Download Study of Molecular Magnetic Materials from Magnetic Exchange

Study of Molecular Magnetic Materials from
Magnetic Exchange Coupling to Slow Relaxation
Inorganic Molecular Materials Lab, Department of Chemistry, Korea University
Kwang Soo Lim
Molecule-based magnetic materials have become attractive one of current research subjects.
Because they exhibit some interesting physical properties such as slow relaxation of the
magnetization, quantum ternneling effect, long-range magnetic ordering and metamagnetic
behavior. Nowadays, the study of control the magnetic properties containing the guestinduced magnetic modulation in coordination polymers and design of the discrete molecules
for stabilizing the magnetic anisotropy, has increased rapidly. These researches are very
important because those provide the basic information to use in real application like magnetic
memory device. To modulate the magnetic properties, I tried to change the coordination
environment around metal ions via hydration/dehydration process, design of some bulky
ligands and to replace the ligands length to give the alteration of magnetic interactions.
First, I prepared EO azide-bridged three CoII, MnII and NiII layers with coordinated water
molecules, which are structurally assisted by long spacer p-XBP4 ligands and unbound azide
anions. The evacuation of as-synthesized samples under vacuum produced dehydrated
samples. The reversible phase transformation accompanied by color and magnetic changes
takes place between hydrated samples and dehydrated samples using a desolvation-solvation
protocol.
Second, I prepared four CoII porous coordination polymers, Co2(dobdc), Co2(dondc),
Co2(dobpdc) and Co2(dotpdc) where H4dobdc = 2,5-dihydroxyterephthalic acid, H4dondc =
3,7-dihydroxynaphthalene-2,6-dicarboxylic
acid,
H4dobpdc
=
4,4’-dioxido-3,3’-
biphenyldicarboxylic acid, and H4dotpdc = 4,4’-dioxido-3,3’-triphenyldicarboxylic acid,
which adopt MOF-74 or extended MOF-74 structures. There are carboxylate bridged
ferromagnetic one dimensional CoII chains. The magnetic interaction between interchain
occurs through the ligands at low temperature, as a result, the metamagnetic transition was
generated. The critical fields in metamagnetism systems could be controlled by coordinated
ligand length and the metamagnetic behavior disappeared completely, when the framework
consist of the longest ligand (dotpdc4-).
Third, two coordination complexes [Dy(LOEt)2](PF6) and [Dy(LO-iPr)2](PF6) were prepared
by employing tripodal bulky diamagnetic ligands, LOR-. The geometry around Dy ion can be
described as octahedral in the crystal structures. This is a very rare case among lanthanide
complexes because they usually possess coordination numbers of more than seven. Dynamic
magnetic susceptibility data for both compounds reveal fast quantum tunnelling at zero dc
field, while conventional slow magnetic relaxation typical for a SIM is evident under optimal
fields. The magnetic dilution with Y ions allows for partial suppression of such tunnelling
process. The single-ion anisotropy was determined to be orientated along the c axis by means
of the angular dependent measurement of a single crystal of [Dy(LOEt)2](PF6).
Lastly, the symmetry around Ln ions is recognized to be a crucial parameter dictating
magnetization relaxation dynamics. I prepared four similar square-antiprismatic complexes,
[Ln(LOMe)2(H2O)2](PF6) and Ln(LOMe)2(NO3) (Ln = Dy and Er) where LOMe =
[CpCo{P(O)(O(CH3))2}3], including either two neutral water molecules or an anionic nitrate
ligand. I demonstrated that in this case relaxation dynamics is dramatically affected by the
introduction of a charged ligand, stabilizing the easy axis of magnetization along the nitrate
direction. I also showed that either the application of a dc field or a chemical dilution
effectively stops quantum tunneling in the ground state of Ln(LOMe)2(NO3).
