Spectroscopic and Theoretical Studies of Charge-Transfer Type Molecular Complexes between Monoölefins and Metal Ions: Selective Complex Formation Abilities of Copper(I), Silver(I) and Mercury(II) Ions

Abstract

Abstract The ultraviolet, infrared and Raman spectra of the cyclohexene-silver perchlorate complex have been measured under various conditions. A new band has been found in the 220∼230 mμ region for the complex in an aqueous solution; it has been found to have the mixing character of the charge-transfer from the olefln to the metal ion and of the Rydberg transition within the olefln molecule. The equilibrium constant (pK) has been evaluated spectro-photometrically as 0∼−2 for the equilibrium C6H10+Ag+\ightleftharpoonsC6H10…Ag+ The 1653 cm-−1ν(C=C) and 716 cm−1δ(=C–H) bands of pure cyclohexene have been found to shift to about 1585 and 745 cm−1 respectively by means of complex formation with silver perchlorate, both in solids and in solutions. This and other facts concerning the vibration spectrum of the complex show that the C=C bond is weakened by the complex formation. The very selective complex formation ability of Cu+, Ag+ and Hg2+ toward monoölefins has been explained by the calculation in which we explicitly took into account the charge number, the ionization potential, the electron affinity, the ionic radius, the hydration (solvation) energy, and the various atomic excitation energies of the ions. It has been pointed out that the roles of the d-electrons of the metal ion and the 3sσ-electrons of the olefln molecule are important in the ground state and the lowest excited state respectively, while the effect of the hydration (or lattice) energy is important in both states.