Synthesis and structural characterisation of the dianion [Co9(C2)(CO)19]2– as its tetramethylammonium salt

Abstract

The dianion [Co₉(C₂)(CO)₁₉]^2– 1 ([NMe₄]⁺ salt) has been obtained by pyrolysis of [NMe₄][Co₆C(CO)₁₄] in diglyme (2,5,8-trioxanonane) at 130 °C, and, as the parent compound, is paramagnetic. The salt [NMe₄]₂[Co₉(C₂)(CO)₁₉] has been characterised by single crystal X-ray diffraction. The Co₉(C₂) core of the anion can be described as a D_3h tricapped trigonal prism of Co atoms with stretched interbasal edges encapsulating an acetylide C₂ unit [C–C 1.39(2) Å]. Nine CO ligands are linearly bonded, one per metal atom, six are edge bridging and four semibridging. The overall molecular symmetry is C_2v or, more accurately, C₂.