Magnetic relationship in new Ni IICu IINi II trinuclear complexes according to nickel(II) geometry

Abstract

Six new [NiCuNi] heterotrinuclear complexes, {[Ni(cth)] 2[Cu(OHpba)]}(ClO 4) 2 ( 1), {[Ni(cth)] 2[Cu(Me 2pba)]}(ClO 4) 2 ( 2), {[Ni(Me 3[12]N 3)] 2[Cu(OHpba)]}(ClO 4) 2 ( 3), {[Ni(Me 3[12]N 3)] 2[Cu(Me 2pba)]}(ClO 4) 2 ( 4), {[Ni(Me 4[12]N 3)] 2[Cu(OHpba)]}(ClO 4) 2 ( 5) and {[Ni(Me 4[12]N 3)] 2[Cu(Me 2pba)]}(ClO 4) 2 ( 6) with the nickel(II) atom in a hexa- ( 1–2) or penta-coordinate ( 3–6) environment, have been synthesized and characterized. Cth is d,1-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane, Me 3[12]N 3 is 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene and Me 4[12]N 3 is the corresponding 9-methyl derivative. OHpba and Me 2pba are the 2-hydroxo and 2,2′-dimethyl derivatives of 1,3-propylenebis (oxamato), respectively. The magnetic properties of all these compounds have been studied. The X m T vs T for 1–6 plot exhibits a minimum at about 100 K, characteristic of this kind of coupled polymetallic complex with an irregular spin-state structure. These new trinuclear complexes present ZFS in the S = 3 2 ground state, which causes a lowering in the X m T vs T plots at low temperature. The highest J values are found for the complexes in which the nickel(II) is penta-coordinate. EPR spectra of 1–6 clearly indicate axial distortion with g = 5.5 and g = 2.2 approximately. This feature agrees with an anisotropic S = ± 1 2 Kramer doublet in the ground state.