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

Abstract

The preparation of new geometrically spin-frustrated magnetic materials [1] that approximate theoretical models [1,2] is a challenge. Although the Mermin-Wagner theorem [3] indicates that long-range magnetic order can exist in two dimensions at zero Kelvin, order can be destroyed either by quantum fluctuations or geometric frustration even at this temperature. Theoretical studies indicate that the ground state of a spin-1/2 Heisenberg antiferromagnet is most likely to be semiclassically ordered.[4] However, the interplay of geometric frustration and quantum fluctuations has been found to give rise to a paramagnetic ground state without semi-classical long-range order in two types of lattice.The first of these lattices is the famous KagomØ lattice (T8) and the second is the so-called "star" lattice (T9; Scheme 1), which may serve as a new example of a quantum paramagnet. [4,5] The triangles are corner-sharing in the KagomØ lattice whereas they are separated by a bridge in the star lattice, which means that their next-nearest-neighbor exchange interactions are different. [4,5] The magnetic J exchange pathways in the KagomØ lattice are all equivalent, whereas the intra-triangular J T pathway in the star lattice is weaker than the inter-triangular J D pathway. In contrast to the rapid development of KagomØ-type antiferromagetic lattices [6, 7] and related, geometrically spin-frustrated lattices, [8] there appears to date to be no report of a compound with a genuine star lattice. [7][8][9] including the desired magnetically frustrated star lattice. This star lattice can be described in vertex notation as 3.12 2 (see Scheme S1 in the Supporting Information), a lattice that is a uniform, three-connected twodimensional net with large voids.[10] Three-connected node subunits that prefer to bond in a planar fashion, such as the basic cationic iron(III) carboxylate cluster [Fe 3 [11] where L may be water, methanol, or pyridine, must be used to avoid three-dimensional connections. These carboxylate clusters are good potential building blocks because they are easily prepared, prefer planar bonding, and the R groups and L ligands can easily be varied. [12] The cationic [Fe 3 + moiety has previously served as a six-or three-connected node (see Scheme S2 in the Supporting Information) to form either three- [12a-e] or zero-dimensional [12f] porous frameworks depending upon the nature of the carboxylate, which may be either fully or partially substituted by dicarboxylates; the L ligands are usually retained as terminal ligands. Although no example is known to date, it should be possible to substitute the L ligands located in the triangular [Fe 3

Synthesis, structure and physical properties of the one-dimensional chain complex of tetrathiafulvalene carboxylate

“…The value of χ M T at room temperature is 3.2 emu·K·mol −1 , which is higher than the value of 1.875 emu·K·mol −1 expected for one isolated spin-only Co Ⅱ ion (S = 3/2), indicating that an important orbital contribution is involved [24,25] . It gives g Co = 2.6 if we assume the ions are uncoupled.…”

3D Magnetically Ordered Open Supramolecular Architectures Based on Ferrimagnetic Cu/Adenine/Hydroxide Heptameric Wheels

“…A recent example published by Zhao et al consists of a (3,6)-connected two-dimensional coordination polymer built from sulfoisophthalate/adeninato-derived Cu II 7 wheels and S = 5/2 ground state . It is worth mentioning the relationship of the spin topology of the wheels with the frustrated triangular anti-ferromagnetic (AF) lattice, which is one of the very few solvable models in spin-frustrated systems . It makes this system an attractive target for displaying magneto caloric effect (MCE) and using it for low-temperature refrigeration purposes.…”

“…From the 3D magnetic ordering temperature values ( T c = 0.5 and 0.6 K) and the Curie–Weiss temperature (θ p = 20.7 and 11.0 K for 1 and 2 , respectively) we can obtain information on the magnetic spin frustration f , given by |θ/ T c | of these open supramolecular structures . The f parameter reaches values of 41.4 and 18.3 for 1 and 2 , respectively, where a value above 10 indicates the presence of strong frustration . Therefore, it indicates that both SMOFs display complex 3D magnetic structures with the presence of stronger spin frustration in the 1 compound.…”

Assembly of oximate-bridged Mn6 cluster to a one-dimensional chain

“…Coordination polymers based on polynuclear molecules form a new family of magnetic materials [10][11][12][13][14][15][16][17][18][19]. By the rational control over the bridging groups between clusters, magnetic properties can be tuned accordingly, for example, single-chain magnetic, modified singlemolecule magnetic, and long-range magnetic ordering dependent on the inter-cluster magnetic coupling [4,[15][16][17][18][19][20][21].…”