Synergetic spin singlet–quintet switching and luminescence in mononuclear Fe(ii) 1,3,4-oxadiazole tetradentate chelates with NCBH3 co-ligand

Abstract

We report the multi-step synthesis of the tetradentate 2-(naphthalen-2-yl)-5-[N,N-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole ligand (L^Tetra-ODA) along with its corresponding [Fe^II(L^Tetra-ODA)(NCBH₃)₂]·1.5CH₃OH (C1) complex, which is the first mononuclear 1,3,4-oxadiazole based Fe(II) spin crossover (SCO) complex, and its zinc analogue [Zn^II(L^Tetra-ODA)(NCBH₃)₂]·0.5H₂O (C2). The spin transition is followed by variable temperature (VT-) X-ray crystallography of [Fe(L^Tetra-ODA)(NCBH₃)₂]·1.5CH₃OH (C1) at 120 and 220 K. The magnetic susceptibility measurements on the bulk sample recorded from 2 to 300 K show that the complex exhibits a complete abrupt reversible spin transition with a T_1/2 of 207 K. The loss of the lattice solvent methanol shifts the T_1/2 slightly to around 210 K. The spin transition in solution for [Fe(L^Tetra-ODA)(NCBH₃)₂]·1.5CH₃OH (C1) was followed using the VT-¹H-NMR Evans method in CD₃CN, with a T_1/2 of 357 K. Solid state VT luminescence studies provide some preliminary evidence of interplay of luminescence and spin transition in the [Fe(L^Tetra-ODA)(NCBH₃)₂]·1.5CH₃OH (C1) complex.