介质协萃效应（Ⅱ）

Synergistic Effects in Extraction Substrates (Ⅱ)

根据空间效应，配置在铀酰赤道平面的配位体不应过挤或过松，可用配位体扇面角和（ＦＡＳ）作估算。ＵＯ２（ＯＡｃ）Ｂｒ（ＴＢＰ）２的ＦＡＳ为１８０°：空间配位最佳，预计形成更稳定的萃合物而呈现更高萃取率。用醋酸钠─醋酸和溴化钠混合介质萃取铀酰离子证实上述预测。保持阴离子总浓度恒定，醋酸根与溴化物浓度比为ｌ：ｌ０时出现协萃效应。用斜率法确证萃合物组成与预测一致。

Based on the steric effect,ligand packing around the uranyl equatorial plane should be neither overcowded nor undercrowded. The sum of Ligand's Fan Angle(FAS)around the uranyl equatorial plane provides a useful criterion for estimating steric crowding.FAS of UO2(OAc)Br(TBP)2 is 180°indecating the most favorable packing. It is therefore expected that a higher extraction efficiency should coincide with the formation of the more stable complex. The above speculation was confirmed by extraction of uranyl ion in the substrates of sodium acetate-acetic acid and sodium bromide. Keeping the total concentration of substractes constant, synergistic extraction is found at l:10 acetate to bromide ratio. The extracted complex was proved to be UO2(OAc)Br(TBP)2 by using the slope method.