The structures of four new compositionally related compounds are described; [Cu(en)2(H2O)2][ox] (1), [Cu(en)3][ox] (2), [Co(en)3]2[ox]3(H2O)3.61 (3), and [Co(en3)]2[ox]3(H2O)7 (4) [en = 1,2-ethylenediamine, ox = oxalate]. These materials all inhabit the broader structural landscape for compounds with a generic Mp(ox)q(en)r(H2O)s composition. Here the competing nature of the ligands; ethylenediamine, oxalate and water, results in complex solution chemistry. In addition the very different structure directing effects of each type of ligand yield a range of crystal architectures. In the present cases ethylenediamine displaces the oxalate dianion, which is non-coordinated in each of these compounds. Compound 3 has disordered water of crystallisation, and is a non-stiochoimetric hydrate, while compound 4 shows a correlated disorder in both ligand conformation and water site occupancies. The H-bond motifs linking pseudo 3-fold symmetric M(en)3n+ cations to pseudo 2-fold symmetric ox2- anions shows frequent occurrence of particular motifs; notably the R22(8) and R22(9) graphs and a tendency to form bifurcated hydrogen bonds. The oxalate geometric parameters of twist and C-C bond length in our compounds are correlated with data from related structures in the CSD.