Anion-directed structural diversification in four new Cd(II) compounds of a flexible polyether-based dicarboxylic acid

Abstract

• With a less explored linker 3,6,9-trioxaundecanedioic acid (H 2 toua) a series of complexes with Cd(II) salts containing different counter anions (Cl - , ClO 4 - , OAc - , and NO 3 - ) were synthesized. • A discrete neutral compound [Cd(H 2 toua)Cl 2 ] . H 2 O ( 1 ) is obtained with Cl - whereas a 1D polymeric chain {[Cd(Htoua)(H 2 O)](ClO 4 )} n ( 2 ) is obtained with ClO 4 - counter anion. • Different morphologies are observed with different counter anion analyzed by SEM technique. • Their thermal behavior, Hirshfeld Surface analysis and luminescent properties were also investigated. In this work, we report the chemistry of an unexplored flexible polyether based dicarboxylic acid (3,6,9-trioxaundecanedioic acid, H 2 toua) with four different cadmium salts. With CdCl 2 . H 2 O or Cd(ClO 4 ) 2 . H 2 O in a 1:1 ratio, it remarkably forms a discrete compound [Cd(H 2 toua)Cl 2 ] . H 2 O ( 1 ) and a polymeric ionic compound, {[Cd(Htoua)(H 2 O)](ClO 4 )} n ( 2 ), respectively, as determined by the single crystal X-ray diffraction. In both cases, for the heptacoordinated Cd(II) all basal donor atoms are from the ligand (three ether oxygen and two oxygen atoms from the fully intact or mono-deprotonated carboxylic acid groups, respectively) but with a major difference in axial (trans to each other) coordinated atom types - two chlorines in 1 while one water molecule and a bridging carboxylate oxygen in 2 . Unlike 1 , the carboxylate group of Htoua bridges between the Cd(II) centers for the formation of a 1D polymeric chain in 2 . Furthermore, Hirshfeld surface analysis of the various intermolecular interactions enables quantifiable contributions to crystal packing, revealing the key differences in the interactions encountered by 1 and 2 . Using Cd(OAc) 2 . 6H 2 O as the metal salt, it is possible to make [Cd(toua)] . H 2 O ( 3 ), due to the formation of easily removable volatile acetic acid by-product. On the other hand, a nitrate analogue of 2 , i.e., {[Cd(Htoua)(H 2 O)](NO 3 )} n ( 4 ) is isolated if Cd(NO 3 ) 2 . 4H 2 O is used. All these compounds were characterized by a number of spectroscopic and microscopic methods. Their thermal behaviour and luminescence properties were also determined.