Here we describe the synthesis and magnetic characterization of a family of 2D polymetallic oxalate-bridged polymeric networks with general formula [M(II)(H(2)O)(2)](3)[M(III)(ox)(3)](2)(18-crown-6)(2) (M(III) = Cr, Fe; M(II) = Mn, Fe, Co, Ni; 18-crown-6 = C(12)H(24)O(6)). Depending on the nature of the trivalent metal ion, they exhibit ferro- (Cr(3+)) or ferrimagnetic (Fe(3+)) ordering in the 3.6-20 K interval. In contrast with most of the oxalate-bridged CPs reported so far, these complexes do not need any additional templating cation for their assembly and represent the first series of oxalate-based polymeric networks which can be considered intrinsically neutral. As previously observed for other crown ether containing oxalate-based coordination polymers, these compounds are soluble in water, whereas they remain nonsoluble in other organic solvents. Furthermore, when these molecular precursors are subjected to a thermally controlled decomposition process, pure phases of mixed oxides with spinel-like structures can be conveniently generated. Among the resulting materials, the (Mn,Co,Fe)(3)O(4) derivative is particularly remarkable, since it behaves as a magnet at room temperature. Finally, taking advantage of the solubility of these molecular precursors, this room-temperature magnetic oxide has been successfully nanostructured onto a Si(110) substrate via the lithographically controlled wetting (LCW) technique.