Two‐Step Electrochemically Directed Synthesis of Pr 4 N(TCNQ) n ( n =1, 2): Preparation, Structure, and Properties of a Magnetically Isolated Dimer and a Quasi‐One‐Dimensional Chain

Solid‐state electrochemistry of a tetracyanoquinodimethane (TCNQ)‐modified electrode in contact with a tetrapropylammonium cation (Pr 4 N + ) electrolyte showed two electron‐transfer steps to give Pr 4 N(TCNQ) 2 ( 1 ) and Pr 4 N(TCNQ) ( 2 ) rather than the traditional one‐electron step to directly give Pr 4 N(TCNQ). Two thermodynamically stable Pr 4 N + TCNQ stoichiometries, 1 and 2 , were synthesized and characterized. The degree of charge transfer ( ρ ) calculated from the crystal structure is −0.5 for the TCNQ moieties in 1 and −1.0 for those in 2 . Raman spectra for Pr 4 N(TCNQ) 2 show only one resonance for the extracyclic CC stretching at 1423 cm −1 , which lies approximately midway between that of TCNQ at 1454 cm −1 and TCNQ − at 1380 cm −1 . Both the magnetic susceptibility and EPR spectra are temperature‐dependent, with a magnetic moment close to that for one unpaired electron per (TCNQ) 2 unit in 1 , whereas 2 is almost diamagnetic. Pressed discs of both complexes show conductivity (1–2×10 −5  S cm −1 ) in the semiconductor range. For 1 , the position of zero current for the steady‐state voltammograms implies 50 % of TCNQ − and 50 % TCNQ 0 is present in solution, thereby supporting a dissociation of (TCNQ) 2 − in solution, but is indicative of only TCNQ − being present for 2 .