Here we report a new highly microporous zirconium phosphonate material synthesized under solvothemal conditions. The specific Brunauer-Emmett-Teller (BET) surface area of the "unconventional metalÀorganic framework" (UMOF) is measured to be~900 m 2 /g, after following an appropriate activation protocol. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows that the material bears a free ÀOH functionality on the phosphonate linker that may interact with CO 2 . CO 2 adsorption isotherms were collected and a measured heat of adsorption of 31 kJ/ mol was obtained. In addition, adsorption isotherms of CO 2 , N 2 , and CH 4 at 298 K combined with Ideal Adsorbed Solution Theory (IAST) show that the material can be expected to display high selectivities for uptake of CO 2 versus N 2 or CH 4 .Keywords: metal-organic frameworks · porous phosphonates · carbon dioxide capture · zirconium-based MOFs Experimental Section MaterialsAcetone (Macron, 98 %), N,N-dimethylformamide (DMF), hexanes (Macron, 99.8 %), dichloromethane (Macron, 99.0 %), deuterated dimethyl sulfoxide (d 6 -DMSO) (Cambridge Isotopes, 99 %), and deuterated sulfuric acid (Cambridge Isotopes, 96-98 % solution in D 2 O) were used as received without further purification. 1,3,5-tris(4-bromophenyl)benzene, triethyl[a] C.

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