Eight-coordinate molecules shape

P2, Z =2 Dx = 1.771, 1.773 R = 0.038 for 1,321 intensities, 0.036 for 2,283 intensities. The proton attached to 0-3 is that removed on salt formation. The ring is planar within 0.05 A (5 pm). The shapes of the side chains of the two ions are different, with 0-4-C-4-C-5-0-5 torsion angles of 56 and 170°, respectively. The other conformational angle of the side chain, 0-5-C-5-C-6-0-6, is 47° in both molecules. The calcium ion is eight-coordinated, in a distorted, square anti-prism, by six oxygen atoms from three L-ascorbate ions and by two water molecules. 

As is shown in Fig. 2.78, the SgO molecule is an eight-membered crown-shaped Sg ring to which an oxygen atom is bonded (Q symmetry). Steudel and coworkers have measured the IR/Raman spectra of SgO and made complete assignments based on normal coordinate analysis [1757,1758]. These workers also reported the Raman spectra of S9O and S iqO, which may acquire similar ring structures [ 1750]. The Raman... 

The (SNH)4 molecule forms the eight-membered crown-shaped of 4 symmetry shown in Fig. 2.78. Figure 2.79 shows the Raman spectra of (SNH)4 and (SND)4 obtained by Steudel and Rose [1770], who have made complete band assignments based on normal coordinate analysis. Later, Steudel further confirmed their assignments by substitution [1771]. Trisulfurdinitrogendioxide (S3N2O2) takes... 

Fig. 18. The hydrogen-bonded sheet structure of l,l,5,5-tetrakis(hydroxydimethylsi-loxy)-3,3,7,7-tetraphenylcyclotetrasiloxane. Note the crown-shaped eight-membered rings of oxygen atoms at the junctions where four of the molecules meet. All hydrogen and carbon atoms have been omitted for clarity. Drawn using coordinates taken from the Cambridge Crystallographic Database.

Comparative absorption spectrophotometry has been used in the studies of lanthanide /J-diketonatc complexes in solids as well as in solutions. The neutral hexacoordinated lanthanide tris diketonate on dissolution in a polar nonaqueous solvent, increased its coordination to eight by accepting two solvent molecules [204]. The addition of water or other oxygenated solvent to Nd(diket)3 in solution resulted in significant changes in the shape and intensity of the band due to 4l9/2 —> 4Gis/2, transition. These changes have been attributed to an increase in coordination number of Nd(III) from 6 to 8 by the coordination of two solvent molecules [238-241]. 

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