Probing Single-Chain Magnets in a Family of Linear Chain Compounds Constructed by Magnetically Anisotropic Metal-Ions and Cyclohexane-1,2-Dicarboxylate Analogues

Discrete unusual mixed-bridged trinuclear CoIII2CoII and pentanuclear NiII coordination complexes supported by a phenolate-based ligand: theoretical and experimental magneto-structural study

We report a combined computational and experimental magnetostructural correlation in trinuclear mixed valence cobalt and pentanuclear nickel complexes.

Spin Ice-like Magnetic Relaxation of a Two-dimensional Network based on Manganese(III) Salen-type Single-Molecule Magnets

Spin ice is an exotic type of magnetism displayed by bulk rare-earth pyrochlore oxides. We discovered a spin ice-like magnetic relaxation of [{Mn(saltmen)}₄ {Mn(CN)₆ }](ClO₄ )⋅13 H₂ O (saltmen^2- =N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminate)). This magnetic system can be considered as a two-dimensional network of Mn^III salen-type single-molecule magnets (SMMs) in which each SMM unit (S_T =4) has two orthogonally oriented axial anisotropies and is connected ferromagnetically through the [Mn(CN)₆ ]^3- unit (S=1). This work illustrates that a two-dimensional SMM network with competition between the ferromagnetic interaction and local noncollinear magnetic anisotropies on SMMs is a new type of magnetic system exhibiting slow relaxation of magnetization with a Davidson-Cole-type broad distribution of the relaxation time.

Single-chain magnets assembled in cobalt(ii) metal–organic frameworks

This feature article discusses the advantages, progress and prospects of constructing single-chain magnets in metal–organic frameworks.

Series of Single-Ion and 1D Chain Complexes Based on Quinolinic Derivative: Synthesis, Crystal Structures, HF-EPR, and Magnetic Properties

By utilizing the quinolinic derivative, 8-carboxymethoxy-2-carboxylicquinoline (L), five transition metal coordination complexes, [M(L)(H₂O)₃]·H₂O] (M = Mn (1), Co (2)), [Ni(L)(H₂O)₂] (3), and {[M(L)](H₂O)} _n (M = Ni (4), Cu (5)), were synthesized by hydrothermal methods employing similar synthetic strategies. The crystal structures, magnetism and high-field EPR were characterized for the obtained compounds. 1-3 are mononuclear compounds. 1 and 2 have pentagonal bipyramidal geometry, while 4 and 5 exhibit one-dimensional zig-zag chain. Direct current magnetic and EPR studies demonstrate that compound 2 has large and positive D value (∼70.4 cm^-1), indicating the easy plane magnetic anisotropies of 2. This D value is the largest one in the reported Co(II) complexes with pentagonal bipyramidal geometry. Field-induced slow magnetic relaxation behavior was observed for 2 by the dynamic ac magnetic susceptibility measurements. The dc magnetic susceptibility studies of 4 and 5 give similar weak M^II-M^II antiferromagnetic interactions ( J = -1.50 and -3.55 K for 4 and 5, respectively). High-field EPR results show that 4 can be considered as a quantum antiferromagnet.

Synthesis, Structure, and Magnetic Properties of 1D {[MnIII(CN)6][MnII(dapsc)]}n Coordination Polymers: Origin of Unconventional Single-Chain Magnet Behavior

Two one-dimensional cyano-bridged coordination polymers, namely, {[Mn^II(dapsc)][Mn^III(CN)₆][K(H₂O)_2.75(MeOH)_0.5]}_n·0.5n(H₂O) (I) and {[Mn^II(dapsc)][Mn^III(CN)₆][K(H₂O)₂(MeOH)₂]}_n (II), based on alternating high-spin Mn^II(dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of U_eff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the Mn^III-CN-Mn^II spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [Mn^III(CN)₆]^3-. The prospects of [Mn^III(CN)₆]^3- complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.

An Ising iron(ii) chain exhibits a large finite-size energy barrier and "hard" magnetic behaviour

One-dimensional spin chains featuring strong axial anisotropic magnetism are promising candidates for isolatable and miniatured information storage materials, the so-called single-chain magnets (SCMs). Here we show a mixed azido/carboxylato bridged metamagnetic iron(ii) chain [Fe(N₃)₂(4-mpc)]_n (4-mpc = N-methylpyridinium-4-carboxylate) with a large energy barrier of 150 K, a large remnant magnetization (1.55Nβ) and coercivity (1.7 T at 2 K) for homo-spin SCMs. Heat capacity and Mössbauer spectroscopy studies corroborate the intrinsic nature of SCM behavior regardless of weak interchain magnetic interactions, which lead to the coexistence of metamagnetism but not long-range magnetic ordering. Moreover, detailed magnetic investigations indicate that the system is not only within the "Ising limit" but also in the "finite-size" regime.

Crystal engineering to control the magnetic interaction between weak ferromagnetic single-chain magnets assembled in a 3D framework

A synthetic strategy of control of the arrangement and the magnetism of the SCMs by assembly of the chains into a high dimensional network was illustrated in a family of a weak antiferromagnetic chain based 3D framework.

