Solid-State Structures of Base-Free Ytterbocenes and Inclusion Compounds of Bis(pentamethylcyclopentadienyl)ytterbium with Neutral Carboranes and Toluene: The Role of Intermolecular Contacts

The base-free ytterbocenes (Me5C5)2Yb, (Me4C5H)2Yb, and [1,3-(Me3C)2C5H3]2Yb have been prepared from their diethyl ether adducts, synthesized by reaction of YbI2 and the sodium salt of the substituted cyclopentadiene anion in diethyl ether. The structures of the base-free molecules have been determined by X-ray crystallography. The molecule (Me5C5)2Yb has been found to crystallize in two different morphologies; the complex also forms inclusion complexes with toluene, ortho-carborane, meta-carborane, and 1,2-dimethyl-ortho-carborane. The ytterbocene molecule in all of the derivatives examined is bent in the solid state with centroid-metal-centroid angles ranging from 132 to 147. A detailed examination of the structures and comparison with the reported structures of (Me5C5)2Eu, (Me5C5)2Sm, [1,3-(Me3Si)2C5H3]2Yb, and [1,3-(Me3Si)2C5H3]2Eu reveal that bending is the general structural preference. Close inter- or intramolecular contacts are observed in every case between the ytterbium atom and one or more carbon atoms other than those of the two cyclopentadienide rings of that ytterbocene fragment. The packing geometry is dictated by the substituents on the cyclopentadienide rings, the molecules arranging so as to minimize crowding in the solid state. The net result is a coordination polymer, dimer, or monomer, depending on the ring substituents