Association Constants of Ferrocene with Cyclodextrins in Aqueous Medium Determined by Solubility Measurements of Ferrocene

The association constants of ferrocene with cyclodextrins (CyD’s) in an aqueous medium at 25 °C have been determined by solubility measurements of ferrocene in both the absence and presence of CyD. The solubility of ferrocene in pure water was found to be (4.25 ± 0.02) × 10−5 mol dm−3 at 25.0 ± 0.1 °C. The β- and γ-CyD’s form only 1 : 1 complexes with ferrocene. The 1 : 1 association constants were determined to be (1.39 ± 0.21) × 102 (α), (1.65 ± 0.04) × 104 (β), and (9.04 ± 0.11) × 102 dm3 mol−1 (γ). The 2 : 1 (CyD : ferrocene) association constant was (2.36 ± 0.06) × 103 dm3 mol−1 (α). Ferrocene-included CyD precipitates were also prepared in water, and their stability upon drying in air was studied. The sublimation enthalpy of ferrocene in the temperature range of 290.65 to 298.15 K was estimated to be 74.2 ± 1.5 kJ mol−1.