Umebayashi Yasuhiro, Shin Mari, Kanzaki Ryo, Ishiguro Si Shin-ichi
Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
J Colloid Interface Sci. 2001 May 15;237(2):167-173. doi: 10.1006/jcis.2001.7457.
Formation of cobalt(II)-thiocyanato complexes in nonionic surfactant solutions of poly(ethylene oxide) type with varying poly(ethylene oxide) chain lengths of 7.5 (Triton X-114), 30 (Triton X-305), and 40 (Triton X-405) has been studied by titration spectrophotometry and calorimetry at 298 K. Data were analyzed by assuming formation of a series of ternary complexes Co(NCS)(n)Y(m)((2-n)+) (Y=surfactant) with an overall formation constant beta(nm). In all the surfactant systems examined, data obtained can be explained well in terms of formation of Co(NCS)(+) and Co(NCS)(2) in an aqueous phase (aq), and Co(NCS)(4)Y(2-) in micelles, and their formation constants, enthalpies, and entropies have been determined. The beta(41)/beta(20) ratio increases and the corresponding enthalpy becomes significantly less negative with an increasing number of ethylene oxide groups. This suggests that micelles of these nonionic surfactants have a heterogeneous inner structure consisting of ethylene oxide and octylphenyl moieties. Indeed, on the basis of molar volumes of ethylene oxide and octylphenyl groups, intrinsic thermodynamic parameters have been extracted for the reaction Co(NCS)(2)(aq)+2NCS(-)(aq)=Co(NCS)(4)Y(2-) (Delta(r)G degrees, Delta(r)H degrees, and Delta(r)S degrees ) at each moiety. The Delta(r)G degrees, Delta(r)H degrees, and Delta(r)S degrees values are -16 kJ mol(-1), -15 kJ mol(-1), and 3 J K(-1) mol(-1), respectively, for the ethylene oxide moiety, and -15 kJ mol(-1), -70 kJ mol(-1), and -183 J K(-1) mol(-1) for octylphenyl. Significantly less negative Delta(r)H degrees and Delta(r)S degrees values for ethylene oxide imply that the hydrogen-bonded network structure of water is extensively formed at the ethylene oxide moiety, and the structure is thus broken around the Co(NCS)(4)(2-) complex with weak hydrogen-bonding ability. Copyright 2001 Academic Press.
通过滴定分光光度法和量热法，在298K下研究了聚环氧乙烷链长分别为7.5（Triton X - 114）、30（Triton X - 305）和40（Triton X - 405）的聚环氧乙烷型非离子表面活性剂溶液中钴（II）-硫氰酸根配合物的形成。通过假设形成一系列具有总形成常数β(nm)的三元配合物Co(NCS)(n)Y(m)((2 - n)+)（Y = 表面活性剂）来分析数据。在所有研究的表面活性剂体系中，所得数据可以很好地用在水相中形成Co(NCS)(+)和Co(NCS)(2)以及在胶束中形成Co(NCS)(4)Y(2 - )来解释，并且已经确定了它们的形成常数、焓和熵。随着环氧乙烷基团数量的增加，β(41)/β(20)比值增大，相应的焓的负值显著减小。这表明这些非离子表面活性剂的胶束具有由环氧乙烷和辛基苯基部分组成的非均相内部结构。实际上，基于环氧乙烷和辛基苯基基团的摩尔体积，已经提取了每个部分中反应Co(NCS)(2)(aq)+2NCS(-)(aq)=Co(NCS)(4)Y(2 - )（Δ(r)G°、Δ(r)H°和Δ(r)S°）的本征热力学参数。对于环氧乙烷部分，Δ(r)G°、Δ(r)H°和Δ(r)S°值分别为 - 16 kJ mol(-1)、 - 15 kJ mol(-1)和3 J K(-1) mol(-1)，对于辛基苯基部分分别为 - 15 kJ mol(-1)、 - 70 kJ mol(-1)和 - 183 J K(-1) mol(-1)。环氧乙烷部分的Δ(r)H°和Δ(r)S°值的负值明显较小，这意味着在环氧乙烷部分广泛形成了水的氢键网络结构，并且在具有弱氢键能力的Co(NCS)(4)(2 - )配合物周围结构被破坏。版权所有2001年学术出版社。
