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

Chiral Honeycomb Lattices of Nonplanar π-Conjugated Supramolecules with Protected Dirac and Flat Bands

The honeycomb lattice is a fundamental two-dimensional (2D) network that gives rise to surprisingly rich electronic properties. While its expansion to 2D supramolecular assembly is conceptually appealing, its realization is not straightforward because of weak intermolecular coupling and the strong influence of a supporting substrate. Here, we show that the application of a triptycene derivative with phenazine moieties, Trip-Phz, solves this problem due to its strong intermolecular π-π pancake bonding and nonplanar geometry. Our scanning tunneling microscopy (STM) measurements demonstrate that Trip-Phz molecules self-assemble on a Ag(111) surface to form chiral and commensurate honeycomb lattices. Electronically, the network can be viewed as a hybrid of honeycomb and kagome lattices. The Dirac and flat bands predicted by a simple tight-binding model are reproduced by total density functional theory (DFT) calculations, highlighting the protection of the molecular bands from the Ag(111) substrate. The present work offers a rational route for creating chiral 2D supramolecules that can simultaneously accommodate pristine Dirac and flat bands.

Designer Spin Models in Tunable Two-Dimensional Nanographene Lattices

Motivated by recent experimental breakthroughs, we propose a strategy for designing two-dimensional spin-lattices with competing interactions that lead to nontrivial emergent quantum states. We consider S = 1/2 nanographenes with C3 symmetry as building blocks, and we leverage the potential to control both the sign and the strength of exchange with first neighbors to build a family of spin models. Specifically, we consider the case of a Heisenberg model in a triangle-decorated honeycomb lattice with competing ferromagnetic and antiferromagnetic interactions whose ratio can be varied in a wide range. On the basis of the exact diagonalization of both Fermionic and spin models, we predict a quantum phase transition between a valence bond crystal of spin singlets with triplon excitations living in a Kagomé lattice and a Néel phase of effective S = 3/2 in the limit of dominant ferromagnetic interactions.

Spin Frustration in Organic Radicals

Spin frustration, which results from geometric frustration and a systematical inability to satisfy all antiferromagnetic (AF) interactions between unpaired spins simultaneously, is under the spotlight for its importance in physics and materials science. Spin frustration is treated as the structural basis of quantum spin liquids (QSLs). Featuring flexible chemical structures, organic radical species exhibit great potential in building spin-frustrated molecules and lattices. So far, the reported examples of spin-frustrated organic radical compounds include triradicals, tetrathiafulvalene (TTF) radicals and derivatives, [Pd(dmit)2 ] compounds (dmit=1,3-dithiol-2-thione-4,5-dithiolate), nitronyl nitroxides, fullerenes, polycyclic aromatic hydrocarbons (PAHs), and other heterocyclic compounds where the spin frustration is generated intra- or intermolecularly. In this Minireview, we provide a brief summary of the reported radical compounds that possess spin frustration. The related data, including magnetic exchange coupling parameters, spin models, frustration parameters, and crystal lattices, are summarized and discussed.

A Dynamic Triradical: Synthesis, Crystal Structure, and Spin Frustration

Polyradicals, i.e., multispin organic molecules, are playing important roles in radical-based material applications for their spin-spin interaction. A dynamic covalently bonded multispin molecule may endow materials with added function such as memory and switching. However, such a species has yet to be reported. We here report the synthesis, characterization, and crystal structure of a dynamic triradical species. It is generated by the self-assembly of two molecules through a Lewis acid coupled electron transfer. The crystalline species is spin-frustrated without Jahn-Teller distortion at low temperature, while it dissociates back to diamagnetic starting material in solution at high temperature. The reversible process is tracked by variable-temperature NMR, EPR, and UV-vis-NIR spectroscopy. Isolation, property study, and dynamic bonding investigation on such a species lay the foundation for the design of functional polyradicals with potential application as memory or switching devices.

