Novel 3d/4f heterometallic three-dimensional (3D) networks, based on Co-II/Gd-III cations and imidazole-4,5-dicarboxylic acid (H3IDC) and oxalate which are acting as main and auxiliary ligand, respectively, were hydro-/solvothermally synthesized using different synthetic strategies. While [Gd (H2O) (C2O4) Co (IDC) (H2O)(1.26)(-) (CH3CH2OH)(0.74)]center dot 1.75H(2)O (1) was obtained in a one-pot synthesis, [Gd(H2O)Co(HIDC)(C2O4)(1.5)]center dot 2.65H(2)O (2) was obtained using a Co-II complex precursor. Both compounds crystallize in a monoclinic system within the centrosymmetric space group C2/c. These structures are characterized by presenting an intricate covalent 3D network. A notable aspect is the fact that in these centrosymmetric structures Co-II(IDC/HIDC) moieties are disposed along the networks forming alternate chiral chains, A and A. From a magnetic point of view, both (1) and (2) have antiferromagnetic interactions, but in (1) a magnetic order appears below 8 K, probably as product of uncompensated antiferromagnetic interactions produced by centers with different spin values. This ferrimagnetic behavior was verified by the hysteresis curve at 1.8 K, and by well-defined maxima, both in the in-phase and out-of-phase ac susceptibilities curves. Remarkably, this work reports efficient synthetic methods through which it is possible to generate 3d/4f networks, these being scarce in the literature.