Octanuclear Rare-Earth Clusters

The polyoxo rare-earth core (Ln = Y, Gd, and Yb) has been synthesized from the appropriate rare-earth chloride hydrate and K₂Se and Se in dmf (dimethylformamide). The cluster core is ligated with a variety of polyselenido chains in addition to a number of dmf molecules. The structure of the Gd₈(dmf)₁₃(₄-O)(₃-OH)₁₂(Se₃)(Se₄)₂(Se₅)₂ cluster, 1, was determined by X-ray diffraction methods. It is similar to an Eu cluster previously characterized. Two new clusters, Yb₈(dmf)₁₁(₄-O)(₃-OH)₁₂(Se₄)₂(Se₅)₂Cl₂·dmf, 2, and Y₈(dmf)₁₂(₄-O)(₃-OH)₁₂(Se₄)₄Cl₂·6 dmf, 3, have also been synthesized and characterized. Clusters 2 and 3 have the same octanuclear core of rare-earth atoms as the Gd cluster but contain two chloro ligands in two isomeric conformations in place of the Se₃^2- ring in the Gd cluster. The geometry of the Ln₈ core is described as a triangulated dodecahedron with ₃-OH groups capping the 12 faces. A ₄-O atom centers the cluster with close contacts to four Ln atoms in an approximate tetrahedral arrangement. Pertinent crystallographic data are: Compound 1, monoclinic, , a= 14.410(3) Å, b = 24.439(5) Å, c = 28.927(6) Å, = 101.05(3)°, V = 9998(3) ų, T = 106(2) K, Z = 4; Compound 2, orthorhombic, , a = 17.049(9) Å, b = 24.68(1) Å, c = 45.03(2)Å, V = 18,945(16) ų, T = 153(2) K, Z = 8; Compound 3, monoclinic, C_2h⁵-P2₁/c, a =18.728(l) Å, b = 29.263( 1) Å, c = 20.548(1) Å, = 90.144(1)°, V = 11,261(1) ų, T = 153(2) K, Z = 4.