Three new 1D Cu(II) coordination polymers and a binuclear Cu(II) complex of two pyrazole derived Schiff base ligands: Heterocyclic ring substitution and anion dependent structural variations – Spectral studies

Abstract

Three new zig-zag 1D coordination polymers and a binuclear complex of Cu(II) involving pyrazole based tri- and pentadentate schiff base ligands (Z)-2-(2-(5-methyl-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L′1) and (Z)-2-(2-(5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbonyl)hydrazono)-2-phenylacetic acid (L′2) are reported in this work. The ligand precursors L1 and L2 have been transformed into L1′ and L2′ during the course of reaction with metal ions in which the ester groups have been changed to carboxylate group. The 1D coordination polymers, namely, [Cu(L′1)(ClO4)2(H2O)]n (1), [Cu(L′2)(ClO4)]n (3), [Cu(L′2)(NO3)]n (4) and a binuclear complex [Cu2(L′1)2Cl2] (2) have been synthesized. The complexes 1–3 are of distorted octahedral geometry and the complex 2 is distorted square pyramidal. Interestingly, these structural variations are dependent on counterions and substituent on the pyrazole ring. These have been characterized by elemental analyses, UV, IR, single crystal X-ray diffraction, electrochemical and photoluminescence studies. L′1 serves as tridentate NNO donor where pyrazole nitrogen, azomethine nitrogen and ligand carboxylate group are coordinatively active, leaving the carbonyl oxygen of carbohydrazide part inactive. The same situation (coordination modes) arises in another pentadentate NNNOO donor L′2 where extra pyridine nitrogen is coordinated. The complexes 3 and 4 have considerable fluorescence emission while the rest of the complexes and the ligand molecules are fluorescent silent.