Predicting ESR Peaks in Copper (II) Chelates Having Quadrupolar Coordinating Sites by NMR, ESR and NQR Techniques: A DFT Study (Full Text)

Abstract

Computational chemistry was helpful in predicting the number of ESR peaks in Cu (II) complexes having a large number of spatially different NMR and ESR active nuclei. The presence of the large Jahn-Teller effect and the high value of spin-orbit coupling constant of the metal ion made the experimental determination of the exact number of ESR peaks quite difficult in such complexes. Fourteen distorted poly-dentate chelating Cu(II) complexes included in this study were of two types such as [Cu(gly)2] , [Cu(edta)]4-,[Cu(tpy)X2] (X= Cl, Br, I, NCS) and [Cu(en)2]2+, [Cu(teta)]2+, Cu(tepa)]2+ ,[Cu(peha)]2+, [Cu(deta)X2] (X= Cl, Br, I, NCS).The latter eight complexes belonged to an important class of ligands called polyethylene polyamines. Density functional theory implemented in ADF: 2010.02 was applied. Three parameters of both the ESR (A ten) and NQR (NQCC,) for the Cu(II) and the coordinating atoms of the ligands were obtained from "ESR/EPR program" and two NMR parameters namely the shielding constants () and chemical shifts () were obtained from “NMR/EPR program” after optimization of the complexes. The species having the same values of these 5 parameterswere expected to be spatially equivalent to undergo the same hyperfine interaction with Cu (II).