Although each of these intriguing molecules has been described in molecular orbital terms, typically based on density functional theory (DFT), a comparative account of quantitative molecular properties seems to be lacking. Here we present a DFT (B3LYP 22,23 -D3 24 /def2QZVP) 25 study of both simple silylenes and of the more unusual divalent silicon species mentioned above (Scheme 1). Besides optimized geometries, we calculated vertical and adiabatic ionization potentials (IPs), electron affinities (EAs) and singlet-triplet gaps (ES-T's) in the hope that they would shed light on the special stability of p-complexes of decamethylsilicocene and silapyramidanes (Table ). Based on long-standing and recent calibration studies in our laboratory, the present level of theory may be expected to yield vertical ionization potentials to within 0.1-0.2 eV of experimental values derived from photoelectron spectroscopy. Indeed, for parent silylene, SiH2, the calculated adiabatic IP and EA (Table ) agree to within 0.1 eV with experimental values, 8.92 eV and 1.12 eV 37 , respectively, providing excellent calibration for the present calculations. As described below, the calculated metrics (Table ) provide valuable insight into -and indeed help quantify under understanding of -the stability of key classes of divalent silicon species. Scheme 1. Molecules studied in this work.