Regulating the proton conductivity of metal organic framework materials through solvent control

MOFs were used as probes through changes in the proton conductivity caused by changes in solvent molecules.

A High-Symmetry Double-Shell Gd30Co12 Cluster Exhibiting a Large Magnetocaloric Effect

A high-nuclearity 3d-4f cluster of [Gd₃₀Co^II₆Co^III₆(OH)₅₆(NO₃)₁₂(CH₃COO)₃₀(H₂O)₃₀]·(NO₃)₂₂·(en)₃·(H₂O)₃ (1) was synthesized through the reaction of Gd(NO₃)₃·6H₂O, Co(NO₃)₂·6H₂O, and sodium acetate in a mixture of ethanediamine (en), ethanol, and deionized water. The cluster core in 1 features a double-shell structure with a Co₁₂ icosahedron encapsulating a Gd₃₀ icosidodecahedron. A magnetic study reveals that separating Co²⁺ ions with Gd³⁺ ions can effectively reduce the magnetic interaction of 3d-4f clusters. Significantly, the magnetocaloric effect (MCE) of 1 at 2 K and 7 T is up to 44.7 J kg^-1 K^-1, the largest MCE reported to date in the 3d-4f metal clusters.

Structural characterization and magnetic property studies of a mixed-valence {CoIIICo} complex with a μ4-oxo tetrahedral {Co} motif

We have synthesized and structurally characterized a new mixed valence pentanuclear Co complex, bearing a rare μ4-O-tetrahedral CoII4 unit, by employing a pyridine-like Schiff base ligand. We have performed DC magnetic susceptibility and magnetization measurements over polycrystalline samples and chemical quantum computations in order to understand the exchange interaction pattern within Co(ii) sites and ground state magnetic anisotropy. This new complex shows an overall antiferromagnetic exchange interaction whose strength strongly depends on the local symmetry of Co(ii) sites. Also, local ion magnetic anisotropy reveals a strongly axial behaviour with the lowest Kramers doublet (KD) at each Co(ii) ion sufficiently isolated from excited states at low temperatures. Two Co(ii) sites show tetrahedral symmetry and the spin only formalism including axial zero-field splitting (ZFS) term properly described them; on the other hand, the other two Co(ii) sites have distorted octahedral and square base pyramidal coordination spheres, and a strong orbital contribution leads to a failure of the spin only formalism. A model of four Seff = 1/2 exchange interacting sites is necessary in order to account for low temperature magnetization behaviour. In view of the strongly anisotropic KD states, the exchange interactions are forced to be modelled as anisotropic ones. Overall, experimental data and quantum chemical computations are in good agreement, supporting the proposed model for magnetic behaviour.

Hierarchical Assembly of a {Co24} Cluster from Two Vertex-Fused {Co13} Clusters and Their Single-Molecule Magnetism

We present the synthesis, structural characterization, and magnetic properties of two high-nuclearity cobalt clusters formulated as [Co₁₃(μ₃-OH)₃(μ₃-Cl)(dpbt)₅(ptd)Cl₁₀][Co(H₂O)₂Cl₂]·(CH₃)₂CHOH (1) and [Co₂₄(μ₃-OH)₆(μ₃-Cl)₂(dpbt)₁₀(ptd)₂Cl₁₆]·2CH₃CH₂OH (2), respectively (H₂dpbt = 5,5'-bis(pyridin-2-yl)-3,3'-bis(1,2,4-triazole) and H₂ptd = 3-(pyridin-2-yl)-1,2,4-triazine-5,6-diol). Compound 1 is composed of an inner [Co₄(μ₃-OH)₃(μ₃-Cl)] cubane and an outer [Co₉(dpbt)₅(ptd)Cl₁₀] defective adamantane. Compound 2 reveals a giant {Co₂₄} cluster possessing a dual-[Co₁₂] skeleton from 1. The hierarchical assembly from 1 to 2 has been established and tracked through high-resolution electrospray ionization (HRESI-MS) analyses from the solvothermal reaction mother solution. Magnetic studies of 1 and 2 revealed the highly correlated spins, a glasslike magnetic phase transition at ca. 8 K, and slow relaxation behavior of SMM nature in the lower-temperature region (below 4 K).

The ferromagnetic [Ln2Co6] heterometallic complexes

Four 3d–4f [Ln₂Co₆] complexes were fabricated. [Dy₂Co₆] (1) and [Ho₂Co₆] (2) displayed ferromagnetic coupling, and [Dy₂Co₆] (1) exhibited slow magnetic relaxation.

