Sorption of benzene vapors to flexible metal-organic framework [Zn2(bdc)2(dabco)]

The isotherms of benzene sorption by the metal-organic coordination polymer [Zn-2(bdc)(2)(dabco)] were studied within the temperature range 25-90 A degrees C at pressures up to 75 torr. The maximal benzene content in [Zn-2(bdc)(2)(dabco)] at room temperature was demonstrated to correspond to the composition [Zn-2(bdc)(2)(dabco)]center dot 3.8C(6)H(6). It was established that the process of benzene desorption from the substance under investigation occurs in three stages. (1) Evaporation of benzene from the phase of variable composition (phase C) with compression and distortion of the unit cell (the composition of the phase C varies from [Zn-2(bdc)(2)(dabco)]center dot 3.8C(6)H(6) to [Zn-2(bdc)(2)(dabco)]center dot 3.2C(6)H(6)). (2) The transformation of the phase C into phase P. The phase P has the same unit cell geometry as that for the empty framework. The maximal benzene content is [Zn-2(bdc)(2)(dabco)]center dot 1.0C(6)H(6). (3) Benzene evaporation from the phase P of variable composition. We studied the temperature dependences of the equilibrium vapor pressure of benzene for the samples with compositions [Zn-2(bdc)(2)(dabco)]center dot 3.0(3)C6H6 and [Zn-2(bdc)(2)(dabco)]center dot 2.0(3)C6H6 within the temperature range 290-370 K. The thermodynamic parameters of benzene vaporization were determined for the latter compound (Delta H-av.(0) - 49 (1) kJ (moleC(6)H(6))(-1); Delta S degrees(av.) = 100(3) J(moleC(6)H(6)K)(-1); Delta G degrees(298) = 19.0(2) kJ(moleC(6)H(6))(-1)).