Dinuclear Co~(II)/Gd~(III) and Co~(III)/Gd~(III) Complexes Derived from Hexadentate Schiff Bases: Synthesis, Structure, and Magnetic Properties

摘要

Two heterodimetallic complexes of formulae [LCo(MeOH)Gd(NO_3)_3] (1) and [LCo(AcO)_2Gd(NO_3)_2] (2) (H_2L = 1,3-bis[(3-methoxysalicylidene)amino]-2,2'dimethylpropane) have been synthesized and characterized. The structure of 1 consists of discrete dinuclear entities. The cobalt(II) ion exhibits a square-pyramidal geometry, in which the basal plane is formed by the N_2O_2 set of the inner Schiff base site and the apical position is occupied b the methanol oxygen atom. The gadolinium(III) ion is ten-coordinate to three bidentate nitrate groups and the four oxygen atoms of the Schiff base. The phenolate oxygen atoms act as a bridge between both metal ions. Complex 2 is also formed by isolated dinuclear species. The cobalt(III) ion shows a distorted octahedral geometry in which the equatorial plane is formed by the N_2O_2 set of the Schiff base, and the axial positions are occupied by two oxygen atoms from both acetate groups. The gadolinium(III) ion is ten-coordinate to two bidentate nitrate groups, two oxygen atoms of the acetate groups, and the four oxygen atoms of the Schiff base. The metal ions are bridged through both the phenolate oxygens and the acetate groups, and latter acting as #mu#_2 ligands. Magnetic measurements on compound 1 allowed, for the first time, a quantitative evaluation of the J(Co,Gd) ferromagnetic interaction parameter (J = 0.90 cm~(1)). The Co~(II) zero-field splitting has to be taken into account to fit the experimental data at low temperature (D = 4.2 cm~(-1)). In complex 2, the magnetically isolated gadoinium center obeys a Curie law.