The Photochemistry of [FeIIIN3(cyclam‐ac)]PF6 at 266 nm |
| |
Authors: | Dr Joel Torres‐Alacan Oliver Krahe Prof?Dr Alexander C Filippou Prof?Dr Frank Neese Prof?Dr Dirk Schwarzer Prof?Dr Peter Vöhringer |
| |
Institution: | 1. Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich‐Wilhelms Universit?t, Wegelerstra?e 12, 53115 Bonn (Germany), Fax: (+49)?228‐73‐7050;2. Max‐Planck‐Institut für bioanorganische Chemie, Stiftsstra?e 34‐36, 45470 Mülheim an der Ruhr (Germany), Fax: (+49)?208‐306‐3951;3. Institut für Anorganische Chemie, Rheinische Friedrich‐Wilhelms Universit?t, Gerhard Domagk Stra?e 12, 53115 Bonn (Germany), Fax: (+49)?228‐73‐5327;4. Max‐Planck‐Institut für biophysikalische Chemie, Am Fassberg 11, 37077 G?ttingen (Germany) |
| |
Abstract: | The photochemistry of iron azido complexes is quite challenging and poorly understood. For example, the photochemical decomposition of FeIIIN3(cyclam‐ac)]PF6 ( 1 ]PF6), where cyclam‐ac represents the 1,4,8,11‐tetraazacyclotetradecane‐1‐acetate ligand, has been shown to be wavelength‐dependent, leading either to the rare high‐valent iron(V) nitrido complex FeVN(cyclam‐ac)]PF6 ( 3 ]PF6) after cleavage of the azide Nα? Nβ bond, or to a photoreduced FeII species after Fe? Nazide bond homolysis. The mechanistic details of this intriguing reactivity have never been studied in detail. Here, the photochemistry of 1 in acetonitrile solution at room temperature has been investigated using step‐scan and rapid‐scan time‐resolved Fourier transform infrared (FTIR) spectroscopy following a 266 nm, 10 ns pulsed laser excitation. Using carbon monoxide as a quencher for the primary iron‐containing photochemical product, it is shown that 266 nm excitation of 1 results exclusively in the cleavage of the Fe? Nazide bond, as was suspected from earlier steady‐state irradiation studies. In argon‐purged solutions of 1 ]PF6, the solvent‐stabilized complex cation FeII(CH3CN)(cyclam‐ac)]+ ( 2 red ) together with the azide radical (N3.) is formed with a relative yield of 80 %, as evidenced by the appearance of their characteristic vibrational resonances. Strikingly, step‐scan experiments with a higher time resolution reveal the formation of azide anions (N3?) during the first 500 ns after photolysis, with a yield of 20 %. These azide ions can subsequently react thermally with 2 red to form FeIIN3(cyclam‐ac)] ( 1 red ) as a secondary product of the photochemical decomposition of 1 . Molecular oxygen was further used to quench 1 red and 2 red to form what seems to be the elusive complex Fe(O2)(cyclam‐ac)]+ ( 6 ). |
| |
Keywords: | kinetics laser chemistry photolysis reaction mechanisms time‐resolved spectroscopy |
|
|