From acetylene complexes to vinylidene structures: The GeC2H2 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 GeC2H2 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‐pVXZ and cc‐pVXZ‐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 GeC2H2 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 (3P) + C2H2( $\widetilde{\rm X}$ 1Σ  g+ ). This system seems particularly well poised for matrix isolation infrared (IR) experiments. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010

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