The luminescent properties of structures built from 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrole-2-olate and copper(I,II) cations

Abstract

Six new salts based on the 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrole-2-olate anion (HA⁻) and Cu²⁺ and Cu⁺ cations, namely {[Cu^II(HA)₂(H₂O)₂]}_n·2nH₂O (1), [Cu^II(HA)₂(H₂O)₄] (2), [Cu^II(HA)₂(H₂O)₄]·0.5H₂O (3), [Cu^II(HA)₂(H₂O)₄]·H₂O (4), {[Cu^I(HA)(CH₃CN)₂]}_n (5) and {[Cu^I(HA)CH₃CN]}_n (6) were synthesized and structurally characterized by single-crystal X-ray diffraction. 1, 5 and 6 are coordination polymers; 2–4 are mononuclear complexes. The luminescent properties of salts 1–6 are reported. Crystals of HA⁻-based salts with Cu⁺ cations luminesce, whereas the anion's coordination to Cu²⁺ totally quenches the luminescence of HA⁻. Surprisingly, addition of Cu²⁺ to a solution of HA⁻ in acetonitrile causes a luminescence enhancement (LE) of the solution. A model explaining the LE effect is proposed.