Dae Won Ryu

Diamine-functionalized metal–organic framework: exceptionally high CO2 capacities from ambient air and flue gas, ultrafast CO2 uptake rate, and adsorption mechanism

A framework en-Mg2(dobpdc) (1-en; en = ethylenediamine) functionalized with the primary amine en was prepared via postmodification. From synchrotron PXRD data, it is revealed that the cell parameters change upon grafting of en and CO2 uptake. The adsorbed CO2 amount of 1-en is 4.57 mmol g−1 (16.7 wt%) at 25 °C and 1 bar and decreases to 3.00 mmol g−1 (11.7 wt%) at 150 °C. Noticeably, 1-en shows a significant CO2 uptake (3.62 mmol g−1, 13.7 wt%) at 0.15 bar, which is comparable to the CO2 partial pressure of a post-combustion flue gas. The CO2 capacity of 1-en at 0.39 mbar, close to atmospheric CO2 concentration, is 2.83 mmol g−1 (11.1 wt%), which marks the highest amount among MOFs. The isosteric heat of adsorption (−Qst) of 1-en in CO2 capture corresponds to 49–51 kJ mol−1, which is supported by DFT calculations (−52.8 kJ mol−1). These results suggest that the adsorption of CO2 onto the free amines of en leads to the formation of a carbamic acid. Adsorption–desorption cyclings of CO2 at the real dilute concentrations of air and flue gas are established with almost retaining CO2 capacities, which could provide superior potential for practical application in CO2 capture. The adsorption rate of CO2 in 1-en exceeds that in some other tested porous materials. The recyclability in CO2 uptake for 1-en is maintained even after exposure to humidity.

An End‐On Azide‐Bridged Antiferromagnetic Single‐Chain Magnet Involving Spin Canting and Field‐Induced Two‐Step Magnetic Transitions

Two-step magnetic transitions: An azide-bridged 1D Mn(III) coordination polymer with a unique single end-on mode was prepared; it displayed atypical antiferromagnetic couplings and field-induced two-step magnetic transitions (see figure). The spin-canted phenomenon in the antiferromagnetic chain complex plays a pivotal role in establishing the slow magnetic relaxation.

pH‐Dependent Proton Conducting Behavior in a Metal–Organic Framework Material

A porous metal-organic framework (MOF), [Ni2(dobdc)(H2O)2]⋅6 H2O (Ni2(dobdc) or Ni-MOF-74; dobdc(4-)=2,5-dioxido-1,4-benzenedicarboxylate) with hexagonal channels was synthesized using a microwave-assisted solvothermal reaction. Soaking Ni2(dobdc) in sulfuric acid solutions at different pH values afforded new proton-conducting frameworks, H(+)@Ni2(dobdc). At pH 1.8, the acidified MOF shows proton conductivity of 2.2×10(-2) S cm(-1) at 80 °C and 95% relative humidity (RH), approaching the highest values reported for MOFs. Proton conduction occurs via the Grotthuss mechanism with a significantly low activation energy as compared to other proton-conducting MOFs. Protonated water clusters within the pores of H(+)@Ni2(dobdc) play an important role in the conduction process.

Microporous Lanthanide-Organic Frameworks with Open Metal Sites: Unexpected Sorption Propensity and Multifunctional Properties

Isostructural lanthanide-organic frameworks were prepared by a solvothermal reaction of the corresponding metal ions and the phosphine-oxide-based tricarboxylate ligand. The gravimetric gas uptake was unexpectedly increased when going from Nd(3+) to Gd(3+), which is associated with the enhanced surface areas and electrostatic interactions between exposed metal ions and gas molecules with quadrupole moments.

A unique tetranuclear ErIII4 cluster exhibiting field-induced single-molecule magnetism

A tetranuclear Er(III) compound chelated with N(2)O(2) donors of a tetradentate Schiff base was produced from the self-assembly of the corresponding chemical species. This intriguing cluster shows field-induced slow relaxation of magnetization.

Magnetic metal–organic framework constructed from a paramagnetic metalloligand exhibiting a significant sorption and reversible magnetic conversions

A Co(II)-Cu(II) framework based on a paramagnetic metalloligand [Co(Tt)(2)] shows a permanent porosity with a record high surface area for magnetic MOFs as well as a reversible magnetic transformation between a paramagnetic-like state and a short-range magnetic order in the low-temperature regime upon solvation-desolvation cyclings.

Octacyanometalate-based ferrimagnetic MVMnIII (M = Mo, W) bimetallic chain racemates with slow magnetic relaxations

Cyanide-bridged M(V)-Mn(III) (M = Mo, W) bimetallic chain complexes with racemic spatial dispositions were constructed by self-assembling [M(CN)(8)](3-) precursors and Mn(III) Schiff bases. Antiferromagnetic couplings between spin centers within a chain result in a ferrimagnetic nature, and slow magnetic relaxations are observed as well.

Spin crossover in the cyanide-bridged Mo(V)Mn(III) single-chain magnet containing Fe(II) cations

A 1D Mo(V)Mn(III) chain compound balanced by {Fe[HC(3,5-Me(2)pz)(3)](2)}(2+) dications was prepared. This complex displays a typical single-chain magnet character associated with the Mo(V)Mn(III) chain and a spin crossover phenomenon arising from cationic Fe(II) subunits. The spin crossover behavior tends to slightly affect single-chain magnetic properties at low temperature.

One-Dimensional Cyanide-Bridged MnIIIWV Bimetallic Complexes: Metamagnetism, Spontaneous Resolution, and Slow Magnetic Relaxation

The reaction of [W(CN)(6)(bpy)](-) with the corresponding Mn Schiff bases led to the formation of two antiferromagnetic (1) and ferromagnetic (2) chains. The formation of the conglomerate (2) is associated with chiral induction by the enantiomeric chelate-ring conformation of the Mn Schiff base. Modulation of the linking groups in the Mn Schiff bases affects the interchain contacts, causing alteration of the magnetic behaviors from metamagnetism (1) to slow magnetic relaxation (2).

Cyanide-Bridged WVMnIII Single-Chain Magnet with Isolated MnIII Moieties Exhibiting Two Types of Relaxation Dynamics

A 5d-3d bimetallic compound was prepared by self-assembling [W(CN)(8)](3-) and the Mn(III) Schiff bases. This neutral complex consists of cyanide-linked W(V)Mn(III) anionic chains and isolated Mn(III) Schiff base cations. We demonstrate that two types of relaxation processes are involved in the system; the low-T dynamics may come from magnetic domain dynamics and the high-T relaxation stems from the anionic chain, revealing single-chain magnet character.