Selective collection of Yb(iii) over La(iii) and Eu(iii) from aqueous solution by bis(tetramethylammonium) salt crystals of p-tert-butylcalix[4]arene-1,3-diphosphonic acid

Crystals of the bis(tetramethylammonium) salt of p-tert -butylcalix[4]arene-1,3-diphosphonic acid have been prepared for the selective collection of Yb( iii ) over La( iii ) and Eu( iii ) from aqueous solution under thermodynamic control.