Synthesis, structures, and magnetic properties of novel mononuclear, tetranuclear, and 1D chain MnIII complexes involving three related asymmetrical trianionic ligands

The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H3L (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, L-i (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 P (1) over bar (No. 2): a = 7.8582(14) Angstrom, b = 10.9225(16) Angstrom, c = 12.4882(18) Angstrom, alpha = 67.231(14)degrees, beta = 72.134(14)degrees, gamma = 82.589(13)degrees, V = 940.6(3) Angstrom(3), Z = 2. Complex 2 crystallizes in the orthorhombic space group Pbcn (No. 60): a = 23.8283(15) Angstrom, b = 11.1605(7) Angstrom, c = 26.152(2) Angstrom, V = 6954.8(8) Angstrom(3), Z = 8, while complex 3 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 11.7443(14) Angstrom, b = 7.5996(10) Angstrom, c = 18.029(2) Angstrom, beta = 100.604(10)degrees, V = 1581.6(3) Angstrom(3), Z = 4. Owing to hydrogen bonds and pi-pi 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 Mn-III-Mn-III 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), D-1 = 2.2 cm(-1), D-2 = -2.8 cm(-1)), D-1 and D-2 being associated to the six- and five-coordinate Mn ions, respectively. A weaker antiferromagnetic interaction (J = - 0.2 cm(-1)) operates through pi-pi stacking in complex 1. Complex 3 is a weak ferromagnet (ordering temperature similar to7 K) as a result of the spin canting originating from the crystal packing.