The structure and magnetic properties of an octanuclear coordination cluster with a {Cu^II ₄Dy^III ₄} core are described and a model for the unusual SMM behaviour is proposed.

We report a family of isostructural nonanuclear Fe ^III –Ln ^III cyclic coordination clusters, [FeIII6LnIII3(μ-OMe) ₉ (vanox) ₆ (benzoate) ₆ ], with a planar core structure built up from three [Fe ₂ Ln] units to give a giant Ln ₃ triangle embedded into an Fe ₆ ring.

Structural, magnetic, and spectroscopic data on a Mn³⁺ spin-crossover complex with Schiff base ligand 4-OMe-Sal₂323, isolated in crystal lattices with five different counteranions, are reported. Complexes of [Mn(4-OMe-Sal₂323)]X where X = ClO₄^– (1), BF₄^– (2), NO₃^– (3), Br^– (4), and I^– (5) crystallize isotypically in the chiral orthorhombic space group P2₁2₁2 with a range of spin state preferences for the [Mn(4-OMe-Sal₂323)]⁺ complex cation over the temperature range 5–300 K. Complexes 1 and 2 are high-spin, complex 4 undergoes a gradual and complete thermal spin crossover, while complexes 3 and 5 show stepped crossovers with different ratios of spin triplet and quintet forms in the intermediate temperature range. High-field electron paramagnetic resonance was used to measure the zero-field splitting parameters associated with the spin triplet and quintet states at temperatures below 10 K for complexes 4 and 2 with respective values: D_S=1 = +23.38(1) cm^–1, E_S=1 = +2.79(1) cm^–1, and D_S=2 = +6.9(3) cm^–1, with a distribution of E parameters for the S = 2 state. Solid-state circular dichroism (CD) spectra on high-spin complex 1 at room temperature reveal a 2:1 ratio of enantiomers in the chiral conglomerate, and solution CD measurements on the same sample in methanol show that it is stable toward racemization. Solid-state UV–vis absorption spectra on high-spin complex 1 and mixed S = 1/S = 2 sample 5 reveal different intensities at higher energies, in line with the different electronic composition. The statistical prevalence of homochiral crystallization of [Mn(4-OMe-Sal₂323)]⁺ in five lattices with different achiral counterions suggests that the chirality may be directed by the 4-OMe-Sal₂323 ligand.

Structural, magnetic and spectroscopic data on four new spin triplet Mn ³⁺ complexes reveals a large magnetic anisotropy. Spin state is sensitive to lattice contents as the spin quintet ground state is stabilized on co-crystallization with ethanol.

Reversible proton‐induced spin state switching of an Fe^III complex in solution is observed at room temperature. A reversible magnetic response was detected in the complex, [Fe^III(sal₂323)]ClO₄ (1), using Evans’ method ¹H NMR spectroscopy which indicated cumulative switching from low‐spin to high‐spin upon addition of one and two equivalents of acid. Infrared spectroscopy suggests a coordination‐induced spin state switching (CISSS) effect, whereby protonation displaces the metal‐phenoxo donors. The analogous complex, [Fe^III(4‐NEt₂‐sal₂323)]ClO₄ (2), with a diethylamino group on the ligand, was used to combine the magnetic change with a colorimetric response. Comparison of the protonation responses of 1 and 2 reveals that the magnetic switching is caused by perturbation of the immediate coordination sphere of the complex. These complexes constitute a new class of analyte sensor which operate by magneto‐modulation, and in the case of 2, also yield a colorimetric response.

A Dy₂ complex, exhibiting SMM behaviour, and its Y analogue were prepared via in situ oxidation of Py₂TTA, a pincer type ligand, followed by dimerisation.