The Electrostatically Paired Bis(dimethyl sulfoxide)(tetrakis(1-methylpyridinium-4-yl)porphinato)iron(III)/(4,4',4'',4'''-Tetrasulfonatophthalocyaninato)zinc(II) System. Solution Structure and Dynamics

Article abstract of DOI:10.1021/j100374a015

The electrostatic pairing interactions between the bis(dimethyl sulfoxide)(tetrakis(1-methylpyridinium-4-yl)porphinato)iron(III) cation, ⁵⁺, and the (4,4',4'',4'''-tetrasulfonatophthalocyaninato)zinc(II) anion, ^4-, have been studied in dimethyl sulfoxide (DMSO) solution.Measurements of the electrostatic pair association constant, K_ep, and its dependence upon ionic strength (Me4NClO4) were made with standard visible spectroscopic techniques while association dynamics were studied by NMR methods in DMSO-d₆ solution.The exchange rate lawfor electrostatic pair formation takes into account DMSO solvent exchange of the iron porphyrin-solvent complex, and the exchange lifetime for the pair at ionic strength of 1 mM is calculated to be ca. 0.24 s at 25 deg C.Solution structural assessments were made by using measurements of the intermolecular dipolar relaxation of the (tetrasulfonatophthalocyaninato)zinc(II) protons due to the paramagnetic high-spin iron(III) center in the electrostatic pair.The structural model developed permitted calculation of a set of possible iron positions with respect to the phthalocyanine plane which are consistent with a cofacial dimeric structure displaying ?-? interactions due to pyrrole ring overlap.