Paul Ankan, Yamaguchi Yukio, Schaefer Henry F
Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA.
J Chem Phys. 2007 Oct 21;127(15):154324. doi: 10.1063/1.2784393.
The observation of several metal cyanides and isocyanides in interstellar space has raised much interest these molecules. Optimum molecular structures, harmonic vibrational frequencies, and dipole moments of the ground electronic states (X1Sigma+), triplet excited states, and open shell singlet excited states of CuCN and CuNC were determined using different levels of nonrelativistic and scalar relativistic (Douglas-Kroll) [Ann. Phys. 82, 89 (1979)] coupled cluster theory in conjunction with atomic natural orbital basis sets and correlation consistent basis sets. For the relativistic computations the specially contracted correlation consistent Douglas-Kroll (DK) basis sets were used. Moreover, barriers to isomerization from CuCN to CuNC were computed. The predicted structures of the X1Sigma+ state for CuCN are re(Cu-C)=1.826 A and re(C-N)=1.167 A, at the most sophisticated level of theory, the scalar relativistic DK-CCSD(T)/cc-pVQZ(DK) method. These results are in excellent agreement with the experimentally determined Cu-C bond length of 1.829 A and C-N bond distance of 1.162 A. At the same level of theory, the zero-point corrected barrier to isomerization from CuCN to CuNC is estimated to be 14.7 kcal mol(-1), and the cyanide is more stable than the isocyanide by 11.5 kcal mol(-1). For both CuCN and CuNC the 3Sigma+ state is the lowest lying excited electronic state. At the DK-CCSD/cc-pVQZ(DK) level of theory, the energetic ordering of excited states of CuCN and CuNC is X1Sigma+<a3Sigma+<b3Pi<2(1)Sigma+ approximately 3Delta<1Pi<1Delta. The variations of CN bond lengths in the optimized structures for the different electronic states and the CN stretching frequencies of the ground state and the excited states suggest that metal dpi to ligand pi charge transfer is insignificant, in contrast to previous results for isoelectronic NiCO.
在星际空间中观测到几种金属氰化物和异氰化物引发了人们对这些分子的浓厚兴趣。使用不同水平的非相对论和标量相对论（道格拉斯 - 克罗尔）[《物理学年鉴》82, 89 (1979)]耦合簇理论，结合原子自然轨道基组和相关一致基组，确定了CuCN和CuNC的基态电子态（X1Σ⁺）、三重激发态和开壳单重激发态的最佳分子结构、谐振动频率和偶极矩。对于相对论计算，使用了特别收缩的相关一致道格拉斯 - 克罗尔（DK）基组。此外，还计算了从CuCN异构化为CuNC的势垒。在最复杂的理论水平，即标量相对论DK - CCSD(T)/cc - pVQZ(DK)方法下，CuCN的X1Σ⁺态预测结构为re(Cu - C)=1.826 Å和re(C - N)=1.167 Å。这些结果与实验测定的Cu - C键长1.829 Å和C - N键距1.162 Å非常吻合。在相同理论水平下，从CuCN异构化为CuNC的零点校正势垒估计为14.7 kcal mol⁻¹，氰化物比异氰化物稳定11.5 kcal mol⁻¹。对于CuCN和CuNC，³Σ⁺态都是最低的激发电子态。在DK - CCSD/cc - pVQZ(DK)理论水平下，CuCN和CuNC激发态的能量排序为X1Σ⁺<a³Σ⁺<b³Π<2¹Σ⁺≈³Δ<¹Π<¹Δ。不同电子态优化结构中CN键长的变化以及基态和激发态的CN伸缩频率表明，与等电子体NiCO的先前结果相反，金属dπ到配体π的电荷转移不显著。
