One-pot reactions of 2,6-dipicolinoylbis(N,N-diethylthiourea) (H2L) with Co (CH3 COO)(2)center dot 4H(2)O and LnCl(3), 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 [LnCo(2)(L)(2)(mu(1,3)-OOCCH3)(2)X] ("CoLnCo" complexes), where X- = kappa(2)-CH3COO- or Cl-. X-ray structure determinations reveal symmetric trinuclear complexes containing two organic ligands (L2-), two terminal Co-II ions, and one central Ln(III) ion. The organic ligands coordinate equatorially to the two Co-II 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 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 chi m(T) 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 Lande values g(x,y) = 2.81(1) and g(z) = 2.00 as well as weak antiferromagnetic interactions between two high-spin Co-II centers with J = -0.49(2) cm(-1). The nature of the magnetic interactions between the Ln(III )ions and the Co-II ions in the "CoLnCo" complexes is deduced by comparing their chi m(T) values to the sum of chi m(T) values of the analogous "CoLaCo" and related "ZnLnZn" complexes. The "CoDyCo" complex reveals an antiferromagnetic interaction, while the remaining "CoLnCo" complexes show ferromagnetic interactions.