Rights statement: This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01364
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Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Effect of Transition Metal Substitution on the Flexibility and Thermal Properties of MOF-Based Solid-Solid Phase Change Materials
AU - Griffiths, K.
AU - Halcovitch, N.R.
AU - Griffin, J.M.
N1 - This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01364
PY - 2021/9/6
Y1 - 2021/9/6
N2 - A series of azobenzene-loaded metal-organic frameworks were synthesized with the general formula M2(BDC)2(DABCO)(AB)x (M = Zn, Co, Ni, and Cu; BDC = 1,4-benzenedicarboxylate; DABCO = 1,4-diazabicyclo[2.2.2]octane; and AB = azobenzene), herein named M-1ABx. Upon occlusion of AB, each framework undergoes guest-induced breathing, whereby the pores contract around the AB molecules forming a narrow-pore (np) framework. The loading level of the framework is found to be very sensitive to the synthetic protocol and although the stable loading level is close to M-1AB1.0, higher loading levels can be achieved for the Zn, Co, and Ni frameworks prior to vacuum treatment, with a maximum composition for the Zn framework of Zn-1AB1.3. The degree of pore contraction upon loading is modulated by the inherent flexibility of the metal-carboxylate paddlewheel unit in the framework, with the Zn-1AB1.0 showing the biggest contraction of 6.2% and the more rigid Cu-1AB1.0 contracting by only 1.7%. Upon heating, each composite shows a temperature-induced phase transition to an open-pore (op) framework, and the enthalpy and onset temperatures of the phase transition are affected by the framework flexibility. For all composites, UV irradiation causes trans → cis isomerization of the occluded AB molecules. The population of cis-AB at the photostationary state and the thermal stability of the occluded cis-AB molecules are also found to correlate with the flexibility of the framework. Over a full heating-cooling cycle between 0 and 200 °C, the energy stored within the metastable cis-AB molecules is released as heat, with a maximum energy density of 28.9 J g-1 for Zn-1AB1.0. These findings suggest that controlled confinement of photoswitches within flexible frameworks is a potential strategy for the development of solid-solid phase change materials for energy storage.
AB - A series of azobenzene-loaded metal-organic frameworks were synthesized with the general formula M2(BDC)2(DABCO)(AB)x (M = Zn, Co, Ni, and Cu; BDC = 1,4-benzenedicarboxylate; DABCO = 1,4-diazabicyclo[2.2.2]octane; and AB = azobenzene), herein named M-1ABx. Upon occlusion of AB, each framework undergoes guest-induced breathing, whereby the pores contract around the AB molecules forming a narrow-pore (np) framework. The loading level of the framework is found to be very sensitive to the synthetic protocol and although the stable loading level is close to M-1AB1.0, higher loading levels can be achieved for the Zn, Co, and Ni frameworks prior to vacuum treatment, with a maximum composition for the Zn framework of Zn-1AB1.3. The degree of pore contraction upon loading is modulated by the inherent flexibility of the metal-carboxylate paddlewheel unit in the framework, with the Zn-1AB1.0 showing the biggest contraction of 6.2% and the more rigid Cu-1AB1.0 contracting by only 1.7%. Upon heating, each composite shows a temperature-induced phase transition to an open-pore (op) framework, and the enthalpy and onset temperatures of the phase transition are affected by the framework flexibility. For all composites, UV irradiation causes trans → cis isomerization of the occluded AB molecules. The population of cis-AB at the photostationary state and the thermal stability of the occluded cis-AB molecules are also found to correlate with the flexibility of the framework. Over a full heating-cooling cycle between 0 and 200 °C, the energy stored within the metastable cis-AB molecules is released as heat, with a maximum energy density of 28.9 J g-1 for Zn-1AB1.0. These findings suggest that controlled confinement of photoswitches within flexible frameworks is a potential strategy for the development of solid-solid phase change materials for energy storage.
U2 - 10.1021/acs.inorgchem.1c01364
DO - 10.1021/acs.inorgchem.1c01364
M3 - Journal article
VL - 60
SP - 12950
EP - 12960
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 17
ER -