Investigation of Magnetic Exchange Pathways in Heterotrinuclear Manganese(III) Schiff Base Complexes Involving Tetrathiocyanidoplatinate(II) Bridges



The first heterotrinuclear manganese(III) Schiff base complexes involving tetrathiocyanidoplatinum(II) bridges with the general formula [{MnIII(L4)(Solv)}2{μ-PtII(SCN)4}] {for which L42– is a tetradentate dianionic Schiff base ligand; L412– = N,N′-benzene-bis(salicylideneiminate) dianion (1a), L422– = N,N′-ethylene-bis(salicylidenebenzeneiminate) dianion (1b), L432– = N,N′-benzene-bis(4-aminodiethylenesalicylideneiminate) dianion (1c), and Solv = CH3OH (1a, 1b) or H2O (1c)} were synthesized and characterized. The two terminal [Mn(L4)(Solv)]+ subunits are covalently bridged by [Pt(SCN)4]2– moieties in a trans arrangement. The coordinated solvent (Solv) ligands form intermolecular hydrogen bonds with the phenolate oxygen atoms of the neighboring molecules, which results in supramolecular 1D chain structures. Extensive networks of weak noncovalent interactions stabilize the crystal structures of all the compounds; moreover, hydrogen bonding within the chains was identified as a dominant exchange pathway. Magnetic analyses including the zero-field splitting term revealed that the antiferromagnetic exchange interaction is stronger for compounds involving water molecules as ligands [1c, J = –1.31(6) cm–1] than for those containing methanol molecules [1a, J = –0.530(9) cm–1; 1b, J = –0.467(7) cm–1]. DFT calculations at the B3LYP/def2-TZVP level supported the experimental findings that dominant antiferromagnetic exchange paths proceed through hydrogen bonds associated with the Solv ligands, whereas the [Pt(SCN)4]2– bridges prevent effective magnetic exchange.