Novel molecular staircase self-assembly from the cations of 1-(40-nitrobenzyl)pyridinium: synthesis, crystal structure, magnetic property and spin dimer analyses

Two salts consisting of 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical and 1-(40-nitrobenzyl)pyridinium ([NO2BzPy]C) with molar ratio of 1:1 (2) and 2:1 (3) have been prepared and structurally characterized. The change of molar ratio between radical of TCNQ and [NO2BzPy]Cleads two salts to exhibit different packing structures. A strong dimer of [(TCNQ)2]2K is formed, and the adjacent dimers slide to each other along the direction of the shorter molecular axis of TCNQK in 2. The weak H-bonding interactions between O-atom of nitro groups and H-atom of benzene rings are observed, which construct a cationic chain as a supramolecular staircase. The radical anions, [(TCNQ)2]K, stack into a tetrad column, in which two types of TCNQ entries, TCNQK1 and TCNQ0, are found in 3, and this kind of chargeordered state is further supported from the results of both IR spectra and molecular orbital calculation. Two neighboring cations of [NO2BzPy]Coverlap into a dimer via p/p stacking between benzene rings. The EPR spectra of polycrystalline samples at room temperature indicated the feature of isotropic signals with g-factor of 2.0056 for 2 and 2.0068 for 3. The temperature dependences of magnetic susceptibility (2–350 K) show spin gap of singlet–triplet feature for two salts. The best simulations to susceptibility data in the range 2–350 K yielded the parameters D/kBZ1813 K and zJ0/kBZK6 K for 2; D/kBZ1882 K and zJ0/kBZK11 K for 3. q 2005 Elsevier B.V. All rights reserved.