The increasingly diverse and advanced applications of materials necessitate new strategies that can combine widely disparate components to provide unique properties and functions. However, the combination of structurally and functionally diverse organic compounds remains challenging owing to structural mismatches. Herein, we demonstrate the engineering of organic molecule-ionic solids (OMISs) using strong ionic interactions to overcome the structural obstacles to inventing new functional materials. We designed a series of multiply charged organic cations and anions having organic skeletons that are mismatched in size, shape, symmetry, flexibility, and characteristics. In water, they formed ion-pair complexes with stoichiometric charges. Structural analysis confirmed the molecular-level combination of ion pairs mainly through ionic interactions. Therefore, the OMISs gained novel and/or enhanced functions different from those of their constituents. The universality of this work demonstrates that myriad new molecular materials can be discovered through this combinatorial approach owing to the diversity of organic compounds.