Joshi Ravi, Ghanty Tapan K, Naumov Sergej, Mukherjee Tulsi
Radiation and Photochemistry Division, and Theoretical Chemistry Section, and Chemistry Group, Bhabha Atomic Research Center, Mumbai 400 085, India.
J Phys Chem A. 2007 Mar 29;111(12):2362-7. doi: 10.1021/jp067757i. Epub 2007 Mar 6.
Ab initio molecular orbital and hybrid density functional methods have been employed to characterize the structure and bonding of (H2O-H2S)+, an asymmetrical dimer radical cation system. A comparison has been made between the two-center three-electron (2c-3e) hemi-bonded system and the proton-transferred hydrogen-bonded systems of (H2O-H2S)+. Geometry optimization of these systems was carried out using unrestricted Hartree Fock (HF), density functional theory with different functionals, and second-order Møller-Plesset perturbation (MP2) methods with 6-311++G(d,p) basis set. Hessian calculations have been done at the same level to check the nature of the equilibrium geometry. Energy data were further improved by calculating basis set superposition error for the structures optimized through MP2/6-311++G(d,p) calculations. The calculated results show that the dimer radical cation structure with H2O as proton acceptor is more stable than those structures in which H2O acts as a proton donor or the 2c-3e hemi-bonded (H2O thereforeSH2)+ system. This stability trend has been further confirmed by more accurate G3, G3B3, and CCSD(T) methods. On the basis of the present calculated results, the structure of H4OS+ can best be described as a hydrogen-bonded complex of H3O+ and SH with H2O as a proton acceptor. It is in contrast to the structure of neutral (H2O...H2S) dimer where H2O acts as a proton donor. The present work has been able to resolve the ambiguity in the nature of bonding between H2O and H2S in (H2O-H2S)+ asymmetrical dimer radical cation.
从头算分子轨道和杂化密度泛函方法已被用于表征不对称二聚体自由基阳离子体系(H2O-H2S)+的结构和键合。对(H2O-H2S)+的双中心三电子(2c-3e)半键合体系和质子转移氢键体系进行了比较。使用无限制Hartree Fock(HF)、具有不同泛函的密度泛函理论以及采用6-311++G(d,p)基组的二阶Møller-Plesset微扰(MP2)方法对这些体系进行几何优化。在同一水平上进行了Hessian计算，以检验平衡几何结构的性质。通过计算经MP2/6-311++G(d,p)计算优化的结构的基组叠加误差，进一步改进了能量数据。计算结果表明，以H2O作为质子受体的二聚体自由基阳离子结构比H2O作为质子供体的结构或2c-3e半键合(H2O…SH2)+体系更稳定。更精确的G3、G3B3和CCSD(T)方法进一步证实了这种稳定性趋势。基于目前的计算结果，H4OS+的结构最好描述为H3O+和SH的氢键复合物，其中H2O作为质子受体。这与中性(H2O…H2S)二聚体的结构相反，在中性二聚体中H2O作为质子供体。本工作能够解决(H2O-H2S)+不对称二聚体自由基阳离子中H2O和H2S之间键合性质的模糊性。
