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

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 1–3 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.