Using density functional theory with generalized gradient approximation for exchange and correlation potential we show that the magnetic coupling between Mn atoms in Mn2Cln molecular systems can be manipulated not only by varying the number of Cl atoms but also by doping simple metal atoms such as Li and Mg. The switching between antiferromagnetic to ferromagnetic couplings is brought about by competition between double exchange and superexchange mechanisms. Ability to control the magnetic coupling in molecular systems can have technological potential for future microelectronics. (C) 2012 Elsevier B. V. All rights reserved.