Two 7,7,8,8-tetracyanoquinodimethane lead and zinc complexes featuring 3D and 0D structure: Synthesis, structure and electrochemical properties

Two 7,7,8,8-tetracyanoquinodimethane (TCNQ) Pb2+ and Zn2+ complexes, namely, {[Pb2(TCNQ)3(H2O)6](TCNQ)}n (1) and Li[Zn2(TCNQ)5(H2O)6]·[Zn(TCNQ)2(H2O)4]·6H2O (2) have been synthesized by the reactions of Li(TCNQ) with PbCl2 and Zn(TPP)2Cl2 (TPP = Triphenylphosphine), respectively. Single-crystal X-ray diffraction analysis reveals that complex 1 features a 3D network structure and complex 2 features a 0D structure in which a neutral molecule of [Zn(TCNQ)2(H2O)4] crystallizes in the crystal. The flexible coordination modes of TCNQ and the metal ions play essential roles on the formation of the novel 3D structures and the unique 0D ionic structure as well as the TCNQ molecules adapt in one-dimensional column of TCNQ through π–π stacking interactions among the TCNQ metal complexes. Cyclic and differential pulse voltammograms for complexes 1 and 2 show the reversible one-electron oxidation and one-electron reduction within the electrochemical window of CH3CN. Their electrochemical HOMO–LUMO gap and reversibility are examined.