Secondary sphere interactions from proximal phenyl side chains control the anion selectivity of dimeric Ln(III)[15-MCCu(II),α-aminoHA-5]3+ metallocavitands. CH–O interactions, which are only possible with certain side chains, are sufficient for overcoming an intrinsic energy barrier to binding saturated dicarboxylates in hydrophobic compartments.
![Graphical abstract: Selective anion encapsulation in solid-state Ln(iii)[15-metallacrown-5]3+ compartments through secondary sphere interactions](http://hg.y866.cn/compound/lib/scimg/usr/1/C3DT50535A.jpg)
