Comparative ab Initio Study of Molecular Structures and Relative Stabilities of Germanone, Germathione, Germaselenone, and Their Structural Isomers

Abstract

The relative stabilities of the H 2 Ge X, trans -HGeXH, and cis -HGeXH (X = O, S, Se) species and the transition states for H 2 Ge Se ↔ trans -HGeSeH and trans -HGeSeH ↔ cis -HGeSeH isomerizations were investigated using post-Hartree−Fock ab initio methods. Geometry optimization and frequency calculations were performed at the HF, MP2, DFT, and QCISD(T) levels using TZP(2d,2p), TZP(2df,2pd), and TZP++(2df,2pd) basis sets. In the cases of oxygen and sulfur, the isomers H 2 Ge O and H 2 Ge S represent the structures with the highest energy, and the global minima corresponds to the trans -HGeSH and cis -HGeOH forms, respectively. In a more detailed study of the potential energy surface of the Ge[H 2 Se] system, we have found that the trans -HGeSeH structure is a global minimum separated at the QCISDT/TZP(2df,2pd) level by only 0.5 and 2.0 kcal/mol from H 2 Ge Se and cis -HGSeH, respectively. In all cases the electron correlation energy plays a dominant role, and reliable assignment of the relative stability of these energetically close-lying isomers was possible using only higher levels of ab initio theory.