Coulombic Aggregations of MnIII salen-Type Complexes and Keggin-Type Polyoxometalates: Isolation of Mn2 Single-Molecule Magnets

Arsenic(III)-Capped 12-Tungsto-2-Arsenates(III) [M2(AsIIIW6O25)2(AsIIIOH)x]n- (M = CrIII, FeIII, ScIII, InIII, TiIV, MnII) and Their Magnetic Properties

Six arsenic(III)-capped 12-tungsto-2-arsenates(III) of the type [M₂(As^IIIW₆O₂₅)₂(As^IIIOH)_x]^n- (M = Cr^III, 1; Fe^III, 2; Sc^III, 3; In^III, 4; Ti^IV, 5; Mn^II, 6) have been synthesized in aqueous medium by direct reaction of the elements using a one-pot strategy and structurally characterized by FT-IR spectroscopy, single-crystal XRD, and elemental analysis. Polyanions 1-6 are comprised of two octahedrally coordinated guest metal ions M sandwiched between two {AsW₆} units, resulting in a structure with C_2h point-group symmetry. Polyanions 1-5 contain tri- and tetravalent metal ion guests M (M = Cr^III, Fe^III, Sc^III, In^III, and Ti^IV, respectively), and they have one {As^IIIOH} group grafted on each {AsW₆} unit, whereas the divalent Mn^II-containing derivative 6 has two such {As^IIIOH} groups grafted on each {AsW₆} unit. Magnetic studies on polyanions 3-5 over the temperature range 1.8-295 K and magnetic fields of 0-7 T confirmed that they are diamagnetic. On the other hand, polyanions 1, 2, and 6 are strongly magnetic and follow the Curie-Weiss law above 30 K. The susceptibility plots of 1 and 6 exhibit broad peaks suggesting short-range antiferromagnetic ordering, while the very weak antiferromagnetic ordering of 2 is overshadowed by traces of a paramagnetic impurity. The magnetization data of 1, 2, and 6 at 1.8 K over 0-7 T were analyzed by using the Heisenberg exchange procedure. Small (negative) values of the obtained J values help in understanding the absence of long-range antiferromagnetic ordering.

A Tellurium-Substituted Heteropolyniobate with Unique π-π Stacking and Ionic Conduction Property

A tetratellurium-substituted heteropolyoxoniobate with the formula K₂H[Cu(phen)(H₂O)]₄[Cu(phen)]₂[(LiNb₈Te₄O₄₀)]·34H₂O (1; phen = 1,10-phenanthroline) was hydrothermally prepared and structurally characterized. The compound represents the first hexavalent tellurium-substituted Keggin-type polyoxometalate (POM) so far. What is more, the POM cluster in 1 can elaborately self-assemble into a stable supramolecular framework with an ion conduction property through unique intermolecular π-π stacking.

Synthesis, Single Crystal X-Ray Structure, Theoretical Studies of Triple-{MnIII-Schiff-Base}-Decorated Molybdate

The design and synthesis of magnets with low dimensionality is currently an attractive research topic. The reaction of a Schiff base metal complex with simple molybdate has led to the formation of a new {MnIII-Schiff-base}-decorated molybdate heterometallic cluster, [{Mn(salpn)(H2O)}3MoO4](CH3COO)·2H2O (1) (salpn = N,N’-(1,3-propylene)bis(salicylideneiminate)). The hybrid aggregate was characterized using a range of methods including elemental analysis, single crystal x-ray diffraction, Infrared spectra (IR) spectroscopy, and x-ray structural analysis. The crystals of 1 are hexagonal: P63/m, a = 14.027(5) Å, c = 17.487(5) Å, V = 1142.6(3) Å3. Structural analyses indicate that we report on the preparation of the first triple metallic-oligomer held by orthomolybdate. Density functional theoretical calculation (DFT) studies have been performed to calculate electronic structure and potential energy landscapes. Additionally, the magnetic property of 1 indicates an antiferromagnetic coupling between the metal centers in the complex.

Utilizing the adaptive precursor [As2W19O67(H2O)]14– to support three hexanuclear lanthanoid-based tungstoarsenate dimers

The photoluminescence properties and polyanionic structures of hexanuclear lanthanoid-based tungstoarsenate dimers.

Two new POM-based compounds modified by lanthanide–Schiff base complexes with interesting NLO properties

Two POM-based lanthanide derivatives, namely {triaqua[2,6-diacetylpyridine bis(semicarbazone)-κ5 O,N,N′,N′′,O′]terbium(III)}-μ-oxido-[tricosa-μ2-oxido-dodecaoxido-μ12-phosphato-dodecamolybdenum(VI)] pentahydrate (1), [Tb(C11H15N7O2)(H2O)3][PMo12O40]·5H2O, and the dysprosium(III) analogue (2), have been isolated successfully by the reaction of Keggin–POM [PMo12O40]3− (abbreviated as PMo12 ), the Ln3+ ion and the Schiff base 2,6-diacetylpyridine bis(semicarbazone) (DAPSC) ligand under hydrothermal conditions. [Ln(DAPSC)(H2O)3][PMo12O40]·5H2O is a PMo12 -supported cluster featuring a lanthanide–Schiff base complex [denoted Ln– L (Schiff base)]. Single-crystal X-ray diffraction analysis reveals that the LnIII ion is in a distorted tricapped trigonal prismatic arrangement, coordinated by six O atoms and three N atoms. Two O atoms and three N atoms are provided by one DAPSC ligand, while the additional O atoms originate from a PMo12 cluster and three water molecules. Hydrogen-bonding interactions between adjacent clusters form an interesting three-dimensional supramolecular structure. The identities of 1 and 2 were characterized by IR spectroscopy, thermogravimetric analysis and powder X-ray diffraction. Interestingly, both compounds possess excellent two-photon absorption (TPA) responses to the third-order nonlinear optics (NLO) (2264 GM for 1 and 941 GM for 2), suggesting that they have potential applications in the field of nonlinear optics (NLO). To our knowledge, 1 and 2 are the first POM-based Ln– L (Schiff base) complexes showing excellent two-photon responses. Meanwhile, the electrochemical properties of both compounds were studied in detail.

