Multi-Magnetic Properties of a Novel SCO [Fe(3-OMe-Sal2trien)]-[Fe(tdas)2]·CH3CN Salt

The multi‐magnetic salt [Fe(3‐OMe‐Sal2trien)][Fe(tdas)2]·CH3CN (1) has been prepared and fully characterized by a variety of methods. The crystal structure of 1, determined at 150, 297 and 350 K, consists of alternating layers composed by a parallel arrangement of the chains of isolated π–π coupled cation pairs of [Fe(3‐OMe‐Sal2trien)]+ and anion pairs of [Fe(tdas)2]–. The complex magnetic behavior of this salt is consistent with the sum of the contributions from spin‐crossover (SCO) cations and strong antiferromagnetically (AFM) coupled dimeric [Fe(tdas)2]22– anions. The observed gradual thermally induced spin transition (T1/2 = 195 K) is relatable to the cation exhibiting disordering of ethylene (–CH2–CH2–) groups between two conformers with a narrow thermal hysteresis of 6 K. The dc magnetization measurements and 57Fe Mössbauer spectroscopy at room temperature are in excellent agreement between γHS(%) value and ratio of disordering of ethylene groups obtained from X‐ray analysis. Mössbauer spectra at 80 K and 296 K indicate a spin transition between S = 1/2 and S = 5/2 for the iron(III) saltrien‐cation and confirms S = 3/2 for the [FeIII(tdas)2]– anion. The experimental results are supplemented with a theoretical Density Functional Theory (DFT) analysis.