New carbide clusters in the cobalt sub-group. Part 9. Preparation and crystallographic characterization of dicarbidododeca-µ-carbonyldodecacarbonyl-polyhedro-tridecacobaltate(4–) as its tetrakis(benzyltrimethylammonium) salt [N(CH2Ph)Me3]4[Co13C2(CO)24]·Me2CO

Abstract

The title complex has been prepared by refluxing the dianion [Co₆C(CO)₁₅]^2– in diglyme under nitrogen for 8 h. The crystal structure of this new species has been determined in the salt [N(CH₂Ph)Me₃]₄[Co₁₃C₂(CO)₂₄]·Me₂CO. It crystallizes in the monoclinic space group P2₁/c with cell constants a= 14.057(7), b= 20.24(1), c= 30.66(1)Å, β= 113.06(5)°, and Z= 4. The structure has been solved from 4 234 X-ray single-crystal diffraction intensities, collected by counter methods, and refined by least-squares calculations down to R= 0.082. The tetra-anion is paramagnetic and contains a Co₁₃C₂ cluster in which the metal atoms are arranged in such a way as to form two prismatic cavities in which two isolated carbon atoms are encapsulated. Average bond distances are Co–Co 2.57, the Co–C(carbide) 1.98 Å. The CO ligands are terminal (12) and edge-bridging (12) and conform to the idealized cluster symmetry C₂. The unusual cluster geometry found in this species is a compromise between contrasting tendencies of the metal atoms towards close-packed polyhedra and the carbon atoms towards prismatic interstices.