CRYSTAL-STRUCTURES OF A TETRANUCLEATING MACROCYCLE AND ITS DIMANGANESE(III) DERIVATIVE, AND MAGNETISM OF THE LATTER

Condensation of 2,6-bis(aminomethyl)-4-methylphenol with 2,6-diformyl- 4-methylphenol gave a macrocyclic tetra-Schiff base containing two of each component as the dihydrochloride salt H-4L.2HCl, which has been s tudied by X-ray crystallography [triclinic, space group P1BAR (no. 2), a = 8.809(1), b = 9.268(2), c = 10.286(3) angstrom, alpha = 89.93(2), beta = 84.70(2), gamma = 72.18(2)degrees; at convergence R = 0.067 an d R' = 0.060 for 982 reflections with I greater-than-or-equal-to 2.5si gma(I)]. The outstanding feature of the structure is that despite the overall dipositive charge resulting from protonation, the dialdehyde-d erived oxygens are present as phenoxide anions. Crystals of compositio n [Mn2(H2L)(mu-O2CMe)(mu-OH)(MeOH)2][ClO4]2.2MeOH obtained from conden sation of the dialdehyde and the diamine in the presence of Mn2+ and d ioxygen were also studied by X-ray diffraction [monoclinic, space grou p C2/c (no. 15), a = 26.673(3), b = 11.069(3), c = 21.185(3) angstrom, beta = 127.44(1)degrees; at convergence R = 0.061 and R' = 0.061 for 2102 reflections with I greater-than-or-equal-to 3sigma(I)]. The two e quivalent manganese centres have tetragonally distorted six coordinate ligand environments consistent with the high-spin d4 configuration of the +III oxidation state, which is confirmed by the magnetic properti es. The magnetic moment per Mn is 4.61 mu(B) at room temperature falli ng to 1.8 mu(B) at 10 K indicative of weak antiferromagnetic coupling with best-fit parameters obtained using a -2JS1.S2. Heisenberg model o f g = 1.99(0.01), J = -4.0(0.1 ) cm-1 and % monomer = 2.3(0.3).