polymers
The preparation and structural characterization
of four novel oxalate-based iron(III) compounds of formulas {(MeNH<sub>3</sub>)<sub>2</sub>[Fe<sub>2</sub>(ox)<sub>2</sub>Cl<sub>4</sub>]·2.5H<sub>2</sub>O}<sub><i>n</i></sub> (<b>1</b>), K(MeNH<sub>3</sub>)[Fe(ox)Cl<sub>3</sub>(H<sub>2</sub>O)] (<b>2</b>), {MeNH<sub>3</sub>[Fe<sub>2</sub>(OH)(ox)<sub>2</sub>Cl<sub>2</sub>]·2H<sub>2</sub>O}<sub><i>n</i></sub> (<b>3</b>), and {(H<sub>3</sub>O)(MeNH<sub>3</sub>)[Fe<sub>2</sub>O(ox)<sub>2</sub>Cl<sub>2</sub>]·3H<sub>2</sub>O}<sub><i>n</i></sub> (<b>4</b>) (MeNH<sub>3</sub><sup>+</sup> =
methylammonium cation and H<sub>2</sub>ox = oxalic acid) are reported
here. <b>1</b> is an anionic waving chain of oxalato-bridged
iron(III) ions with peripheral chloro ligands, the charge balance
being ensured by methylammonium cations. <b>2</b> is a mononuclear
complex with a bidentate oxalate, three terminal chloro ligands, and
a coordinated water molecule achieving the six-coordination around
each iron(III) ion. Its negative charge is balanced by potassium(I)
and methylammonium cations. <b>3</b> and <b>4</b> are
made up of oxalate-bridged and either hydroxo (<b>3</b>)- or
oxo-bridged (<b>4</b>) iron(III) chiral three-dimensional (3D)
networks of formulas [Fe<sub>2</sub>(OH)(ox)<sub>2</sub>Cl<sub>2</sub>]<sub><i>n</i></sub><sup><i>n</i>−</sup> (<b>3</b>) and [Fe<sub>2</sub>O(ox)<sub>2</sub>Cl<sub>2</sub>]<sub><i>n</i></sub><sup>2<i>n</i>−</sup> (<b>4</b>) with methylammonium (<b>3</b> and <b>4</b>)
and hydronium (<b>4</b>) as counterions. The common point these
compounds share is related to their synthetic strategy, which consists
of the use of mixed alkaline/alkylammonium cations as templating agents
for the growth of the 1D or 3D iron(III) motifs. Interestingly, even
in the presence of any given alkaline cation in the reaction solutions,
the resulting coordination polymers (<b>1</b>, <b>3</b>, and <b>4</b>) exclusively contain the methylammonium cation,
revealing the highly selective character of the 1D and 3D networks.
Furthermore, the isolation of the very unstable compound <b>1</b> could be only achieved in the presence of the KCl salt, suggesting
a probable templating effect of the potassium(I) cations. Finally,
a study of the variable-temperature magnetic properties of the 3D
compounds <b>3</b> and <b>4</b> showed the occurrence
of weak ferromagnetic ordering due to a spin canting, the value of
the critical temperature (<i>T</i><sub>c</sub>) being as
high as 70 K
New Magnetic Thin Film Hybrid Materials Built by the Incorporation of Octanickel(II)-oxamato Clusters Between Clay Mineral Platelets
We report on a new method based on the combination of Langmuir–Schaefer deposition with self-assembly to insert highly anisotropic Ni<sub>8</sub> molecules in a hybrid organic–inorganic nanostructure. Spectroscopic, crystallographic, and magnetic data prove the successful insertion of the guest cationic molecule between templating clay platelets. These results open a new route toward the highly controlled fabrication of tailored functional organic–inorganic nanomaterials
Antisymmetric Exchange in Triangular Tricopper(II) Complexes: Correlation among Structural, Magnetic, and Electron Paramagnetic Resonance Parameters
Two new trinuclear copper(II) complexes, [Cu<sub>3</sub>(μ<sub>3</sub>-OH)(daat)(Hdat)<sub>2</sub>(ClO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>3</sub>](ClO<sub>4</sub>)<sub>2</sub>·2H<sub>2</sub>O (<b>1</b>) and [Cu<sub>3</sub>(μ<sub>3</sub>-OH)(aaat)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>](ClO<sub>4</sub>)<sub>2</sub>·3H<sub>2</sub>O (<b>2</b>) (daat = 3,5-diacetylamino-1,2,4-triazolate,
Hdat = 3,5-diamino-1,2,4-triazole, and aaat = 3-acetylamino-5-amino-1,2,4-triazolate),
have been prepared from 1,2,4-triazole derivatives and structurally
characterized by X-ray crystallography. The structures of <b>1</b> and <b>2</b> consist of cationic trinuclear copper(II) complexes
with a Cu<sub>3</sub>OH core held by three <i>N</i>,<i>N</i>-triazole bridges between each pair of copper(II) atoms.
