Compressed and Expanded Lattices - Barriers to Spin-State Switching in Mn Complexes.

We report the structural and magnetic properties of two new Mn complex cations in the spin crossover (SCO) [Mn(R-sal323)] series, in lattices with seven different counterions in each case. We investigate the effect on the Mn spin state of appending electron-withdrawing and electron-donating groups on the phenolate donors of the ligand. This was achieved by substitution of the and positions on the phenolate donors with nitro and methoxy substituents in both possible geometric isomeric forms. Using this design paradigm, the [MnL1] () and [MnL2] () complex cations were prepared by complexation of Mn 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 - with the 3-nitro-5-methoxy-phenolate donors, and spin triplet, spin quintet and thermal SCO in complexes - 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 Mn with related ligands by comparison of bond length and angular distortion data of previously reported analogues in the [Mn(R-sal323)] family. The structural and magnetic data published to date suggest a barrier to switching may exist for high spin forms of Mn 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-NO-5-OMe-sal323)] complexes - reported here which were all low spin in the solid state at room temperature.