NMR spectra of dinuclear manganese and iron compounds containing 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane

NMR spectra of paramagnetic dinuclear mu-oxo-bis-mu-acetato-dimanganese(III) and diiron(III) compounds containing 1,4,7-triazacyclononane (L) and 1,4,7-trimethyl-1,4,7-triazacyclononane (L') capping ligands are reported and discussed in detail. The asymmetrically ligated [LMnIII(mu-O)(mu-CH3COO)(2)(MnL)-L-III'](ClO4)(2) crystallizes in the monoclinic space group P2(1)/c, a=12.010(2), b=18.688(4), c=14.090(3) Angstrom, beta=91.31(3)degrees, Z=4. The formation of this compound from a 1:1 mixture of the symmetric compounds [Mn-2(III)(mu-O)-(mu--CH3COO)(2)L-2](2+) and [Mn-2(III)(mu-O)(mu-CH3COO)(2)L'(2)](2+) has been followed by NMR spectroscopy. A partially deuterium-labelled macrocyclic ligand and deuterated acetic acid have been used to facilitate the assignment of the NMR spectra. The large chemical shifts observed for the dinuclear manganese compounds have been attributed to the presence of two paramagnetic (d(4)), weakly coupled Mn(III) centres. [Fe-2(III)(mu-O)(mu-CH3COO)(2)L'(2)](2+) exhibits a relatively strong antiferromagnetic coupling between the metal centres and, consequently, the chemical shifts for the protons are much smaller than those for the analogous manganese complex. The different magnetic behaviour of these compounds is also reflected in the opposite temperature dependence of the chemical shifts observed. (C) 1998 Elsevier Science S.A.