The Ruthenium Nitrosyl Moiety in Clusters: Trinuclear Linear μ-Hydroxido Magnesium(II)-Diruthenium(II), μ3-Oxido Trinuclear Diiron(III)-Ruthenium(II), and Tetranuclear μ4-Oxido Trigallium(III)-Ruthenium(II) Complexes

The ruthenium nitrosyl moiety, {RuNO}6, is important as a potential releasing agent of nitric oxide and is of inherent interest in coordination chemistry. Typically, {RuNO}6 is found in mononuclear complexes. Herein we describe the synthesis and characterization of several multimetal cluster complexes that contain this unit. Specifically, the heterotrinuclear μ3-oxido clusters [Fe2RuCl4(μ3-O)(μ-OMe)(μ-pz)2(NO)(Hpz)2] (6) and [Fe2RuCl3(μ3-O)(μ-OMe)(μ-pz)3(MeOH)(NO)(Hpz)][Fe2RuCl3(μ3-O)(μ-OMe)(μ-pz)3(DMF)(NO)(Hpz)] (7·MeOH·2H2O) and the heterotetranuclear μ4-oxido complex [Ga3RuCl3(μ4-O)(μ-OMe)3(μ-pz)4(NO)] (8) were prepared from trans-[Ru(OH)(NO)(Hpz)4]Cl2 (5), which itself was prepared via acidic hydrolysis of the linear heterotrinuclear complex {[Ru(μ-OH)(μ-pz)2(pz)(NO)(Hpz)]2Mg} (4). Complex 4 was synthesized from the mononuclear Ru complexes (H2pz)[trans-RuCl4(Hpz)2] (1), trans-[RuCl2(Hpz)4]Cl (2), and trans-[RuCl2(Hpz)4] (3). The new compounds 4-8 were all characterized by elemental analysis, ESI mass spectrometry, IR, UV-vis, and 1H NMR spectroscopy, and single-crystal X-ray diffraction, with complexes 6 and 7 being characterized also by temperature-dependent magnetic susceptibility measurements and Mössbauer spectroscopy. Magnetometry indicated a strong antiferromagnetic interaction between paramagnetic centers in 6 and 7. The ability of 4 and 6-8 to form linkage isomers and release NO upon irradiation in the solid state was investigated by IR spectroscopy. A theoretical investigation of the electronic structure of 6 by DFT and ab initio CASSCF/NEVPT2 calculations indicated a redox-noninnocent behavior of the NO ancillary ligand in 6, which was also manifested in TD-DFT calculations of its electronic absorption spectrum. The electronic structure of 6 was also studied by an X-ray charge density analysis.

A new compound BaNa2Co7Te3O18 with distorted 2-uniform lattice (T13) showing unusual magnetic behaviors. Chem Commun (Camb) 2022;58:10937-10940. [DOI: 10.1039/d2cc03616a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Search for transition-metal compounds with unique spin lattices is a great challenge. Herein, we report on a successful exploration of a new compound BaNa2Co7Te3O18, featuring a unique spin network of...

A pentanuclear {Co5} cluster motif forming a capped breathing kagomé lattice

A new pentanuclear {Co5} cluster motif is found to have a D3h oblate trigonal bipyramidal geometry, which is extended into a 3D triangle network, forming a unique capped breathing kagomé lattice. Magnetic results confirmed a paramagnetism down to 2 K, accompanying the disappearance of two-thirds of the spin moment at low-temperature and the appearance of a 1/5 magnetization plateau.

Cluster-Based Coordination Polymers of Mn/Fe-Oxo Pivalates and Isobutyrates

Polynuclear coordination clusters can be readily arranged in cluster-based coordination polymers (CCPs) by appropriate bridging linkers. This review provides an overview of our recent developments in exploring structurally well-defined Mn/Fe-oxo pivalate and isobutyrate building blocks in the formation of CCPs assemblies with an emphasis on synthetic strategies and magnetic properties.

