Substituent effects on the potential energy surface of XGeBi (X = H, Li, Na, BeH, MgH, BH2, AlH2, CH3, SiH3, NH2, PH2, OH, SH, F, and Cl) were investigated by using B3LYP/Def2-TZVP, B3PW91/Def2-TZVPP, and CCSD(T) methods. The isomers include structures with formal double (Ge=BiX) and triple (XGe=Bi) bonds to germanium-bismuth, so a direct comparison of these types of species is possible. Our model calculations indicate that electropositively substituted: Ge=BiX species are thermodynamically and kinetically more stable than their isomeric XGe=Bi molecules. Moreover, the theoretical findings suggest that F, OH, and CH3 substitutions prefer to shift the double bond (:Ge=BiX) by forming a triple bond (XGe=Bi). (C) 2012 Elsevier B.V. All rights reserved.