Interaction of triatomic germanium with lithium atoms:: Electronic structure and stability of Ge3Lin clusters

Quantum chemical calculations were applied to investigate the electronic structure of mono-, di-, and tri- lithiated triatomic germanium (Ge3Lin) and their cations (n = 0-3). Computations using a multiconfigurational quasidegenerate perturbation approach (MCQDPT2) based on complete active space CASSCF wavefunctions, MRMP2 and density functional theory reveal that Ge3Li has a (2)A' ground state with a doublet-quartet gap of 24 kcal/mol. Ge3Li2 has a singlet ground state with a singlet-triplet ((3)A' '-(1)A(1)) gap of 30 kcal/mol, and Ge3Li3 a doublet ground state with a doublet-quartet ((4)A' '-(2)A') separation of 16 kcal/mol. The cation Ge3Li+ has a (1)A' ground state, being 18 kcal/mol below the (3)A' state. The computed electron affinities for triatomic germanium are EA((1)) = 2.2 eV (experimental value is 2.23 eV), EA((2)) = -2.5 eV, and EA((3)) = -5.9 eV, for Ge-3(-), Ge-3(2-), and Ge-3(3-), respectively, indicating that only the monoanion is stable with respect to electron detachment, in such a way that Ge3Li is composed of Ge3-Li+ ions. An atoms in molecules (AIM) analysis shows the absence of a Ge-Ge-Li ring critical point in Ge3Li. An electron localization function (ELF) map of Ge3Li supports the view that the Ge-Li bond is predominantly ionic; however, a small covalent character could be anticipated from the Laplacian at the Ge-Li bond critical point. The ionic picture of the Ge-Li bond is further supported by the natural bond orbital (NBO) results. The calculated Li affinity value for Ge-3 is 2.17 eV, and the Li+ cation affinity value for Ge-3(-) amounts to 5.43 eV. The larger Li+ cation affinity of Ge-3(-) favors an electron transfer, resulting in a Ge3-Li+ interaction.