Ferromagnetic and Antiferromagnetic Intermolecular Interactions in a New Family of Mn4 Complexes with an Energy Barrier to Magnetization Reversal

Magnet-in-ferroelectric crystals exhibiting photomultiferroicity

Growing crystallographically incommensurate and dissimilar organic materials is fundamentally intriguing but challenging for the prominent cross-correlation phenomenon enabling unique magnetic, electronic, and optical functionalities. Here, we report the growth of molecular layered magnet-in-ferroelectric crystals, demonstrating photomanipulation of interfacial ferroic coupling. The heterocrystals exhibit striking photomagnetization and magnetoelectricity, resulting in photomultiferroic coupling and complete change of their color while inheriting ferroelectricity and magnetism from the parent phases. Under a light illumination, ferromagnetic resonance shifts of 910 Oe are observed in heterocrystals while showing a magnetization change of 0.015 emu/g. In addition, a noticeable magnetization change (8% of magnetization at a 1,000 Oe external field) in the vicinity of ferro-to-paraelectric transition is observed. The mechanistic electric-field-dependent studies suggest the photoinduced ferroelectric field effect responsible for the tailoring of photo-piezo-magnetism. The crystallographic analyses further evidence the lattice coupling of a magnet-in-ferroelectric heterocrystal system.

Metamagnetism and canted antiferromagnetic ordering in two monomeric CoII complexes with 1-(2-pyrimidyl)piperazine. Hirshfeld surface analysis and theoretical studies

Here we present the magnetic properties of two cobalt complexes formulated as: [Co(SCN)2(L)2] (1) and (H2L)2[Co(SCN)4]·H2O (2) (L = 1-(2-pyrimidyl)piperazine). The two compounds contain isolated tetrahedral CoII complexes with important intermolecular interactions that lead to the presence of a canted antiferromagnetic order below 11.5 and 10.0 K, with coercive fields at 2 K of 38 and 68 mT, respectively. Theoretical calculations have been used to explain this behaviour. Hirshfeld surface analysis shows the presence of strong intermolecular interactions in both compounds. The crystal geometries were used for geometry optimization using the DFT method. From the topological properties, electrostatic potential maps and molecular orbital analysis, information about the noncovalent interaction and chemical reactivity was obtained.

Pressure-controlled magnetism in 2D molecular layers

Long-range magnetic ordering of two-dimensional crystals can be sensitive to interlayer coupling, enabling the effective control of interlayer magnetism towards voltage switching, spin filtering and transistor applications. With the discovery of two-dimensional atomically thin magnets, a good platform provides us to manipulate interlayer magnetism for the control of magnetic orders. However, a less-known family of two-dimensional magnets possesses a bottom-up assembled molecular lattice and metal-to-ligand intermolecular contacts, which lead to a combination of large magnetic anisotropy and spin-delocalization. Here, we report the pressure-controlled interlayer magnetic coupling of molecular layered compounds via chromium-pyrazine coordination. Room-temperature long-range magnetic ordering exhibits pressure tuning with a coercivity coefficient up to 4 kOe/GPa, while pressure-controlled interlayer magnetism also presents a strong dependence on alkali metal stoichiometry and composition. Two-dimensional molecular interlayers provide a pathway towards pressure-controlled peculiar magnetism through charge redistribution and structural transformation.

Three-Dimensional (3-D) Ferromagnetic Network of Mn12 Single-Molecule Magnets: Subtle Environmental Effects and Switching to Antiferromagnetic

