Architectural diversity in the solid-state behaviour of crown ether and [2.2.2]-cryptand complexes of K+TCNQ˙− salts

Abstract

The solid-state behaviour of five ionophore-encapsulated TCNQ complexes: (18-crown-6)K(TCNQ)_2.5 (1), ([2.2.2]-cryptand)K(TCNQ)_2.5 (2), (benzo-18-crown-6)K(TCNQ)₂ (3), (dibenzo-18-crown-6)K(TCNQ)₂ (4), and (dicyclohexano-18-crown-6)K(TCNQ)₃ (5) has been explored. For both 1 and 2, the TCNQ components assemble as a pentameric repeat unit within infinite TCNQ columns with the cation complex sitting in a cavity between the columns; whereas for 3 and 4, neighbouring (crown ether)K⁺ complexes form dimers involving K⁺–π interactions which further assemble into one-dimensional columns sitting between infinite TCNQ stacks. In the solid-state complex 5, the crown ether adopts a chair conformation with the resulting (crown ether)K⁺ complex assembling into a one-dimensional ladder. Pairs of TCNQ dimers separated by an isolated TCNQ unit form infinite TCNQ columns. IR and Raman spectroscopy reveal the presence of partially charged TCNQ units within all five TCNQ complexes (1–5) and resistivity studies indicate that all five TCNQ complexes (1–5) are more conductive than the corresponding simple KTCNQ salts. Preliminary EPR studies of 1 and 2 indicate typical behaviour of complex TCNQ salts (containing both TCNQ⁰ and TCNQ˙⁻).