Directed synthesis of {Mn18Cu6} heterometallic complexes

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero-Multinuclear Metal-Oxo Clusters within Polyoxometalate Ligands

Precise structural design of large hetero-multinuclear metal-oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single-molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero-multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one-step condensation reaction of metal cations and ligands. Herein, we report a "cationic metal glue strategy" for increasing the size and nuclearity of hetero-multinuclear metal-oxo clusters by using lacunary-type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn4 )Mn2 Ln2 (FeMn4 )} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero-multinuclear metal-oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn4 } oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the "cationic metal glue strategy" would be a powerful tool to construct desired large hetero-multinuclear metal clusters precisely and effectively.

Elucidating the exchange interactions in a {GdIIICuII4} propellor

The multinucleating ligand 2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxymethyl)-propane-1,3-diol] (bis-tris propane, H₆L) is used in the design of a new family of 3d-4f complexes that display an unusual {LnCu₄} four-blade propeller topology. We report the synthesis, structure and magnetic characterisation of [LnCu₄(H₄L)₄](Cl)₂(ClO₄)·6CH₃OH, where Ln = Gd (1), Tb (2), Dy (3), La (4). Previously we have used CH₃COO^- and NO₃^- as co-ligands with bis-tris propane, but here the use of Cl^- and ClO₄^- leads to coordination of four {Cu(H₄L)} units around the central Ln ion. A magneto-structural analysis reveals that the geometrical arrangement of the Cu(II) centres defined by the H₄L^2- ligands controls the magnetic communication between the different metal centres. DFT calculations performed on the isotropic (Gd) and diamagnetic (La) systems 1 and 4 help to unravel the intriguing exchange interactions.

Asymmetric Assembly of Chiral Lanthanide(III) Tetranuclear Cluster Complexes Using Achiral Mixed Ligands: Single-molecule Magnet Behavior and Magnetic Entropy Change

It is challenging to use achiral ligands to spontaneously construct chiral molecular magnets. In this work, two new Ln4 cluster complexes based on N,N'-(1,3-propanediyl)bis[N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]amine] (H6L) have been assembled, which are crystallized in a chiral space group due to the asymmetric distribution of acetate (OAc-) groups and hexafluoroacetylacetonate (F6acac-) groups on both sides of the parallelogram-like Ln4 core. Complex 1, [Dy4(H3L)2(OAc)3(F6acac)3]·5MeOH·2H2O, exhibits single-molecule magnet properties at the zero field with the U eff/k value of 48.4 K; notably, besides the Orbach process, the Raman process is also prominent for the magnetic relaxation of 1. Complex 2, [Gd4(H3L)2(OAc)3(F6acac)3]·4MeOH·2.5H2O, displays a large magnetocaloric effect, whose largest -ΔS m value is 21.88 J kg-1 K-1 (when T = 2 K and ΔH = 5 T); it thus can be utilized as a good magnetic refrigeration molecular material.

Heterometallic chiral [Mn13Cu8] single-molecule magnets

An enantiomeric pair of 3d-3d heterometallic clusters of {Mn^IIMn^III₁₂Cu^II₈} has been synthesized in an aqueous solution without heating. The crystal structures reveal a five-layered core of {Mn^IIMn^III₁₂Cu^II₈}, which is a slightly distorted {Mn^IIMn^III₁₂} tetradecahedron with its eight triangular faces capped by a Cu^II ion respectively. The magnetic measurement results establish that anisotropic Mn^III atom-containing clusters L-1 and D-1 exhibit slow relaxation of their magnetization vectors.

Self-Organization into Preferred Sites by MgII, MnII, and MnIII in Brucite-Structured M19 Cluster

