63Cu nuclear magnetic resonance (NMR) and viscosity studies of 0:064M 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 d and linewidth D for the 63Cu signals have been recorded referenced to a 0:064M CuClO4 solution in anhydrous AN. The copper quadrupole coupling constants (e2Qq=h) have been calculated in all cases. The variation of the d 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.
