A Heterobimetallic Ruthenium(II)−Copper(II) Donor−Acceptor Complex as a Chemodosimetric Ensemble for Selective Cyanide Detection

A trinuclear heterobimetallic Ru(II)-Cu(II) donor-acceptor complex, {Ru^II(^tBubpy)(CN)₄-[Cu^II(dien)]₂}(ClO₄)₂ (^tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine; dien = diethylenetriamine) (1), has been synthesized and successfully used as an chemodosimetric ensemble for the specific detection of cyanide in aqueous DMF. X-ray crystallography, solid and solution IR spectroscopy, and conductivity measurements reveal that complex 1 is a one-dimensional polymer in the crystalline state and dissociates into its {Ru^II(^tBubpy)(CN)₂[(CN)Cu^II(dien)L]₂}²⁺ (L = solvent) monomeric units in polar solvents. The MLCT transition and luminescence properties of the solvatochromic [Ru^II(^tBubpy)(CN)₄]^2- donor are perturbed by the coordination of two Cu(II) acceptors but restored in the presence of CN^-. Spectroscopic and mass spectrometric studies confirm the cleavage of the cyano bridge between Ru(II) and Cu(II) of the chemodosimetric ensemble after the binding of cyanide to the Cu(II) centers. The overall binding constant, K_B, between 1 and CN^- is measured to be (7.39 ± 0.23) × 10⁶ M^-2. A detection limit of 1.2 μM (0.03 ppm) of CN^- in aqueous DMF (pH 7.4) is achievable. Thermodynamic evaluation shows that the analyte specificity of chemodosimeter 1 is attributable to the relative stability of the donor-acceptor complex to that of adducts formed between the acceptor metal center and the analytes.