Crystal structure of tri--carbonyl-octacarbonyl-iodo-tetrahedro-tetracobaltate(1-) as its tetraethylammonium salt

The complex [NEt4][Co4(CO)11I] crystallizes in the orthorhombic space group Cmca with unit-cell dimensions a= 16.97(1), b= 26.72(1), c= 12.10(1)Å, and Z= 8. The structure has been solved from X-ray single-crystal counter data and refined by least-squares calculations to R= 0.063 for 1 874 significant diffraction intensities. The structure of the anion is derived from that of the parent [Co4(CO)12]. Three of the carbonyl groups are edge bridging, defining a basal triangle, and eight are terminal, two per metal atom. The iodine atom, contrary to expectation, is terminally bonded to the apical cobalt atom. The molecular symmetry is Cs-m. The Co–I distance is 2.642(2)Å, and the Co–Co interactions have mean values 2.47 and 2.52 Å for the bridged and unbridged edges, respectively. A slight disorder, caused by the presence of 2% of an isomer with the iodine in a basal position, is present.