Center for Computational Quantum Chemistry, University of Georgia, 140 Cedar Street, Athens, Georgia 30602, USA.
Phys Chem Chem Phys. 2019 Dec 11;21(48):26438-26452. doi: 10.1039/c9cp05777c.
The lowest lying singlet and triplet states of HBCN-, HCCN, HNCN+, HAlCN-, HSiCN, HPCN+, HGaCN-, HGeCN, and HAsCN+ were studied using the CCSDT(Q)/CBS//CCSD(T)/aug-cc-pVQZ level of theory. Periodic trends in geometries, singlet-triplet gaps, and barriers to linearity were established and analyzed. The first row increasingly favors the triplet state, with a singlet-triplet gap (ΔEST = Esinglet - Etriplet) of 3.5 kcal mol-1, 11.9 kcal mol-1, and 22.6 kcal mol-1, respectively, for HBCN-, HCCN, and HNCN+. The second row increasing favors the singlet state, with singlet-triplet gaps of -20.4 kcal mol-1 (HAlCN-), -26.6 kcal mol-1 (HSiCN), and -26.8 kcal mol-1 (HPCN+). The third row also favors the singlet state, with singlet-triplet gaps of -26.8 kcal mol-1 (HGaCN-), -33.5 kcal mol-1 (HGeCN), and -33.1 kcal mol-1 (HAsCN+). The HXCN species have larger absolute singlet-triplet energy gaps compared to their parent species XH2 except for the case of X = N+. The effect of the substitution of hydrogen with a cyano group was analyzed with isodesmic bond separation analysis and NBO.
采用 CCSDT(Q)/CBS//CCSD(T)/aug-cc-pVQZ 理论水平研究了 HBCN-、HCCN、HNCN+、HAlCN-、HSiCN、HPCN+、HGaCN-、HGeCN 和 HAsCN+的最低单重态和三重态。建立并分析了几何形状、单重态-三重态能隙和线性化势垒的周期性趋势。第一周期越来越有利于三重态，HBCN-、HCCN 和 HNCN+的单重态-三重态能隙（ΔEST = Esinglet - Etriplet）分别为 3.5 kcal mol-1、11.9 kcal mol-1 和 22.6 kcal mol-1。第二周期越来越有利于单重态，单重态-三重态能隙分别为-20.4 kcal mol-1（HAlCN-）、-26.6 kcal mol-1（HSiCN）和-26.8 kcal mol-1（HPCN+）。第三周期也有利于单重态，单重态-三重态能隙分别为-26.8 kcal mol-1（HGaCN-）、-33.5 kcal mol-1（HGeCN）和-33.1 kcal mol-1（HAsCN+）。与母体物种 XH2 相比，HXCN 物种具有更大的绝对单重态-三重态能隙，除了 X = N+的情况。用等电子键分离分析和 NBO 分析了氢被氰基取代的影响。
