An iron(III )trichloride adduct of N-isopropylsalicylaldimine:: preparation, X-ray structure and NMR spectroscopic characterization

The reaction of anhydrous iron(III)trichloride and N-isopropylsalicylaldimine ((LH)-H-ipr) in benzene yields the adduct Fe((LH)-H-ipr)Cl-3. The X-ray crystal structure of the compound shows a mononuclear tetrahedral iron(III) center with only the oxygen atom of the potentially bidentate Schiff base ligand coordinated to iron(III)trichloride. The imine nitrogen of the coordinated ligand is protonated and non-coordinating with (LH)-H-ipr binding to iron in its phenolate-iminium (zwitterion) form with a {Fe-O---H-N=C} intraligand hydrogen bond. The solid-state infrared spectrum of Fe((LH)-H-ipr)Cl-3 exhibits an increase in the energy of the C=N stretch from 1631 cm(-1) in the free ligand to 1649 cm(-1) consistent with the protonation of the imine upon coordination. The solution H-1 NMR spectrum of Fe((LH)-H-ipr)Cl-3 and the solution H-2 NMR spectrum of its deuterated derivative Fe((LD)-D-ipr)Cl-3 also support this coordination mode displaying isotropically shifted iminium C-H-1 and N-H-2 resonances at 21.8 and -43.7 ppm. respectively, A well-resolved solid-state N-15 magic angle spinning NMR resonance with a centerband at 970 ppm can be observed at 25 degreesC with the N-15 enriched derivative of Fe((LH)-H-ipr)Cl-3. (C) 2002 Elsevier Science B.V. All rights reserved.