Relationship between the Electric Polarizability and Aromaticity of Metallocene-Containing Macrocycles

Magnetically induced ring currents, aromaticity, as well as polarizability and second hyperpolarizability of the metallocenothiaporphyrins with transition metals of group VIII (Fe, Ru) and isoelectronic cations of group IX (Co+, Rh+) and metallocene-containing annulenes ((C5H5)2\M[n = 18-24] where M is Fe, Co+) have been studied computationally at Density Functional level of Theory (DFT). The calculations show that the value of average polarizability of the studied compounds depends on their character of the aromaticity. Aromatic structures are characterized by larger polarizability than their corresponding antiaromatic congeners. The average polarizability of metallocenothiaporphyrins also depends on the magnitude of magnetically induced ring currents, which quantify the degree of electron delocalization. An increase in the number of electrons in conjugation pathway plays a key role in the growth of polarizability. Aromaticity also influences on the second hyperpolarizability of metallocene-containing annulenes. In the case of compounds with the same number of conjugated electrons, the second hyperpolarizability is larger for more aromatic systems. To conclude, our results pinpoint the importance of electron delocalization on the polarizability and second hyperpolarizability of the studied metallocene-containig macrocycles.