Eight-coordinate molecules square antiprismatic

The malonate complex of Eu(III), Eu2(malonate)3 8H2O is interesting since there are two different coordination geometries, and only five of the water molecules are coordinated [167], One of the Eu ions is eight-coordinate in the form of a distorted square antiprism and the other Eu ion is nine-coordinate, distorted tricapped trigonal prism. In the analogous neodymium complex, six water molecules are coordinated because of the difference in ionic radius. The neodymium complex is nine-coordinate with monocapped antiprismatic geometry [168]. 

Another route to complete halide extraction involves the use of SbCls and SbCls together (see Scheme (4)). The cation contains a Sc " " ion sandwiched between two 12-crown-4 molecules in approximately square antiprismatic eight-coordination with Sc—O distances in the range 2.160(8)-3.274(9)A, averaging... 

Structural pictures of the systems studied. A detailed analysis of the first coordination shell [67] showed that for the light lanthanide ions (Nd " "), the nine water molecules form a tricapped trigonal prism similar to that found by solid state X-ray diffraction studies on [Ln(H20)9] + with counterions CF3SOJ, EtOSO, and BrO [68j. The eight H2O molecules in contact with the smaller heavy lanthanide ions (Yb +) form a square antiprismatic geometry with equal ion-oxygen distances. 

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