The hydrothermal syntheses, single-crystal X-ray structures and magnetic properties of [Co(C4O4)(H2O)(2)] (1), [Co-3(OH)(2)(C4O4)(2)] center dot 3H(2)O (2) and [Fe(OH)(2)(C4O4)] (3) are described. Pale yellow cubes of 1 and brown red crystals of 2 were obtained from the reaction of Co(OH)(2) and squaric acid at 200 degrees C. Brown needle of 3 were obtained similarly from Fe(SO4) center dot 7H(2)O, squaric acid and NaOH. 1 consists of a cubic sodalite arrangement with empty cavities where the Co atoms are connected by mu(4)-squarate and two trans-water molecules each, while 2 and 3 contain metal-hydroxide double-chains of edge-sharing octahedral, brucite-type for 2 and goethite for 3, connected by mu(6)-squarate. 2 contains water molecules in the channels which can be removed and re-inserted repeatedly without loss of crystallinity. All three compounds possess 3D frameworks made up of coordination and hydrogen bonds. 1 behaves as a paramagnet while 2 and 3 are antiferromagnets and 2 transforms to a ferromagnet reversibly upon dehydration and rehydration. The structures of two one-dimensional polymers employing 2,5-pyridinedicarboxylate, [Co-2(H2O)(6)(2,5-pydc)(2)] center dot 2H(2)O (4) and Cu(2,5-pydc)(2) (5), are also reported.