Octahedral co-carbide carbonyl clusters decorated by [AuPPh₃]⁺ fragments: synthesis, structural isomerism, and aurophilic interactions of Co₆C(CO)₁₂(AuPPh₃)₄.

Abstract

The Co6C(CO)12(AuPPh3)4 carbide carbonyl cluster was obtained from the reaction of [Co6C(CO)15](2-) with Au(PPh3)Cl. This new species was investigated by variable-temperature (31)P NMR spectroscopy, X-ray crystallography, and density functional theory methods. Three different solvates were characterized in the solid state, namely, Co6C(CO)12(AuPPh3)4 (I), Co6C(CO)12(AuPPh3)4·THF (II), and Co6C(CO)12(AuPPh3)4·4THF (III), where THF = tetrahydrofuran. These are not merely different solvates of the same neutral cluster, but they contain three different isomers of Co6C(CO)12(AuPPh3)4. The three isomers I-III possess the same octahedral [Co6C(CO)12](4-) carbido-carbonyl core differently decorated by four [AuPPh3](+) fragments and showing a different Au(I)···Au(I) connectivity. Theoretical investigations suggest that the formation in the solid state of the three isomers during crystallization is governed by packing and van der Waals forces, as well as aurophilic and weak π-π and π-H interactions. In addition, the closely related cluster Co6C(CO)12(PPh3)(AuPPh3)2 was obtained from the reaction of [Co8C(CO)18](2-) with Au(PPh3)Cl, and two of its solvates were crystallographically characterized, namely, Co6C(CO)12(PPh3)(AuPPh3)2·toluene (IV) and Co6C(CO)12(PPh3)(AuPPh3)2·0.5toluene (V). A significant, even if minor, effect of the cocrystallized solvent molecules on the structure of the cluster was observed also in this case.