This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.

This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.

Focusing on case studies relevant to solar energy conversion, the replacement of lead with a layer of germanium or isolated germanium atoms in CsPbCl3 and CsPbBr3, we develop a novel geometric approach to design optimal environments for perovskite dopants. In doing so, we extend the sphere-packing arguments that motivate Goldschmidt tolerance factors beyond bulk ABX3 perovskite compounds to doped and substituted perovskite superstructures. To assess the stability of our proposed superstructures relative to competing phases and structural distortions, we compute total energies and phonon frequencies using density functional theory (DFT)-based methods. We extend these ideas toward the formulation of a generalized tolerance factor that applies to perovskite dopant environments and identify superstructures in which the stability of these dopants is significantly improved relative to the bulk parent compounds. This approach holds promise in uncovering general design rules for stable doped perovskites.

A strained, "springloaded" FeL iminopyridine mesocate shows highly variable reactivity upon postassembly reaction with competitive diamines. The strained assembly is reactive toward transimination in minutes at ambient temperature and allows observation of kinetically trapped intermediates in the self-assembly pathway. When diamines are used that can only form less favored cage products upon full equilibration, trapped ML fragments with pendant, "hanging" NH groups are selectively formed instead. Slight variations in diamine structure have large effects on the product outcome: less rigid diamines convert the mesocate to more favored self-assembled cage complexes under mild conditions and allow observation of heterocomplex intermediates in the displacement pathway. The mesocate allows control of equilibrium processes and direction of product outcomes via small, iterative changes in added subcomponent structure and provides a method of accessing metal-ligand cage structures not normally observed in multicomponent Fe-iminopyridine self-assembly.

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