Electrochemically-lnduced TCNQ/Mn[TCNQ]2(H2O) 2 (TCNQ = 7,7,8,8tetracyanoquinodimethane) solid-solid interconversion: Two voltammetrically distinct processes that allow selective generation of nanofiber or nanorod network morphologies

Unlike the case with other divalent transition metal M[TCNQ] 2(H2O)2 (M=Fe, Co, Ni) analogues, the electrochemically Induced solid-solid phase interconversion of TCNQ microcrystals (TCNQ=7,7,8,8-tetracyanoqulnodimethane) to Mn[TCNQ] 2(H2O)2 occurs via two voltammetrically distinct, time dependent processes that generate the coordination polymer in nanoflber or rod-like morphologies. Careful manipulation of the voltammetrlc scan rate, electrolysis time, Mn (aq) concentration, and the method of electrode modification with solid TCNQ allows selective generation of either morphology. Detailed ex situ spectroscopic (IR, Raman), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) characterization clearly establish that differences in the electrochemically synthesized Mn-TCNQ material are confined to morphology. Generation of the nanoflber form is proposed to take place rapidly via formation and reduction of a Mn-stablllzed anionic dimer Intermediate, [(Mn2+)(TCNQ-TCNQ)2-], formed as a result of radical-substrate coupling between TCNQ- and neutral TCNQ, accompanied by Ingress of Mn2+ ions from the aqueous solution at the triple phase TCNQ/electrode/electrolyte boundary. In contrast, formation of the nanorod form is much slower and is postulated to arise from dlsproportionatlon of the [(Mn2+)(TCNQ-TCNQ)-2] intermediate. Thus, identification of the time dependent pathways via the solid-solid state electrochemical approach allows the crystal size of the Mn[TCNQ]2(H2O)2 material to be tuned and provides new mechanistic insights into the formation of different morphologies. © 2009 American Chemical Society.