Mn(III) complexes with nitro-substituted ligands-Spin states with a twist

Structural, magnetic, and computational data on two new Mn(III) complex cations in lattices with five different counterions and varying levels of solvation are compared to investigate the influence of the position of the electron-withdrawing ligand nitro-substituent on the thermal spin crossover profile. The [MnL1](+) (a) and [MnL2](+) (b) complex cations were prepared by complexation of Mn(III) to the Schiff base chelates formed from condensation of 3-nitrosalicylaldehyde or 5-nitrosalicylaldehyde, respectively, with 1,2-bis(3-aminopropylamino) ethane and were crystallized with NO3-, (1a/b), ClO4-, (2a/b), PF6-, (3a/b), CF3SO3- (4a/b), and BPh4- (5a/b) counterions. Magnetostructural analysis reveals a minor trend in the spin state preference depending on the position of the nitro substituent where the orientation is dependent on crystal packing. Compounds using the 3-NO2-sal(2)-323 ligand, H2L1, where the nitro group is bent out-of-plane to the benzene ring of the Schiff base, tend to stabilize the triplet state, S = 1, while those with the 5-NO2-sal(2)-323 Schiff base, H2L2, where the nitro group is almost perfectly aligned in-plane with the benzene ring, mostly stabilize the spin-quintet form, S = 2. Density functional theory calculations correctly describe the energetics of intermediate spin/high spin transitions in the complexes. The intrinsic molecular magnetic properties are only marginally dependent on the position of the nitro groups; the out-of-plane orientation for the 3-NO2 is stabilized by an intramolecular hydrogen bonding interaction between the nitro group and the equatorial sal ligand. This demonstrates that the control of magnetic behavior in the solid state is mainly a cooperative effect from the size and distribution of counterions, crystal packing, and intermolecular interactions. Three potential structural phase transitions were identified, in complexes 3a, 4a, and 5a center dot 2MeCN including one which is not coupled to a spin state change. Finally, a break in the pattern of Jahn-Teller distortion typical for [Mn(R-Sal2-323)](+) complexes was observed in two of the complexes with the 5-NO2 ligand, where elongation of the Mn-O bond lengths on warming replaced the usual pattern of elongation of only Mn-N distances. (c) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license