Magnetic Properties of a Manganese(III) Chain with Monoatomic Bridges: catena-MnF(salen)

Low-Dimensional Metal-Organic Magnets as a Route toward the S = 2 Haldane Phase

Metal-organic magnets (MOMs), modular magnetic materials where metal atoms are connected by organic linkers, are promising candidates for next-generation quantum technologies. MOMs readily form low-dimensional structures and so are ideal systems to realize physical examples of key quantum models, including the Haldane phase, where a topological excitation gap occurs in integer-spin antiferromagnetic (AFM) chains. Thus, far the Haldane phase has only been identified for S = 1, with S ≥ 2 still unrealized because the larger spin imposes more stringent requirements on the magnetic interactions. Here, we report the structure and magnetic properties of CrCl₂(pym) (pym = pyrimidine), a new quasi-1D S = 2 AFM MOM. We show, using X-ray and neutron diffraction, bulk property measurements, density-functional theory calculations, and inelastic neutron spectroscopy (INS), that CrCl₂(pym) consists of AFM CrCl₂ spin chains (J₁ = -1.13(4) meV) which are weakly ferromagnetically coupled through bridging pym (J₂ = 0.10(2) meV), with easy-axis anisotropy (D = -0.15(3) meV). We find that, although small compared to J₁, these additional interactions are sufficient to prevent observation of the Haldane phase in this material. Nevertheless, the proximity to the Haldane phase together with the modularity of MOMs suggests that layered Cr(II) MOMs are a promising family to search for the elusive S = 2 Haldane phase.

Assembling organic-inorganic building blocks for high-capacity electrode design

Metal-organic electrode materials have exhibited extraordinary promise for green and sustainable electrochemical energy storage devices, but usually suffer from low specific capacity, and poor cycling stability and rate capability because of limited active sites at organic functional groups. To address this issue, activating transition metals and carbon conjugate rings has become significantly effective to make transferred electrons dispersed in the whole molecule. In this work, we demonstrate that assembling inorganic-organic building blocks into "local" composite metal-organic materials could synergistically activate transition metal ions and carbon conjugate rings to operate cationic and anionic redox, respectively. Based on first-principles calculations, the composite inorganic-organic material FeF₃(4,4'-bpy) generates 8-electron transfer redox processes of Fe³⁺ + 2e^-→ Fe⁺ and 2 -C[double bond, length as m-dash]N- + 2e^-→ 2 (-C-N-)^- and 4 -C[double bond, length as m-dash]C- + 4e^-→ 4 (-C-C-)^-, achieving a high specific capacity of 796.7 mA h g^-1, maintaining structural stability, and reducing the band gap. The strongly electronegative F-ions in inorganic structure [FeF₄]^2- play an important role in making highly oxidized Fe³⁺ through forming a strong ligand field and electrochemically activating -C[double bond, length as m-dash]C-via electrostatic interaction with Li⁺. In addition, electrochemical measurements also reveal that the central metal Fe, and -C[double bond, length as m-dash]C and -C[double bond, length as m-dash]N bonds of the FeF₃(4,4'-bpy) electrode are the active sites for Li-ion storage to deliver a high reversible capacity (793.1 mA h g^-1 at 50 mA g^-1) and excellent rate capability, which are echoes of the DFT calculations. Through this design principle, we found a series of high-capacity metal organic electrode materials such as MnF₃(4,4'-bpy) (799.6 mA h g^-1) and VF₃(4,4'-bpy) (811.7 mA h g^-1).

A Series of Manganese(III) Salen Complexes as a Result of Team-Based Inquiry in a Transnational Education Programme

The development of a team-based approach to research-led transnational practical chemistry teaching is described in which a team of five Chinese students on an articulated transnational degree programme, supported by a team of academic and technical staff, carried out a study examining the structural chemistry of a series of manganese(III) salen complexes. A series of four crystallographically characterized manganese(III) salen complexes with ancillary carboxylate ligands are reported here. The carboxylate coordination modes range from the bridging syn-anti μ² -κO : κO' mode observed in the predominant cyclohexanoate and isobutyrate species, to a capping terminal monodentate mode for the adamantanoate species, and an unusual mixture of bridging and terminal coordination modes observed in a second minor phase of the cyclohexanoate species. The variation on extended structures based on the weakly interacting aliphatic backbones may provide a useful basis for further structural studies.

Antiferromagnetic ordering in MnF(salen)

Antiferromagnetic order at [Formula: see text] K has been identified in Mn(III)F(salen), salen  =  H14C16N2O2, an S  =  2 linear-chain system. Using single crystals, specific heat studies performed in magnetic fields up to 9 T revealed the presence of a field-independent cusp at the same temperature where (1)H NMR studies conducted at 42 MHz observed dramatic changes in the spin-lattice relaxation time, T 1, and in the linewidths. Low-field (less than 0.1 T) magnetic susceptibility studies of single crystals and randomly-arranged microcrystalline samples reveal subtle features associated with the transition.

Field-induced slow relaxation of magnetization in dinuclear and trinuclear CoIII⋯MnIII complexes

Magnetic anisotropy and field-induced slow relaxation of magnetization were studied in dinuclear and trinuclear heterobimetallic Co^III⋯Mn^III complexes.

Single-molecule magnet engineering: building-block approaches

Tailoring the specific magnetic properties of any material relies on the topological control of the constituent metal ion building blocks. Although this general approach does not seem to be easily applied to traditional inorganic bulk magnets, coordination chemistry offers a unique tool to delicately tune, for instance, the properties of molecules that behave as "magnets", the so-called single-molecule magnets (SMMs). Although many interesting SMMs have been prepared by a more or less serendipitous approach, the assembly of predesigned, isolatable molecular entities into higher nuclearity complexes constitutes an elegant and fascinating strategy. This Feature article focuses on the use of building blocks or modules (both terms being used indiscriminately) to direct the structure, and therefore also the magnetic properties, of metal ion complexes exhibiting SMM behaviour.