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Anion-Directed Coordination Networks of a Flexible S‑Pivot Ligand and Anion Exchange in the Solid State

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posted on 04.11.2015, 00:00 by Eunji Lee, Huiyeong Ju, Seulgi Kim, Ki-Min Park, Shim Sung Lee
Using an S-pivot joint flexible ligand bis­(4-cyanobenzyl)­sulfide (bcbs), three silver­(I) complexes [Ag­(bcbs)­ClO4]n (1), [Ag2(bcbs) (CF3CO2)2]n (2), and {[Ag3(bcbs)4]­(PF6)3·4CH2Cl2}n (3) have been isolated. Configurations (“V”-, “L”-, and “W”-shapes) of the bcbs ligand in 13 can be tuned as a result of changing the anions of the silver­(I) salts, which ultimately form a series of infinite low to high dimensional frameworks with different structures. The perchlorato compound 1 shows a stairway type 1-D ribbon structure, in which the anion acts as a monodentate terminal ligand. The bcbs ligand in 1 shows a gauche–anti arrangement, adopting an L-shape configuration. The π–π stacking interaction between adjacent ribbons in 1 yields a pseudo-2-D structure with a herringbone pattern. Compound 2 is composed of silver­(I)–bcbs helical channels, which are further interlinked via monodentate bridging CF3CO2 ions forming a 3-D multichannel framework with a dmd topology. Unlike 1, the bcbs ligand in 2 shows an anti–anti arrangement, adopting a W-shape configuration. The corresponding PF6 complex 3 exhibits a 2-fold interpenetrated 3-D framework. The preferred anion-free structure in 3 presumably reflects the strong coordination of the donor set and the weak affinity of the PF6 toward the metal center. Similar to 1, the bcbs ligand in 3 adopts an L-shape configuration. In this work, the structural variations of the resulting coordination polymers are mainly associated with the diverse configurations of the flexible ligand, as well as the different coordination modes and abilities for the anions. Anion exchange accompanying an irreversible structural conversion from 2 or 3 to 1 was monitored in the crystalline state by IR and PXRD studies. AFM images and height profiles for the crystal surface before and after the anion-exchange were observed. On the basis of the above measurements, a mechanistic process from the 3-D structured 3 (PF6 form) to the 1-D structured 1 (ClO4 form) by the anion exchange was also proposed.