Dicyanogermylenes: A Tale of Isomers and Interconversions

A systematic investigation is carried out using the B3LYP, BLYP, and BHLYP functionals and MP2 level of theory to characterize the low-lying electronic singlet and triplet GeC<sub>2</sub>N<sub>2</sub> isomers. The basis sets used are of double-ζ plus polarization quality with additional s- and p-type diffuse functions, DZP++. Three bent isomers Ge­(CN)<sub>2</sub>, CNGeCN, and Ge­(NC)<sub>2</sub> are located on the singlet and triplet potential energy surfaces. In visualizing the reaction pathways for the singlet isomerization of the bent isomers, two three-membered [Ge, C, N] cyclic systems, with exocyclic −C–CN and −C–NC bonding, appear on the energy surface. Four types of electron affinities reported are: the adiabatic electron affinity, the zero-point vibrationally corrected electron affinity, the vertical electron affinity, and the vertical detachment energy of the anion. The ionization energies and singlet–triplet gaps for all isomers are also reported. The energetic ordering (kcal mol<sup>–1</sup>) (B3LYP) with zero-point vibrational energy corrections for the singlet ground state isomers follows: Ge­(CN)<sub>2</sub> (global minimum) < CNGeCN (2.3) < Ge­(NC)<sub>2</sub> (3.3) < Cyc_exo_CCN (15.3) < Cyc_exo_CNC (30.6). All the bent and cyclic isomers are found to be below the dissociation limit to Ge (<sup>3</sup>P) + C<sub>2</sub>N<sub>2</sub> (<sup>1</sup>Σ<sub>g</sub>). The rate constants for all interconversions are evaluated using transition state theory.