Modulating the relaxation dynamics of the Na2Mn3 system via an auxiliary anion change

This paper reports two closely related heteropentanuclear manganese complexes, namely, {Na₂Mn₃(opch)₃(μ₄-O)(μ₂-N₃) (μ₂-AcO)(μ₂-MeO)}·6CH₃OH·0.5H₂O (1) and {Na₂Mn₃(opch)₃(μ₄-O)(μ₂-N₃)₂(μ₂-AcO)}·2.5CH₃OH·2H₂O (2), where H₂opch is (E)-N'-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide. Single-crystal X-ray diffraction analysis reveals that the trigonal bipyramidal skeletons in both complexes are comparable, where a perfect triangular Mn₃ motif occupies the equatorial plane. Magnetic investigations suggest that overall antiferromagnetic coupling is present within the triangles of 1 and 2. However, their dynamic magnetic properties are drastically distinct. Indeed, complexes 1 and 2 show two kinds of dual slow magnetic relaxation processes that correspond to anisotropy barriers (Δ) of 9.2 cm^-1 (11.4 cm^-1 for 2) and 12.8 cm^-1 (30.0 cm^-1 for 2) for the low- and high-frequency domains, respectively. More importantly, a further comparative study of the structure and magnetism indicates that the coordination sphere of these two model complexes with the homologous hydrazone-based coordination sites undergoes an alteration from methoxide-O to azide-N upon a subtle change of the auxiliary anion accompanied by modulating octahedron geometries, leading to a further influence on different relaxation dynamics.

Single-molecule magnet achieved through topological tuning with sodium ions

A triangular MnIII3-based 2D framework exhibiting SMM properties was achieved by tuning the topological arrangement of cluster units and the intra-unit parameters through the linkage of diamagnetic Na(i) ions.

A family of 3d metal clusters based on N–N single bonds bridged quasi-linear trinuclear cores: the Mn analogue displaying single-molecule magnet behavior

The reactions of the diacylhydrazine ligands N,N′-bisalicyl-2,6-pyridine dicarbohydrazide (H₆sphz) and N,N′-bis(3-methoxysalicyl)-2,6-pyridine dicarbohydrazide (H₆msphz) with various 3d metal salts, afforded a series of coordination clusters, namely, [Mn^III₂Mn^II(sphz)(acac)₂(CH₃OH)₄] (1, acac⁻ = acetylacetone anions), [Ni^II₃(msphz)(Py)₄] (2, Py = pyridine), [Cu^II₆(sphz)₂(Py)₄] (3) and [Cu^II₆(msphz)₂(Py)₄]·2DMF·2H₂O (4). Cluster 1 and 2 are single ligand assembled quasi-linear trinuclear structures. Both 3 and 4 consist a pair of quasi-linear {Cu₃} cores, which are linked together by two crossed ligands. The adjacent 3d metal ions in all trinuclear cores of 1–4 are bridged by N–N single bonds of ligands, which convey ferromagnetic (FM) interactions between 3d metal centers of 1, and antiferromagnetic (AFM) interactions between those of 2–4. In particular, the FM interactions and linear arrangement of mixed-valence Mn centers in 1 result in a large spin ground states value (S_T) of 13/2, as well as single-molecule magnet (SMM) behavior of slow relaxation and hysteresis of magnetization.

A family of 3d metal clusters featuring N–N single bonds bridged quasi-linear trinuclear cores were designed and synthesized. The Mn analogue represents a very rare case of quasi-linear 3d SMM using N–N single bonds as magnetic coupling pathways.

Synthesis and magnetochemistry of heterometallic triangular FeLnIII (Ln = La, Gd, Tb, Dy, and Ho) and FeYIII complexes

A series of Fe₂Ln (Ln = La, Gd, Tb, Dy and Ho) and Fe₂Y complexes have been synthesized via metal substitution and characterized by single crystal X-ray diffraction. All the molecules are isostructural and have a Fe₂LnO triangular core with the oxygen atom existing as an μ₃-oxo^2- anion. DC and AC magnetic susceptibility studies were performed on all the molecules. For Fe₂Ln (Ln = Gd, La) and Fe₂Y, the data were fitted to Van Vleck equations and the magnetic coupling constants were obtained. In all cases, the two Fe(iii) spins were found to be antiparallel to each other in the ground state leaving the heterometal to remain essentially uncoupled.

