2D Bimetallic Oxalate-Based Ferromagnets with Inserted [Fe(4-Br-sal2-trien)]+ and [Fe(3-R-sal2-trien)]+ (R = Br, Cl and CH3O) FeIII Spin-Crossover Complexes

The syntheses, structures and magnetic properties of the compounds of formula [Fe-III(4-Br-sal(2)-trien)][Mn(II)cr(III)-(ox)(3)](0.67)Cl-0.33 center dot CH3OH_solvate(1), [Fe-III(3-Br-sal(2)-trien)][(MnCrIII)-Cr-II-(ox)(3)]center dot(CH3CN)(2) (2), [Fe-III(3-Cl-sal(2)-trien)][Mn(II)cr(III)(ox)(3)]center dot(CH3OH)(2)center dot(CH3CN)(2) (3) and [Fe-III(3-CH3O-sal(2)-trien)][(MnCrIII)-Cr-II(ox)(3)]center dot(CH3OH)center dot(H2O)(1.5)center dot(CH2Cl2)(0.5) (4) are reported. The four structures present a 2D honeycomb anionic layer formed by Mn-II and Cr-III ions linked through oxalate ligands and a cationic layer of the Fe-III complexes intercalated between the 2D oxalate network. The main differences compared with previous 2D oxalate-based structures are the presence of double layers of cations in compounds 1, 3 and 4 and porous channels in the structures of 1 and 4 filled with disordered solvent molecules. The magnetic properties indicate that the inserted Fe-III cations undergo an almost complete spin crossover above 300 K in 1 and a partial spin crossover in 3 and 4 that coexists with a ferromagnetic ordering of the oxalate network. In the case of 2, the inserted cation remains in the HS from 2 to 300 K. Therefore, 1, 3 and 4 are multifunctional compounds with coexistence of spin crossover and magnetic ordering. Conversely, photomagnetic characterization shows that 1 and 3 do not present a LIESST effect in contrast to the 2D compound [Fe-III(sal(2)-trien)]-[Mn(III)cr(III)(ox)(3)]center dot(CH2Cl2). These results could help to clarify this rare property for a Fe-III complex.