(η⁴-Cyclooctatetraene)(η ⁸-cyclooctatetraene) iodidotantalum(V)

The title complex, [Ta(-4-C₈H₈)(-8-C ₈H₈)I], lies across a crystallographic mirror plane that includes the TaV atom and the iodide ligand. One cyclooctatetraene (cot) ring is-4-coordinating and is bisected by the mirror plane. The fold angle between the plane of the coordinating butadiene portion and the middle plane of the ring is 27.4 (4)-. An additional minor fold angle of 9.3 (7)-exists between the final plane in the ring and the middle plane. The other cot ring is-8-coordinating and is also cut by the mirror plane. In this case, the ring is disordered over the mirror plane, and one position is modeled with appropriate restraints and constraints with respect to distances, angles and displacement parameters (the second position is generated by symmetry). This ring is nearly planar, with an r.m.s. deviation of only 0.05 Åwhen all eight C atoms are included in the calculation. Pairs of intermolecular-8-cot rings are parallel stacked and slightly off center, with a centroid-centroid distance of 3.652 Å. No other significant intermolecular interactions are observed. The compound is of interest as the first structurally characterized mixed halogen-cot complex of the group 5 metals and contains the longest terminal Ta-I distance [3.0107 (5) Å] reported to date.