Correlated ab Initio Study of the Excited State of the Iron-Coordinated-Mode Noninnocent Glyoxalbis(mercaptoanil) Ligand Sabri Messaoudi, ² Vincent Robert,* ,² Nathalie Guihe ´ ry, ‡ and Daniel Maynau ‡ Laboratoire de Chimie, UMR 5182, Ecole normale supe ´ rieure de Lyon, 46 alle ´ e d’Italie, 69364 Lyon Cedex 07, France, and Laboratoire de Physique Quantique, UMR 5626, IRSAMC, UniVersite ´ Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 04, France Received September 7, 2005 The intriguing and theoretically unresolved magnetic coupling in the Fe(gma)CN (1) compound [gma ) glyoxalbis- (mercaptoanil)] has been investigated by means of first-principle correlated ab initio calculations. The low-energy spectrum of the complex has been studied using the difference dedicated configuration interaction method, which is a dynamically correlated multiconfigurational method. In agreement with available spectroscopic information, we found that the ground-state doublet is dominated by the coupling between an iron-centered quartet and the first excited triplet on the gma ligand. The open-shell character of the electronic structure of the ligand clarifies its noninnocent nature. The low-energy spectrum reveals the presence of a first excited quartet of different symmetry lying 200 cm -1 above. The lowest excitation energy in the ground-state symmetry is found at 4790 cm -1 , thus ruling out the simple description of the system based on a Heisenberg Hamiltonian. Introduction A variety of intriguing ligands that may display different oxidation states when coordinated to metallic centers has been under intense investigation over the past decade. As prototypes of such, 1,2-bis(2-pyridinecarboxamido)benzene [H 2 (bpb)], 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene [H 4 (tpb)], and 1,2,4,5-tetrakis(4-tert-butyl-2-2-pyridinecar- boxamido)benzene [H 4 (tbpb)] have been reported in the literature. 1-3 It was initially suggested that transition-metal complexes with coordinating carboxamido N atoms were very sensitive to oxidation at both the metal and ligand centers. 4 Originally, experimentalists put much effort into the design of macrocyclic ligands to stabilize unusually high valences of transition metals such as Co IV and Fe IV . 5,6 However, the use of carboxamido-derived ligands led to rather different conclusions when, for instance, photolysis of Fe III (bpb)(N 3 ) 2 was performed. 4 The noninnocent term was thus suggested to emphasize the fact that such treatment might result in ligand oxidation. Indeed, some ligands may not necessarily possess a closed-shell configuration and the traditional definition of the formal oxidation state may not be appropriate for this class of compounds. Therefore, the possibility of generating radical ligands in coordination compounds has given rise to intense investigation because interesting magnetic materials can be anticipated. Mono- nuclear as well as dinuclear complexes of Co and Fe were synthesized and characterized. 1,3 On the basis of electro- chemical and spectroscopic experiments, the noninnocent character was fully established. The comparison between the Mo ¨ssbauer spectra of the oxidized compound Fe(bpb)(CN) 2 and its parent Na[Fe III (bpb)(CN) 2 ] clearly demonstrated that the oxidation is essentially ligand-centered. 1,2 A similar conclusion was drawn for the dinuclear cyano complexes [N(n-Bu) 4 ] 2 [Fe III 2 (tpb)(CN) 4 ] and [N(n-Bu) 4 ] 2 [Co III 2 (tbpb)- (CN) 4 ]. 3 From both experimental and theoretical points of view, other classes of ligands, namely, aminophenolate and amino- thiophenolate, have also attracted a lot of attention. 7-10 * To whom correspondence should be addressed. E-mail: vrobert@ ens-lyon.fr. Tel: 33 4 72 72 88 42. Fax: 33 4 72 72 88 60. ² Ecole normale supe ´rieure de Lyon. ‡ Universite ´ Paul Sabatier. (1) Dutta, S. K.; Beckmann, U.; Eckhard, B.; Weyhermu ¨ller, T.; Wieghardt, K. Inorg. Chem. 2000, 39, 3355. (2) Patra, A. K.; Ray, M.; Mukherjee, R. Inorg. Chem. 2000, 39, 652. (3) Beckmann, U.; Eckhardt, B.; Weyhermu ¨ ller, T.; Wieghardt, K. Inorg. Chem. 2003, 42, 1045. (4) Ray, M.; Mukherjee, R.; Richardson, J. F.; Buchanan, R. M. J. Chem. Soc., Dalton Trans. 1993, 2451. (5) Collins, T. J.; Uffelman, E. S. Angew. Chem., Int. Ed. Engl. 1989, 28, 1509. (6) Kostka, K. L.; Fox, B. G.; Hendrich, M. P.; Collins, T. J.; Rickard, C. E. F.; Wright, L. J.; Munck, E. J. Am. Chem. Soc. 1993, 115, 6746. (7) Herebian, D.; Bothe, E.; Bill, E.; Weyhermu ¨ller, T.; Wieghardt, K. J. Am. Chem. Soc. 2001, 123, 10012. Inorg. Chem. 2006, 45, 3212-3216 3212 Inorganic Chemistry, Vol. 45, No. 8, 2006 10.1021/ic051526t CCC: $33.50 © 2006 American Chemical Society Published on Web 03/14/2006