A {Na2Fe10} isobutyrate cluster, interlinked into 1D chains

The coordination cluster [Na₂Fe₁₀O₆(OH)₄(isobutyrate)₁₄(MeO)₂(MeCN)₂], derived from a {Fe₃(μ₃-O)(isobutyrate)₆} precursor, features a cluster shell of corner-sharing {Fe₃(μ₃-O)} motifs, capped by two sodium ions.

Synthesis of the Elusive S = 1/2 Star Structure: A Possible Quantum Spin Liquid Candidate

Materials with two-dimensional, geometrically frustrated, spin-¹/₂ lattices provide a fertile playground for the study of intriguing magnetic phenomena such as quantum spin liquid (QSL) behavior, but their preparation has been a challenge. In particular, the long-sought, exotic spin-¹/₂ star structure has not been experimentally realized to date. Here we report the synthesis of [(CH₃)₂(NH₂)]₃[Cu^II₃(μ₃-OH)(μ₃-SO₄)(μ₃-SO₄)₃]·0.24H₂O with an S = ¹/₂ star lattice. On the basis of the magnetic susceptibility and heat capacity measurements, the layered Cu-based compound exhibits antiferromagnetic interactions but no magnetic ordering or spin freezing down to 2 K. The spin-frustrated material appears to be a promising QSL candidate.

Homochiral hexanuclear nickel(ii) metallocyclic structures with high activity for the photocatalytic degradation of organic dyes

Two chiral hexanuclear nickel(ii) metallocyclic rings with new chiral ligands exhibit excellent activity for the photocatalytic degradation of organic dyes.

Cobalt(II) Magnetic Metal-Organic Framework with an Effective Kagomé Lattice, Large Surface Area, and High Spin-Canted Ordering Temperature

To make a porous material with high magnetic ordering temperature is challenging because the low density of the material is adverse to the dense magnetic moment, a prerequisite to high-performance magnets. Herein, we report a hollow magnetic metal-organic framework (MMOF) [Co₃(bpdc)₃(tpt)_0.66] 1 (H₂bpdc = 4,4'-biphenyldicarboxylic acid) with a Langmuir surface area of 1118 m²/g and spin-canted long-range magnetic ordering up to 22 K. Such a high performance is owing to the unique antiferromagnetic Kagomé lattice made of ferromagnetic Co₃ clusters and conjugated 2,4,6-tri(4-pyridinyl)-1,3,5-triazine (tpt) ligands, which is closely coupled with each other via double-interpenetration of the porous networks. Moreover, a parameter defined as the product of magnetic ordering/blocking temperature and the surface area for measuring the performance of porous molecular magnets is proposed.

Topological magnon bands in ferromagnetic star lattice

The experimental observation of topological magnon bands and thermal Hall effect in a kagomé lattice ferromagnet Cu(1-3, bdc) has inspired the search for topological magnon effects in various insulating ferromagnets that lack an inversion center allowing a Dzyaloshinskii-Moriya (DM) spin-orbit interaction. The star lattice (also known as the decorated honeycomb lattice) ferromagnet is an ideal candidate for this purpose because it is a variant of the kagomé lattice with additional links that connect the up-pointing and down-pointing triangles. This gives rise to twice the unit cell of the kagomé lattice, and hence more interesting topological magnon effects. In particular, the triangular bridges on the star lattice can be coupled either ferromagnetically or antiferromagnetically which is not possible on the kagomé lattice ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge modes, and thermal magnon Hall effect on the star lattice ferromagnet in different parameter regimes. The star lattice can also be visualized as the parent material from which topological magnon bands can be realized for the kagomé and honeycomb lattices in some limiting cases.

