Quenching luminescence, thermolysis and SMM behavior of new TbIII, EuIII, GdIII complexes with 4-nitro-N'-(pyridin-2-ylmethylene)benzohydrazide

Abstract

The reaction of 4-nitro-N'-(pyridin-2-ylmethylene)benzohydrazide (HL) with Ln(OAc)3·4H2O in MeOH makes it possible to synthesize mononuclear complexes [Ln(L)2(OAc)(MeOH)]·2H2O (Ln = TbIII (1), EuIII (2) and GdIII (3)) with chelate acetate and L‒ anions. Compound 1 can be crystallized in reaction with molar ratio HL:Ln = 1:1, 2:1, 3:1, and we successfully synthesized complex with three chelate L anions [Tb(L)3]2·2MeOH·H2O (4) by interaction of TbCl3∙6H2O with deprotonated HL (HL:Ln = 3:1). Terbium(III) compound 1 starts to decompose at ∼323 K and becomes stable up to 552 K according to the STA. Compound 1 shows slow magnetic relaxation with parameters Δeff/kB = (6.75 ± 0.02) K, τ0 = (1.71 × 10−6±1 × 10−8) s. Complexes 1 and 2 exhibit only fluorescence and phosphorescence of the L‒. Ion-centered luminescence of the Tb3+ or Eu3+ ion is not observed. Using the tangent method at the high-energy edge of the phosphorescence spectrum of Gd3+, complex 3 T1 energy level of L‒ is estimated to be 19700 cm−1. Reasons of luminescence quenching are discussed. Structures of 1 and 4 were determined by single crystal X-ray diffraction, and compounds 1–3 were characterized by powder X-ray diffraction (PXRD).