A possible deduction is proposed of channel length distribution in one-dimensional porous materials from the kinetic data obtained in isothermal thermogravimetry (TG). The method utilizes the absorption/desorption of small molecules into one-dimensional nano-channel. In the surface-controlled absorption/desorption, the second derivative with respect to time is directly proportional to the channel-length distribution function. Even in the diffusion-controlled case, the second derivative with respect to the square root of time gives rough information on the distribution function.
(J. Therm. Anal. Calor., 92, 391-394 (2008))
Three new coordination polymers, [CoCl2(4-pmna)2]n, {[Co(NCS)2(4-pmna)2].2Me2CO}n, and {[Co(4-pmna)2(H2O)2](NO3)2.2CH3OH}n (3 with 2H2O.2MeOH) [4-pmna = N-(pyridin-4-ylmethyl)nicotinamide], have been synthesized and characterized using single-crystal X-ray diffraction. The cobalt(II) atoms are bridged by 4-pmna ligands in all three compounds to form double-stranded one-dimensional "repeated rhomboid-type" chains with rectangular-shaped cavities. In [CoCl2(4-pmna)2]n, each chain slips and obstructs the neighboring cavities so that there are no guest-incorporated pores. Both {[Co(NCS)2(4-pmna)2].2Me2CO}n and {[Co(4-pmna)2(H2O)2](NO3)2.2CH3OH}n do not have such a staggered arrangement and have pores that can be filled with a guest molecule. Compound {[Co(4-pmna)2(H2O)2](NO3)2.2CH3OH}n traps guest molecules with multiple hydrogen bonds and shows a reversible structural rearrangement during adsorption and desorption. The new crystalline compound, 3, is stabilized by forming hydrogen bonds with the amide moieties of the 4-pmna ligands and was characterized using infrared spectroscopy. The clathration enthalpy of the reaction 3 + 2H2O(l) + 2MeOH(l) <-> {[Co(4-pmna)2(H2O)2](NO3)2.2CH3OH}n (ca. 35 kJ/mol) was estimated from differential scanning calorimetry data by considering the vaporization enthalpies of H2O and MeOH. The desorption process of {[Co(4-pmna)2(H2O)2](NO3)2.2CH3OH}n -> 3 follows a single zero-order reaction mechanism under isothermal conditions. The activation energy of ca. 100 kJ/mol was obtained by plotting the logarithm of the reaction time for the same reacted fraction versus the reciprocal of the temperature. Moreover, the distribution of the one-dimensional channels in {[Co(4-pmna)2(H2O)2](NO3)2.2CH3OH}n was estimated using the observation that the reaction rate is directly proportional to the total sectional area.
(J. Am. Chem. Soc., 128, 16122-16130 (2006))