From acetylene complexes to vinylidene structures: The GeC 2 H 2 system

The expansion of germanium chemistry in recent years has been rapid. In anticipation of new experiments, a systematic theoretical investigation of the eight low lying electronic singlet GeC 2 H 2 stationary points is carried out. This research used ab initio self‐consistent‐field (SCF), coupled cluster (CC) with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory and a variety of correlation–consistent polarized valence cc‐pV X Z and cc‐pV X Z‐DK (Douglas‐Kroll) (where X = D, T, and Q) basis sets. At all levels of theory used in this study, the global minimum of the GeC 2 H 2 potential energy surface (PES) is confirmed to be 1‐germacyclopropenylidene ( Ge‐1S ). Among the eight singlet stationary points, seven structures are found to be local minima and one structure ( Ge‐6S ) to be a second‐order saddle point. For the seven singlet minima, the energy ordering and energy differences (in kcal mol −1 , with the zero‐point vibrational energy corrected values in parentheses) at the cc‐pVQZ‐DK (Douglas‐Kroll) CCSD(T) level of theory are predicted to be 1‐germacyclopropenylidene ( Ge‐1S ) [0.0 (0.0)] < vinylidenegermylene ( Ge‐3S ) [13.9 (13.5)] < ethynylgermylene ( Ge‐2S ) [17.9 (14.8)] < Ge ‐ 7S [37.4 (33.9)] < syn ‐3‐germapropenediylidene ( Ge‐8S ) [41.2 (37.9)] < germavinylidenecarbene ( Ge‐5S ) [66.6 (61.6)] < nonplanar germacyclopropyne ( Ge‐4S ) [67.8 (63.3)]. These seven isomers are all well below the dissociation limit to Ge ( 3 P) + C 2 H 2 ( $\widetilde{\rm X}$ 1 Σ   g + ). This system seems particularly well poised for matrix isolation infrared (IR) experiments. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010