Two novel bi-functional hybrid materials constructed from POMs and a Schiff base with excellent third-order NLO and catalytic properties

The first polyoxometalates modified by a porphyrin-resembling planar Schiff base have been successfully designed and synthesized under hydrothermal conditions. The third-order NLO responses indicated that they are excellent third-order NLO materials. Their catalytic performances are also investigated.

Slow magnetic relaxation in a dimeric Mn2Ca2 complex enabled by the large Mn(iii) rhombicity

A large single-ion transverse anisotropy at Mn(iii) sites induces slow magnetic relaxation at zero magnetic field of the ferromagnetic Mn dimers in a singular Mn₂Ca₂ complex.

A cascade approach to hetero-pentanuclear manganese-oxide clusters in polyoxometalates and their single-molecule magnet properties

Hetero-pentanuclear clusters {MMn₄} with large uniaxial magnetic anisotropy and SMM behavior were successfully synthesized by sequential introduction of metal cations into the trivacant lacunary polyoxometalates.

Hydrothermal synthesis, X-ray structure and DFT and magnetic studies of a (H2SiW12O40)2− based one-dimensional linear coordination polymer

In this paper, we report the synthesis and characterization of a novel POM-based inorganic–organic hybrid with an in situ transformation of pyridine-2,3-dicarboxylic acid into nicotinic acid and 2-hydroxynicotinic acid under hydrothermal conditions.

Field-induced slow magnetic relaxation of octahedrally coordinated mononuclear Fe(iii)-, Co(ii)-, and Mn(iii)-containing polyoxometalates

Polyoxometalates with highly distorted octahedrally coordinated mononuclear Fe(iii)-, Co(ii)-, and Mn(iii) ions have been synthesized, and they showed large magnetic anisotropy and single-molecule magnet behavior.

The O–P–O bridged Mn2(salen)2chains showing coexistence of single chain magnet and metamagnet behaviour

Three chain compounds in which the Mn₂(salen)₂dimers are bridged by O–P–O units are reported, two of which display coexistence of SCM behavior and metamagnetism at low temperature.

Effect of structural isomerism on magnetic dynamics: from single-molecule magnet to single-chain magnet

This Paper reports the first examples of O-P-O bridged Mn2(salen)2 (salen = N,N'-bis(salicylidene)ethylenediamine) chain compounds, namely, [Mn2(salen)2(2-FC6H4PO3H)](ClO4)·1/2CH3OH (1) and [Mn2(salen)2(4-FC6H4PO3H)](ClO4) (2). The phosphonate ligands adopt a syn-anti bidentate bridging mode in 1 and a syn-syn bidentate bridging mode in 2, originated from the isomeric phosphonate ligands. The different bridging modes cause a significant change in the Mn-O···O-Mn torsion angle over the O-P-O bridge, which are 96.6 and 1.9° for 1 and 2, respectively. As a result, the antiferromagnetic (AF) exchange couplings mediated through the O-P-O pathway are extremely weak in 1, and the overall magnetic behaviors are dominated by the Mn2(salen)2 moieties. Single-molecule magnetic behavior is observed in 1. For compound 2, the AF interaction over the O-P-O bridge is much stronger. The coexistence of metamagnetism and single-chain magnetic behavior is observed for 2.

Controlled association of single-molecule magnets (SMMs) into coordination networks: towards a new generation of magnetic materials

The field of molecular magnetism has rapidly expanded since the discovery of single-molecule magnets (SMMs) at the beginning of the 1990s. Numerous SMMs have been studied and a broad community currently works on these systems to improve their magnetic characteristics. However, it has also become an important strategy to diversify a part of our research activity toward the organization of these magnetic molecules in order to move closer to future applications. One of the possible ways is to utilize SMMs as molecular building blocks and assemble them with the help of coordination chemistry. This strategy presents a significant challenge since the intrinsic magnetic properties of the parent SMMs can be modified, which consequently also provides a unique opportunity to investigate new behaviours at the frontier between SMMs and classical bulk magnets. Furthermore, the design of systems with "enhanced" SMM properties or magnet behaviour is theoretically possible by choosing coordinating linkers that could favour an effective ferromagnetic arrangement of the SMMs. In this perspective article, we will give an overview of the known networks based on SMMs with an emphasis on the synthetic strategies, magnetic properties, and finally possible routes to a new generation of molecular magnetic materials.