冠醚的空腔及其与希土硝酸盐配合物结构的关系

CAVITY OF THE CROWN ETHER AND ITS RELATIONSHIP WYYH THE STRUCTURE OF RARE EARTH NITRATE COMPLEXES

本文计算了五十多种希土硝酸盐冠醚配合物中冠醚的空腔直径Ｄｃ及希土离子直径（Ｄｉ）与Ｄｃ之比值（Ｄｉ／Ｄｃ）．冠醚的空腔受许多因素影响．诸如希土元素的离子半径，希土离子与冠醚之间的结合力，冠醚环上的取代基等．Ｄｉ／Ｄｃ数值所处的范围与所形成的配合物结构类型密切相关，遵循下列四个近似规则：（１）如Ｄｉ／Ｄｃ＞１．４，所形成的配合物结构中三个阴离子占据冠醚的同一侧（结构类型Ⅰ）；（２）若０．８＜Ｄｉ／Ｄｃ＜０．９，配合物中金属离子被包围在冠醚空腔中．三个阴离子占据冠醚环的两侧（结构类型Ⅱ）；（３）如Ｄｉ／Ｄｃ＜０．８，配合物中冠醚分了一般与配位水分子以氢键相连（结构类型Ⅲ）；（４）若０．９＜Ｄｉ／Ｄｃ＜１．４，配合物一般为结构类型Ⅲ，在某些情况下也可为结构类型Ⅳ，它由几个配位阴离子及一个多硝酸根配阴离子形成．

avity diameters of the crown ether (Dc) and ratios of rare earth ionic diameter(Di)to Dc (Di/ Dc)for over fifty rare earth nitrate complexes have been calculated.The crown cavity is affected by many factors, such as the ionic radius of the rare earth clement, the bonding force between the crown ligand and the RE(Ⅲ) ion, the substitutes on the crown ring, et al. The range of the Di / Dc value is closely related to the type of complex formed. Four approximate rules hold: (1) if Di/ Dc >1.4,the complex formed has a structure in which three anions occupy the same side of the crown ether (struct.type Ⅰ),(2) if 0.8 < Di / Dc< 0.9, the metal ion in the complex isolated is most possibly encapsulated in the crown cavity with three anions residing on the two opposite sides of the crown ether (struct. type Ⅱ); (3) if Di / Dc< 0.8,the crown ligand in the complex is probably hydrogen bonded with the coordinated water molecules (struct. type Ⅲ); (4) if 0.9 < Di / Dc <1 .4, the structure of complex generally belongs to struct. type Ⅲ, in some cases it can be of struct. type Ⅳ which is composed of complex cations and a polynitrato anionic spccies.