409 - Inorg. Chem. 2007, 46, 45354547 Diversity of New...

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Diversity of New Structural Types in Polynuclear Iron Chemistry with a Tridentate N,N,O Ligand Rashmi Bagai, ² Saiti Datta, Amalia Betancur-Rodriguez, Khalil A. Abboud, ² Stephen Hill, and George Christou* Department of Chemistry and Department of Physics, Uni V ersity of Florida, Gaines V ille, Florida 32611-7200 Received January 21, 2007 The syntheses, crystal structures, and magnetochemical characterization of four new iron clusters [Fe 7 O 4 (O 2 CPh) 11 - (dmem) 2 ]( 1 ), [Fe 7 O 4 (O 2 CMe) 11 (dmem) 2 2 ), [Fe 6 O 2 (OH) 4 (O 2 CBu t ) 8 (dmem) 2 3 ), and [Fe 3 O(O 2 CBu ) 2 (N 3 ) 3 (dmem) 2 ] ( 4 ) (dmemH ) Me 2 NCH 2 CH 2 N(Me)CH 2 CH 2 OH) ) 2- { [2-(dimethylamino)ethyl]methylamino } ethanol) are reported. The reaction of dmemH with [Fe 3 O(O 2 CR) 6 (H 2 O) 3 ](NO 3 )(R ) Ph ( 1 ), Me ( 2 ), and Bu ( 3 )) gave 1 , 2 , and 3 , respectively, whereas 4 was obtained from the reaction of 3 with sodium azide. The complexes all possess rare or novel core topologies. The core of 1 comprises two [Fe 4 ( μ 3 -O) 2 ] 8 + butterfly units sharing a common body Fe atom. The core of 2 consists of a [Fe 3 O 3 ] ring with each doubly bridging O 2 - ion becoming μ 3 by also bridging to a third, external Fe atom; a seventh Fe atom is attached on the outside of this core via an additional μ 3 -O 2 - ion. The core of 3 consists of a [Fe 4 ( μ 3 -O) 2 ] 8 + butterfly unit with an Fe atom attached above and below this by bridging O atoms. Finally, the core of 4 is an isosceles triangle bridged by a μ 3 -O 2 - ion with a rare T-shaped geometry and with the azide groups all bound terminally. Variable-temperature, solid-state dc, and ac magnetization studies were carried out on complexes 1 - 4 in the 5.0 - 300 K range. Fitting of the obtained magnetization ( M ) vs field ( H ) and temperature ( T ) data by matrix diagonalization and including only axial anisotropy (zero-field splitting) established that 1 , 2 , and 4 each possess an S ) 5 / 2 ground state spin, whereas 3 has an ) 5 ground state. As is usually the case, good fits of the magnetization data could be obtained with both positive and negative D values. To obtain more accurate values and to determine the sign of , high-frequency EPR studies were carried out on single crystals of representative complexes 1 4MeCN and 3 2MeCN, and these gave ) + 0.62 cm - 1 and | E | g 0.067 cm - 1 for 1 4MeCN and ) - 0.25 cm - 1 for 3 2MeCN. The magnetic susceptibility data for 4 were fit to the theoretical l M vs expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed the pairwise exchange parameters to be antiferromagnetic with values of J a ) - 3.6 cm - 1 and b ) - 45.9 cm - 1 . The combined results demonstrate the ligating flexibility of dmem and its usefulness in the synthesis of a variety of Fe x molecular species. Introduction Polynuclear iron compounds with oxygen-based ligation are relevant to a variety of fields such as bioinorganic chemistry and magnetic materials. Iron - oxo centers are found in several non-heme metalloproteins and metalloen- zymes; for example, in mammals, iron is stored as ferritin,
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409 - Inorg. Chem. 2007, 46, 45354547 Diversity of New...

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