279Mn2bpyfullIC - Inorg. Chem. 2003, 42, 14831492 Symmetric...

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Symmetric and Asymmetric Dinuclear Manganese(IV) Complexes Possessing a [Mn IV 2 ( μ -O) 2 ( μ -O 2 CMe)] 3 + Core and Terminal Cl - Ligands Sumit Bhaduri, ² Anastasios J. Tasiopoulos, ² Milissa A. Bolcar, Khalil A. Abboud, ² William E. Streib, and George Christou* ,²,‡ Department of Chemistry, Uni V ersity of Florida, Gaines V ille, Florida 32611-7200, and Department of Chemistry and Molecular Structure Center, Indiana Uni V ersity, Bloomington, Indiana 47405-7102 Received September 19, 2002 The synthesis of new dinuclear manganese(IV) complexes possessing the [Mn IV 2 ( μ -O) 2 ( μ -O 2 CMe)] 3 + core and containing halide ions as terminal ligands is reported. [Mn 2 O 2 (O 2 CMe)Cl 2 (bpy) 2 ] 2 [MnCl 4 ]( 1 ; bpy ) 2,2 -bipyridine) was prepared by sequential addition of [MnCl 3 (bpy)(H 2 O)] and (NBzEt 3 ) 2 [MnCl 4 ]toaCH 2 Cl 2 solution of [Mn 3 O 4 - (O 2 CMe) 4 (bpy) 2 ]. The complex [Mn IV 2 O 2 (O 2 CMe)Cl(bpy) 2 (H 2 O)](NO 3 ) 2 ( 2 ) was obtained from a water/acetic acid solution of MnCl 2 4H 2 O, bpy, and (NH 4 ) 2 [Ce(NO 3 ) 6 ], whereas the [Mn IV 2 O 2 (O 2 CR)X(bpy) 2 (H 2 O)](ClO 4 ) 2 [X ) Cl - and R ) Me ( 3 ), Et ( 5 ), or C 2 H 4 Cl (6 ); and X ) F - ,R ) Me ( 4 )] were prepared by a slightly modified procedure that includes the addition of HClO 4 . For the preparation of 4 , MnF 2 was employed instead of MnCl 2 4H 2 O. [Mn 2 O 2 (O 2 - CMe)Cl 2 (bpy) 2 ] 2 [MnCl 4 ] 2CH 2 Cl 2 ( 1 2CH 2 Cl 2 ) crystallizes in the monoclinic space group C 2/ c with a ) 21.756(2) Å, b ) 12.0587(7) Å, c ) 26.192(2) Å, R) 90 ° , ± ) 111.443(2) ° , γ ) 90 ° , V ) 6395.8(6) Å 3 , and Z ) 4. [Mn 2 O 2 (O 2 CMe)Cl(H 2 O)(bpy) 2 ](NO 3 ) 2 H 2 O( 2 H 2 O) crystallizes in the triclinic space group P 1 h with a ) 11.907(2) Å, b ) 12.376(2) Å, c ) 10.986(2) Å, 108.24(1) ° , ± ) 105.85(2) ° , γ ) 106.57(1) ° , V ) 1351.98(2) Å 3 , and Z ) 2. [Mn 2 O 2 (O 2 CMe)Cl(H 2 O)(bpy) 2 ](ClO 4 ) 2 MeCN ( 3 MeCN) crystallizes in the triclinic space group P 1 h with a ) 11.7817(7) Å, b ) 12.2400(7) Å, c ) 13.1672(7) Å, 65.537(2) ° , ± ) 67.407(2) ° , γ ) 88.638(2) ° , V ) 1574.9(2) Å 3 , and Z ) 2. The cyclic voltammogram (CV) of 1 exhibits two processes, an irreversible oxidation of the [MnCl 4 ] 2 - at E 1 / 2 0.69 V vs ferrocene and a reversible reduction at E 1 / 2 ) 0.30 V assigned to the [Mn 2 O 2 (O 2 CMe)Cl 2 (bpy) 2 ] +/ 0 couple (2Mn IV to Mn IV Mn III ). In contrast, the CVs of 2 and 3 show only irreversible reduction features. Solid-state magnetic susceptibility ( l M ) data were collected for complexes 1 1.5H 2 O, 2 H 2 O, and 3 H 2 O in the temperature range 2.00 - 300 K. The resulting data were fit to the theoretical l M T vs T expression fo raMn IV 2 complex derived by use of the isotropic Heisenberg spin Hamiltonian ( H ) - 2 JS ˆ 1 S ˆ 2 ) and the Van Vleck equation. The obtained fit parameters were (in the format J / g ) - 45.0(4) cm - 1 /2.00(2), - 36.6(4) cm - 1 /1.97(1), and - 39.3(4) cm - 1 /1.92(1), respectively, where J is the exchange interaction parameter between the two Mn IV ions. Thus, all three complexes are antiferromagnetically coupled. Introduction The four-electron oxidation of water to form O 2 is a light- driven process that occurs in the complex protein cluster called photosystem II (PSII). This reaction is responsible for nearly all of the atmospheric dioxygen on earth and is catalyzed by the water-oxidizing complex (WOC), which
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279Mn2bpyfullIC - Inorg. Chem. 2003, 42, 14831492 Symmetric...

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