Trinuclear CoIILnIIICoII Complexes (Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb) with 2,6-Dipicolinoylbis(N,N-diethylthiourea): Synthesis, Structures, and Magnetism.

Abstract

One-pot reactions of 2,6-dipicolinoylbis(N,N-diethylthiourea) (H2L) with Co(CH3COO)2·4H2O and LnCl3, where Ln = La, Ce, Nd, Sm, Gd, Dy, Er, and Yb, in warm methanol in the presence of Et3N, give stable trinuclear complexes of the composition [LnCo2(L)2(μ1,3-OOCCH3)2X] ("CoLnCo" complexes), where X- = κ2-CH3COO- or Cl-. X-ray structure determinations reveal symmetric trinuclear complexes containing two organic ligands (L2-), two terminal CoII ions, and one central LnIII ion. The organic ligands coordinate equatorially to the two CoII ions via two bidentate (O,S) N-acylthiourea moieties and tridentate to the central Ln ion via the (O,N,O) 2,6-dipicolinoyl moieties. Two acetate bridges established between each of the terminal Co and central Ln ions complete the square-pyramidal coordination spheres of CoII. All products possess an additional chlorido ligand axially coordinated to the lanthanide except the gadolinium(III) and lanthanum(III) complexes, where bidentate acetato ligands are coordinated. Fitting the χmT versus T data of the "CoLaCo" complex gives the axial and rhombic zero-field-splitting parameters D = 24.3(4) cm-1 and E = -1.0(2) cm-1, respectively, and anisotropic Landé values gx,y = 2.81(1) and gz = 2.00 as well as weak antiferromagnetic interactions between two high-spin CoII centers with J = -0.49(2) cm-1. The nature of the magnetic interactions between the LnIII ions and the CoII ions in the "CoLnCo" complexes is deduced by comparing their χMT values to the sum of χMT values of the analogous "CoLaCo" and related "ZnLnZn" complexes. The "CoDyCo" complex reveals an antiferromagnetic interaction, while the remaining "CoLnCo" complexes show ferromagnetic interactions.