Exploration of Charge-Transfer Solids Utilizing Nucleobases: Nanoarchitectures by Hydrogen-Bonds in the Ionic Assemblies of Guanine and TCNQ Derivatives

We studied formation and structural
characteristics of charge-transfer
solids of 9-n-butylguanine (BuG) with
fluorinated tetracyanoquinodimethane derivatives (FnTCNQ, n = 4, 2, and 1). Complex formation
in a methanol (MeOH)-containing solvent generated two types of salts
composed of either a methoxy-substituted anion or a fully ionic anion
radical of FnTCNQ. In all anion radical
salts, BuG existed as a protonated or a hemiprotonated
species, BuGH+ or (BuG)­(BuGH+), respectively, and
formed hydrogen-bonded (H-bonded) assemblies. In these BuGH+ assemblies, FnTCNQ•– molecules were fixed and aligned
periodically, providing H-bonded polycationic templates. In (BuGH+)­(F4TCNQ•–), BuGH+ dimers by complementary
H-bonds formed a two-dimensional (2D) polycationic sheet. The F4TCNQ•– face-to-face dimers formed
a one-dimensional (1D) segregated column aided by formation of H-bonds
with BuGH+. In (BuGH+)­(F2TCNQ•–)­(MeOH), BuGH+ dimers by complementary
double H-bonds formed a 1D polycationic ribbon supported by MeOH-mediated
H-bonds. A 1D mixed stack column of (BuGH+)2 and (F2TCNQ•–)2 dimers was formed owing to their complementary geometry
and size. In (BuG)­(BuGH+)­(F1TCNQ•–), a new type
of BuG–BuGH+ pair formed a 1D ribbon supported by complementary H-bonds, and
F1TCNQ•– dimers were aligned by
H-bonds with the BuG–BuGH+ ribbon.