Magnon Hall effect without Dzyaloshinskii-Moriya interaction

Topological magnon bands and magnon Hall effect in insulating collinear ferromagnets are induced by the Dzyaloshinskii-Moriya interaction (DMI) even at zero magnetic field. In the geometrically frustrated star lattice, a coplanar/noncollinear [Formula: see text] magnetic ordering may be present due to spin frustration. This magnetic structure, however, does not exhibit topological magnon effects even with DMI in contrast to collinear ferromagnets. We show that a magnetic field applied perpendicular to the star plane induces a non-coplanar spin configuration with nonzero spin scalar chirality, which provides topological effects without the need of DMI. The non-coplanar spin texture originates from the topology of the spin configurations and does not need the presence of DMI or magnetic ordering, which suggests that this phenomenon may be present in the chiral spin liquid phases of frustrated magnetic systems. We propose that these anomalous topological magnon effects can be accessible in polymeric iron (III) acetate-a star-lattice antiferromagnet with both spin frustration and long-range magnetic ordering.

X-Ray Diffraction and Mössbauer Spectroscopy Studies of Pressure-Induced Phase Transitions in a Mixed-Valence Trinuclear Iron Complex

The mixed-valence complex Fe3 O(cyanoacetate)6 (H2 O)3 (1) has been studied by single-crystal X-ray diffraction analysis at pressures up to 5.3(1) GPa and by (synchrotron) Mössbauer spectroscopy at pressures up to 8(1) GPa. Crystal structure refinements were possible up to 4.0(1) GPa. In this pressure range, 1 undergoes two pressure-induced phase transitions. The first phase transition at around 3 GPa is isosymmetric and involves a 60° rotation of 50 % of the cyanoacetate ligands. The second phase transition at around 4 GPa reduces the symmetry from rhombohedral to triclinic. Mössbauer spectra show that the complex becomes partially valence-trapped after the second phase transition. This sluggish pressure-induced valence-trapping is in contrast to the very abrupt valence-trapping observed when compound 1 is cooled from 130 to 120 K at ambient pressure.

BaCo4(OH)2(H2PO4)(HPO4)2(PO4): Archimedean lattice T11 in distorted layers built from Co4O12(OH)4 squares

The family of Archimedean lattices has eleven numbers, yet several of these lattices have not been reported for transition metal oxides. Here, the last number of Archimedean lattice was firstly realized in a layered phosphate.

A heterometallic (Fe6Na8) cage-like silsesquioxane: synthesis, structure, spin glass behavior and high catalytic activity

The exotic “Asian Lantern” heterometallic cage silsesquioxane [(PhSiO_1.5)₂₀(FeO_1.5)₆(NaO_0.5)₈(n-BuOH)_9.6(C₇H₈)] (I) was obtained and characterized by X-ray diffraction, EXAFS, topological analyses and DFT calculation.

A discrete CuII6 cluster and a 3D MnII–CuII framework based on assembly of Mn2Cu4 clusters: synthesis, structure and magnetic properties

Two new magnetic metal–organic coordination compounds, a 0D Cu₆ cluster and a 3D heterometallic framework with MnII2CuII4 secondary building units are synthesized. Detailed magnetic studies are performed with proper magneto-structural correlation.

Assembly of 1D, 2D and 3D lanthanum(iii) coordination polymers with perchlorinated benzenedicarboxylates: positional isomeric effect, structural transformation and ring-opening polymerisation of glycolide

Eight La(iii) coordination polymers were prepared from isomeric perchlorinated benzenedicarboxylate ligands, and their catalytic activities have been described.

A one-dimensional coordination polymer based on Cu3-oximato metallacrowns bridged by benzene-1,4-dicarboxylato ligands: structure and magnetic properties

A one-dimensional linear coordination polymer {[Cu₃(μ₃-OH)(2-pyao)₃(bdc)]·6(H₂O)}_n (1) composed of trinuclear metallacrown cores has been obtained.

Divalent metal ions modulated strong frustrated M(ii)–Fe(iii)3O (M = Fe, Mn, Mg) chains with metamagnetism only in a mixed valence iron complex

Using divalent ions to link the frustrated Fe(iii)₃O units two isostructural chains were generated with distinct magnetic behaviour: frustrations and metamagnetism in mixed valence complex, but magnetic frustrations in heterometallic complexes.

