Unlike lanthanide ions, 1^st-order spin-orbit coupling (SOC) is cancelled by the ligand field for transition metal ions, and achieving high magnetic anisotropy is generally considered the Holy Grail for these ions. Results obtained with Fe(II) show that a contribution from first-order SOC coupling is not confined to low-coordination number complexes but can be implemented in a pentagonal bipyramid complexes (figure) by proper chemical design. This is confirmed by theoretical calculations and experimental magnetic behaviors consistent with the existence of large magnetic anisotropy, most salient feature being the SMM behaviors with large energy barriers for magnetization reversal. The observation of such a behavior without an applied static magnetic field is quite unique for a mononuclear 3d complex.