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.

Seven 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 as PowerPoint slide