Two hybrid salts, viz. bis (guanidinium) bis (oxalato) cuprate (II)(1) and bis (2-aminopyridinium) bis (oxalato) cuprate (II) trihydrate (2) have been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction and SQUID magnetometry. Compounds 1 and 2 crystallize in the monoclinic P2 1/c and triclinic P 1¯ space groups, respectively. In both structures, the four-coordinated Cu (II) ion in [Cu (C 2 O 4) 2] 2− unit weakly interacts with two axial O-atoms of neighboring units to build a prolate CuO 6 octahedron, with regular axial Cu–O bonds of 2.825 Å in 1, whereas in 2 two different Cu–O bonds (2.814 Å and 2.701 Å) are found. In 1, stacking of [Cu (C 2 O 4) 2] 2− units across internal symmetry-related O-atoms results in equidistantly spaced monomers, thus forming straight Cu (II) chains with regular spacing of Cu⋯ Cu= 3.582 Å. By contrast, in 2, stacking of the [Cu (C 2 O 4) 2] 2− entities occurs via external symmetry-related O-atoms, yielding zigzag Cu (II) chains with shorter intra-dimer spacing of [Cu⋯ Cu] intra= 3.430 Å and longer inter-dimer spacing of [Cu⋯ Cu] inter= 4.961 Å. The anhydrated compound 1 is stable up to 250° C, whereas the hydrated compound 2 shows a significant weight loss of solvent water molecules at about 70° C, followed by the decomposition of the network. The magnetic measurements in the 2–300 K temperature range revealed weak antiferromagnetic coupling in the two hybrid salts.