New solid-state materials and devices may depend on ordered crystalline networks. But connecting crystals with various properties—such as color, magnetism, or porosity—while maintaining structural order is challenging. One approach is to capitalize on similarity in crystal structures to help weld crystals together, reports a team led by Mir Wais Hosseini and Sylvie Ferlay of the University of Strasbourg (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b10586). The researchers took advantage of a system in which an organic cation is paired with a metallic anion complex that contains Mn2+, Fe2+, Co2+, Ni2+, Cu2+, or Zn2+. The cation and anion interact through hydrogen bonds and electrostatic interactions to yield crystals that are similar in structure and unit cell dimensions, regardless of the metal they contain. The researchers then took two of one type of metallic crystal, immobilized them 45–255 µm apart, and immersed them in an unsaturated solution of building blocks containing a different metal. The original crystals served as seeds to allow a crystalline weld to grow between them, yielding a single crystalline product with discrete areas that have different properties.