Ferro- to Antiferromagnetic Crossover Angle in Diphenoxido- and Carboxylato-Bridged Trinuclear NiII2-MnII Complexes: Experimental Observations and Theoretical Rationalization

Three new trinuclear heterometallic Ni-II-Mn-II complexes have been synthesized using a [NiL] metalloligand, where H2L = N,N'-bis(salicylidene)-1,3-propanediamine. The complexes [(NiL)(2)Mn(OCnn)(2)(CH3OH)(2)]center dot CH3OH (1), [(NiL)(2)Mn(OPh)(2)(CH3OH)(2)][(NiL)(2)Mn(OPh)(2)]center dot H2O (2), and [(NiL)(2)Mn(OSal)(2)(CH3OH)(2)]center dot 2[NiL] (3) (where OCnn = cinnamate, OPh = phenylacetate, OSal = salicylate) have been structurally characterized. In all three complexes, in addition to the double phenoxido bridge, the two terminal Ni-II atoms are linked to the central Mn-II by means of a syn-syn bridging carboxylate, giving rise to a linear structure. Complexes 1 and 2 with Ni-O-Mn angles of 97.24 and 96.43 degrees, respectively, exhibit ferromagnetic interactions (J(Ni-Mn) = +1.38 and +0.50 cm(-1), respectively), whereas 3 is antiferromagnetic (J(Ni-Mn) = 0.24 cm-1), having an Ni-O-Mn angle of 98.51 degrees. DFT calculations indicate that there is a clear magneto-structural correlation between the Ni-O-Mn angle and J(Ni-Mn) values, which is in agreement with the experimental results.