A “Star” Antiferromagnet: A Polymeric Iron(III) Acetate That Exhibits Both Spin Frustration and Long-Range Magnetic Ordering

Diverse topologies of seven d10 coordination polymers constructed from a long ligand and different carboxylates

Seven d¹⁰ coordination complexes exhibiting diverse architectures from 1D chain to 3D entangled frameworks based on long flexible 1,10-bis(1,2,4-triazol-1-yl)decane and different carboxylate anions have been synthesized and characterized by single-crystal X-ray diffraction analyses.

Oxo-Bridged Trinuclear Fe(III) Complexes: Structural and Magnetic Properties

The crystal structure of (µ3-Oxo)-hexakis(µ2-cyanoacetato)-triaqua-tri-iron(III) nitrate pentahydrate shows that the trinuclear ferric complex has an equilateral molecular structure which is manifested in the 57Fe Mössbauer spectrum single doublet. The magnetic measurements reveal antiferromagnetic exchange interactions of –22.85 cm-1, between the metal centers, that compel the system to a total spin ground state of S = ½.

Origin of long-range ferromagnetic ordering in metal-organic frameworks with antiferromagnetic dimeric-Cu(II) building units

Even though metal-organic frameworks (MOFs) derived from antiferromagnetic dimeric-Cu(II) building units and nonmagnetic molecular linkers are known to exhibit unexpected ferromagnetic behavior, a comprehensive understanding of the underlying mechanism remains elusive. Using a combined theoretical and experimental approach, here we reveal the origin of the long-range ferromagnetic coupling in a series of MOFs, constructed from antiferromagnetic dimeric-Cu(II) building blocks. Our studies show that the strong localization of copper vacancy states favors spontaneous spin polarization and formation of local moment. These copper vacancy-induced moments are coupled via the itinerant electrons in the conjugated aromatic linkers to establish a long-range ferromagnetic ordering. The proposed mechanism is supported by direct experimental evidence of copper vacancies and the magnetic hysteresis (M-H) loops.

The quantum anomalous Hall effect on a star lattice with spin-orbit coupling and an exchange field

We study a star lattice with Rashba spin-orbit coupling and an exchange field and find that there is a quantum anomalous Hall effect in this system, and that there are five energy gaps at Dirac points and quadratic band crossing points. We calculate the Berry curvature distribution and obtain the Hall conductivity (Chern number ν) quantized as integers, and find that ν =- 1,2,1,1,2 when the Fermi level lies in these five gaps. Our model can be viewed as a general quantum anomalous Hall system and, in limit cases, can give what the honeycomb lattice and kagome lattice give. We also find that there is a nearly flat band with ν = 1 which may provide an opportunity for realizing the fractional quantum anomalous Hall effect. Finally, the chiral edge states on a zigzag star lattice are given numerically, to confirm the topological property of this system.

A C2-symmetric, basic Fe(III) carboxylate complex derived from a novel triptycene-based chelating carboxylate ligand

A triptycene-based bis(benzoxazole) diacid ligand H(2)L2(Ph4) bearing sterically encumbering groups was synthesized. Treatment of H(2)L2(Ph4) with Fe(OTf)(3) afforded a C(2)-symmetric trinuclear iron(III) complex, [NaFe(3)(L2(Ph4))(2)(μ(3)-O)(μ-O(2)CCPh(3))(2)(H(2)O)(3)](OTf)(2) (8). The triiron core of this complex adopts the well known "basic iron acetate" structure where the heteroleptic carboxylates, comprising two Ph(3)CCO(2)(-) and two (L2(Ph4))(2-) ligands, donate the six carboxylate bridges. The (L2(Ph4))(2-) ligand undergoes only minor conformational changes upon formation of the complex.

Cluster-based networks: 1D and 2D coordination polymers based on {MnFe2(μ3-O)}-type clusters

A straightforward approach to heterometallic Mn-Fe cluster-based coordination polymers is presented. By employing a mixed-valent μ(3)-oxo trinuclear manganese(II/III) pivalate cluster, isolated as [Mn(II)Mn(III)(2)O(O(2)CCMe(3))(6)(hmta)(3)]·(solvent) (hmta = hexamethylenetetramine; solvent = n-propanol (1), toluene (2)) in the reaction with a μ(3)-oxo trinuclear iron(III) pivalate cluster compound, [Fe(3)O(O(2)CCMe(3))(6)(H(2)O)(3)]O(2)CCMe(3)·2Me(3)CCO(2)H, three new heterometallic {Mn(II)Fe(III)(2)} cluster-based coordination polymers were obtained: the one-dimensional polymer chain compounds {[MnFe(2)O(O(2)CCMe(3))(6)(hmta)(2)]·0.5MeCN}(n) (3) and {[MnFe(2)O(O(2)CCMe(3))(6)(hmta)(2)]·Me(3)CCO(2)H·(n-hexane)}(n) (4) and the two-dimensional layer compound {[MnFe(2)O(O(2)CCMe(3))(6)(hmta)(1.5)]·(toluene)}(n) (5). Single-crystal X-ray diffraction analysis reveals a μ(3)-oxo trinuclear pivalate cluster building block as the main constituent in all polymer compounds. Different M:hmta ratios in 1-5 are related to the different structural functions of the N-containing ligand. In clusters 1 and 2, three hmta ligands are monodentate, whereas in chains 3 and 4 two hmta ligands act as bridging ligands and one is a monodentate ligand; in 5, all hmta molecules act as bidentate bridges. Magnetic studies indicate dominant antiferromagnetic interactions between the metal centers in both homometallic {Mn(3)}-type clusters 1 and 2 and heterometallic {MnFe(2)}-type coordination polymers 3-5. Modeling of the magnetic susceptibility data to a isotropic model Hamiltonian yields least-squares fits for the following parameters: J(1)(Mn(II)-Mn(III)) = -6.6 cm(-1) and J(2)(Mn(III)-Mn(III)) = -5.4 cm(-1) for 1; J(1) = -5.5 cm(-1) and J(2)(Mn(III)-Mn(III)) = -3.9 cm(-1) for 2; J(1)(Mn(II)-Fe(III)) = -17.1 cm(-1) and J(2)(Fe(III)-Fe(III)) = -43.7 cm(-1) for 3; J(1) = -23.8 cm(-1) and J(2) = -53.4 cm(-1) for 4; J(1) = -13.3 cm(-1) and J(2) = -35.4 cm(-1) for 5. Intercluster coupling plays a significant role in all compounds 1-5.

Fermionic Magnons, non-Abelian spinons, and the spin quantum Hall effect from an exactly solvable spin-1/2 Kitaev model with SU(2) symmetry

We introduce an exactly solvable SU(2)-invariant spin-1/2 model with exotic spin excitations. With time reversal symmetry (TRS), the ground state is a spin liquid with gapless or gapped spin-1 but fermionic excitations. When TRS is broken, the resulting spin liquid exhibits deconfined vortex excitations which carry spin-1/2 and obey non-Abelian statistics. We show that this SU(2) invariant non-Abelian spin liquid exhibits the spin quantum Hall effect with quantized spin Hall conductivity σ(xy)(s)=ℏ/2π, and that the spin response is effectively described by the SO(3) level-1 Chern-Simons theory at low energy. We further propose that a SU(2) level-2 Chern-Simons theory is the effective field theory describing the topological structure of the non-Abelian SU(2) invariant spin liquid.