A new member of the Mn₁₂ family of single-molecule magnets (SMMs) has been prepared and found to be the first of this family to give a 3-D ferromagnetic network. [Mn₁₂O₁₂(O₂CC₆H₄-p-F)₁₆(H₂O)₄] (2) was prepared by carboxylate substitution on the acetate derivative with p-F-benzoic acid and crystallizes as 2·8MeCN in space group I4̅2m with extensive formation of intermolecular C-H···F hydrogen-bonding. The latter leads to a combination of ferromagnetic (F) and antiferromagnetic (AF) interactions and an overall F network that gives a χ_MT value at low T that is abnormally high for an S = 10 ground state. 2·8MeCN undergoes solvent loss under vacuum to 2, with a decrease in unit-cell volume of 17%, primarily due to a 13% decrease in the c-axis. The χ_MT vs T plot for 2 indicates a switch to a net AF network. Exposure to air causes hydration to 2·3H₂O, a concomitant increase in unit cell volume, and a switch back to a F network. The same conversion of 2·8MeCN to 2·3H₂O can also be accomplished in one step rather than two steps, by leaving crystals of the former exposed to air at ambient temperature and pressure for 10 days, giving the same magnetic plots. Interestingly, the desolvation/solvation processes cause Jahn-Teller isomerism to occur, but the ratio of the faster-relaxing isomer to the normal slowly relaxing one does not change monotonically. Single-crystal micro-SQUID studies on 2·8MeCN show the expected magnetization hysteresis loops for a SMM and a small exchange-bias from the intermolecular interactions that is unexpectedly AF. Since the micro-SQUID study only identifies interactions along the easy-axis (z-axis) of the crystal, this is readily rationalized as due to the J_z components of the intermolecular interactions in 2·8MeCN being net AF. The combined results offer useful insights into the degree of sensitivity of the magnetic properties to small environmental perturbations.

Cyanide Single-Molecule Magnets Exhibiting Solvent Dependent Reversible "On" and "Off" Exchange Bias Behavior

The syntheses, structures, and magnetic properties of four new complex salts, (PPN){[Mn(III)(salphen)(MeOH)]2[M(III)(CN)6]}·7MeOH (Mn2M·7MeOH) (M = Fe, Ru, Os and Co; PPN(+) = bis(triphenylphosphoranylidene)ammonium cation; H2salphen = N,N'-bis(salicylidene)-1,2-diaminobenzene), and a mixed metal Co/Os analogue (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)0.92Os(III)0.08(CN)6]}·7MeOH were undertaken. It was found that all compounds exhibit switchable single-molecule magnet (SMM) and exchange-bias behavior depending on the interstitial methanol content. The pristine (PPN){[Mn(salphen)(MeOH)]2[Os(CN)6]}·7MeOH (Mn2Os·7MeOH) behaves as an SMM with an effective barrier for the magnetization reversal, (Ueff/kB), of 17.1 K. Upon desolvation, Mn2Os exhibits an increase of Ueff/kB to 42.0 K and an opening of the hysteresis loop observable at 1.8 K. Mn2Os·7MeOH shows also exchange-bias behavior with magnetic hysteresis loops exhibiting a shift in the quantum tunneling to 0.25 T from zero-field. The Fe(III) and Ru(III) analogues were prepared as reference compounds for assessing the effect of the 5d versus 4d and 3d metal ions on the SMM properties. These compounds are also SMMs and exhibit similar effects but with lower energy barriers. These findings underscore the importance of introducing heavy transition elements into SMMs to improve their slow relaxation of the magnetization properties. The (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)(CN)6]}·7MeOH (Mn2Co·7MeOH) analogue with a diamagnetic Co(III) central atom and the mixed Co/Os (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)0.92Os(III)0.08(CN)6]}·7MeOH (Mn2Co/Os·7MeOH) "magnetically diluted" system with a 9:1 Co/Os metal ratio were prepared in order to further probe the nature of the energy barrier increase upon desolvation of Mn2Os. In addition, inelastic neutron scattering and frequency-domain Fourier-transform THz electron paramagnetic resonance spectra obtained on Mn2Os·7MeOH and Mn2Os in combination with the magnetic data revealed the presence of anisotropic exchange interactions between Mn(III) and Os(III) ions.

