Zhe-Ming Wang

An organometallic single-ion magnet.

An organometallic single-ion magnet is synthesized with only 19 non-hydrogen atoms featuring an erbium ion sandwiched by two different aromatic ligands. This molecule displays a butterfly-shaped hysteresis loop at 1.8 K up to even 5 K. Alternating-current (ac) susceptibility measurement reveals the existence of two thermally activated magnetic relaxation processes with the energy barriers as high as 197 and 323 K, respectively.

A Mononuclear Dysprosium Complex Featuring Single-Molecule-Magnet Behavior†

Single-molecule magnets (SMMs) have received much attention owing to their quantum tunneling and slow relaxation. These behaviors can be observed when the molecule has large ground spin state with a uniaxial magnetic anisotropy, namely negative zero-field splitting (ZFS) parameter D. Besides a large ground state, to increase the SMMs energy barrier and blocking temperature, it is of fundamental importance to control the magnetic anisotropy. It is also of great complexity to understand the conditions that determine the anisotropy or zero-field splitting properties for a cluster. As a result, SMMs containing only one spin carrier are of great interest because of the simplification in the analysis of local anisotropy and ZFS. Recently, some molecules with isolated 3d or 4f metal ions were observed to show a direct-current (dc) field-induced slow magnetic relaxation. Studies show that this kind of dc-field-dependent relaxation phenomenon is thermally activated, and the quench of fast quantum tunneling by the dc field could give rise to the slow relaxation. However, as commented by Benelli and Gatteschi, it is an unexpected and puzzling behavior, and the underlying mechanism is still unclear. Ishikawa et al. reported that the phthalocyanine (Pc) double-decker anion complexes [Pc2Ln] with a single Tb or Dy ion show slow relaxation without a dc field. A single Er ion in the polyoxometallate system [ErW10O36] 9 showed similar relaxation behavior in zero static magnetic field. The first single-actinide complex [U(Ph2BPz2)3] (containing the U III ion; Ph2BPz2 = diphenylbis(pyrazolylborate)) reported by Rinehart and Long shows a similar slow relaxation. Owing to the single-ion features, these complexes could be called “single-ion magnets”. In these complexes, ligand fields with a high-order single axis Cn (n> 2; n = 4 for Ref. [8, 9] and n = 3 for Ref. [10]) split the (2J + 1) degenerate ground states into new sublevels, which produces a uniaxial anisotropy, thus giving rise to a higher energy barrier for relaxation. The Dy ion, which possesses a Kramers ground state of H15/2, is an appealing paramagnetic source for the construction of SMMs in a suitable ligand-field symmetry and strength. Moreover, among reported SMMs, some of them are clusters containing Dy : Dy2, [11] Dy3, [12] Dy4, [13] Dy5, [14] Dy-containing chain, and tens of Dycontaining 3d–4f clusters. All three reported types of single-ion magnets are found with a high-order single axis defining the local symmetry. Pursuing this clue, we synthesized a series of mononuclear Ln compounds with a local symmetry close to D4d. Crystal analysis shows that the isomorphous complexes consist of a neutral mononuclear [Ln(acac)3(H2O)2] complex (Ln = Dy, Ho, Er, acac = acetylacetonate) together with an uncoordinated water molecule and an uncoordinated ethanol molecule (Figure 1a). In the Dy complex, Dy is coordinated by eight oxygen atoms with Dy O bonds of 2.311–2.434 , six of which come from the acetylacetonate ligand and two from coordinated water molecules. The eight oxygen atoms form an approximately square-antiprismatic coordination polyhedron, and the local symmetry of Dy is nearly D4d (Figure 1b). Actually, a similar lanthanide acac complex was firstly reported in 1968, but the uncoordinated water and

Constructing magnetic molecular solids by employing three-atom ligands as bridges

The combination of some three-atom bridges with paramagnetic 3d transition metal ions results in the systematic isolation of molecular magnetic materials, ranging from single-molecule and single-chain magnets to layered weak ferromagnets and three-dimensional porous magnets. The design strategy and role of secondary components, such as co-ligands, templates and other mixed short ligands are discussed.

Coexistence of magnetic and electric orderings in the metal-formate frameworks of [NH4][M(HCOO)3].

