Antiferromagnetic interactions through phenoxo bridges and lattice water: Synthesis, structure, and magnetic properties of new Mn(III) Schiff base complexes in combination with thiocyanate ligand

The Schiff base ligands, N,N'-bis(2-hydroxyacetophenone)-1,2-diaminoethane (acphenH(2)) and N,N'-bis(2-hydroxyacetophenone)-1,3-diaminopropane (acphpnH(2)), prepared in situ were used to synthesise two new Mn(III) complexes which were characterised by crystallography and variable temperature magnetic measurements. [Mn(acphen)NCS](2) is a phenoxo-bridged dimeric compound with the thiocyanate coordinating in the usual bent mode (Mn-N-C angle, 152 degrees) and is weakly antiferromagnetic. Since there are no significant inter-dimer contacts in the crystal, the low temperature magnetic behaviour is influenced by single ion zero-field splitting. Exact diagonalisation of the spin Hamiltonian was performed to derive the following parameters: J = -0.7 cm (1), D = -0.6 cm (1). Mn(acphpn)(H2O)NCS is monomeric with an unusual linearly coordinated thiocyanate (Mn-N-C angle, 178 degrees). Two lattice water molecules link the Mn( III) complex molecules through hydrogen bonds to form one-dimensional chains in the crystal. Magnetic exchange along the chain makes this compound also weakly antiferromagnetic with J similar to -2 cm (1). (C) 2009 Elsevier B. V. All rights reserved.