Editing Lanthanide (section)

====Ln(III) compounds====
The trivalent lanthanides mostly form ionic salts. The trivalent ions are [[hsab theory|hard]] acceptors and form more stable complexes with oxygen-donor ligands than with nitrogen-donor ligands. The larger ions are 9-coordinate in aqueous solution, [Ln(H<sub>2</sub>O)<sub>9</sub>]<sup>3+</sup> but the smaller ions are 8-coordinate, [Ln(H<sub>2</sub>O)<sub>8</sub>]<sup>3+</sup>. There is some evidence that the later lanthanides have more water molecules in the second coordination sphere.<ref>{{cite book|last=Burgess|first=J.|title=Metal ions in solution|publisher=Ellis Horwood|location= New York|year=1978|isbn=978-0-85312-027-8}}</ref> Complexation with [[monodentate]] ligands is generally weak because it is difficult to displace water molecules from the first coordination sphere. Stronger complexes are formed with chelating ligands because of the [[chelate effect]], such as the tetra-anion derived from 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid ([[DOTA (chelator)|DOTA]]).

:[[File:Lanthanide nitrates.png|thumb|650px|center|Samples of lanthanide nitrates in their hexahydrate form. From left to right: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.]]
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