Photo- and Thermochromic and Adsorption Properties of Porous Coordination Polymers Based on Bipyridinium Carboxylate Ligands

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• 作者：Oksana Toma ; Nicolas Mercier ; Magali Allain ; Abdel Adi Kassiba ; Jean-Pierre Bellat ; Guy Weber ; Igor Bezverkhyy
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：September 21, 2015
• 年：2015
• 卷：54
• 期：18
• 页码：8923-8930
• 全文大小：556K
• ISSN：1520-510X

文摘

The zwitterionic bipyridinium carboxylate ligand 1-(4-carboxyphenyl)-4,4鈥?bipyridinium (hpc1) in the presence of 1,4-benzenedicarboxylate anions (BDC^{2鈥?/sup>) and Zn2+ ions affords three porous coordination polymers (PCPs): [Zn₅(hpc1)₂(BDC)₄(HCO₂)₂]路2DMF路EtOH路H₂O (1), [Zn₃(hpc1)(BDC)₂(HCO₂)(OH)(H₂O)]路DMF路EtOH路H₂O (2), and [Zn₁₀(hpc1)₄(BDC)₇(HCO₂)₂(OH)₄(EtOH)₂]路3DMF路3H₂O (3), with the formate anions resulting from the in situ decomposition of dimethylformamide (DMF) solvent molecules. 1 and 3 are photo- and thermochromic, turning dark green as a result of the formation of bipyridinium radicals, as shown by electron paramagnetic resonance measurements. Particularly, crystals of 3 are very photosensitive, giving an eye-detectable color change upon exposure to the light of the microscope in air within 1鈥? min. A very nice and interesting feature is the regular discoloration of crystals from the 鈥渆dge鈥?to the 鈥渃ore鈥?upon exposition to O₂ (reoxidation of organic radicals) due to the diffusion of O₂ inside the pores, with this discoloration being slower in an oxygen-poor atmosphere. The formation of organic radicals is explained by an electron transfer from the oxygen atoms of the carboxylate groups to pyridinium cycles. In the structure of 3鈥?/b>, [Zn₁₀(hpc1)₄(BDC)₇(OH)₆(H₂O)₂], resulting from the heating of sample 3 (desolvation and loss of CO molecules due to the decomposition of formate anions), no suitable donor鈥揳cceptor interaction is present, and as a consequence, this compound does not exhibit any chromic properties. The presence of permanent porosity in desolvated 1, 2, and 3鈥?/b> is confirmed by methanol adsorption at 25 掳C with the adsorbed amount reaching 5 wt % for 1, 10 wt % for 3鈥?/b>, and 13 wt % for 2. The incomplete desorption of methanol at 25 掳C under vacuum points to strong host鈥揼uest interactions.}