EPR spectra in γ‐irradiated PPN + HFeW(CO) 9 − crystals

Single crystals of PPN + HFeW(CO) 9 − prepared from THF · W(CO) 5 and PPN + HFe(CO) 4 − exhibit weak single‐line EPR spectra corresponding to the presence of two paramagnetic impurities. One of the spectra increases in intensity by an order of magnitude on 60 Co γ‐irradiation. The g 2 matrices for both species in an orthogonal crystal‐axis system were assembled from measurements of g values made at 77 K on crystallographically oriented samples. The intense spectrum has principal g values of 2.0064, 2.0468 and 2.1320 and principal directions of g which lie close to bonds emanating from the Fe nucleus of the undamaged anion. Consideration of the principal g values and directions for this species leads to an assignment to a FeW(CO) 9 − radical in which the unpaired electron is principally located in a Fe 3d   z   2orbital directed along the FeH bond of the host anion. The other signal has principal g values (2.0229, 2.0425, 2.0950) close to those established for the singly bridged isomer of Fe 2 (CO) 8 − , but their directions do not correlate well with bond directions within the host anion. It is concluded that small amounts of the persistent Fe 2 (CO) 8 − radical generated in the preparative procedures substitute for the host anion in the crystals of PPN + HFeW(CO) 9 − .