CuI complexes with N,N',S,S' scorpionate ligands: evidence for dimer-monomer equilibria.

The heteroscorpionate N,N′,S,S′ donor ligands 4-methoxy-3,5-dimethyl-2-(3-(methylthio)-1-(3-(2-(methylthio)phenyl)-1H-pyrazol-1-yl)propyl)pyridine (La) and 4-methoxy-3,5-dimethyl-2-(2-(methylthio)-1-(3-(2-(methylthio)phenyl)-1H-pyrazol-1-yl)ethyl)pyridine (Lb) were prepared. The CuI complexes [Cu(La)]2(BF4)2 (a2(BF4)2) and [Cu(Lb)]2(BF4)2 (b2(BF4)2) were synthesized and characterized by X-ray crystallography. Both compounds exhibit a dinuclear structure, presenting each CuI center in a distorted N,N′,S,S′ tetrahedral environment. On the basis of nuclear magnetic resonance (NMR) and ESI−mass data, the presence of a mononuclear complex in equilibrium with the dimer was hypothesized for both complexes. The dimerization constants of the processes, 2a+ = a22+ and 2b+ = b22+, were obtained by 1H NMR dilution experiments (fast-exchange regime) in CD3CN: log K(a22+) = 3.55(6) and log K(b22+) = 3.23(5) at 300 K. Thermodynamic parameters were determined by a van’t Hoff analysis (280−310 K temperature range): ΔH0(a2...