In this work, we propose a coalitional control solution for a multi-agent networked system. The idea is to use a flexible communication topology, in which the communication links are enabled or disabled between sub-systems, depending on their shared task. The control methodology is designed in an optimal control framework, by computing an optimal state feedback gain matrix corresponding to each communication topology. The proposed control algorithm was validated in simulation, and tested in real-time experiments using a heterogeneous vehicle platoon consisting of four mobile robots. Both simulation and experimental results illustrate the efficacy of our proposed methodology.