Solvent effect on second-sphere coordination of ferrioxamine B with substituted 18-crown-6 and 30-crown-10 crown ethers in dichloromethane as compared to chloroform

Stability constants for the second-sphere association of picrate and perchlorate salts of ferrioxamine B (FeHDFB+) with the substituted crown ethers (CE) 18-crown-6, cis-dicyclohexano-18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6 and dibenzo-30-crown-10 were determined in dichloromethane and compared with corresponding data collected in chloroform. The stability of the supramolecular assembly {FeHDFB+ ,CE,X-} is increased in wet CH2Cl2 compared to wet CHCl3 by 0.21 to 0.74 log units. This represents a deviation from the expected trend of higher host-guest stability constants in a less polar solvent. The complexity of the molecular recognition process is discussed in the context of the role of the solvent in relation to the role of the cation and anion, and their hydration shells, and the crown ether structure, in determining the stability of the supramolecular assembly.

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