Manganese clusters of aromatic oximes: synthesis, structure and magnetic properties

With the aim of tuning the structures by using oxime ligands with different non-coordinating groups, three aromatic oxime ligands were designed by fusing oxime groups ([double bond, length as m-dash]N-OH) onto different non-coordinating groups. Their reactions with the corresponding Mn(ii) salts gave five manganese clusters [Mn(μ₃-O)(L¹)₃(DMF)(H₂O)₃Cl]·2DMF·CH₃OH (1), [Mn(μ₃-O)(L²)₃(OAc)(CH₃OH)₂] (2), [Mn(μ₃-O)₂(L²)₆(H₂O)(py)₇](ClO₄)₂·py·0.5CH₃OH·2H₂O (3), [MnO₄(L²)₈(DMF)₄]·DMF·6CH₃CN (4), and [MnMnO₄(L³)₁₂]·3DMF·6H₂O (5), in which H₂L¹, H₂L² and HL³ represent indane-1,2,3-trione-1,2-dioxime, acenaphthenequinone dioxime, and 9,10-phenanthrenedione-9-oxime, respectively. Their structures were determined and studied in detail. 1 and 2 show planar triangular trinuclear Mn structures. 3 has a hexanuclear Mn skeleton formed from two Mn triangular units through inter-trinuclear mutual coordination. 4 and 5 present octanuclear skeletons constructed from planar triangular Mn₃O and tetrahedral Mn₄O secondary building units, respectively, with different symmetries and different oxidation states of the manganese ions. Their structural studies reveal a significant contribution of the parent rings for fusing oxime groups, different non-coordinating groups and anions to the formation of different cluster skeletons. Their magnetic properties were investigated and simulated, which revealed the presence of dominant antiferromagnetic interactions between the metal ions in these compounds.

A single-chain magnet based on linear [Mn(III)2Mn(II)] units

The synthesis, structural characterization and magnetic properties of a 1D coordination polymer based on a linear mixed valent [Mn(III)2Mn(II)] repeating unit are described. It displays single-chain magnet (SCM) behaviour with an energy barrier of ∼38 K and represents the first example of a mixed valent Mn-carboxylate SCM with a linear architecture.

Single molecule magnet behaviour in a rare trinuclear {CrIIIDyIII2} methoxo-bridged complex

A new neutral hetero-trinuclear {Cr^III–DyIII2} coordination complex exhibiting single molecule magnet behaviour has been synthesized.

A first-principles approach to the calculation of the on-site zero-field splitting in polynuclear transition metal complexes

The interpretation of electron paramagnetic resonance spectra of polynuclear transition metal complexes in terms of individual contributions from each paramagnetic center can be greatly facilitated by the availability of theoretical methods that enable the reliable prediction of local spectroscopic parameters. In this work we report an approach that enables the application of multireference ab initio methods for the calculation of local zero field splitting tensors, one of the leading terms in the spin Hamiltonian for exchange-coupled systems of high nuclearity. The method referred to as local complete active space configuration interaction (L-CASCI) represents a multireference calculation with an active space composed of local orbitals of the center of interest. By successive permutation of the active space to include the localized orbitals corresponding to a particular center of the complex, all on-site parameters can be easily obtained at a high-level of theory with a corresponding low computational cost. Benchmark calculations on synthetic complexes confirm the validity of the approach. As an example of the applicability of the L-CASCI method to large systems, we determine the local anisotropy of the Mn(III) ion of the tetranuclear manganese cluster of photosystem II in both structural forms of its S2 state.

A family of novel Mn3Ln4 clusters displaying single-molecule magnet behavior

A family of novel Mn₃Ln₄ clusters: single-molecule magnets and the first structurally characterized 3d/4f clusters containing the 3-methyloxysalicylaldoximate ligand.