"Naked" [Mn3O](7+) Triangles: The Effect of Auxiliary Ligands on Magnetic Exchange

The reaction between Mn(ClO4)(2)center dot 6H(2)O, Et-saoH(2) (Et-saoH(2) = 2-hydroxypropiophenone oxime), NEt4OH and [Ni(pao)(2)(py)(2)] (paoH = 2-pyridylaldoxime) in MeOH forms the complex [(Mn3O)-O-III(Et-sao)(3)(HCO2)(MeOH)(5)] (1) in good yields. The reaction of MnCl2 center dot 4H(2)O, Me-saoH(2) (Me-saoH(2) = 2-hydroxyphenylethanone oxime), NEt4OH and DL-valine in MeOH gives the complex [(Mn3O)-O-III(Me-sao)(3)(MeOH)(5)]Cl (2) in moderate yields. In both complexes the building block consists of a triangular {(Mn3O)-O-III(R-sao)(3)} unit (R = Et, Me for 1 and 2, respectively). In the case of 2, the [Mn-3] unit can be considered "naked" as there is no capping ligand present, whereas in the case of 1 a formate ion is terminally bonded to one metal centre. DC magnetic susceptibility measurements for 1 and 2 reveal the presence of both ferromagnetic and antiferromagnetic intramolecular interactions, depending on the Mn-N-O-Mn torsion angles within each cluster, leading to a ground state S 2 for both complexes. Rationalization of this result is attempted by structural comparison of previously reported triangular [Mn-3] oximate complexes on the basis of "flat" and "twisted" torsion angles and the effect of the auxiliary ligands.