A three dimensional magnetically frustrated metal–organic framework via the vertices augmentation of underlying net

A 3D magnetically frustrated MOF was successfully constructed from the augmentation on the vertices of a simple 3-connected underlying net. This MOF features a unique interpenetrating geometric spin frustration framework.

Pillared-bilayer zinc(ii)–organic laminae: pore modification and selective gas adsorption

Three Zn(ii)-based pillared-bilayer MOFs were systematically synthesized. Their unusual structural characteristics allow these pillared-bilayer MOFs to serve as excellent models for studies of gas adsorption properties.

Synthesis, structure and magnetic properties of phenylhydroxamate-based coordination clusters

The strategic recombination of preformed coordination clusters in the presence of polymodal bridging ligands has successfully led to the characterisation of five new compounds of structural and magnetic interest. Indeed using the dinuclear complex [M2(H2O)(piv)4(Hpiv)4] (M = Co, Ni; Hpiv = pivalic acid) as starting material and reacting it with phenylhydroxamic acid (H2pha) has yielded the four tetrametallic coordination clusters [Co4(Hpha)2(piv)6(Hpiv)4] (1), [Ni4(Hpha)2(piv)6(Hpiv)2(DMF)2] (2), [Co4(Hpha)2(piv)6(EtOH)2(H2O)2] (3), [Ni4(Hpha)2(piv)6(EtOH)2(H2O)2] (4) and the hexanuclear complex [Co6(Hpha)4(piv)8(EtOH)2]·EtOH (5). All the compounds have been structurally characterised revealing a particular binding mode for the hydroxamate ligand. The study of their magnetic properties has been performed and the modelling of these properties has been done using the appropriate hamiltonians for each compound. The experimental data and their modelling show non-zero spin ground states for compounds 4 and 5.

Candidate quantum spin liquid due to dimensional reduction of a two-dimensional honeycomb lattice

As with quantum spin liquids based on two-dimensional triangular and kagome lattices, the two-dimensional honeycomb lattice with either a strong spin-orbital coupling or a frustrating second-nearest-neighbor coupling is expected to be a source of candidate quantum spin liquids. An ammonium salt [(C₃H₇)₃NH]₂[Cu₂(C₂O₄)₃](H₂O)_2.2 containing hexagonal layers of Cu²⁺ was obtained from solution. No structural transition or long-range magnetic ordering was observed from 290 K to 2 K from single crystal X-ray diffraction, specific heat and susceptibility measurements. The anionic layers are separated by sheets of ammonium and H₂O with distance of 3.5 Å and no significant interaction between anionic layers. The two-dimensional honeycomb lattice is constructed from Jahn-Teller distorted Cu²⁺ and oxalate anions, showing a strong antiferromagnetic interaction between S = 1/2 metal atoms with θ = −120 (1) K. Orbital analysis of the Cu²⁺ interactions through the oxalate-bridges suggests a stripe mode pattern of coupling with weak ferromagnetic interaction along the b axis, and strong antiferromagnetic interaction along the a axis. Analysis of the magnetic susceptibility shows that it is dominated by a quasi-one-dimensional contribution with spin chains that are at least as well isolated as those of well-known quasi-one-dimensional spin liquids.

Detection of host–guest interactions in clathrates of heterocyclic molecules adsorbed in a porous MOF with Cu2 cluster nodes via vibration spectra and magnetic properties

A 3-D MOF Cu₂(EBTC)(H₂O)₂·[G] was used to encapsulate benzopyrrole, benzofuran and benzothiophene molecules. The host–guest interactions were studied via vibration spectra and magnetic susceptibility.

A bilayer triangular lattice with crown-like Co7 spin cluster SBUs exhibiting high spin frustration

An unprecedented crown-like Co₇(OH)₆ spin cluster is assembled in a bilayer triangular lattice, showing high spin frustration.