Spin crossover compounds have attracted considerable research interest over the last few years due to their great potential for technological use in memory, sensors, switching, and display devices. They manifest a diverse phase transition behavior upon application of various physical stimuli, such as, heat, light, and pressure. The theoretical framework of this study is the so-called atom-phonon coupling model, which presumes elastic interactions between nearest-neighbor molecules with elastic constants depending on the electronic state of each molecule. The atom-phonon coupling model has been successful in approximating characteristics of the spin crossover compounds behavior, but has only been applied to a chain of molecules. In this paper we present results obtained for compounds with a 2D structure and we study the role of the elastic constants ratio on the phase diagram. © 2011 American Institute of Physics.