Assembly of anion-controlled cadmium(II) coordination polymers from the use of 2-acetyl-pyridyl-isonicotinoylhydrazone

Abstract

Four Cd(II) coordination polymers have been synthesized, utilizing a tetradentate pyridine-based Schiff base ligand, namely 2-acetyl-pyridyl-isonicotinoylhydrazone (HL), and different anions (CH3COO−, N3−, SCN−). The products {[Cd2(L)2(CH3COO)2]·C2H5OH}n (1), {[Cd1.5(L)(CH3COO)(N3)(H2O)]·C2H5OH}n (2), {[Cd(HL)(SCN)2]·CH3OH}n (3) and [Cd3(HL)2(SCN)6]n (4), were characterized with single-crystal X-ray diffraction, IR spectroscopy, and luminescence studies. The ligand in 1 and 2 is singly-deprotonated and coordinates to the cadmium centre in the enolic form (N–NC–O) while in compounds 3 and 4 it coordinates in its neutral keto form (N–NH–CO). The tetradentate ligand in 2 acts as a linker and leads to the formation of a one-dimensional coordination polymer. The CH3COO− in 1 and SCN− in 3 and 4, further act as bridges, forming two-dimensional coordination polymers (1 and 3) and a three-dimensional network (4). Structural diversity is thus induced by the anions, due to the variable steric hindrance they impose as well as differing bridging capacity; metal-organic network formation is also evident via different Van der Waals forces.