Quadrupole coupling constant studies of Cu(I) in binary mixtures of acetonitrile with N,N-dimethylacetamide and Adiponitrile

Copper(I) nuclear magnetic resonance (NMR) studies of 0.064 M CuClO4 have been made in binary mixtures of acetonitrile (AN) with N,N-dimethylacetamide (DMA) and adiponitrile (ADN) co-solvents containing 100, 95, 90, 85, 80 and 75 mol % of acetonitrile at 298 K using Brüker 500 MHz NMR spectrometer. Chemical shift (d) and linewidth (D) for 63Cu and 65Cu signals have been recorded relative to 0.064 M CuClO4 solution in pure anhydrous AN. Quadrupole relaxation rates (1/T2)Q, reorientational correlation times (tR) and copper quadrupole coupling constants (e2Qq/h) have been calculated in all cases. The variation of these NMR parameters has been examined as a function of mol % of co-solvent to compare the relative effects of co-solvents on the solvation behaviour of copper (I) and hence on the stabilization of copper (I) complexes formed. The variation of quadrupole coupling constant with solvent composition shows that the (e2Qq/h) values in all composition increases with the increase of mol % of co-solvent, which indicates the formation of mixed complexes of the form [Cu(CH3CN)4−x(S)x]+ (x = 1-4) due to the replacement of AN molecules by the co-solvent molecules (S) from the original complex [Cu(CH3CN)4]+ formed in pure AN. Comparison of 63Cu and 65Cu NMR signals in pure AN shows that 63Cu is more sensitive nucleus while 65Cu yields slightly narrower signals.

Author(s): Rahul Gupta

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