M^+ AsF_6^-(M=Li,Na,K,Rb和Cs)离子对的结构和振动光谱

Theoretical Study on Structure and Vibrational Spectra of M^+ AsF_6^-(M=Li,Na,K,Rb and Cs) Contact Ion Pairs

利用abinitio计算方法研究了AsF6-阴离子和M+AsF6-(M+=Li+,Na+,K+,Rb+和Cs+)直接接触离子对的结构和光谱行为。结果表明,具有C3V结构三齿相互作用的M+AsF6-最稳定,二齿配位的结构只有在特定条件下才可能稳定存在。当形成离子对后,阳离子与AsF6-的相互作用将改变AsF6-的结构,这其中Li+的影响最大。另外,AsF6-光谱的变化可用来指认溶液中离子的缔合和离子对的种类。

The present paper reports the possible geometries and vibrational spectra of AsF6^- anion and M^＋AsF6^-（M^＋=Li^＋,Na^＋,K^＋,Rb^＋ and Cs^＋） contact ion pairs.It was shown that the tridentate C3V structure of M^＋AsF6^- was preferred over the monodentate and bidentate geometry.In the tridentate structure,the symmetry of AsF6^- in the coordination is lowered because of the presence of M^＋,and its structural parameters and vibrational modes largely differ from its original octahedral structure.The effect of Li＋ on the structure of AsF6^- was greater due to its larger charge/radius ratio.The calculated bands for AsF6^- in M^＋AsF6^-,located in the range of 600-800 cm^-1,could be used to fingerprint what kind of ion pair was present in solutions.