Jinhee Kang

Consequences of the intrachain dimer–monomer spin frustration and the interchain dimer–monomer spin exchange in the diamond-chain compound azurite Cu3(CO3)2(OH)2

The spin lattice appropriate for azurite Cu(3)(CO(3))(2)(OH)(2) was determined by evaluating its spin exchange interactions on the basis of first principles density functional calculations. It is found that azurite is not well described as an isolated diamond chain with no spin frustration, but is better modeled as a two-dimensional spin lattice in which diamond chains with spin frustration interact through the interchain spin exchange in the ab-plane. Our analysis indicates that the magnetic properties of azurite at low temperatures can be approximated on the basis of two independent contributions, i.e., isolated dimer and effective uniform chain contributions. This prediction was verified by analyzing the magnetic susceptibility and specific heat data for azurite.

Ferromagnetically Coupled Shastry-Sutherland Quantum Spin Singlets in (CuCl)LaNb2O7

A thorough crystal structure determination at very low temperature of (CuCl)LaNb₂O₇, originally proposed as a spin-1/2 square-lattice antiferromagnet, is reported thanks to the use of single-crystal x-ray diffraction and powder neutron diffraction. State-of-the-art calculations (maximum entropy method) reveal that (CuCl)LaNb₂O₇ is orthorhombic with Pbam symmetry. First-principles calculations demonstrate that the dominant magnetic interactions are antiferromagnetic between fourth nearest neighbors with a Cu-Cl-Cl-Cu exchange path, which lead to the formation of spin singlets. The two strongest interactions between the singlets are ferromagnetic, which makes (CuCl)LaNb₂O₇ the first system of ferromagnetically coupled Shastry-Sutherland quantum spin singlets.

Influence of HF2- geometry on magnetic interactions elucidated from polymorphs of the metal-organic framework [Ni(HF2)(pyz)2]PF6 (pyz = pyrazine).

A tetragonal polymorph of [Ni(HF(2))(pyz)(2)]PF(6) (designated β) is isomorphic to its SbF(6)-congener at 295 K and features linear Ni-FHF-Ni pillars. Enhancements in the spin exchange (J(FHF) = 7.7 K), Néel temperature (T(N) = 7 K), and critical field (B(c) = 24 T) were found relative to monoclinic α-PF(6). DFT reveals that the HF(2)(-) bridges are significantly better mediators of magnetic exchange than pyz (J(pyz)), where J(FHF) ≈ 3J(pyz), thus leading to quasi-1D behavior. Spin density resides on all atoms of the HF(2)(-) bridge whereas N-donor atoms of the pyz ring bear most of the density.

Pressure-induced local structure distortions in Cu(pyz)F2(H2O)2.

We employed infrared spectroscopy along with complementary lattice dynamics and spin density calculations to investigate pressure-driven local structure distortions in the copper coordination polymer Cu(pyz)F(2)(H(2)O)(2). Here, pyz is pyrazine. Our study reveals rich and fully reversible local lattice distortions that buckle the pyrazine ring, disrupt the bc-plane O-H···F hydrogen-bonding network, and reinforce magnetic property switching. The resiliency of the soft organic ring is a major factor in the stability of this material. Interestingly, the collective character of the lattice vibrations masks direct information on the Cu-N and Cu-O linkages through the series of pressure-induced Jahn-Teller axis switching transitions, although Cu-F bond softening is clearly identified above 3 GPa. These findings illustrate the importance of combined bulk and local probe techniques for microscopic structure determination in complex materials.

[Ni(HF2)(3-Clpy)4]BF4 (py = pyridine): evidence for spin exchange along strongly distorted F···H···F- bridges in a one-dimensional polymeric chain.

[Ni(HF(2))(3-Clpy)(4)]BF(4) (py = pyridine) is a simple one-dimensional (1D) coordination polymer composed of compressed NiN(4)F(2) octahedra that form chains with bridging HF(2)(-) ligands. In spite of significant distortion of the HF(2)(-) bridge, a quasi-1D antiferromagnetic (AFM) behavior was observed with J(FHF) = 4.86 K.

Spin-Peierls transition in the S=1/2 compound TiPO4 featuring large intrachain coupling

We investigated the magnetic and structural properties of the quasi-one dimensional 3

On the High Magnetic-Ordering Temperature of the 5d Magnetic Oxide Ca3LiOsO6 Crystallizing in a Trigonal Crystal Structure: Density Functional Analysis

d^1

Symmetry-dependent strong reduction of the spin exchange interactions in Cs2CuCl4 by the 6p orbitals of Cs+ ions.

-quantum chain system TiPO

Importance of halogen···halogen contacts for the structural and magnetic properties of CuX2(pyrazine-N,N′-dioxide)(H2O)2 (X = Cl and Br).

_4

Structural, electronic, and magnetic properties of quasi-1D quantum magnets [Ni(HF2)(pyz)2]X (pyz = pyrazine; X = PF6(-), SbF6(-)) exhibiting Ni-FHF-Ni and Ni-pyz-Ni spin interactions.

(