this invention describes a new type of covalent - network ternary inorganic metal sulfide compounds m 1 m 2 s 4 and a process for preparing the biocompatible nanoparticles of such compounds . the nanoparticles are surface - modified with a capping agent and / or a biocompatible polymer and have the size from a few nanometers to several thousand nanometers . these nanoparticles are nontoxic and can be internalized by cells to deplete copper ions via a highly selective ion - exchange reaction between the intracellular copper ions and the divalent ion bound in the nanoparticles for the application of inhibiting angiogenesis in cancer and other diseases .