Effects of transition metal cations and temperature on the luminescence of a 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1 H -pyrrole-2-olate anion

• Published in: New journal of chemistry 2021-12, Vol.45 (46), p.21684-21691
• Main Authors: Gurskiy, Stanislav I., Maklakov, Sergey S., Dmitrieva, Natalia E., Tafeenko, Viktor A.
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/D1NJ01225H

Two new mononuclear complexes based on the anion 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1 H -pyrrol-2-olate (C 8 HN 4 O 2 − = HA − ) and Mn 2+ or Zn 2+ cations, namely [Mn(HA) 2 (H 2 O) 4 ]·2H 2 O (1) and [Zn(HA) 2 (H 2 O) 4 ] (2), were synthesized and characterized by single-crystal X-ray diffraction and photoluminescence spectroscopy. Complexes 1 and 2 crystallize in the triclinic space group P 1̄. Units [M(HA) 2 (H 2 O) 4 ] (M = Mn, Zn) are the basic building blocks in both 1 and 2 crystal structures. The metal cation, located on an inversion center, is bound to two nitrogen atoms of two HA − and four water oxygen atoms. Units [M(HA) 2 (H 2 O) 4 ] are connected by π–π stacking interactions between anions HA − and by hydrogen bonds to form a 3D crystal structure. Complexes 1 and 2 are isostructural with previously reported complexes [Cd(HA) 2 (H 2 O) 4 ]·2H 2 O and [Cu(HA) 2 (H 2 O) 4 ], respectively. A comparison between the luminescence properties of isostructural complexes confirms that the incompletely filled 3d subshell (3d 5 , 3d 9 ) of a divalent metal cation is a key factor leading to the total luminescence quenching of anion HA − upon complexation with metal cations. Salts M(HA) 2 (M = Mn, Cd, Cu, or Zn) adsorbed on cellulose paper display thermo-sensitive luminescence. The luminescence is due to HA − anions. The intensity of the luminescence peak reversibly decreases by 6–7 times upon heating from 27 up to 123 °C.