CHARGE-TRANSFER STRUCTURES OF AROMATIC EDA COMPLEXES WITH NORMAL-HETEROATOM-SUBSTITUTED PYRIDINIUM CATIONS

X-Pyridinium cations with N-heteroatomic substituents such as X = halogen, nitro, alkoxy and acyloxy (i.e., X-NC5H5+), in common with the ubiquitous N-alkylpyridinium cations, interact spontaneously with different benzene, naphthalene and anthracene donors (ArH) to afford a series of 1 :1 charge-transfer complexes showing characteristic absorption spectra in the visible region. Quantitative evaluation of the electron-acceptor properties of X-Py+ (via an electrochemical reduction potential E(p)c) indicates that the N-nitropyridinium (Ec = +0.10 V), N-fluoropyridinium (E(p)c = -0.66 V), N-acetoxypyridinium (E(p)c = -0.81 V), and N-methoxypyridinium (E(p)c = -1.02 V) cations are strong electrophiles in their charge-transfer interaction with aromatic donors to produce cofacial acceptor-donor pairs [X-Py+, ArH] that are structurally related to the more common N-methylpyridinium (E(p)c = -1.32 V) analogues.