Novel linear transition metal clusters of a heptadentate bis-β-diketone ligand

The synthesis and the structure of the new potentially heptadentate ligand 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene (H5L) is described. The reaction in pyridine or DMF of this ligand with various M(AcO)(2) salts (M = Ni-II, Co-II, Mn-II) leads to very different products depending on the metal. Thus, the dinuclear complexes [M-2(H3L)(2)(py)(4)] (M = Ni-II, 1; Co-II, 2) or the linear zigzag tetranuclear clusters [Mn-4(H2L)(2)(AcO)(2)(py)(5)] (3) and [Mn-4(H2L)(2)(AcO)(2)(dmf)(4)] (4) have been synthesized and characterized crystallographically. Slow oxidation of complex 3 leads to the formation of the novel mixed-valence linear complex [Mn-3(HL)(2)(py)(6)] (5), displaying an unprecedented asymmetric (MnMnMnII)-Mn-III-Mn-III topology. The coordination geometry of complexes 1 to 5 has been analyzed and discussed by means of continuous shape measures. Magnetic measurements of 3 and 5 demonstrate that the metals within these complexes weakly interact magnetically with coupling constants of J(1) = -1.13 cm(-1) and J(2) = -0.43 cm(-1) (S = 0) for complex 3 and J(1) = -5.4 cm(-1) and J(2) = -0.4 cm(-1) (S = (5)/(2)) for complex 5 (using the H = -Sigma 2J(ij)S(i)S(j) convention). These results are consistent with X-band EPR measurements on these compounds.