Titration Calorimetry System for Measurement of Formation Enthalpies of Organometal Complexes

为了对有机过渡金属配合物的形成进行量热测量，我们研制了一种新的滴定量热容器。用新容器（2 cmφ x 4 cmh）将初始供试品溶液的体积减少至4 ml。热传感器是一对热敏电阻，可以检测10度的温度变化<-5>。本文研究了软金属配体Ag^+-EPh_3（E = P，As，Sb）体系在乙腈中的络合作用。[Ag（EPh_3）]^+的形成常数按P &gt; As &gt; Sb的顺序减小，在AN中形成单、双、三、四种PPh_3配合物。并与吡啶（Py）作了比较，Py是比DMSO更强的π受体和σ供体。因此，软Ag^+离子显示出与AN和Py的特定dπ-π相互作用，但与DMSO没有。[Ag（PPh_3）_4]^+在AN中存在，而在DMSO和Py中不存在。[Ag（PPh_3）_n]^+（n = 0-3）从DMSO到AN的转移焓表明，当n=0时，[Ag（PPh_3）_n]^+（n = 0-3）的转移焓接近于零，随着n的增加，[Ag（PPh_3）_n]^+-AN的转移焓变正，表明结合的PPh_3配体削弱了[Ag（PPh_3）_n]^+-AN的特定的dπ-π Ag^+相互作用。类似地，单个[Ag（PPh_3）_n]^+（n = 0-3）从DMSO到Py的转移谱图显示，当n=0时，该值为负值且较大，随着n的增加，络合物的负值变小，而[Ag（PPh_3）_3]^+的值略为负值。这表明，在PPh_3配体的作用下，特异性的dπ-π Ag^+-Py相互作用几乎消失。结果表明，AN的弱dπ-π相互作用和弱的σ贡献能力是形成四面体[Ag（PPh_3）_4]^+配合物的必要条件。

With the aim of calorimetric measurement for the formation of organo-transition metal complexes, we prepared a new vessel for titration calorimetry. The volume of initial test solution is reduced to 4 ml with a new vessel (2 cmφ x 4 cmh). Heat sensor is a couple of thermistors, which can detect temperature changes by 10^<-5> degree. In the present work, we studied complexation of soft-metal soft-ligand Ag^+-EPh_3 (E = P, As, Sb) systems in acetonitrile, which is a stronger π acceptor but weaker σ donor than dimethyl sulfoxide (DMSO). The formation constant of [Ag(EPh_3)]^+ reduced in the order P > As > Sb, and the mono-, bis-, tris- and tetrakis-PPh_3 complexes are formed in AN. The result is compared with that in pyridine (Py), which is a stronger π acceptor and σ donor than DMSO. The soft Ag^+ ion thus shows a specific dπ-π interaction with AN and Py but not with DMSO. The [Ag(PPh_3)_4]^+ is found in AN but not in DMSO and Py. Enthalpies of transfer of individual [Ag(PPh_3)_n]^+ (n = 0-3) species from DMSO to AN show that the value is close to zero for n=0 and become more positive for the complex with increasing n, indicating that the specific dπ-π Ag^+-AN interaction is weakened by bound PPh_3 ligand. Similarly, enthalpies of transfer of individual [Ag(PPh_3)_n]^+ (n = 0-3) species from DMSO to Py show that the value is negative and large for n=0 and become less negative for the complex with increasing n, and the value is slightly negative for [Ag(PPh_3)_3]^+. This indicates that the specific dπ-π Ag^+-Py interaction is almost disappeared by bound PPh_3 ligand. These facts leads to the conclusion that weakened dπ-π interaction and weak σ donating ability of AN is essential for the formation of tetrahedral [Ag(PPh_3)_4]^+ complex.