The vibrations inside diatomic molecules are well modeled by the Morse potential and, therefore, the Morse nonlinear coherent states can be considered as approximations of diatomic molecules coherent states. Currently, the experimental realization of nonlinear coherent states for molecular systems is an interesting subject of investigation. In this paper, we analyze the nonclassical properties of different coherent states for a particle in the Morse potential. We find that the su(2) algebra can be generalized by using an appropriate monotonically increasing function and that the bound states of particular diatomic molecules can be well described by the introduced algebra. We construct two types of generalized su(2) coherent states satisfying all necessary requirements, mainly the resolution of identity, for the molecule 27Al1H. We notice an anti-bunching effect for both types of coherent states by analyzing the second order correlation function.