Covalent embedding of Ni2+/Fe3+ cyanometallate structures in silica by sol-gel processing

Compound [Ni(AEAPTS)2]3[Fe(CN)6]2 (AEAPTS = N-(2-aminoethyl)-3-aminopropyltrimethoxysilane), in which Ni(2+) and Fe(3+) ions are ferromagnetically coupled through cyano bridges, was prepared. Sol-gel processing of the AEAPTS derivative resulted in incorporation of the cyanometallate in silica. The obtained material is magnetically ordered below 22 K with an effective magnetic moment μeff of 4.46 μB at room temperature, a maximum of 8.60 μB at approximately 15 K and a narrow hysteresis at 2 K, with a saturation remanence of about 300 emu mol(-1) and a coercitivity of 0.03 T.

Disentangling steric and electronic factors in monomeric bis(2-bromo-4-chloro-6-{[(2-hydroxyethyl)imino]methyl}phenolato-κ2N,O)copper(II)

The title compound, [Cu(C9H8BrClNO2)2], is a square-planar complex. The potentially tridentate dibasic 2-bromo-4-chloro-6-{[(2-hydroxyethyl)imino]methyl}phenolate ligand coordinates in atrans-bis fashion to the CuIIcentreviathe imine N and phenolate O atoms. The CuIIatom lies on the centre of inversion of the molecule. The potentially coordinating hydroxyethyl group remains protonated and uncoordinated, taking part in intermolecular hydrogen bonds with vicinal groups, leading to the formation of a two-dimensional hydrogen-bond network with sheets parallel to the (10\overline{1}) plane. Substituent effects on the crystal packing and coordination modes of the ligand are discussed.

{Dy(α-fur)3}n: from double relaxation single-ion magnet behavior to 3D ordering

The synthesis and magnetostructural properties of a new low-dimensional magnetic system based on α-furoate ligands, {[Dy(α-C4H3OCOO)(μ-(α-C4H3OCOO))2(H2O)3]}n, abbreviated {Dy(α-fur)3}n, are reported. X-ray diffraction experiments results evidence the presence of two different Dy coordination environment types differing only in the position of one of the furoate ligands. The crystallographic structure is formed by polymeric chains along the c-axis, each composed of just one Dy type, coupled within the bc-plane with chains of the same Dy type. These planes, each of them containing only one Dy type, are randomly stacked along the a-axis. The magnetic behaviour was studied by magnetization, static and dynamic susceptibility, heat capacity measurements and ab initio simulations. The directions of the easy axes of magnetization, gyromagnetic values and energy level structures of the two Dy types were obtained from ab initio calculations. {Dy(α-fur)3}n exhibits slow magnetic relaxation dynamics below 10 K. The two Dy types with different coordination environments behave as single-ion magnets, with different thermal activation energies of 80.5(6) K and 32.4(5) K, until they reach, upon cooling, a quantum tunneling (QT) regime. Magnetic diluted samples, substituting Dy by Y, {Y(x)Dy(1-x)(α-fur)3}n, were prepared to study the effect of intercluster interactions. Decreasing the Dy interaction by dilution by 90-95% leaves the activation energy unchanged, but shifts the transition to the QT regime to lower temperatures. At T = 2.4 K the tunneling time constant has been shown to decrease weakly with the field in the x = 0 case, and more strongly for x = 0.9. As the external field increases, quantum tunneling is quenched and a new slow relaxation appears that is identified at high fields as caused by a direct relaxation process. As the temperature is decreased, interchain AF coupling becomes effective and gives rise to the occurrence of an antiferromagnetic 3D order transition at T(N) = 0.66 K. From all the evidence, it is concluded that within each bc-plane Dy ions arrange in chains along the c-direction, having weak uncompensated ferromagnetic spin-canted intrachain coupling and antiferromagnetic interchain coupling.

