Cooperation and frustration. In a molecular complex, cooperation is the energetic gain of the complex due to the formation of a larger complex, whereas frustration is the sacrifice paid by individual molecules to form such a complex. They are the two sides of the same coin, with the former focusing on the systems level and the latter on the individual component. Recently, for a complex with n building blocks ABn, where B is the building block and A is the axillary component, we employed the interaction energy per building block, En, to quantify the cooperativity effect ,