The copper atoms are five-coordinate with distorted square-pyramidal
geometries. The magnetic properties of <b>1</b> and <b>2</b> and those of five other related 1,2,4-triazolato tricopper(II) complexes
with the same triangular structure (<b>3–7</b>) (whose
crystal structures were already reported) have been investigated in
the temperature range of 1.9–300 K. The formulas of <b>3–7</b> are [Cu<sub>3</sub>(μ<sub>3</sub>-OH)(aaat)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>](NO<sub>3</sub>)<sub>2</sub>·H<sub>2</sub>O (<b>3</b>), {[Cu<sub>3</sub>(μ<sub>3</sub>-OH)(aat)<sub>3</sub>(μ<sub>3</sub>-SO<sub>4</sub>)]·6H<sub>2</sub>O}<sub><i>n</i></sub> (<b>4</b>), and [Cu<sub>3</sub>(μ<sub>3</sub>-OH)(aat)<sub>3</sub>A(H<sub>2</sub>O)<sub>2</sub>]A·<i>x</i>H<sub>2</sub>O [A = NO<sub>3</sub><sup>–</sup> (<b>5</b>), CF<sub>3</sub>SO<sub>3</sub><sup>–</sup> (<b>6</b>), or ClO<sub>4</sub><sup>–</sup> (<b>7</b>); <i>x</i> = 0 or 2] (aat =3-acetylamino-1,2,4-triazolate). The magnetic
and electron paramagnetic resonance (EPR) data have been analyzed
by using the following isotropic and antisymmetric exchange Hamiltonian: <i>H</i> = –<i>J</i>[<i>S</i><sub>1</sub><i>S</i><sub>2</sub> + <i>S</i><sub>2</sub><i>S</i><sub>3</sub>] – <i>j</i>[<i>S</i><sub>1</sub><i>S</i><sub>3</sub>] + <i>G</i>[<i>S</i><sub>1</sub> × <i>S</i><sub>2</sub> + <i>S</i><sub>2</sub> × <i>S</i><sub>3</sub> + <i>S</i><sub>1</sub> × <i>S</i><sub>3</sub>]. <b>1</b>–<b>7</b> exhibit strong antiferromagnetic coupling
(values for both –<i>J</i> and –<i>j</i> in the range of 210–142 cm<sup>–1</sup>) and antisymmetric
exchange (<i>G</i> varying from to 27 to 36 cm<sup>–1</sup>). At low temperatures, their EPR spectra display high-field (<i>g</i> < 2.0) signals indicating that the triangles present
symmetry lower than equilateral and that the antisymmetric exchange
is operative. A magneto-structural study showing a lineal correlation
between the Cu–O–Cu angle of the Cu<sub>3</sub>OH core
and the isotropic exchange parameters (<i>J</i> and <i>j</i>) has been conducted. Moreover, a model based on Moriya’s
theory that allows the prediction of the occurrence of antisymmetric
exchange in the tricopper(II) triangles, via analysis of the overlap
between the ground and excited states of the local Cu(II) ions, has
been proposed. In addition, analytical expressions for evaluating
both the isotropic and antisymmetric exchange parameters from the
experimental magnetic susceptibility data of triangular complexes
with local spins (<i>S</i>) of <sup>1</sup>/<sub>2</sub>, <sup>3</sup>/<sub>2</sub>, or <sup>5</sup>/<sub>2</sub> have been
purposely derived. Finally, the magnetic and EPR results of this work
are discussed and compared with those of other tricopper(II) triangles
reported in the literature
High-Temperature Spin Crossover in a Mononuclear Six-Coordinate Cobalt(II) Complex
The six-coordinate cobalt(II) complex
of formula [Co(tppz)<sub>2</sub>](tcm)<sub>2</sub> exhibits a thermally
induced spin-crossover behavior from a high spin (<i>S</i> = <sup>3</sup>/<sub>2</sub>) at higher temperatures to a low spin
(<i>S</i> = <sup>1</sup>/<sub>2</sub>) at lower temperatures,
with the low-spin phase being achieved at <i>T</i> ≤
200 K