Anion influence in the structural diversity of cadmium coordination polymers constructed from a pyridine based Schiff base ligand

•Seven Cd(II) polymers based on pyridine based Schiff base ligand were prepared.•The ligand plays a predominant role in construction of coordination polymers.•The ligand has different types of coordination modes either with N3 and N3O donors.•Different counter ions cause different coordination modes and structures.•The structures show the capacity of Cd(II) to form complexes with 5, 6 and 7 C.N.

A series of seven coordination polymers based on Cd and potentially tetradentate pyridine based Schiff base ligand with different anions (CH3COO−, NO2−, Cl−, I−, N3−, SCN−), [Cd(L)(CH3COO)(OH2)]n (1),{[Cd2(L)2(NO2)2(CH3OH)2]·CH3OH}n (2), {[Cd2(L)2Cl2(CH3OH)2]·CH3OH}n (3), [Cd(HL)I2]n (4), [Cd3(L)2(N3)4]n (5), [Cd(L)(SCN)(OH2)]n (6) and [Cd(HL)(SCN)2]n (7) {HL = 2-pyridinecarbaldehyde isonicotinoyl hydrazone (HPCIH)} in order to rationalize the effect of the anion, have been synthesized and characterized by elemental analyses, FT-IR spectroscopy, single crystal X-ray data diffraction, etc. The results show the influence of the counter-ions on the coordination mode of the cadmium ion that is capable of forming compounds with five-, six- and seven-coordination numbers. The ligand acts as a negatively charged tetradentate N3O-donor ligand and coordinates to the cadmium center in the enolic form (NNCO) in 1–3 and 5–6 while in compounds 4 and 7 coordinates as N3- and N3O-donor neutral ligand in keto form (NNHCO), respectively. Cadmium centers in 1–4 and 6, bridging by the HPCIH ligand cause to form one-dimensional coordination polymers and the anions act as terminal ligands. In compounds 5 and 7, the N3− and SCN− also act as bridging ligands to the metal centers, and form 3D and 2D metal–organic polymers respectively.

Graphical abstractSeven Cd(II) coordination polymers derived from 2-pyridinecarbaldehyde isonicotinoyl hydrazone in the existence of different anions. The results show significant anion-dependent effect on the formation of polymeric structures from 1D chain to 3D network.Figure optionsDownload full-size imageDownload as PowerPoint slide