The search for functional materials, for example those aiming at microelectronics, magnetic recording, and catalysis, often ventures into mixed metal systems to achieve optimization of the properties. Thus, understanding site preference and self-organization is crucial but hard to implement. Herein, we present a system whereby Mg^II, Mn^II, and Mn^III ions selectively locate exact positions within the Brucite-structured cluster, Mn₁₃Mg₆, [Mn^III⊂Mg^II₆⊂Mn^II₉Mn^III₃( L)₁₈(OH)₁₂(N₃)₆](ClO₄)₆·12CH₃CN, H L = 1-(hydroxymethyl)-3,5-dimethylpyrazolate). The Mn^III being small (78 pm) takes up the core position; while 6 Mg^II (86 pm) are located in the inner ring, and the 9 large Mn^II (97 pm) and 3 Mn^III occupy the outer ring. The factors (a) ionic radii, (b) regularity in coordination geometry, oxophilicity, and softness of Mg^II compared to Mn^II, and (c) Jahn-Teller distortion of Mn^III may all be implicated synergistically. Electrospray ionization mass spectrometry reveals the M₁₉ disc remains an integral unit when crystals are dissolved, and exchange between Mg and Mn occurs within the disc during its formation. Diamagnetic Mg^II doping insulates the magnetic exchange between the central Mn^III and those in the outer ring, thus giving an overall antiferromagnetic exchange interaction between nearest-neighbors of the outer ring. The work reveals the underlying rule for site-preference of main group metal versus transition metal in disc-like Brucite-structured cluster and provides an elegant new avenue to assemble heterometallic clusters in a stepwise fashion.

Fine Tuning the Energy Barrier of Molecular Nanomagnets via Lattice Solvent Molecules

Solvents play important roles in our lives, they are also of interest in molecular materials, especially for molecular magnets. The solvatomagnetic effect is generally used for trigger and/or regulation of magnetic properties in molecule-based systems, however, molecular nanomagnets showing solvatomagnetic effects are very difficult to obtain. Here we report four 3d-4f heterometallic cluster complexes containing ROH lattice solvent molecules, [Cu₃Tb₂(H₃L)₂(OAc)₂(hfac)₄]∙2ROH {H₆L = 1,3-Bis[tris(hydroxymethyl)methylamino]propane, hfac^- = hexafluoroacetylacetonate; R = CH₃, 1; R = C₂H₅, 2; R = C₃H₇, 3; R = H, 4}. Single-molecule magnet (SMM) properties of these four complexes were observed to be dependent on the ROH lattice solvent molecule. There is an interesting magneto-structural correlation: the larger the R group, the higher the energy barrier. For the first time, the solvatomagnetic effect is used for the continuous fine adjustment of the energy barrier of 0D molecular nanomagnets. Additionally, [Cu₃Dy₂(H₃L)₂(OAc)₂(hfac)₄]∙2MeOH (5), an analogue of [Cu₃Tb₂(H₃L)₂(OAc)₂(hfac)₄]∙2MeOH (1), is also reported for comparison.

Details make the difference: a family of tetranuclear CuIIMnIII complexes with cube-like and double open cube-like cores

The "direct synthesis" approach, namely one-pot reaction of metal powders and ammonium salt with a methanol solution of a polydentate Schiff base (H₂L) formed in situ from salicylaldehyde and ethanolamine, has been successfully used for the preparation of the new heterometallic compounds [Cu₃Mn(L)₄(CH₃OH)₃]I₃ (1), [Cu₃Mn(L)₄(CH₃OH)₃(H₂O)]NCS·H₂O (2), [Cu₃Mn(L)₄(CH₃OH)(H₂O)_2.55]Br·0.45H₂O (3) and [Cu₃Mn(L)₄(H₂O)_3.4]BF₄·0.6H₂O (4). Crystallographic analysis revealed that 1-4 are based on the tetranuclear core {CuMn^III(μ₃-O)₄} where the metal centres are joined by the oxygen bridges of Schiff base ligands forming a cube-like arrangement. The novel heterometallic compound [Cu₃Mn(L)₄(CH₃OH)₃]₂[Mn(NCS)₄]·2CH₃OH (5) has been obtained by the "building block" approach using the reaction of [Cu(HL)₂] with manganese acetate and NH₄NCS in methanol. The crystal structure of 5 revealed the {CuMn^III(μ-O)₂(μ₃-O)₂} metal core which can be viewed as a double open cube. In spite of a similar {Cu₃MnO₄} atom set in the cores of 1-5, the complexes show rather different molecular structures and significantly differ by the number and combinations of coordinated CH₃OH/H₂O solvent molecules. Variable-temperature (2-300 K) magnetic susceptibility along with variable-field magnetization measurements of 1-5 showed a decrease of the effective magnetic moment value at low temperature, indicative of the antiferromagnetic coupling of medium size (-55 to -22 cm^-1). For these systems resembling a compressed prism the coupling constant in walls J₄ correlates with the averaged bonding angles in walls α: J₄vs. α develops approximately according to a straight line.

