Search For Electron Delocalization From [Fe(Cn)(6)](3-) To The Dication Of Viologen In (Dnp)(3)[Fe(Cn)(6)](2)Center Dot 10h(2)O

K3Fe(CN)(6) reacts with the viologen 1,1'-bis(2,4-dinitropheny1)4,4'-bipyridinium dication, (DNP)(2+), to form a supramolecular complex, (DNP)(3)[Fe-(CN)(6)](2)center dot 10H(2)O (1). The crystal structure of 1 reveals that there are two [Fe(CN)(6)](3-) anions within an organic framework of three (DNP)(2+) cations with the Shortest Pe(III)center dot center dot center dot Fe(III) distances of ca. 9.8 angstrom, distances that minimize extensive long-range magnetic exchange coupling interactions between the [Fe(CN)(6)](3-) anions, and, thus, 1 is paramagnetic above ca. 17 K and exhibits weak ferromagnetic coupling between 17 and 3 K and antifertomagnetic coupling between 3 and L8 K. The long Fe(ILI)center dot center dot center dot Fe(III) distances permit slow spin-spin and slow spin-lattice paramagnetic relaxation, relative to the iron-57 Latmor precession frequency, as is evidenced by the Mossbauer spectra measured between 3 and 60 K; between 85 and 295 K, rapid paramagnetic relaxation is observed. Both the slow spin-spin and slow spin-lattice relaxation are mediated by the organic, pi-conjugated viologen cations. The Fe-C distances, the Mossbauer isomer shifts, the temperature dependence of the magnetic susceptibility, and the 3 K magnetization results all indicate the presence of low-spin Fe(III) ions in the [Fe(CN)(6)](3-) anions in 1. There is no unequivocal indication of the presence of any formal electron delocalization or transfer from the [Fe(CN)(6)](3-) anion to the (DNP)(2+) cations in the results obtained from X-ray crystallography, magnetic measurements, and Mossbauer spectra. Because of enhancement of the spin-orbit coupling by the heavy-atom or-ion effect, the Fe(III) ions in the [Pe(CN)(6)](3-) anions interact with the (DNP)(2+) cations, causing them to fluoresce with increasing intensity upon cooling from 90 to 25 K when excited at 300 nm. The resulting luminescence of the viologen (DNP)2 cation induced by the [Fe(CN)(6)](3-) anions indicates the presence of significant mixing of the molecular orbitals derived from the [Fe(CN)6]3- anions and the molecular orbitals associated with the (DNP)(2+) cations to yield bonding supramolecular orbitals in 1, a mixing that is also observed between 50 and 3 K in the temperature dependence of the isomer shift of 1.