COORDINATION IN CYCLOPENTADIENYL COMPOUNDS .3. CRYSTAL-STRUCTURE OF [YB(C5H4CH3)2NH2]2

The reaction of methylcyclopentadiene with ytterbium in liquid ammonia yields bis(η5-methylcyclopentadienyl)ytterbiumamide, [Yb(mecp)2NH2]2 as a byproduct. [Yb(mecp)2NH2]2 crystallizes in the orthorhombic space group Pbca with a 998.4(2), b 1876.7(3), c 1193.(2) pm; ρcalc 2.064 g/cm3 for Z = 4. Every ytterbium atom is pseudo-tetrahedrally coordinated by the centres Z of two methylcyclopentadienyl rings and two bridging N-atoms. The angle between the plane containing 3he Yb-atoms and the ring centres and the Yb2N2 ring plane is approximately 90°. X-ray crystallography of the compounds formulated as Mcp2X have revealed the existence of monomers, dimers, trimers, tetramers and linear polymers. Our model of the "Cyclopentadienylkugel" can be used to reliably predict whether a compound will be monomeric or associated (n ≥ 2). Likewise, if n = 2, the model successfully predicts whether the dimer is of the type cp2M(μ-X)2Mcp2 (type A) or cp2M(μ-X)-MXcp2 (type B). In the lanthanide and actinide series (M = Ln, Ac) it is possible to predict the important structural features of these compounds. © 1989.