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

Three new trinuclear heterometallic NiII–MnII complexes have been synthesized using a [NiL] metalloligand, where H2L = N,N′-bis­(salicylidene)-1,3-propanediamine. The complexes [(NiL)2Mn­(OCnn)2(CH3OH)2]·CH3OH (1), [(NiL)2Mn­(OPh)2(CH3OH)2]­[(NiL)2Mn­(OPh)2]·H2O (2), and [(NiL)2Mn­(OSal)2(CH3OH)2]·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 NiII atoms are linked to the central MnII 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°, respectively, exhibit ferromagnetic interactions (JNi–Mn = +1.38 and +0.50 cm–1, respectively), whereas 3 is antiferromagnetic (JNi–Mn = −0.24 cm–1), having an Ni–O–Mn angle of 98.51°. DFT calculations indicate that there is a clear magneto-structural correlation between the Ni–O–Mn angle and JNi–Mn values, which is in agreement with the experimental results.