CSi2Ga2: a neutral planar tetracoordinate carbon (ptC) building block.

Ever being a large curiosity, the "anti-van't Hoff/Le Bel" realm that is associated with tetracoordinate or hypercoordinate planar centers has made rapid progress. In particular, it has been disclosed that silicon and gallium can be embedded in various planar species. However, to our best knowledge, assembly of silicon- and gallium-embedded planar units has never been reported, though such assembled species might be used as potential nanoscale devices. Here we report the first attempt on how to design assembled molecular compounds featuring silicon- and gallium embedded planar tetracoordinate carbon (ptC) units. Taking the special silicon- and gallium-embedded ptC unit CSi2Ga2as an example, we performed density functional calculations on a series of model compounds [DM(CSi2Ga2)](q+) as well as the saturated compounds (Cl-)q[CpM(CSi2Ga2)](q+) (D = CSi2Ga2, Cp-(C5H5-); M = Li, Na, K, Be, Mg, Ca)and the more extended sandwich-like species. For the six metals, CSi2Ga2 can only be assembled in the "heterodecked sandwich" scheme (e.g., [CpM(CSi2Ga2)](q+)) so as to avoid cluster fusion. Interestingly, among all the designed sandwich species, CSi2Ga2 generally prefers to interact with the partner deck at the corner (Ga atoms) or face (CSi2Ga2 planes) sites. Such interaction types serve as an interesting growth pattern that might be applicable to the assembly of Si- and Ga-embedded ptC unit CSi2Ga2 into highly extended sandwich-like complexes. Our results for the first time showed that the Si- and Ga-embedded ptC unit CSi2Ga can act as a new type of building block. The present results are expected to enrich planar tetracoordinate carbon chemistry and metallocenes.