Luminescent coordination polymers with oxidized
ligand for sensing toxic substances
Inorganic Molecular Materials Lab, Department of Chemistry, Korea University
Jong Hyeon Lee
New
structures
of
Coordination
Polymers
(CPs)
H2dmbdc(H2dmbdc=2,5-dimercapto-1,4-benzenedicarboxylic
were
acid)
synthesized
with
by
Cd(NO3)2,
Mg(NO3)2, Dy(NO3)2 and Tb(NO3)2. During the solvothermal reaction, nitrate used as a
oxidizing agent
and
H2dmbdc oxidized to
dsbdc4-(dsbdc4-=2,5-disulfo-1,4-benzene
carboxylate). It linked with different metals and expanded different structures. These
compounds mutually showed two-dimensional frameworks. Compound 3 and 4 confirmed
that were isostructures by using XRD, TGA.
In compound 1 and 2, they had luminescence caused by intra-ligand interactions. In their
luminescent properties, it could be used as ‘turn-off’ sensor for small molecules. Especially
nitro aromatic compounds had quenching effect for ppm scales. The sensing processes were
reversible, and the crystallinity of compounds 1 was maintained by X-ray diffractometer.
Also it had requirements for sensor, including sensitivity, selectivity.
In compound 3 and 4, they displayed metal-based luminescence caused by characteristic
transitions in metal orbitals. As a sensor for metal ions, it could be used. In particular, 3
showed ‘turn-on’ sensing for Cd2+ ion. In order to identify incorporated metal ions, energy
dispersive X-ray spectroscopy were carried out. X-ray photoelectron spectroscopy analysis
was performed to monitor interactions between metal ions.
Polyamine-functionalized Mg2(dobpdc) with
ultrahigh amine density for CO2 capture
Inorganic Molecular Materials Lab, Department of Chemistry, Korea University
Kyu Hyun Yeom
A metal–organic framework, which adopts an expanded MOF-74 structure type
[Mg2(dobpdc)(DMF)2]∙1.8H2O(1∙DMF) (dobpdc4- = 4,4’-dioxido-3,3’-biphenyldicarboxylate),
was prepared by a microwave method. Compound 1 is fully evacuated at 390 oC for 12 h
under vacuum resulting in unsaturated metal center lining the channel directions (c-axis). The
activated-1 was functionalized with polyamine by a post-synthetic method. The
functionalized products are deta-Mg2(dobpdc) (1-deta), teta-Mg2(dobpdc) (1-teta), and tepaMg2(dobpdc) (1-tepa), where deta= diethylenetriamine, teta= triethylenetetramine, and tepa=
tetraethylenepentamine.
Structural variations of the materials under different conditions were observed by PXRD,
with Pawley refinement (by Materials Studio modules). These porous compounds exhibit gas
sorption properties for CO2 capture. The gas sorption data were collected with a sorption
apparatus and TGA. To know the optimized desorption temperature, the thermal steps of 1deta, 1-teta, and 1-tepa were measured by TGA. In addition, the mechanism of CO2
adsorption in amine-grafted compounds was demonstrated by in-situ IR spectroscopy using a
manufactured cell, and the effect of the amine group on the CO2 adsorption was confirmed.
Pd/C-CaO-catalyzed α-alkylation and
hydrodeoxygenation of an acetone-butanol-ethanol
mixture for biogasoline synthesis
Inorganic Molecular Materials Lab, Department of Chemistry, Korea University
Seung Mi Yeo
A solvent-free α-alkylation of acetone with butanol and ethanol was conducted using a
mixture of Pd/C and CaO as heterogeneous catalysts. After reaction at 180 °C for 20 h,
alkylated products, including C5-C11 ketones and alcohols, were obtained with a total yield of
78.1%. After this α-alkylation, consecutive hydrodeoxygenation at 270 °C for 20 h under H2
at 500 psig yielded 74.7% C5–C11 alkanes based on the amount of acetone. The product could
be used as a bio-gasoline. After alkylation, the catalyst was isolated and characterized using
XRD, TGA, XPS, and TEM to elucidate the deactivation of the catalyst. The main reason
was found to be decreased basicity of Ca species by conversion of CaO to CaCO 3 during the
reaction. The Pd/C particles were slightly agglomerated after alkylation, but still retained
their catalytic activity during successive reuses for the alkylation reaction. In subsequent runs,
the activity of the used catalyst could be recovered by adding a sufficient amount of CaO, or
by decarboxylation of CaCO3 to CaO at 500 °C, under H2.