pH-Dependent Assembly and Conversions of Six Cadmium(II)-Based Coordination Complexes

Abstract

Six cadmium(II) complexes containing the N 2 O 2 donor tetradentate asymmetrical Schiff base ligand 2-{[2-(dimethylamino)ethylimino]methyl}-6-methoxyphenol (HL 5 ), namely, 6), have been synthesized using cadmium(II) chloride and the asymmetrical Schiff base ligand HL 5 under different pH conditions at room temperature. The diverse structures show the marked sensitivity of the structural chemistry of the tetradentate asymmetrical Schiff base ligand HL 5 . Complex 1 formed at pH = 10 exhibits a rare zero-dimensional structure of trinuclear cadmium(II). At pH = 8-9, a dinuclear cadmium(II) complex 2 is formed. The reaction at pH = 5-7 leads to two one-dimensional structures of 3 and 4. A further decrease of the pH to 3-5 results in a zero-dimensional structure 5. Owing to the departure of lattice water molecules in the crystal, complex 5 at room temperature can gradually undergo single-crystal-to-single-crystal transformation to result in complex 6. The results further show that conversions of complex 1-5 can also be achieved by adjusting the pH value of the reaction solution, 1 f 2 pH=8 f 5 pH=3 and 3 f 4 pH=5 . Comparing these experimental results, it is clear that the pH plays a crucial role in the formation of the resulting structures, which simultaneously provides very effective strategies for constructing the Cd II compounds with N 2 O 2 donor tetradentate asymmetrical Schiff base ligand. The strong fluorescent emissions of the six compounds (1-6) make them potentially useful photoactive materials. Furthermore, six Schiff base cadmium complexes (1-6), with 2,2-dipheny1-1-picrylhydrazy1 (DPPH) as a cooxidant exhibited the stronger scavenging activity.

Mono, di and trinuclear photo-luminescent cadmium(II) complexes with N2O and N2O2 donor salicylidimine Schiff bases: Synthesis, structure and self assembly

“…In the present work, we have used four different Schiff bases, produced by the condensation of N-substituted-1,2-diaminoethane and salicylaldehyde or its derivatives, to form cadmium(II) complexes. We have selected cadmium(II) as the metal centre for its ability to exhibit varieties of geometries as a result of its d 10 electronic configuration with no CFSE in any crystal field, steric requirements of ligands controlling the geometries and coordination numbers [30][31][32]. Our intension was to examine the changes, if any, in their crystalline and supra-molecular architectures with the change in denticity of Schiff base ligands and with the presence of different co-ligands in the reaction medium.…”

Halide Ion Mediated Aldehyde‐Amine Condensation Leading to Schiff–base and Cyclized Non‐Schiff–base Ligand Complexes of CdII: A Combined Experimental and Theoretical Investigation

“…Metal ions having d 10 electronic configuration are observed to be more prone to exhibit structural diversity owing to their softness and lack of LFSE. Amongst the post‐transition metals, Cd(II) shows better ability in adopting several coordination numbers and structural motifs and in recent time the importance of Cd(II) in bioinorganic chemistry with the discovery of Cd(II) containing carbonic anhydrase as well as in making emitting materials has boosted research on the coordination chemistry of Cd(II) . The nature of co‐ligands is another parameter in controlling structural diversity .…”

A zipper-like double chain coordination polymer constructed from a novel pseudo-macrocyclic binuclear Cu(II) complex

“…The design and synthesis of polydentate ligands with endogenous bridging groups have been demonstrated to be one of the promising approaches to synthesizing such complexes [5]. In this respect, we have reported complexes of aminophenol and multihydroxyl ligands [6], wherein the endogenous alkoxo or phenoxo groups act as bridges to afford binuclear and polynuclear structures.…”