Tetra- and Decanuclear Iron(III) Phosphonates: Observance of a Rare P-C Bond Cleavage in a Homogeneous Medium Ramaswamy Murugavel,* ,†,‡ Nayanmoni Gogoi, † and Rodolphe Cle ´rac §,⊥ Department of Chemistry and Centre for Research in Nanotechnology and Science (CRNTS), Indian Institute of TechnologysBombay, Powai, Mumbai-400076, India, and CNRS, UPR 8641, Centre de Recherche Paul Pascal (CRPP), Equipe “Matériaux Moléculaires Magnétiques”, 115 aVenue du Dr. Albert Schweitzer, Pessac, F-33600, France, and Uni Versité de Bordeaux, UPR 8641, Pessac, F-33600, France Received September 12, 2008 Reactions of tert-butylphosphonic acid ( t BuPO 3 H 2 ) with two different Fe(III) precursors have been investigated. The reaction of precursor complex [Fe 3 (µ 3 -O)(O 2 CPh) 6 (H 2 O) 3 ]Cl with t BuPO 3 H 2 in pyridine (py) leads to the formation of tetranuclear iron(III)phosphonate [Fe 4 O( t BuPO 3 ) 3 (O 2 CPh) 3 (py) 3 Cl] · 3.5py (1) as single crystals. The change of the Fe(III) source to FeCl 3 under similar reaction conditions results in the isolation of decanuclear complex [Fe 10 (OH) 8 (HPO 4 )( t BuPO 3 ) 8 ( t BuPO 3 H) 4 (py) 8 ] · 4py · 5H 2 O(2). Compounds 1 and 2 have been characterized by elemental analysis, spectroscopic studies, and single-crystal X-ray diffraction studies. While the structure of 1 could be described as a tetrahedral cluster supported by benzoate and phosphonate ligands, the molecular structure of 2 is unprecedented in metal phosphonate chemistry. In the course of formation of 2, t BuPO 3 H 2 undergoes a rare P-C bond cleavage at room temperature and produces the phosphate anion, which then acts as a template for the construction of a novel decanuclear iron-phosphate-phosphonate with a hitherto unknown core architecture. The temperature dependence of the T product in 2 reveals dominant antiferromagnetic interactions between Fe(III) centers. Introduction There has been considerable interest in the use of main group compounds containing many acidic hydrogen atoms (e.g., hydroxyl, amino, and acid groups) to build cagelike molecules, extended polymers, and three-dimensional frame- work solids including metal-organic frameworks. Polycar- boxylic acids, organosilanetriols, and phosphonic/phosphoric acids have been extensively used for this purpose in the past decade. 1 We have been particularly interested in a room- temperature building-block approach for the rational syn- thesis of cagelike and zeolite-like metal phosphonate or phosphate materials. 2-4 In this endeavor, after having incorporated main group elements in the zeolite SBU look- * Author to whom correspondence should be addressed. Fax: +91-22- 2572 3480. E-mail: rmv@chem.iitb.ac.in. † Department of Chemistry. IITsBombay. ‡ CRNTS, IITsBombay. § CNRS, UPR8641 CRPP. ⊥ Université de Bordeaux. (1) (a) Murugavel, R.; Choudhury, A.; Pothiraja, R.; Walawalkar, M. 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(i) Murugavel, R.; Sathiyendiran, M.; Pothiraja, R.; Butcher, R. J. Chem. Commun. 2003, 2546. Inorg. Chem. 2009, 48, 646-651 646 Inorganic Chemistry, Vol. 48, No. 2, 2009 10.1021/ic8017562 CCC: $40.75  2009 American Chemical Society Published on Web 12/16/2008