In this work we report the structural and magnetic characterization of a new three-dimensional porous metal-organic framework (MOF) based on iron(III) and the formate anion, [Fe(HCO2)(3)](n)center dot nHCO(2)H (1), which was obtained by solvothermal synthesis. The tridimensional structure crystallizes in the trigonal space group R (3) over barc and is formed by highly regular octahedral Fe(OHCO)(6) units. These units contain six equal Fe-O distances, with angles slightly different from 90 degrees or 180 degrees. The packing of 1 corresponds to a 3D covalent network defined by face sharing between the parallelepipeds, which are formed by the interactions of Fe(OHCO)(6) units through formate ligands, thus generating a 4(12)6(3) topology. This topology contains channels in the three spatial directions, in which it is possible to find guest molecules of formic acid. The thermogravimetric analysis shows that 1 remains stable till 180 degrees C; after this temperature the decomposition of 1 begins. From a magnetic point of view, the reported MOF presents an antiferromagnetic behaviour in the 296 to 20 K range. The fit of the experimental data between room temperature and 50 K, using the high temperature series model (HTS model), permits us to estimate a J value of -1.01 cm(-1), which is in agreement with the reported values for analogous systems based on transition metal ions and formate ligands. Below this temperature, a weak ferromagnetism as a product of spin canting was observed due to the anti-anti coordination mode of the bridging ligand, which satisfies the requirement for Dzyaloshinsky-Moriya antisymmetric interactions between the Fe-III ions. The isothermal magnetization obtained at 2 K shows that the magnetization increases linearly with the applied magnetic field, reaching a value of 0.49N beta at the highest applied field of 50 kOe, indicating the antiferromagnetic character of the ground state. DFT calculations using a dinuclear fragment confirm the magnitude and nature of the magnetic phenomena of this extended system at high temperatures.