2nd coordination sphere

Solid-state NMR spectroscopy is a powerful technique for the determination of structure in amorphous solids and for species in solution. Extensive studies of NMR shieldings of electropositive or cationic atoms, such as Si, have established that shieldings are strongly influenced by the composition of the 1st coordination sphere and also show significant, consistent and easily measurable trends related to the identify and geometry of 2nd coordination sphere atoms. Atoms in the 3rd and more distant coordinate spheres generally have little effect upon the shielding. 

Fig. 14. The separation of the RDF for the 1 M erbium(III) chloride solution in Fig. 13 into a RDF involving only the metal ions (upper curve) and a reduced RDF for the remaining nonmetal interactions (lower curve). Theoretical peaks for eight water molecules (1st coordination sphere) and 16 water molecules (2nd coordination sphere) are shown for comparison (upper curve).

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