The electronic and geometric structures of paramagnetic iron dinitrosyl complexes have been investigated using electron spin resonance, infrared spectroscopy, and X-ray crystallography. It is concluded that these compounds are best described as 17 electron complexes with a d 9 configuration rather than the d 7 configuration assumed by most previous investigators. The anisotropy of the g values, determined from the electron spin resonance spectra of frozen solutions, varies considerably from complex to complex. The results are consistent with the supposition that all of the complexes have a distorted tetrahedral geometry, but the nature of the distortion changes as the ligands are varied. As a result of this variation there are changes in the nature of the spin-containing d orbital. Ligands containing hard, nonpolarizable donor atoms such as oxygen or fluorine produce a distortion towards a planar geometry, placing the odd electron in a predominantly d, 2-, 2 orbital, while those containing softer donor atoms such as phosphorus or sulfur give complexes with a different type of distortion, leading to placement of the odd electron in a predominantly dz2 orbital. Nitrogen and halide donor ligands produce smaller distortions, leading to spin-containing molecular orbitals with contributions from a mixture of d orbitals. In accordance with this model, the crystal structure of [Fe(NO),I,]-has been found to be only slightly distorted from regular tetrahedral coordination about the iron atom. TRACI R. BRYAR et DONALD R. EATON. Can. J. Chem. 70, 1917Chem. 70, (1992. Faisant appel 2 la resonance paramagnetique Clectronique (rpe), a la spectroscopie infrarouge et i la diffraction des rayons X, on a CtudiC les structures Clectroniques et geometriques des complexes paramagnetiques du dinitrosyl fer. On en conclut que la meilleure f a~o n de dCcrire ces composCs est de les considerer comme des complexes 2 17 klectrons possidant une configuration d 9 plut6t que la configuration d7 utilisee par la plupart des auteurs qui en ont trait6 anterieurement. L'anisotropie des valeurs g, determinee par les spectres rpe de solutions congelees, varie beaucoup d'un complexe 2 l'autre. Les resultats sont en accord avec l'hypothkse selon laquelle tous les complexes possedent une gkomktrie tCtraCdrique dCformCe, mais que la nature de la distorsion varie avec la nature des ligands. Un rksultat de cette variation amkne des changements dans la nature de l'orbitale contenant le spin. Les ligands contenant des atomes donneurs durs et non-polarisables, comme l'oxygkne ou le fluor, provoquent une distorsion vers une gComCtrie plane forqant 1'Clectron celibataire 2 1 occuper une orbitale principalement dX2-y2 alors que ceux qui contient des atomes donneurs plus mous, comme le phosphore ou le soufre, donnent des complexes~avec un type de distorsion different, conduisant . [Traduit par la rkdaction]
