On the Nature of Hypercoordination in Dihalogenated Perhalocyclohexasilanes

Hypercoordination in silicon has long been reviewed. Dihalogenated perhalocyclohexasilane inverse sandwich complexes (ISCs) are the only group of hypercoordinate Si complexes with anion donors that contact six neutral silicon atoms; opening prospective applications in Si self assembled nanostructures. Hypercoordinate bonds in 16 such ISCs were studied and their anion ring interactions have been understood with respect to halides. mu(6) mode of coordination was confirmed by the presence of 6 equivalent (3,-1) bond critical points through Bader's QTAIM perspective. The presence of Lewis acid sites above and below the flat Si rings were examined through a reduced density gradient (RDG) analysis, and the ability of halide anions (X' = F, Cl, Br, I) to hypercoordinate has been understood. Role of the ring halides (X) in tuning size and acidity of Lewis sites has been addressed. While the total interaction between the two anions and the ring is quantified through EDA, each SiX' hypercoordinate bond was identified as either purely ionic or transient through QTAIM computations. CDA shows that these complexes are of donor-acceptor type with significant back donation The analysis shows that BrF' and IF' were found to reach maximum covalency within the group. Hence in future, tuning these ISCs for construction of nanocrystalline Si structures for optoelectronic properties can essentially utilize the collective, weak yet hypercoordinate Si in these complexes.