From 1D homoleptic to 2D heteroleptic pillared coordination polymers containing oxonato bridges

Four novel coordination compounds of formula [M(Hoxonato)]n·xnH2O (1M⊂xH2O; H3oxonic: 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·nH2O (2Zn⊂H2O; bpy: 4,4′-bipyridine) and [Ni(Hoxonato)(bpy)]n·6nH2O (3Ni⊂6H2O). 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 N2 (77 K) and CO2 (273 K) revealed that activated 3Ni⊂6H2O possesses permanent porosity. Dynamic gas separation studies towards CH4:CO2 mixtures (0.73:0.27 v/v, 273 K) proved that this system is able to selectively capture CO2 up to 0.16 mmol per gram of material.

Graphical abstractThe oxonate dianion has been coupled to divalent transition metal ions, allowing the isolation of coordination polymers of formula [M(Hoxonato)]n·xnH2O (M = Mn, Co, Ni, Zn), [Zn(Hoxonato)(bpy)0.5]n·nH2O and [Ni(Hoxonato)(bpy)]n·6nH2O. The latter, after thermal activation, is capable to selectively adsorb carbon dioxide over methane.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► 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 CO2 over CH4.