The porous magnet [Fe3(HCOO)6], the iron member of the [M3(HCOO)6] family (where M = Mn, Fe, Co, Ni, etc.), based on a diamond framework consisting of Fe-centered FeFe4 tetrahedral nodes, is prepared successfully by using a solution-chemistry method. The as-prepared compound, [Fe3(HCOO)6](CH3OH)1.5(H2O)0.5 (1-parent), exhibits facile removal of its guests, methanol, and water, to give the desolvated framework [Fe3(HCOO)6] (2-empty) that displays permanent porosity and thermal stability up to 270 °C. The flexibility of the framework and the amphiphilic nature of the surface of the pores consisting of both C–H and O arrays allows 2-empty to take up significant H2 and N2 at liquid-nitrogen temperatures and a wide spectrum of both polar and nonpolar guests of different sizes. A series of guest-inclusion compounds, [Fe3(HCOO)6](I2)0.84 (3-iodine), [Fe3(HCOO)6](C4H8O) (4-THF), [Fe3(HCOO)6](C4H4O) (5-furan), [Fe3(HCOO)6](C6H6) (6-benzene), [Fe3(HCOO)6](CH3CN) (7-acetonitrile), and [Fe3(HCOO)6]((CH3)2CO) (8-acetone) are successfully prepared by vapor diffusion of the guest into the pores of 2-empty and their structures are characterized by using single-crystal X-ray crystallography. Zigzag molecular arrays of the guest are formed in the confined channels of the host framework, and the weak hydrogen-bonding provides the main host–guest interaction. All the compounds show 3D long-range magnetic ordering and guest-modulated Curie temperatures, coercive fields, and remnant magnetization as a consequence of the subtle rearrangement of the magnetic framework that conforms to the size of the guests and the difference in host–guest interactions. A possible magnetic structure of the framework is proposed to account for magnetic competition and geometrical frustration. The thermal and spectroscopic properties of the compounds are also reported.