The energy barrier for magnetization reversal of a molecular magnet (i.e. SMM or SCM) is intimately related to the zero-field splitting characteristics (D) of its individual building units. However, it is still challenging for chemists to control the actual magnetic anisotropy of the complexes, all the more so when they get involved in the construction of heterometallic magnets. We will discuss our approach using heptacoordinates 3d metal with pentagonal bipyramid geometry (Figure). In this environment FeII and NiII complexes are characterized by significant Ising-type anisotropy (i.e. D ~-15 cm-1) [1] and may even behave as single-center nanomagnets [2]. Taking advantage of their exchangeable apical positions, heteronuclear compounds were obtained and indeed found to exhibit slow magnetic relaxation [3]. We aimed also at optimizing two other parameters of importance in nanomagnets, namely the co-alignment of the axis of anisotropy and reduced inter-molecular interactions. This resulted in a CrFe single chain magnet characterized by an energy gap for the magnetization reversal of delta/kB = 113 K [4].