Tetranuclear Lanthanide(III) Complexes with a Zigzag Topology from the Use of Pyridine-2,6-dimethanol: Synthetic, Structural, Spectroscopic, Magnetic and Photoluminescence Studies

Reaction between Ln(NO3)(3)center dot xH(2)O (x = 5 or 6) and the potentially tridentate (N,O,O) chelating/bridging ligand pyridine-2,6-dimethanol (pdmH(2)), in the presence of base NEt3, affords a family of isostructural tetranuclear [Ln(4)(III)(NO3)(2)(pdmH)(6)(pdmH(2))(2)](NO3)(4) (Ln(III) = Eu-III, Tb-III, Dy-III, Ho-III, Er-III, Yb-III) complexes with a rare zigzag topology. All complexes contain a [Ln(4)(mu-OR)(6)](6+) core with bridging ligation provided by the alkoxido arms of six eta(1):eta(1):eta(2):mu pdmH(-) groups. The Ln(III) ions are eight coordinate with distorted geometries. Direct current magnetic susceptibility studies revealed predominant weak antiferromagnetic exchange interactions between the metal centers, which were quantified in the case of isotropic Gd-4(III) to give J = -0.09(1) cm(-1) and g = 2.00(1). The observation of out-of-phase (chi ''(M)) ac susceptibility signals suggested that the Dy-4(III) analogue might be a molecular nanomagnet. Solid-state photoluminescence studies showed that the Eu-4(III) and Tb-4(III) compounds exhibit intense, sharp, and narrow emission bands in the red and green visible regions, respectively, which arise from the characteristic D-5(0) -> F-7(J) and D-5(4) -> F-7(J) transitions. The combined results demonstrate the ability of pdmH2 ligand to yield homometallic 4f clusters with interesting magnetic and optical properties.