Synthesis of heptanuclear Ni4Dy3 coordination aggregate using tridentate ligand: X-ray structure, magnetism and theoretical studies

The Schiff base ligand, 2-(((2-hydroxybenzyl)imino)methyl)phenol (H2L) having ONO donor centres are utilized to synthesize {Ni4Dy3} coordination aggregate following the support of six benzoate bridging groups. Sequential addition of Dy(NO3)3·6H2O and NiCl2·6H2O to H2L followed by PhCO2Na completes the coordination driven aggregation of heptanuclear Na[Ni4Dy3(L)4(μ3-OH)4(μ1,1,3,3-PhCO2)2(μ1,3-PhCO2)4(CH3OH)4]∙CH2Cl2·9H2O (1) having 2,3,6M7 − 1 topology. Two adjacent perpendicular inverse Ni2Dy2 partial di-cubane units sharing a common vertex through the central DyIII ion resulted a new structural arrangement within the Ni − Dy family of coordination aggregates. The complex shows no slow magnetic relaxation under zero applied fields and only shows a very weak field dependent magnetization. The DFT calculations revealed weak ferromagnetic exchange between benzoato-bridged NiII ions, whereas the CASSCF calculations were used to identify magnetic anisotropy in NiII and DyIII ions resulting in low-lying excited states of DyIII ions with significant probability for the quantum tunneling of the magnetization, which rationalize the observed fast dynamics in the magnetic properties.