Dynamic magnetism of an iron(II)-chlorido spin chain and its hexametallic segment

An air-stable iron(ii) chain compound [Fe(phen)(Cl)2]n (, phen = 1,10-phenanthroline) was prepared and exhibits intrachain ferromagnetic interactions as well as competing interchain antiferromagnetic interactions that are mediated by π-π stacking of the phen ligands, resulting in metamagnetic behaviour. The interchain interactions can be altered by changing the external magnetic field, and disparate magnetic dynamics was thus observed from zero to the critical field of 1500 Oe. Zero-field cooled (ZFC) and field-cooled (FC) magnetization and heat capacity measurements indicate that long-range antiferromagnetic ordering occurs at lower fields, and this ordering disappears when the external field is larger than 1500 Oe. The low-frequency ac susceptibility data are consistent with the exponential increase of the temperature-dependent dc data, indicating a Glauber-type dynamics under the field of 1500 Oe. Thus, is considered as a metamagnetic single-chain magnet. For further analysis, a discrete hexametallic segment of the chain, [Fe6(phen)6(Cl)12] (), was also isolated and was shown to possess a high-spin ground state and display slow magnetic relaxations like single-molecule magnets. Magnetic analysis using CONDON suggests weak ferromagnetic interactions between the metal centres. The polymeric compound can be viewed as being constructed using the hexametallic unit which is of a low energy barrier, suggesting the significance of intrachain ferromagnetic interactions in enhancing the spin-reversal energy barrier of the short chains.

Field-induced dynamic magnetic behaviour of a canted weak ferromagnetic chain material

A 1-D [Mn^III₃O] based magnetic chain material amazingly exhibits the coexistence of spin-glass, spin-canting, and metamagnetic behaviours as well as slow relaxation of magnetization under different applied magnetic fields.

Bis[2,6-bis-(1H-pyrazol-1-yl)pyridine]-deca-kis-(μ2-3-nitro-benzoato)bis-(3-nitro-benzoato)tetra-dysprosium(III): a linear tetra-nuclear dysprosium compound based on mixed N- and O-donor ligands

The title compound, [Dy4(C7H4NO4)12(C11H9N5)2] or Dy4(L1)12(L2)2, where HL1 = 3-nitro-benzoic acid and HL2 = 2,6-bis-(1H-pyrazol-1-y1)pyridine, is a linear tetra-nuclear complex possessing inversion symmetry. The two central inversion-related Dy(III) atoms are seven-coordinate, DyO7, with a monocapped triangular-prismatic geometry. The outer two Dy(III) atoms are eight-coordinate, DyO5N3, with a bicapped triangular-prismatic geometry. The outer adjacent Dy(III) atoms are bridged by three L1(-) carboxyl-ate groups, while the inner inversion-related Dy(III) atoms are bridged by four L1(-) carboxyl-ate groups. The L2 ligands are terminally coordinated to the outer Dy(III) atoms in a tridentate manner. In the crystal, mol-ecules are linked via C-H⋯O hydrogen bonds, forming a two-dimensional network parallel to (001). Two carboxyl-ate O atoms, and N and O atoms of three nitro groups, are disordered over two positions, with a refined occupancy ratio of 0.552 (6):0.448 (6).

An unusual water-bridged homospin CoII single-chain magnet

A 3D coordination polymer has been constructed by linking water-bridged cobalt chains via dicarboxylic ligands to show interesting SCM behaviour.

A triple-bridged azido-Cu(ii) chain compound fine-tuned by mixed carboxylate/ethanol linkers displays slow-relaxation and ferromagnetic order: synthesis, crystal structure, magnetic properties and DFT calculations

A triple-bridged azido-Cu(ii) compound has been synthesized and magnetically characterized.

Synthesis, structures and properties of two metal-organic coordination polymers derived from manganese(ΙΙ), thiabendazole and polydentate carboxylic acids

Two novel binuclear Mn(II) metal-organic coordination complexes [Mn2(TBZ)2(CDC)(C2O4)]n (1), {[Mn2(TBZ)2(BDC)(0.5)(BTC)(H2O)2]·ET}n (2), (where TBZ = thiabendazole, H2CDC = trans-1,4-cyclohexanedicarboxylic acid, H2C2O4 = oxalic acid, H3BTC = 1,3,5-benzenetricarboxylic acid, ET = ethanol, H2BDC = 1,4-benzenedicarboxylate) have been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, electrochemical analysis and single crystal X-ray diffraction. The X-ray structure analysis reveals that 1 is s two-dimensional layer and 2 is s one-dimensional chain. In complex 1, it reveals 2-D layers composed of multi-(bidentate) bridging ligands (CDC and C2O4), and in 2, the coordinated BTC ligands adopt a monodentate mode and with BDC ligands adopt alternately chelating Mn1 and Mn2 bridges into 1-D chains. The 3-D structures of the two complexes are stabilized by π-π stacking interactions and hydrogen bonds.