A family of three-dimensional chiral metal-formate frameworks of [NH(4)][M(HCOO)(3)] (M = Mn, Fe, Co, Ni, and Zn) displays paraelectric to ferroelectric phase transitions between 191 and 254 K, triggered by disorder-order transitions of NH(4)(+) cations and their displacement within the framework channels, combined with spin-canted antiferromagnetic ordering within 8-30 K for the magnetic members, providing a new class of metal-organic frameworks showing the coexistence of magnetic and electric orderings.

Disorder―Order Ferroelectric Transition in the Metal Formate Framework of [NH4][Zn(HCOO)3]

A three-dimensional chiral metal formate framework compound, [NH(4)][Zn(HCOO)(3)], undergoes a paraelectric-ferroelectric phase transition at 191 K triggered by the disorder-order transition of NH(4)(+) cations within the structure.

Mn3(HCOO)6: a 3D porous magnet of diamond framework with nodes of Mn-centered MnMn4 tetrahedron and guest-modulated ordering temperature

Mn3(HCOO)6, a 3D highly stable and flexible porous diamondoid framework based on Mn-centered MnMn4 tetrahedral nodes, exhibits a wide spectrum of guest inclusion behaviour and long-range magnetic ordering with guest-modulated critical temperature.

Formate-Based Magnetic Metal–Organic Frameworks Templated by Protonated Amines

A systematic study has been carried out on the 3d divalent metal formate 3D magnetic frameworks templated by protonated amines, and the achievements have revealed that metal formate frameworks are very malleable, and their structures depend on the size, shape, charge, and hydrogen bonding geometries of the templating cations. Six kinds of metal formate frameworks have been created. They are chiral frameworks with a (4(9) . 6(6)) topology, perovskite ones with a (4(12) . 6(3)) topology, bi-nodal frameworks of (4(12) . 6(3))(4(9) . 6(6))(n) (n = 1, 2, 3) topologies, and porous diamond frameworks with 6(6) topology. These materials display promising and abundant magnetic, dielectric, porous, and optical properties and the possible combination of them. Therefore, they are of great interest for the study of molecule-based materials. It has been demonstrated that formate, being the smallest and simplest carboxylate, cheap and with low toxicity, thus more biocompatible and environmentally friendly, and having been more or less ignored, will find an important role in the construction of molecule-based materials and provide new materials with interesting properties.

Series of Lanthanide Organometallic Single-Ion Magnets

The synthesis, structures, and magnetic properties of a series of lanthanide organometallic mixed sandwich molecules, (Cp*)Ln(COT), are investigated, where Cp* is the pentamethylcyclopentadiene anion and COT is the cyclooctatetraene dianion and Ln represents Tb(III), Dy(III), Ho(III), Er(III), and Tm(III). Among the five complexes, Dy and Ho complexes are determined to be single-ion magnets in addition to the previously reported Er complex. Both Dy and Ho complexes show obvious quantum tunneling magnetization relaxation in the absence of a static field. The diluted Ho complex behaves two sets of thermally activated relaxation as we reported previously in Er due to the COT ring static disorder. A stair-shaped hysteresis for the Er compound can be observed at 1.6 K with Hc = 1 kOe at a sweeping rate over 700 Oe/s. The quantum tunneling decoherence relaxation rate increases from Er to Ho to Dy, which may be caused by the relative increase of transverse anisotropy coming from the larger tilting of the two aromatic rings within the molecule. The fine electronic structure is analyzed with ligand-field theory employing the effective Hamiltonian method. The zero-field splitting is determined to be Ising type, and the energy gap between the ground state and the first excited one is consistent with the barrier obtained by Arrhenius analysis.

A 64-Nuclear Cubic Cage Incorporating Propeller-like FeIII8 Apices and HCOO− Edges

A 64-nuclear cubic cage with corners of a propeller-like FeIII8 cluster and anti-anti HCOO- edges displays strong antiferromagnetism resulting in a zero spin ground state.

Zero-field slow magnetic relaxation from single Co(II) ion: a transition metal single-molecule magnet with high anisotropy barrier

An air-stable star-shaped CoIICoIII3 complex with only one paramagnetic Co(II) ion in the D3 coordination environment has been synthesized from a chiral Schiff base ligand. Magnetic studies revealed that this complex exhibits slow magnetic relaxation in the absence of an applied dc field, which is one of the main characteristics of single-molecule magnets (SMMs). The relaxation barrier is as high as 109 K, which is quite large among transition-metal ion-based SMMs. The complex represents the first example of zero-field SMM behavior in a mononuclear six oxygen-coordinate Co(II) complex.