The oxonate dianion has been coupled to divalent transition metal ions, allowing the isolation of coordination polymers of formula M(Hoxonato) n · xnH 2O (M = Mn, Co, Ni, Zn), Zn(Hoxonato)(bpy) 0.5 n · nH 2O and Ni(Hoxonato)(bpy) n ·6 nH 2O. The latter, after thermal activation, is capable to selectively adsorb carbon dioxide over methane. Display omitted ► Isolation and characterization of oxonate-containing coordination polymers. ► Retrieval of key structural features and responses to temperature by XRPD. ► Selective capture of the greenhouse gas CO 2 over CH 4. Four novel coordination compounds of formula M(Hoxonato) n · xnH 2O ( 1 M ⊂ x H 2O ; H 3oxonic: 4,6-dihydroxy-1,3,5-triazine-2-carboxylic acid; M = Mn, Co, Zn, x = 3; M = Ni, x = 4) were prepared and characterized. The isomorphous Mn(II), Co(II) and Zn(II) derivatives contain densely packed 1D helical chains. To increase the dimensionality of these systems, the M(Hoxonato) n secondary building unit was coupled to rod-like N, N′-spacers, allowing the isolation of Zn(Hoxonato)(bpy) 0.5 n · nH 2O ( 2 Z n ⊂ H 2O ; bpy: 4,4′-bipyridine) and Ni(Hoxonato)(bpy) n ·6 nH 2O ( 3 Ni ⊂ 6H 2O ). The M(Hoxonato) n chains are pillared by the bpy spacers within 2D corrugated layers in the former, into 2D rectangular grid layers in the latter. The thermal behavior of all the species was investigated by coupling simultaneous thermal analysis and thermodiffractometry. Static gas adsorption measurements with N 2 (77 K) and CO 2 (273 K) revealed that activated 3 Ni ⊂ 6H 2O possesses permanent porosity. Dynamic gas separation studies towards CH 4:CO 2 mixtures (0.73:0.27 v/v, 273 K) proved that this system is able to selectively capture CO 2 up to 0.16 mmol per gram of material.