Assembly of alternating spin-chains with magnetically anisotropic cobalt(II) dimers

A dimeric carboxylato complex of cobalt(II), [Co(2)(II)(1,2-chedc)(2)(Im)(2)] (1) (1,2-chedc = cyclohex-1-ene-1,2-dicarboxylate and Im = imidazole), has been isolated. This complex can be further linked by chloro- or carboxylato-ligands, affording respectively one-dimensional chain structures of (1)(∞)[Co(2)(II)(μ-Cl)(2)(1,2-chedc)(Im)(2)] (2) and (1)(∞)[Co(II)(1,2-chedc)(Im)] (3). Compound 1 shows weak antiferromagnetic interactions passing through the body of the dicarboxylate as well as substantial single-ion magnetic anisotropy (zero-field splitting energy Δ = 8.5 cm(-1)). Both 2 and 3 exhibit typical alternating spin-chain behaviour in the higher-temperature region, but they display disparate behaviours at lower temperatures. For 2, alternating F-AF interactions compete (J(1) = 6.7 K and J(2) = -8.2 K), resulting in paramagnet-like behaviour with no clear evidence of three-dimensional contact. Compound 3 exhibits stronger intrachain AF-AF exchange-coupling interactions (J(1) = -9.3 K and J(2) = -4.3 K), leading to non-diamagnetic ground state due to the tiling of adjacent spins. Long-range magnetic ordering was observed below 10 K. Its narrow hysteresis loop suggests the use of 3 as a soft magnet.

Slow magnetic relaxation in two new 1D/0D Dy(III) complexes with a sterically hindered carboxylate ligand

Two carboxylate-bridged Dy(III) complexes, [Dy(2)(piv)(5)(μ(3)-OH)(H(2)O)](n) (1) and [Dy(2)(piv)(6)(phen)(2)] (2) (pivH = pivalic acid; phen = 1,10-phenanthroline), have been synthesized and structurally characterized. Complex 1 takes a one-dimensional (1D) chain structure based on [Dy(4)(μ(3)-OH)(2)(piv)(8)(H(2)O)(2)](2+) units, while complex 2 is a dinuclear structure bridged by syn,syn-carboxylates. Magnetic investigation indicates weak ferromagnetic interaction between adjacent Dy(III) ions of the Dy(4) unit in 1 and weak intramolecular antiferromagnetic interaction between Dy(III) ions and/or depopulation of the Dy(III) excited-state Stark sublevels in 2. Alternating-current susceptibility measurements revealed frequency- and temperature-dependent out-of-phase signals under a zero direct-current field in 1, with typical slow magnetic relaxation behavior with an anisotropic barrier U ≈ 4.5 K, while 2 exhibits field-induced single-molecule-magnet behavior with ΔE/k(B) = 28.43 K under a 2 kOe external field.

Incorporation of spin-5/2 chain into 2D network with conformational pure e,a-cis-cyclohexane-1,4-dicarboxylato linker

A two-dimensional coordination network, (2)(∞)[Fe(III) (OH)(e,a-cis-1,4-chdc)] (1,4-chdc: cyclohexane-1,4-dicarboxylate), featuring one-dimensional iron(III)-hydroxy chains that are transversely bridged by 1,4-chdc in its pure e,a-cis conformation have been isolated. The magnetic study shows a typical spin-5/2 Heisenberg chain above 20 K, but canted antiferromagnetic ordering at lower temperatures.

catena-Poly[[diaqualithium]-μ-[rac-cis-(2-carboxycyclohexane-1-carboxylato-κ2O1:O2]]

In the structure of the title compound, [Li(C₈H₁₁O₄)(H₂O)₂]_n, the distorted tetra­hadral LiO₄ coordination sphere comprises two water mol­ecules and two carboxyl O-atom donors from separate bridging cis-2-carb­oxy­cyclo­hexane-1-carboxyl­ate monoanions [Li—O = 1.887 (4)–1.946 (3) Å], giving chain substructures which extend along [010]. Water–water and water–carboxyl O—H⋯O hydrogen bonds stabilize these chain structures and provide inter­chain links, resulting in a two-dimensional layered structure extending parallel to (100).

From molecules to materials: molecular paddle-wheel synthons of macromolecules, cage compounds and metal-organic frameworks

Metal-organic frameworks (MOF) are becoming a more and more important class of functional materials. Yet, very often, the synthesis of MOFs is not easy to control and requires a profound knowledge and experience in solid state chemistry. One of the most frequently used metal connectors is the so-called 'paddle-wheel' (PW) unit, which is a well-known molecular compound type in inorganic coordination chemistry. Depending on the ligands, the geometry of PWs strictly directs the assembly of ordered networks. This review focuses on the question, to what extent ordered network structures can be accessed by typical molecular syntheses in solution, starting from molecular PW complexes to ordered macromolecules, finite cage compounds and finally, three-dimensional superstructures.