Ferromagnetism, paramagnetism, and thermally induced magnetism in photomagnetic CrIII/MnII and CrIII oxalates with the 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f]quinolinium cation

Abstract

Single crystals of the new cationic chromene, 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f-quinolinium iodide (C25H20NO)I (1), were synthesized. The crystal structure of the new compound was studied, and quantum chemical calculation for the open and closed forms were carried out. The bifunctional compounds containing mono- and bimetallic 3d metal (tris)oxalates with the chromenium cation, (C25H20NO)3[Cr(C2O4)3] · 4H2O (2) and (C25H20NO)[CrMn(C2O4)3] · H2O (3), were prepared. Compound 1 is paramagnetic due to low-lying thermally excited states of the chromene molecules. At low temperatures (∼2 K), the paramagnetic states are frozen, and the compound becomes diamagnetic. Compound 2 is paramagnetic and its magnetic properties are determined mainly by the Cr3+ ions and the thermally induced paramagnetic states of the chromene molecules. At high temperatures, the magnetic moment of compound 3 consists of the contributions of the paramagnetic Cr3+ and Mn2+ ions and the thermally induced paramagnetic states of chromenes. At low temperatures (2–3 K), the thermally induced magnetism of organic molecules is frozen, and the magnetically ordered (and, probably, spin-glass) state is observed in the two-dimensional network of metal oxalates (Tc = 3 K in the zero magnetic field). The UV irradiation leads to an increase in the magnetic moment of the compound in the paramagnetic region due to the generation of radiation defects.