Luminescent properties of three structures built from 3-cyano-4-dicyano­methyl­ene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate and cadmium

Yellow–orange tetra­aqua­bis(3-cyano-4-dicyano­methyl­ene-5-oxo-4,5-dihydro-1H-pyrrol-2-olato-κN³)cadmium(II) dihydrate, [Cd(C₈HN₄O₂)₂(H₂O)₄]·2H₂O, (I), and yellow tetra­aqua­bis­(3-cyano-4-dicyano­methyl­ene-5-oxo-4,5-dihydro-1H-pyrrol-2-ol­ato-κN³)­cadmium(II) 1,4-dioxane solvate, [Cd(C₈HN₄O₂)₂(H₂O)₄]·C₄H₈O₂, (II), contain centrosymmetric mononuclear Cd²⁺ coordination complex mol­ecules in different conformations. Dark-red poly[[deca­aquabis­(μ₂-3-cyano-4-dicyano­methyl­ene-5-oxo-4,5-dihydro-1H-pyrrol-2-olato-κ²N:N′)bis­(μ₂-3-cyano-4-dicyano­methyl­ene-1H-pyrrole-2,5-diolato-κ²N:N′)­tricadmium] hemihydrate], [Cd₃(C₈HN₄O₂)₂(C₈N₄O₂)₂(H₂O)₁₀]·0.5H₂O, (III), has a polymeric two-dimensional structure, the building block of which includes two cadmium cations (one of them located on an inversion centre), and both singly and doubly charged anions. The cathodoluminescence spectra of the crystals are different and cover the wavelength range from UV to red, with emission peaks at 377 and 620 nm for (III), and at 583 and 580 nm for (I) and (II), respectively.