Synthesis and Characterization of the Mn(II) Complex of [15]aneN5

The complex Mn15]aneN₅CIPF₆ has been prepared by the reaction of MnCI₂ 15]aneN₅.3HPF₆, and NaOH in water (15]aneN₅ is 1,4,7,10,13-pentaazacyclopentadecane). The complex is obtained as a white solid formulated as Mn(C₁₀H₂₅N₅)Cl](PF₆).3/2H₂O. It is a 2: 1 electrolyte in H₂O and a 1:1 electrolyte in CH₃CN, The complex contains high spin Mn(II), μ_eff = 5.83 B.M., and the EPR spectrum of the polycrystalline solid is indicative of rhombic symmetry at the metal site. The proton NMR relaxation enhancement of aqueous solvent by the complex is 2.3 mM^?1S ^?1 at 24 MHz and 25°C and is indicative of one rapidly exchanging water molecule in the coordination sphere of the solvated complex. The stability constant for the formation of the complex in aqueous solution as measured by potentiometric titration (IogK = 10.7) is four orders of magnitude greater than the comparable linear polyamine. In all, the characterization data are consistent with Mn(lI) strongly bound to a distorted or folded ligand and able to accommodate only one additional ligand.