Self-assembly and supramolecular isomerism in copper (II) coordination compounds of pyridine-4-carboxamide based ligand

Abstract

Supramolecular isomerism and structural transformations have been studied for four coordination compounds of Cu(II) with L as N, N-diisopropylisonicotinamide. Three different compounds [Cu(L)2(NO3)2(H2O)1.5] (1), [Cu(L)2(NO3)2]n (2) and [Cu(L)(NO3)2]n (3) were synthesized from the same reactants having metal-to-ligand ratio of 1:1 or 3:1, under different reaction conditions. 1 is a simple coordination compound while 2 and 3 are 1D coordination polymers (CPs). 1 shows a thermally induced, irreversible single crystal to single crystal phase transformation to 2, which is confirmed by Powder X-ray diffraction (PXRD), Thermo gravimetric analysis (TGA) and differential scanning calorimeteric (DSC) analysis. In the presence of KBr, 3 shows, a rare, metal bound anion exchange which induces structural transformation to a new CP, [Cu(L)2(Br)2]n (4). Attempts for a reverse anion induced transformation of 4, in the presence of KNO3, gives 1 instead of 3. Crystal structures of all the four compounds have been solved. Hirshfeld surface analyses were performed to visualize and highlight the differences in supramolecular interactions between the single-crystal-to-single-crystal (SCSC) transformed products 1 and 2. Further Compound 1 and 2 are used in the synthesis of CuO nanoparticles.