The importance of dihydrogen complexes HnGe(H2)+ (n=0,1) to the chemistry of cationic germanium hydrides: advanced theoretical and mass spectrometric analysis

Investigations of Ge,Hn]-/0/- (n = 2,3) have been performed using a four-sector mass spectrometer. The results reveal that the complexes HnGe(H2)+ (n = 0,1) play an important role in the unimolecular dissociation of the metastable cations. Theoretical calculations support the experimental observations in most instances, and the established view that the global minimum of Ge,H2]+ is an inserted structure may need reexamination; CCSD(T,full)/cc-pVTZ//CCSD(T)/6-311 ++ G(d,p) and B3LYP/cc-pVTZ studies of three low-lying cation states (2A1 HGeH+, 2B2 Ge(H2)+ and 2B1 Ge(H2)+) indicate a very small energy difference (ca. 4 kcal mol(-1)) between 2A1 HGeH+ and 2B2 Ge(H2)+; B3LYP favours the ion-molecule complex, whereas coupled-cluster calculations favour the inserted structure for the global minimum. Single-point multireference (MR) averaged coupled-pair functional and MR-configuration interaction calculations give conflicting results regarding the global minimum. We also present theoretical evidence indicating that the orbital-crossing point implicated in the spin-allowed metastable dissociation HGeH+* --> Ge(H2)+* --> Ge+ + H2 lies above the H-loss asymptote. Thus, a quantum-mechanical tunneling mechanism is invoked to explain the preponderance of the H2-loss signal for the metastable ion.