The crystal and molecular structures of (η5-pentamethylcyclopentadienyl)(η7-cycloheptatrienyl)zirconium and -hafnium

The crystal structures of (η5-C5Me5)(η7-C7H7)M (M = Zr, Hf) were determined utilizing single crystal X-ray diffraction data. The two compounds are isostructural with the previously determined Ti analog [1], crystallizing in the orthorhombic space group Pnma. Cell data at -140 °C are: M = Zr, a 10.464(4), b 12.318(5), c 11.277(3) Å and Dcalc 1.45 g cm-3 for Z = 4; M = Hf, a 10.442(2), b 12.354(4), c 11.246(2) Å, and Dcalc 1.85 g cm-3 for Z = 4. The metal atom and one carbon of each aromatic ring reside on a crystallographic mirror plane. The M-C(η5) and M-C(η7) separations average 2.485(2) and 2.332(3) Å, respectively for M = Zr and 2.455(3) and 2.296(6) Å for M = Hf. The centroid(η5)-M-centroid(η7) angles deviate significantly from linearity, 170.3° for M = Zr and 172.2° for M = Hf