Much of modern materials science is underpinned by the ability to prepare crystalline phases of transition-metal compounds. Most such solids have been prepared by solution methods (eg for coordination framework materials [1] and salts of complex ions [2]) or by high-temperature (ceramic) methods for ionic solids (of monoatomic ions, oxides, etc.).[3] We report herein a range of modest-temperature, solid-state methods for the preparation of crystalline metal complexes in which the transformations between phases are achieved by chemical and mechanochemical procedures without the use of solutions. Such methods have been cited as providing “green” approaches to crystalline materials by minimizing solvent use, at least in this stage of the synthesis.[4] We have developed and applied a strategy for crystal synthesis based on molecular tectonics using charged building blocks (tectons).[5] In this approach, the crystalline product salts contain complex ions—typically anionic metal complexes and organic cations. The peripheral functional groups of the component tectons are chosen to allow control of their supramolecular interactions; in particular the ligands of complexes are hydrogen-bond acceptors such as halides, and the cations are protonated nitrogen bases such as pyridines. The resultant pyridinium perchlorometalate crystal structures therefore contain NH··· Cl-M interactions in well-defined arrangements such as A.