Distinct Fold-Mode Formation of Crystalline Cu(I) Helical Coordination Polymers with Alternation of the Solid-State Emission Using Shape of the Counter Anions

One-dimensional cationic coordination
polymers have been a promising
platform for designing solid-state physical properties through diverse
coordination geometries. In particular, the folding mode of the coordination
polymers that form a helical structure directly determines the metal-centered
coordination environment. Herein, we report N-heterocyclic
carbene (NHC) Cu­(I) cationic coordination polymers with pyrazine as
the linker, which construct a 4-fold or 3-fold helical column in luminescent
crystals using octahedral anions (SbF6– and PF6–) or a tetrahedral anion (BF4–), respectively. Single-crystal XRD studies
revealed that the folding modes depend on the structural shape of
the counteranions, which form H–F interactions between ligands
and anions. Indeed, the folding mode change from 4-fold to 3-fold
by including a different shape of the counteranions, resulting in
red-shifted emission from approximately 580 to 687 nm, which is difficult
to modulate in the solid state.