A series of Cu(II) based di-hydrazide complexes obtained through solvent exchange: Their efficient dye degradation and magnetic study

Abstract

The Cu(II) complex [Cu2(L)(H2O)2(MeOH)2](NO3)2 (1) was synthesized, where H2L = N,N′bis(2-hydroxy-3-methoxybenzyledene)succinohydrazide. Upon dissolving single crystals of 1 in H2O, the two coordinated MeOH molecules were replaced by two H2O molecules around the coordination sphere of the Cu(II) ion, resulting in the formation of [Cu2(L)(H2O)4](NO3)2 (2). Further, to see the effect, if any, of the anion in the molecular assembly process, [Cu2(L)(H2O)2(MeOH)2]·(2MeOH)·(ClO4)2 (3) was synthesized. Complex 3 also displayed a phase transformation to [Cu2(L)(H2O)4]·(ClO4)2 (4) by a solvent exchange process. However, interestingly, the reaction of H2L with Cu(BF4)2 in MeOH resulted in [Cu2(L)(H2O)4]·(4H2O)·(SiF6) (5). No MeOH was coordinated in this case and 5 did not show any transformation. The mechanistic pathway of the transformation, from DFT calculations, shows a stepwise exchange of MeOH by H2O and supports the transformation from a thermodynamic point of view. Single crystal X-ray crystallography reveals that the flexible H2L ligand is stretched to its maximum length and almost linear structures were obtained for all the complexes. Further complex 1 shows efficient dye degradation with Rhodamine B, Congo red as well as methylene blue, where Congo red and Rhodamine B dye can be easily separated as precipitates from solution. UV–Vis and photoluminescence studies confirm the dye degradation process. The structural transformation also brings about a change in the intermolecular magnetic exchange. Magnetic studies of complex 1 reveal antiferromagnetic interactions through intermolecular hydrogen bonding interactions and a coupling constant (J) of −1.6 cm−1 was obtained from the fitting. However, for complex 2, the coupling constant (J) was changed to −2.1 cm−1.