Crystal transformation synthesis of a highly stable phosphonate MOF for selective adsorption of CO2

A 2D phosphonate MOF {[Ni(Hptz)(2)]center dot 7H(2)O}(n) (H(2)ptz = 4-(1,2,4-triazol- 4-yl) phenylphosphonic acid) (2) is obtained through crystal transformation from a trinuclear compound [Ni-3(Hptz)(6)center dot(H2O)(6)]center dot 9H(2)O (1). Studies of chemical stability show that 2 retains its crystallinity in boiling water and organic solvents. 2 also exhibits high adsorption capacity for CO2 (80 cm(3)(STP) g(-1)) and selective separation of CO2 over N-2.