Ligand-Shell Softness Directs Symmetry Transitions in Nanotripod Superstructures

Low-symmetry, nonconvex nanocrystals offer access to superlattices with structural motifs that are difficult to realize from convex building blocks. Here, we show that polymer-grafted Gd2O3 nanotripods assemble into compact achiral and open chiral nanoporous superstructures. By tuning tripod aspect ratio, polymer ligand length, and ligand shell architecture, we direct phase selection among p2, pmg, pgg, and p6 wallpaper symmetries. In the p6 phase, planar chirality emerges through arm-to-arm interlocking. Direct ligand exchange generates mixed ligand shells with softer effective interactions, expanding the accessible phase space beyond that obtained by two-step ligand exchange. Coarse-grained simulations incorporating ligand-mediated attractions reproduce the experimental phase behavior and identify competition between translational entropy and polymer-polymer enthalpic interactions as a key driver of phase selection. These results establish ligand shell softness as a tunable design parameter for coupling nonconvex particle geometry to long-range order, enabling porous and chiral nanocrystal superstructures beyond dense, high-symmetry packing.