Single stranded helical supramolecular architecture with a left handed helical water chain in ternary copper(II) tryptophan/diamine complexes

Abstract

The ternary copper(II) complexes [Cu( l-trp)(bpy)](ClO 4) ( 1) and [Cu( l-trp)(phen)] (ClO 4) · 3H 2O ( 2) (where l-trp = l-tryptophan, bpy = bipridyl, phen = phenanthroline) have been synthesized. The single crystal X-ray structures for these complexes revealed that the monocationic Cu II-units are interlinked through Cu–OCO–Cu connectivity and exist as helical coordination polymers. The two different helical strands composed with Cu1 and Cu2 independently, possess a similar pitch distance of 7.713 Å in complex 1. For complex 2, existing in the hydrated form, the Cu(II) polymeric strand and the hydrated water molecules have gained a supramolecular helical architecture with a similar pitch distance of 8.133 Å. The two helical strands in complex 1 are associated with right handed ( PP) supramolecular chirality, while the helical water chain and the Cu II-strand in 2 are self assembled into left handed ( MM) helicity in the solid state. The solid state CD recorded for 1 and the dehydrated form of 2 exhibit a positive optical sign at their respective d–d band [ λ max = 667 nm, 1; λ max = 630 nm, 2], the solution state CD for both these complexes are found to be inverted into a negative optical sign, which could be attributed to inversion of their associated supramolecular helicity. The TGA curve illustrates two distinct weight losses at 60 °C and 87 °C, equivalent to one and two water molecules, respectively. The PXRD pattern for the hydrated and dehydrated forms of 2 indicated a change, on comparison with the simulated diffractograph. The fluorescence properties of both these complexes, possessing tryptophan and bipy/phen, were investigated.