Synthesis, Structures, and Magnetic Properties of Novel Mononuclear, Tetranuclear, and 1D Chain Mn^III Complexes Involving Three Related Asymmetrical Trianionic Ligands

The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H3Li (i = 4−6). These ligands are obtained through reaction of salicylaldehyde with “half-units”, the latter resulting from monocondensation of different diamines with phenylsalicylate,. Upon deprotonation, Li (i = 4−6) possess an inner N2O2 coordination site with one amido, one imine, and two phenoxo functions, and an outer amido oxygen donor. The trianionic character of such ligands yields original neutral complexes with the L/Mn stoichiometry. The crystal and molecular structures of three complexes have been determined at 190 K (1) or 180 K (2 and 3). Complex 1 crystallizes in the triclinic space group P1̄ (No. 2): a = 7.8582(14) Å, b = 10.9225(16) Å, c = 12.4882(18) Å, α = 67.231(14)°, β = 72.134(14)°, γ = 82.589(13)°, V = 940.6(3) Å3, Z = 2. Complex 2 crystallizes in the orthorhombic space group Pbcn (Νο. 60): a = 23.8283(15) Å, b = 11.1605(7) Å, c = 26.152(2) Å, V = 6954.8(8) Å3, Z = 8, while complex 3 crystallizes in the monoclinic space group P21/c (No. 14) with a = 11.7443(14) Å, b = 7.5996(10) Å, c = 18.029(2) Å, β = 100.604(10)°, V = 1581.6(3) Å3, Z = 4. Owing to hydrogen bonds and π−π stackings, the mononuclear neutral molecules of 1 are arranged in a 2D network while complexes 2 and 3 are tetranuclear and polymeric (1D chain) species, respectively, owing to the bridging ability of the oxygen atom of the amido function. The experimental magnetic susceptibilities of complexes 2 and 3 indicate the occurrence of similarly weak MnIII−MnIII antiferromagnetic interactions (J = −1.1 cm-1). Single ion zero-field splitting of manganese(III) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry in 2 (J = − 1.1 cm-1, D1 = 2.2 cm-1, D2 = −2.8 cm-1), D1 and D2 being associated to the six- and five-coordinate Mn ions, respectively. A weaker antiferromagnetic interaction (J = − 0.2 cm-1) operates through π−π stacking in complex 1. Complex 3 is a weak ferromagnet (ordering temperature ∼7 K) as a result of the spin canting originating from the crystal packing.