Non-centrosymmetric spin-switchable systems are of interest for their prospective applications as magnetically active non-linear optical materials and in multiferroic devices. Chiral resolution of simple spin-crossover chelate complexes into the Δ and Λ forms offers a facile route to homochiral magnetic switches, which could be easily enantiomerically enriched. Here, we report the spontaneous resolution of a new hysteretic spin-crossover complex, [Mn III -(sal 2 323)]SCN • EtOH (1), into Δ and Λ forms, without the use of chiral reagents, where sal 2 323 is a Schiff base resulting from condensation of 1,2-bis(3-aminopropylamino)ethane with 2-hydroxybenzaldehyde. The enantiopurity of the Δ and Λ isomers was confirmed by single crystal X-ray diffraction and circular dichroism. Quantum chemistry calculations were used to investigate the electronic structure. The opening of a wide 80 K thermal hysteresis window at high temperature highlights the potential for good magneto-optical function at ambient temperature for materials of this type.

We report the structural and magnetic properties of two new Mn3+ complex cations in the spin crossover (SCO) [Mn(R-sal2323)]+ series, in lattices with seven different counterions in each case. We investigate the effect on the Mn3+ spin state of appending electron-withdrawing and electron-donating groups on the phenolate donors of the ligand. This was achieved by substitution of the ortho and para positions on the phenolate donors with nitro and methoxy substituents in both possible geometric isomeric forms. Using this design paradigm, the [MnL1]+ (a) and [MnL2]+ (b) complex cations were prepared by complexation of Mn3+ to the hexadentate Schiff base ligands with 3-nitro-5-methoxy-phenolate or 3-methoxy-5-nitro-phenolate substituents, respectively. A clear trend emerges with adoption of the spin triplet form in complexes 1a–7a, with the 3-nitro-5-methoxy-phenolate donors, and spin triplet, spin quintet and thermal SCO in complexes 1b–7b with the 3-methoxy-5-nitro-phenolate ligand isomer. The outcomes are discussed in terms of geometric and steric factors in the 14 new compounds and by a wider analysis of electronic choices of Mn3+ with related ligands by comparison of bond length and angular distortion data of previously reported analogues in the [Mn(R-sal2323)]+ family. The structural and magnetic data published to date suggest a barrier to switching may exist for high spin forms of Mn3+ in those complexes with the longest bond lengths and highest distortion parameters. A barrier to switching from low spin to high spin is less clear but may operate in the seven [Mn(3-NO2-5-OMe-sal2323)]+ complexes 1a–7a reported here which were all low spin in the solid state at room temperature.