Strong proton transfer from phenolic ring to imine functionality in 1D azido and dicyanamido bridged Mn(II) coordination polymers: Synthesis, crystal structure and magnetic studies

Abstract

In this research, two new 1D coordination polymers of Mn(II), [Mn(LH)2(µ1,5-dca)2]n (1) and [Mn(LH)2(µ1,3-N3)(CH3OH)(N3)]n (2) were synthesized and characterized by elemental analysis, spectroscopic methods, single crystal X-ray analysis and magnetic measurements (LH = Schiff base ligand obtained from the reaction of 2-hydroxy-1-naphthaldehyde and 2-amino-5-chloropyridine). These compounds were synthesized by the reaction of LH, MnCl2·4H2O and NaN(CN)2 (for compound 1) or NaN3 (for compound 2) in 1:1:2 M ratio in methanol. The spectroscopic and structural studies indicated that strong intramolecular proton transfer from naphtholic oxygen to the imine nitrogen is occurred in the ligand and due to this; the nitrogen atom of imine functionality is not coordinated to the metal core. As a result, the ligand is coordinated to the metal core as monodentate neutral ligand. The proton transfer process was attributed to the strong electron withdrawing properties of 5-chloropyridine ring. In the structure of compound 1 and 2, the manganese ions are connected to each other through µ1,5-dca and µ1,3-azide bridges, respectively to form 1D coordination polymers. The magnetic measurements showed the presence of antiferromagnetic interactions between Mn∙∙∙Mn cores in both of the obtained 1D coordination polymers, whereat the exchange interaction is an order of magnitude stronger in azido compared to dicyanamido bridged compound (–3.7 cm−1 vs. –0.30 cm−1).