Solvation behaviour of some copper(I) perchlorate complexes has been investigated in binary mixtures of acetonitrile (AN) and dimethylsulphoxide (DMSO) containing 1.0, 0.8, 0.6, 0.4, 0.2 and 0 mol fraction of AN at 298 K by molar conductances and viscosity measurements. The conductance data have been analyzed by using the Shedlovsky method to calculate limiting molar conductance (Λ o ) and the viscosity data by the Jones–Dole equation to evaluate viscosity B-coefficients of various salts. Limiting ion conductances (λ i o ), solvated radii (ri ) and ionic viscosity B ± coefficients in all solvent systems have been evaluated using Gill´s modification based on Bu4NBPh4 as a reference electrolyte. The studies show that all copper(I) complexes are solvated and the extent of solvation is stronger in AN and AN rich regions than in DMSO and DMSO rich regions. The ClO4 - ion is poorly solvated in AN+DMSO mixtures. The viscosity results are in good agreement with the results obtained from the conductance studies.

Ultrasonic velocity (u) and density (ρ) of the binary mixtures of acetonitrile (AN) with nitromethane (NM) and dimethylsulfoxide (DMSO) as well as of the solutions of Bu4NBPh4, Bu4NClO4, [Cu(CH3CN)4]ClO4, [Cu(Phen)2]ClO4, [Cu(DMPhen)2]ClO4 and [Cu((NH2)2CS)4]ClO4 have been measured over the entire composition range at 298.15 K. Using these data, isentropic compressibilities (K s) and apparent molal isentropic compressibilities (K s, ϕ ) for various salts have been calculated and used for the evaluation of limiting apparent molal isentropic compressibilities (K s, ϕ 0). The K s, ϕ 0 values of various salts have been split into the contribution of individual ions (K s, ϕ 0)±. The (K s, ϕ 0)± values for all copper (I) cations [Cu(CH3CN)4]+, [Cu(Phen)2]+, [Cu(DMPhen)2]+ and [Cu((NH2)2CS)4]+ are negative and large, for Bu4N+ and Ph4B− are positive and large at all compositions in both AN + NM and AN + DMSO mixtures but for ClO4 − are negative in AN + DMSO mixtures and positive in AN + NM mixtures. The variation of (K s, ϕ 0)± values with solvent composition indicates that both DMSO and NM interact with complex copper (I) cations forming complex ions of the type [Cu(CH3CN)4 − x (S) x ]+ (x = 1–4 and S = co-solvent) and [Cu(ligand)2]+(CH3CN) y (S) z in which AN is systematically replaced by the co-solvents. DMSO interacts more strongly with complex copper (I) cations and ClO4 − ion as compared to NM. Bu4N+ and Ph4B− show some special interaction with AN which decreases with the increase of NM or DMSO composition in the mixture.

Ultrasonic velocities and densities of some copper(I), silver(I), and tetrabutylammonium salts have been measured in the concentration range of (0.002 to 0.28) m in binary mixtures of acetonitrile (AN) + adiponitrile (ADN) containing 1.0, 0.9, 0.8, 0.7, 0.6, and 0.5 mol fraction of AN at 298.15 K. The isentropic compressibility (κ s ) and apparent molal isentropic compressibility (κ s,φ ) in various solvent systems have been calculated by using ultrasonic velocity (u) and partial molal volume (V φ ) data, respectively. Limiting apparent molal isentropic compressibilities (κ s,φ o ) for various salts have been evaluated from κ s,φ versus m 1/2 plots and split into the contributions of individual ions (κ s,φ o ) ( . The (κ s,φ o ) ( values for copper(I) and silver(I) ions are found to be negative over the entire solvent composition range which indicates strong solvation of these ions. The (κ s,φ o ) ( values becoming more and more negative with an increase in the ADN composition shows that the extent of solvation increases with an increase in ADN composition. The large and positive (κ s,φ o ) ( values for Bu 4 N + and Ph 4 B -indicate some special type of interaction with the solvent molecules, which increases with the increase of ADN composition in the mixture.

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