Multifunctional Triple-Decker Inverse 12-Metallacrown‑4 Sandwiching Halides

A family of six triple-decker complexes,
{(MX)2[(pz)4]3} (Hpz = 4-nitropyrazole,
MX = NaCl, 1; NaBr, 2; NaI, 3; KCl, 4;
KBr, 5, and KI, 6), exhibiting inclusion
of halides into inverse 12-metallacrown-4 [inv-(12-MCCu(I),pz-4)] array has been realized. Single-crystal X-ray crystallography
of each compound reveals a common structural feature consisting of
four CuI ions bonded by four pz to form a square metallomacrocycle
comprising four metal centers and eight N atoms, thus giving an inv-[12-MCCu(I),pz-4] motif. Two halides are sandwiched by three inv-[12-MCCu(I),pz-4] to form triple-deckers that are further extended
in an offset stacking mode by ligand-unsupported cuprophilicity interactions
to form a one-dimensional chain structure. Halides are attached to
six CuI centers with weak CuI···halogen
interaction, resembling anion templates. High-resolution electrospray
ionization mass spectrometry reveals that the predominant fragments
corresponding to a half of the triple-decker structures of 1–3 exist in solution. Compounds 4, 5, and 6 showed excellent electrocatalytic activities toward the
reduction of nitrite and can also be used as selective “turn-off”
sensors for Ag­(I) in water. The present results will be helpful for
the future design and synthesis of functional inverse metallacrowns
and their multiple-decker complexes.