Chlorido[4-chloro-2-(pyridin-2-yl-methyl-imino-meth-yl)phenolato-κ(3)N,N',O]copper(II)

In the title complex, [Cu(C₁₃H₁₀ClN₂O)Cl], the Cu^II ion is coordinated by one O atom and two N atoms of the tridentate Schiff base ligand and one chloride ion, forming a slightly distorted square-planar geometry. Weak Cu⋯Cl inter­actions [2.793 (5) Å] result in the formation of a chain along the a axis.

Syntheses, crystal structures and magnetic properties of a novel family of penta-manganese complexes derived from an assembly system containing polydentate hydroxy-rich Schiff-base ligands

The syntheses, crystal structures, and magnetochemical characterization are reported of a novel family of four pentanuclear manganese complexes, namely, [Mn(III)(5)(mu(3)-O)(2)(L(1))(4)(O(2)CMe)(3)(CH(3)OH)].1.5CH(3)OH.2.5H(2)O (1), [Mn(III)(5)(mu(3)-O)(2)(L(1))(4)(O(2)CPh)(3)(CH(3)OH)].2CH(3)OH.2.25CH(3)CN.1.5H(2)O (), [Mn(II)Mn(III)(4)(HL(2))(2)(L(2))(2)(O(2)C Me)(4))].CH(3)OH.H(2)O (3) and [Mn(II)Mn(III)(4)(HL(2))(2)(L(2))(2)(O(2)CPh)(4))].1.5H(2)O (4), where H(2)L(1) is 3,5-dibromosalicylidene-2-ethanolamine and H(3)L(2) is 3-(2-hydroxy-3,5-dibromobenzylideneamino)propane-1,2-diol. All the complexes can be obtained from a reaction system containing the trinuclear species [Mn(3)O(O(2)CR)(6)(Py)(3)](0/+) (R = Me or Ph) and H(2)L(1) or H(3)L(2) with similar procedures. Both cores in complexes 1 and 2 feature two mu(3)-O(2-) atoms, four L(1)(2-) ligands together with three RCO(2)(-) groups (R = Me or Ph) bridging five Mn(III) atoms to form an incomplete cubane extended at one face by an incomplete adamantane unit, which is an unprecedented structural type in Mn chemistry. Complexes 3 and 4 both have a rare [Mn(II)Mn(III)(4)(mu(2)-O(alkoxide))(6)](8+) core, which can be regarded as two {Mn(II)Mn(III)(2)(mu(2)-O(alkoxide))(3)} scalene triangles, sharing the Mn(II) vertex. The dc magnetic susceptibility studies in the 2-300 K range for complexes 1-4 reveal the presence of overall antiferromagnetic intracluster interactions. A simple 3-J model was found to be adequate to describe the variable-temperature dc susceptibility data of complexes 1-4. The results have allowed us to compare the obtained magnetic exchange with magneto-structural correlations found previously for manganese-oxo clusters.

Aqua-[2-(2-pyridylmethyl-imino-meth-yl)phenolato]nickel(II) nitrate monohydrate

In the title compound, [Ni(C(13)H(11)N(2)O)(H(2)O)]NO(3)·H(2)O, the Ni(II) ion is coordinated by one O atom and two N atoms of the Schiff base ligand and the O atom from a water mol-ecule, forming a slightly distorted square-planar geometry. A one-dimensional double-chain structure is formed along [001] by O⋯H-O hydrogen bonds and the Ni⋯O [2.617 (3) Å] inter-actions.

2,2'-[1,1'-(Decane-1,10-diyldioxy-dinitrilo)diethyl-idyne]diphenol

The salen-type bis-oxime title compound, C₂₆H₃₆N₂O₄, lies about a crystallographic inversion centre. Classical intra­molecular O—H⋯N hydrogen bonds generate two S(6) ring motifs. In the crystal structure, pairs of weak inter­molecular C—H⋯O hydrogen bonds link adjacent mol­ecules into an infinite one-dimensional supra­molecular structure.