The green compound poly[(tetra-hydro-furan)-tris-[μ-η5:η5-1-(tri-methyl-sil-yl)cyclo-penta-dien-yl]caesium(I)ytterbium(II)], [CsYb(C8H13Si)3(C4H8O)] n or [(THF)Cs(μ-η5:η5-Cp')3YbII] n was synthesized by reduction of a red THF solution of (C5H4SiMe3)3YbIII with excess Cs metal and identified by X-ray diffraction. The compound crystallizes as a two-dimensional array of hexa-gons with alternating CsI and YbII ions at the vertices and cyclo-penta-dienyl groups bridging each edge. This, based off the six-electron cyclo-penta-dienyl rings occupying three coordination positions, gives a formally nine-coordinate tris-(cyclo-penta-dien-yl) coordination environment to Yb and the Cs is ten-coordinate due to the three cyclo-penta-dienyl rings and a coordinated mol-ecule of THF. The complex comprises layers of Cs3Yb3 hexa-gons with THF ligands and Me3Si groups in between the layers. The Yb-C metrical parameters are consistent with a 4f 14 YbII electron configuration.