The stereochemistry of transition metal cyclooctatetraenyl complexes: di-h3,h3′ cyclooctatetraenedinickel,a sandwich compound with two enveloped nickel atoms

The crystal structure of dicyclooctatetraenedinickel, [(COT)Ni]₂, has been determined from three-dimensional, single crystal X-ray data collected by counter methods. Crystals of [(COT)Ni]₂, belong to the monoclinic system with a = 8.2906(3), b = 11.4185(5), c = 7.2340(3) Å, β = 115.978(2)°, d(calc) = 1.757 gcm^?3, Z = 2. The space group is C²_2h-P2₁/a. The structure was refined anisotropically (hydrogen atoms and a nickel atom fragment isotropically) by fullmatrix least-squares techniques. Final values of R and R_w were 0.046 and 0.079, respectively, for the 1055 unique, absorption and extinction corrected reflections with I > 2σ(I). Crystals of [(COT)Ni]₂ consists of discrete molecules with crystallographic C_i ($\text{1}$) symmetry. The compound possesses a sandwich structure with both metal atoms between the COT rings. Each nickel atom forms π-allyl type bonds to three carbon atoms of each COT ring. The nickel atoms are disordered over three sites. The effect of this disorder on the interpretation of the derived structural parameters is discussed.