Abstract
The Si-Si bond lengths of trans-bent disilenes are sensitive to the substitutents. However, they are good constants if the molecules are forced to be planar. Similar situation is found for the substituted disilyne systems. Herein, we present a detailed structural and bonding analysis of the trans-bent and planar disilenes or disilynes based on molecular orbital (MO) arguments. One interest of this work is to identify some similarities between disilenes and disilynes in the bonding pattern with respect to the substitution. We also search for stable triplet disilyne species of mixed substitutents R1SiSiR2 and silaacetylene systems R1SiCR2. We observe some correlation of structure pattern between singlet/triplet and cation/anion species.