Ferro- to anti-ferromagnetic crossover angle in diphenoxido- and carboxylato-bridged trinuclear Ni^II₂–Mn^II complexes: experimental observations and theoretical rationalization

Abstract

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)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 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°, 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°. 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.