Novel molecular staircase self-assembly from the cations of 1-(4 '-nitrobenzyl)pyridinium: synthesis, crystal structure, magnetic property and spin dimer analyses

摘要

Two salts consisting of 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical and 1-(4'-nitrobenzyl)pyridinium ([NO(2)BzPy](+)) 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 [NO(2)BzPy](+) leads two salts to exhibit different packing structures. A strong dimer of [(TCNQ)(2)](2-) is formed, and the adjacent dimers. slide to each other along the direction of the shorter molecular axis of TCNQ(-) 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)](-), stack into a tetrad column, in which two types of TCNQ entries, TCNQ(-1) and TCNQ(0), are found in 3, and this kind of charge-ordered state is further supported from the results of both IR spectra and molecular orbital calculation. Two neighboring cations of [NO(2)BzPy](+) overlap into a dimer via π...π 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 &UDelta;/k(B) = 1813 K and zJ'/k(B) = -6 K for 2; &UDelta;/k(B) = 1882 K and zJ'/k(B) = -11K for 3. © 2005 Elsevier B.V. All rights reserved.