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[24]Pentaphyrin(2.1.1.1.1) 1 was synthesized by dehydrogenation of dihydropentaphyrin(2.1.1.1.1) 2 as the first example of vinylogous pentaphyrin. Pentaphyrin 1 takes a roughly planar structure and shows strong antiaromatic character, reflecting a 24p-conjugated circuit. In spite of the antiaromatic character and the relatively small circuit, 1 is stable under ambient conditions. [ABSTRACT FROM AUTHOR]

Metal ion adsorbents are indispensable materials for the recovery of noble metal ions in a sustainable society. Herein, we report that poly(isopyrazole-3,5-diyl-trans-vinylene) (1) effectively adsorbed group 10 metal ions from solution in acetonitrile. Owing to its fully π-conjugated and rigid structure, polyimine 1 was virtually insoluble in common organic solvents and water, making it advantageous for metal ion adsorption via a solid/liquid interface. Inductively coupled plasma (ICP) analysis showed that ≥90% of Ni2+, Pd2+, and Pt2+ ions were adsorbed at a concentration of 10 µM (order of ≤2 ppm) after stirring suspensions at room temperature. Metal ion desorption was achieved by treatment with ethylenediaminetetraacetic acid disodium salt (EDTA⋅ 2Na), and the adsorbent was reused. Theoretical calculations supported that the desolvation energy was an important factor for effective adsorption in acetonitrile. [ABSTRACT FROM AUTHOR]