The Silicon Carbonyls Revisited: On the Existence of a Planar Si(CO)4

Recently, some works have focused attention on the reactivity of silicon atom with closed-shell molecules. Silicon may form a few relatively stable compounds with CO, i.e. Si(CO), Si(CO)₂, SiC₂O₂], while the existence of polycarbonyl (n>2) silicon complexes has been rejected by current literature. In this paper, the reaction of silicon with carbonyl has been reinvestigated by density functional calculations. It has been found that the tetracoordinated planar Si(CO)₄ complex is thermodynamically stable. In Si(CO), silicon carbonyl, and Si(CO)₂, silicon dicarbonyl, the CO are datively bonded to Si; Si(CO)₄, silicon tetracarbonyl, may be viewed as a resonance between the extreme configurations (CO)₂Si + 2CO and 2CO + Si(CO)₂; while SiC₂O₂], c-silicodiketone, is similar to the compounds formed by silicon and ethylene. A detailed orbital analysis has shown that the Si bonding with two CO is consistent with the use of sp ²-hybridized orbitals on silicon, while the Si bonding with four CO is consistent with the use of sp ² d-hybridized orbitals on silicon, giving rise to a planar structure about Si.