Solution studies indicate that the Cu2L(OH)3+ complex, where L is a large octaaza cryptand, reacts with NH3, KSCN and NaN3 to form the binuclear tertiary complexes Cu2L(NH3)24+, Cu2L(SCN)3+ and Cu2L(N3)3+. The equilibrium constants show a special stabilisation of the complexes with ligands able to bridge the CuII centres, with a maximum stabilisation for azide. Upon addition of an excess of acid, all the complexes decompose with release of Cu2+ and the protonated ligands. The kinetics of the acid-promoted decomposition have been studied under pseudo-first order conditions of excess acid. The decomposition of the OHâ, SCNâ and NH3 complexes is first order with respect to H+, although with a clear tendency to saturation, and the values
of the rate constants depend on the nature of the ancillary ligand. In contrast, Cu2L(N3)3+ decomposes with a second order dependence on the acid concentration. These results are interpreted in terms of modifications induced by the ancillary ligand in the kinetics of the acid-assisted dissociation of CuâN(cryptate) bonds. Depending on the steric requirements of the ancillary ligand, the CuâN(cryptate) bonds are strained at different degrees and the more distorted complexes decompose faster. In the case of azide, there is an optimum fit between the ancillary ligand and the Cu2L4+ site that causes a change in the rate-determining step from dissociation of the first CuâN bond to the second.
溶液研究表明,Cu2L(OH)3+ 复合物(其中 L 是一个大的八氮杂隐含体)与 NH3、KSCN 和 NaN3 反应生成双核三级复合物 Cu2L(NH3)24+、Cu2L(SCN)3+ 和 Cu2L(N3)3+。平衡常数显示,能桥接 CuII 中心的
配体对配合物具有特殊的稳定作用,
叠氮化物的稳定作用最大。加入过量的酸后,所有络合物都会分解,释放出 Cu2+ 和质子化
配体。我们在过量酸的伪一阶条件下研究了酸促进分解的动力学。相对于 H+,OHâ、SCNâ 和 NH3 复合物的分解是一阶的,尽管有明显的饱和趋势,而且速率常数的值取决于辅助
配体的性质。相反,Cu2L(N3)3+ 的分解与酸浓度呈二阶关系。这些结果可以从辅助
配体对 CuâN(隐酸盐)键的酸性解离动力学所引起的改变来解释。根据辅助
配体的立体要求,CuâN(隐胞酸盐)键在不同程度上受到约束,扭曲程度越高的配合物分解得越快。在
叠氮化物的情况下,辅助
配体和 Cu2L4+ 位点之间存在最佳配合,导致决定速率的步骤从第一个 CuâN 键的解离转变为第二个 CuâN 键的解离。