Antiferro- to ferromagnetic crossover in diphenoxido bridged Ni^II₂Mn^II complexes derived from N₂O₂ donor Schiff base ligands

Abstract

Three new trinuclear Ni^II–Mn^II complexes have been synthesized using three different “metalloligands” [NiL¹], [NiL²] and [NiL³] derived from the Schiff bases H₂L¹ = N,N′-bis(salicylidene)-1,3-pentanediamine, H₂L² = N,N′-bis(salicylidene)-1,3-propanediamine and H₂L³ = N,N′-bis(salicylidene)-1,3,-diaminopropan-2-ol), respectively. In all three complexes, [(NiL¹)₂Mn(OOCPh)₂(H₂O)₂]•CH₃OH (1), [(NiL²)₂Mn(OOCPh)₂(CH₃OH)₂]•CH₃OH (2) and [(NiL³)₂Mn(OOCPh)₂(H₂O)₂]•CH₃OH (3), 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 benzoate, giving rise to a linear structure. Complex 1 with Ni–O–Mn angle of 97.35° exhibits antiferromagnetic interactions (J_Ni–Mn = −0.60 cm⁻¹) whereas ferromagnetic exchange is observed in 2 and 3 (J_Ni–Mn = +2.00 and +1.10 cm⁻¹ respectively) having Ni–O–Mn angle 97.34° (in 2), 97.27° (in 3). Theoretical calculations have been performed in order to understand the effect of structural parameters that can tune the magnetic properties of this type of complexes such as small differences in the Ni–O–Mn angle and/or slight variations in intermolecular contacts within the crystal.