Magnetic Anisotropy Transfer from Mono- to Polymetallic Complexes

The reaction of multi-bidentate oxamate-based copper(II) complexes with the [Ni((i)Prtacn)Cl-2] complex ((i)Prtacn:1,4,7-triisopropyl-1,4,7-triazacyclononane) has been investigated. X-ray diffraction studies reveal that for all compounds the oxamato kappa O,kappa Omicron' bidentate coordination site replaces the two chloride ions in [Ni(iPrtacn)Cl-2] to form trimetallic {CuNi2} (1-3), hexametallic {Cu2Ni4} (4) and enneametallic {Cu3Ni6} (5) complexes. The investigation of the magnetic properties shows that Cu-Ni interactions through the oxamato bridge are in the expected range (-111 cm(-1), -68 cm(-1)). For 1-3, both the sign and strength of the magnetic couplings are computed independently from DFT calculations, and these estimates broadly agree with the experiments. The magnetization measurements and EPR studies reveal that 1-3 are anisotropic: a significant portion of the large anisotropy of the [Ni((i)Prtacn)Cl-2] complex is retained, resulting in a D value for the S=3/2 ground state of 5 cm(-1) on average. This is no longer the case for 4 and 5 where the anisotropy of the Ni(II) complexes is diluted due to the high nuclearity of the final edifices. These results show that it is possible to obtain trimetallic complexes with a high anisotropy and a high spin value for the ground state by a judicious choice of the interacting metal ions.