Trend of variation of hydration number of tris[β-diketonato]lanthanoids(III) in chloroform across lanthanoid series

The hydration number of tris[pivaloyltrifluoroacetonato]lanthanoids(III) (Ln(PTA)3) has been determined across the lanthanoid series on the basis of the water content in the Ln(PTA)3/chloroform solution saturated with water measured by Karl–Fischer coulometory. The hydration number of Ln(PTA)3 was between 2.0 and 2.5 across the series. The number seems to increase slightly from La to around Tb, and then decrease towards the heavy lanthanoids. It may reflect the change in the size as well as in charge density of lanthanoids(III).