Pseudohalides regulated diverse helicity in copper(II) coordination polymers derived from a bis(aminoethoxy) ligand.

This paper reports the syntheses and structural characterization of three new Cu(II) coordination polymers, namely [Cu(BAEE)(N 3 ) 2 ] ∝ ( 1 ), [Cu(BAEE)(NCO) 2 ] ∝ ( 2 ) and [Cu(BAEE)(NCS) 2 ] ∝ ( 3 ), where BAEE is 1,2-bis(2-aminoethoxy)ethane. Compound 1 is a one-dimensional (1D) single-stranded normal helical structure, while compounds 2 and 3 are extraordinary single-stranded meso-helical polymers. The influence of pseudohalides in these systems is observed as the azide ions are cis coordinated in 1 and the thiocyanate ions are trans coordinated in 3 , while alternate metal centers are either cis or trans coordinated with cyanate ions in 2 . These geometrical preferences play a crucial role in the diverse helicity in these chain structures, where the cis arrangement (in 1 ) favors a uniform helicity in the structure and the trans arrangement (in 2 and 3 ) of the pseudohalide ligands around the copper(II) center brings meso-helicity in the chains. The energetic difference of the cis / trans isomers and the formation energies of the different assemblies using DFT calculations suggest that the different H-bond acceptor ability of the thiocyanate ion determines the different architecture observed in 3 . Our results highlight how the geometrical preferences of the pseudohalides around the copper(II) center influence the helical diversity in these systems and thereby provide a clue toward the development of uncommon coordination polymers with amazing meso-helical character. [ABSTRACT FROM AUTHOR]