Phosphonate Based High Nuclearity Magnetic Cages

Transition metal based high nuclearity molecular magnetic cages are a very important class of compounds owing to their potential applications in fabricating new generation molecular magnets such as single molecular magnets, magnetic refrigerants, etc. Most of the reported polynuclear cages contain carboxylates or alkoxides as ligands. However, the binding ability of phosphonates with transition metal ions is stronger than the carboxylates or alkoxides. The presence of three oxygen donor sites enables phosphonates to bridge up to nine metal centers simultaneously. But very few phosphonate based transition metal cages were reported in the literature until recently, mainly because of synthetic difficulties, propensity to result in layered compounds, and also their poor crystalline properties. Accordingly, various synthetic strategies have been followed by several groups in order to overcome such synthetic difficulties. These strategies mainly include use of small preformed metal precursors, proper choice of coligands along with the phosphonate ligands, and use of sterically hindered bulky phosphonate ligands. Currently, the phosphonate system offers a library of high nuclearity transition metal and mixed metal (3d-4f) cages with aesthetically pleasing structures and interesting magnetic properties. This Account is in the form of a research landscape on our efforts to synthesize and characterize new types of phosphonate based high nuclearity paramagnetic transition metal cages. We quite often experienced synthetic difficulties with such versatile systems in assembling high nuclearity metal cages. Few methods have been emphasized for the self-assembly of phosphonate systems with suitable transition metal ions in achieving high nuclearity. We highlighted our journey from 2005 until today for phosphonate based high nuclearity transition metal cages with V(IV/V), Mn(II/III), Fe(III), Co(II), Ni(II), and Cu(II) metal ions and their magnetic properties. We observed that slight changes in stoichiometry, reaction conditions, and presence or absence of coligand played crucial roles in determining the final structure of these complexes. Most of the complexes included are regular in geometry with a dense arrangement of the above-mentioned metal centers in a confined space, and a few of them also resemble regular polygonal solids (Archimedean and Platonic). Since there needs to be a historical approach for a comparative study, significant research output reported by other groups is also compared in brief to ensure the potential of phosphonate ligands in synthesizing high nuclearity magnetic cages.

Nanoscopic molecular magnets

This review highlights fundamental concepts and synthetic strategies of SMMs and selected examples of 3d, 4f, 5f and mixed 3d–4f, 4d–5d and 3d–5f based SMMs are discussed.

Synthesis and characterization of nickel(II) phosphonate complexes utilizing pyridonates and carboxylates as co-ligands

The synthesis and structures of five new nickel complexes containing phosphonate ligands are reported. The compounds utilize pivalic acid (HPiv) and 6-chloro-2-pyridonate (Hchp) as co-ligands with the resulting complexes being of formulas [Ni10(chp)4(Hchp)4.5(O3P(t)Bu)3(Piv)5(HPiv)2(OH)6(H2O)4.5](HNEt3)·0.5MeCN·2.5H2O 1, [Ni12(chp)12(Hchp)2(PhPO3)2(Piv)5(HPiv)2(OH)2(H2O)6](F)·4.5MeCN·2H2O 2, [Ni10(chp)6(O3PCH2Ph)2(Piv)8(F)2(MeCN)4] 3, [Ni10(chp)6(O3PMe)2(Piv)8(F)2 (MeCN)4]·5MeCN·2H2O 4, and [Ni10(chp)6(O3PCH2Nap)2(Piv)8(F)2(MeCN)2(H2O)2] 5. The metallic core of compounds 1 and 2 display tetra- and hexa-capped trigonal prismatic arrangements, while the metallic and phosphorus core of 3, 4, and 5 display three face-sharing octahedra. Variable temperature direct current (dc) magnetic susceptibility measurements reveal dominant antiferromagnetic exchange interactions within each cluster, with diamagnetic spin ground states found.

Modulating the magnetic properties by structural modification in a family of Co-Ln (Ln = Gd, Dy) molecular aggregates

Two types of 3d–4f cages are reported where the Gd analogues show significant magnetic refrigeration and the Dy containing compounds display SMM behaviour.

Magnetic refrigeration and slow magnetic relaxation in tetranuclear lanthanide cages (Ln = Gd, Dy) with in situ ligand transformation

Three tetranuclear lanthanide cages featuring either hemicubane (1 and 2) or distorted hemicubane (3) like cores are reported. Magnetic studies reveal significant magnetic entropy changes for complex 1 and a slow relaxation of magnetisation for 3.