Spin Distribution in Electron-Rich Piano-Stool Iron(III) Pyridylalkynyl Radical Cations Containing [(η²-dppe)(η⁵-C₅Me₅)FeCC]⁺ End Groups

This experimental and theoretical contribution is aimed at investigating the electronic structure of cationic electron-rich ethynylpyridyl Fe(III) derivatives of the formula [(η2-dppe)(η5-C5Me5)FeCC(x-C5H4N)][PF6] (x = 4, 3, 2; 1a−c[PF6]) and [(η2-dppe)(η5-C5Me5)FeCC(2,5-C5H3NX)][PF6] (X = Cl, Br; 2a,b[PF6]). The Mössbauer, NMR, and ESR characterization of these paramagnetic species are reported and discussed in connection with DFT results. Special emphasis is put on the electronic effect of the nitrogen atom and of the halogen substituent on the spin distribution within the pyridyl unit. It is shown that 1H NMR constitutes a straightforward empirical way to investigate the slight changes in spin distribution taking place on the heteroaryl ring.