A topologically unique alternating {CoIII3GdIII3} magnetocaloric ring

A building block approach to molecule-based refrigerants: using diamagnetic Co(iii) to decrease the interaction between Gd(iii) ions and hence, enhance the adiabatic temperature change.

Self-assembly generation, structural features, and oxidation catalytic properties of new aqua-soluble copper(ii)-aminoalcohol derivatives

Multidentate aminoalcohols were applied as unexplored building blocks to generate two novel Cu(ii) coordination compounds that act as efficient catalysts for the mild and acid-promoter-free oxidation of C₅–C₈ cycloalkanes.

Ligand-directed synthesis of {MnIII5} twisted bow-ties

3,5-Diamino-1,2,4-triazole derivatives direct the assembly of {MnIII5} twisted bow-ties.

Enhancement of Tb(III) -Cu(II) Single-Molecule Magnet Performance through Structural Modification

We report a series of 3d-4f complexes {Ln2 Cu3 (H3 L)2 Xn } (X=OAc(-) , Ln=Gd, Tb or X=NO3 (-) , Ln=Gd, Tb, Dy, Ho, Er) using the 2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxylmethyl)propane-1,3-diol] (H6 L) pro-ligand. All complexes, except that in which Ln=Gd, show slow magnetic relaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisation in the {Tb2 Cu3 (H3 L)2 Xn } complexes is seen by changing the auxiliary ligands (X=OAc(-) for NO3 (-) ). This leads to the largest reported relaxation barrier in zero applied dc field for a Tb/Cu-based single-molecule magnet. Ab initio CASSCF calculations performed on mononuclear Tb(III) models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the Tb(III) coordination environment (C4v versus Cs ).

Rational serendipity: “undirected” synthesis of a large {MnIII10CuII5} complex from pre-formed MnII building blocks

Use of an aminopolyalcohol-based Mn^II complex in solvothermal Cu^II chemistry leads to a rare example of a high nuclearity heterometallic {MnIII10CuII5} system, in which four {Cu^II(H₁Edte)} units trap an inner {MnIII10Cu^II} oxide core.

A single-stranded {Gd18} nanowheel with a symmetric polydentate diacylhydrazone ligand

A {Gd₁₈} nanowheel was solvothermally synthesized. It features a rare single-stranded skeleton that looks like a Reuleaux triangle with vertices buckled in, represents the highest nuclearity and the largest size in any pure Ln wheels reported, and shows a large MCE.

A high-nuclearity metal-cyanide cluster [Mo6Cu14] with photomagnetic properties

A high-nuclearity metal-cyanide cluster [Mo₆Cu₁₄] has been prepared and its photomagnetic properties investigated.

A ferromagnetically coupled Fe42 cyanide-bridged nanocage

Self-assembly of artificial nanoscale units into superstructures is a prevalent topic in science. In biomimicry, scientists attempt to develop artificial self-assembled nanoarchitectures. However, despite extensive efforts, the preparation of nanoarchitectures with superior physical properties remains a challenge. For example, one of the major topics in the field of molecular magnetism is the development of high-spin (HS) molecules. Here, we report a cyanide-bridged magnetic nanocage composed of 18 HS iron(III) ions and 24 low-spin iron(II) ions. The magnetic iron(III) centres are ferromagnetically coupled, yielding the highest ground-state spin number (S=45) of any molecule reported to date.

One area of interest in the field of molecular magnetism is the development of high-spin molecules. Here, the authors report a cyanide-bridged nanocage consisting of 18 high-spin iron(III) ions ferromagnetically coupled through 24 low-spin iron(II) ions, with a ground state spin of S=45.

Directed synthesis of {CuII2ZnII2} and {CuII8ZnII8} heterometallic complexes

The polydentate ligand Bis–tris propane is used to assemble two Cu/Zn heterometallic complexes: a tetramer which displays an unusually strong Cu(ii)⋯Cu(ii) exchange given the Cu⋯Cu separation or, in the presence of base, a hexadecanuclear complex with a remarkable double-concentric ring structure.

Circular serendipity: in situ ligand transformation for the self-assembly of an hexadecametallic [CuII16] wheel

A [Cu₁₆^II] wheel has been isolated serendipitously from the reaction of acetylacetone dioxime with Cu^II and Ln^III ions. The ligand has been transformed in situ to three different forms, all found within the [Cu₁₆], with the original ligand absent.