Cyanide-Bridged Fe(III)−Mn(III) Bimetallic Systems Assembled from the fac-Fe Tricyanide and Mn Schiff bases: Structures, Magnetic Properties, and Density Functional Theory Calculations

Reaction of [(Tp)Fe(CN)3] [Tp = hydrotris(pyrazolyl)borate] with respective Mn(III) Schiff bases led to the formation of four dimeric molecules, [(Tp)Fe(CN)3][Mn(1-napen)(H2O)]·MeCN·4H2O [1; 1-napen = N,N′-ethylenebis(2-hydroxy-1-naphthylideneiminato) dianion], [(Tp)Fe(CN)3][Mn(5-Clsalen)(H2O)] [2; 5-Clsalcy = N,N′-(trans-1,2-cyclohexanediylethylene)bis(5-chlorosalicylideneiminato) dianion], [(Tp)Fe(CN)3][Mn(2-acnapen)(MeOH)]·MeOH [3; 2-acnapen = N,N′-ethylenebis(1-hydroxy-2-acetonaphthylideneiminato) dianion], [(Tp)Fe(CN)3][Mn(3-MeOsalen)(H2O)] [4; 3-MeOsalen = N,N′-ethylenebis(3-methoxysalicylideneiminato) dianion], and a one-dimensional (1D) zigzag chain [(Tp)Fe(CN)3][Mn(2-acnapen)]·H2O (5). The dimers contain multiple intermolecular interactions such as hydrogen bonds, face-to-face π−π contacts, and edge-to-face CH−π forces, raising molecular dimensions from one-dimensional (1D) up to three-dimensional (3D) arrays, whereas there are no π−π stacking interactions in the 1D chain compound. Magnetic measurements reveal that ferromagnetic couplings are obviously operative between Mn(III) and Fe(III) spin centers transmitted by CN bridges for 13 and 5, and antiferromagnetic interactions are however unexpectedly present in 4. On the basis of the proper spin Hamiltonians, magnetic exchange couplings are estimated to be in the span from 1.79 to 7.48 cm−1 for the ferromagnetically coupled systems and −1.40 cm −1 for the antiferromagnetic dimer. A slow magnetic relaxation is tangible in 5, which is in connection with isolated chains devoid of any intermolecular noncovalent interactions. Density Functional Theory (DFT) calculations and comparison of structural parameters suggest that the observed magnetic behaviors are mainly associated with the bending of the Mn−NC angle in the bridging pathway.