Synthesis, Photophysical, Thermal and Crystallographic Studies of 3‐Aminocoumarin Based Monobasic κ3‐O,N,O‐tridentate/ κ2‐N,O‐bidentate Schiff Base Divalent Complexes

Abstract

AbstractThe reaction of 3‐Amino coumarin based Schiff base ligands HL1 and HL2 with metal acetates in refluxing ethanol affords access to a new series of neutral mononuclear divalent complexes [MII‐κ3‐bis‐O,N,O‐tridentate Schiff base‐ HL1/ HL2] {HL1, MII=Co (1), Ni (2) or Zn (3); HL2, MII=Co (4), Ni (5) or Zn (6)}, [CuII‐κ2‐bis‐N,O‐bidentate Schiff base‐HL1] (7) and [CuII‐κ2‐bis‐N,O‐bidentate Schiff base‐HL2] (8). Compounds were characterized by microanalysis, standard spectroscopic (viz. MALDI‐TOF‐MS, IR, 1H and 13C NMR, UV‐visible absorption and emission) and TGA/DTA methods. The unambiguous crystal structure of HL1, HL2, complexes 2 and 3 was determined crystallographically. The IR, UV‐visible, EPR spectral and magnetic studies clearly suggest the κ3‐O,N,O‐tridentate‐ coordination mode of HL1 and HL2 towards cobalt(II), nickel(II) and zinc(II) metal ions in 1–6 and κ2‐N,O‐bidentate‐coordination mode towards copper(II) metal ions in 7 and 8. Notably, compounds fluoresce a medium to strong emissions in the visible region is observed with concomitant Stokes shifts of ≈ 90 nm. UV‐visible transmittance spectral study reveals the semiconducting nature of HL1, HL2, complexes 1–8 gave with band gap energy of 1.57‐2.24 electron volts. The molecules of HL1, HL2, 2 and 3 are stabilized by various intermolecular CH…π, CH…O and π…π contacts that efficiently managed the growth of self‐assembly in three dimensions and form infinite molecular layers in the solid state.