Tuning the Mesomorphism and Redox Response of Anionic‐Ligand‐Based Mixed‐Valent Nickel(II) Complexes by Alkyl‐Substituted Quaternary Ammonium Cations

• Published in: Chemistry : a European journal 2018-05, Vol.24 (29), p.7398-7409
• Main Authors: Nakamura, Yuichi, Matsumoto, Takeshi, Sakazume, Yasutaka, Murata, Junnosuke, Chang, Ho‐Chol
• Format: Article
• Language: English
• Subjects: Ammonium; Anions; Cations; Chain branching; Chains; Chemistry; Crystallography; Indium; Ions; ligand effects; Ligands; Mesophase; metallomesogens; Molecular chains; Nickel; Oxidation; Phases; redox chemistry; Substitutes; Temperature; Tin; Tin oxide; Tin oxides
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201706006

The combination of the redox‐active mesogenic anion [NiII(Bdt)(BdtSQ)]− (Bdt=1,2‐benzenedithiolato; BdtSQ=1,2‐dithia‐semi‐benzoquinonato) with alkyl‐substituted ammonium cations afforded a series of redox‐active ionic complexes of the type [NR4][NiII(Bdt)(BdtSQ)] [R=nC16H33 (NC164Ni) and C8,10 (NC8,104Ni); C8,10=6‐octylhexadecyl] or [NMe2R2][NiII(Bdt)(BdtSQ)] [R=nC16H33 (NMe2C162Ni) and C8,10 (NMe2C8,102Ni)]. X‐ray crystallographic analyses of NMe2C162Ni and NC164Ni revealed the formation of cation‐dependent integrated ionic layers separated by interdigittated alkyl chains. Complexes NMe2C162Ni and NC164Ni commonly form crystalline phases at room temperature, whereas complexes NMe2C8,102Ni and NC8,104Ni, which contain branched alkyl chains, form a metastable mesophase and an amorphous phase at the same temperature, respectively. Furthermore, complexes NMe2C162Ni, NMe2C8,102Ni, and NC164Ni commonly form a smectic A phase (SmA) at 375, 317, and 342 K, respectively. For the four complexes, well‐defined cyclic voltammetry responses, derived from ligand‐based oxidation and reduction, were observed in solution and the condensed phases, that is, upon casting these complexes on an indium‐doped tin oxide working electrode. The present study demonstrates the tunability of the mesomorphism of ionic molecular assemblies composed of alkyl‐substituted quaternary ammonium cations, while maintaining the well‐defined redox responses of the anions even in the condensed phases. In tune: This study demonstrates the tunability of the mesomorphism of anionic‐ligand‐based mixed‐valent NiII complexes through alkyl‐substituted quaternary ammonium cations. The potential redox activity of these complexes in the condensed phases is also examined. The results should provide valuable guidelines for the design of electrochemically active molecular assemblies.