The aim of this communication is to probe the possibility of increasing the barrier for reversal of magnetization in the family of new cyano-bridged pentanuclear Mn(III)2Mn(II)3 clusters in which single molecule magnet behavior has been recently discovered. In this context, we analyze the global magnetic anisotropy arising from the unquenched orbital angular momenta of ground terms3T1(t2 4) of the two apical Mn(III) ions. The model takes into account the trigonal component of the crystal field, spin-orbit interaction in 3T1(t24), and an isotropic exchange interaction between Mn(III) and Mn(II) ions. The height of the barrier is shown to be sensitive to the change of the trigonal field stabilizing orbital doublet 3E, which carries the first-order orbital magnetic contribution and enhances with an increase of the trigonal field. This result is expected to be useful for the more rational design of new cyano-bridged SMMs with high blocking temperatures.