Series of Trinuclear Ni<sup>II</sup>Ln<sup>III</sup>Ni<sup>II</sup> Complexes Derived from 2,6-Di(acetoacetyl)pyridine:  Synthesis, Structure, and Magnetism

Eighteen trinuclear Ni<sup>II</sup><sub>2</sub>Ln<sup>III</sup> complexes of 2,6-di(acetoacetyl)pyridine (H<sub>2</sub>L) (Ln = La−Lu except for Pm) were prepared by a “one-pot reaction” of H<sub>2</sub>L, Ni(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O, and Ln(NO<sub>3</sub>)<sub>3</sub>·<i>n</i>H<sub>2</sub>O in methanol. X-ray crystallographic studies indicate that two L<sup>2-</sup> ligands sandwich two Ni<sup>II</sup> ions with the terminal 1,3-diketonate sites and one Ln<sup>III</sup> ion with the central 2,6-diacylpyridine site, forming the trinuclear [Ni<sub>2</sub>Ln(L)<sub>2</sub>] core of a linear NiLnNi structure. The terminal Ni assumes a six-coordinate geometry together with methanol or water molecules, and the central Ln assumes a 10-coordinate geometry together with two or three nitrate ions. The [Ni<sub>2</sub>Ln(L)<sub>2</sub>] core is essentially coplanar for large Ln ions (La, Ce, Pr, Nd) but shows a distortion with respect to the two L<sup>2-</sup> ligands for smaller Ln ions. Magnetic studies for the Ni<sub>2</sub>Ln complexes of diamagnetic La<sup>III</sup> and Lu<sup>III</sup> indicate an antiferromagnetic interaction between the terminal Ni<sup>II</sup> ions. A magnetic analysis of the Ni<sub>2</sub>Gd complex based on the isotropic Heisenberg model indicates a ferromagnetic interaction between the adjacent Ni<sup>II</sup> and Gd<sup>III</sup> ions and an antiferromagnetic interaction between the terminal Ni<sup>II</sup> ions. The magnetic properties of other Ni<sub>2</sub>Ln complexes were studied on the basis of a numerical approach with the Ni<sub>2</sub>La complex and analogous Zn<sub>2</sub>Ln complexes, and they indicated that the Ni<sup>II</sup>−Ln<sup>III</sup> interaction is weakly antiferromagnetic for Ln = Ce, Pr, and Nd and ferromagnetic for Ln = Gd, Tb, Dy, Ho, and Er.