Fig. 1. Comparison of heteroleptic self-assemblies based on square-planar metal cations. (a) Supramolecular rectangle [{M(en)}₄L^A₂L^B₂] formed from cis-protected cations with two different ligands, (b) [M₂L^AL^BL^CL^D] cage formed from ‘naked’ cations and four different ligands.