Described herein are improved 3D printing methods for fabricating structures made of metals, including metal alloys, and dielectrics. Such structures may be used in various components of integrated circuits, such as e.g. interconnects, interlayer dielectrics, electrodes, and transistors. Methods provided herein are based on using reactive inks comprising molecular metal and dielectric precursors that react to form desired resulting materials once deposited on a print surface, i.e. 3D printing inks that need to react on the print surface in order to form the desired materials. Through the use of reactive inks, strong covalent or metallic bonds can be formed between printed layers, leading to more robust structures with improved isotropic properties. Because molecular precursors are reacted on the print surface, dense continuous traces may be fabricated. In addition, molecular precursors proposed herein enable 3D printing of intricate structures, e.g. with intricate internal cavities, made of materials with unique compositions.