A Comparative Nuclear Magnetic Resonance Study of the Solvation of CuClO<sub>4</sub> in Binary Mixtures of Acetonitrile with Pyridine and Picolines at 298 K

⁶³Cu nuclear magnetic resonance (NMR) and viscosity studies of 0.064 M CuClO₄ solutions have been reported in binary mixtures of acetonitrile (AN) with pyridine (Py) and 2, 3, and 4-picolines (2,3,4-Pic) at 298 K using a Bruker 500 MHz NMR spectrometer and an Ubbelohde viscometer, respectively. Chemical shift δ and linewidth Δ for the ⁶³Cu signals have been recorded referenced to a 0.064 M CuClO₄ solution in anhydrous AN. The copper quadrupole coupling constants (e²Qq/h) have been calculated in all cases. The variation of the δ and e²Qq/h values as a function of mol fraction of the co-solvent show that all these bases interact with Cu⁺ more strongly than AN. They replace AN from the Cu⁺ complexed with AN in the form [Cu(AN)₄]⁺ and form a mixed complex of the type [Cu(AN)₄–x(S)x]⁺ (x = 1–4) where S stands for the base. At relatively high mole fraction of the co-solvents, the mixed solvated complex gradually changes to a more symmetrical complex of the type [Cu(S)₄]⁺ which remains stable in the solution. The solvating effect of 2-Pic and 4-Pic is observed to be stronger than that of Py and 3-Pic.