An inorganic model approach to the photosynthetic water oxidation enzyme has been initiated, and synthetic entry into tetranuclear Mn complexes containing [Mn402]6+,7+,8+ cores has been achieved. They have been obtained by bipyridine (bipy)-mediated conversion of trinuclear [Mn30]-containing species, with the product oxidation level governed by the exact identity of the [Mn30] reagent employed. Treatment of Mn30(02CMe)6(py)3 with ~3 equiv of bipy in MeCN yields
The synthesis, single-crystal X-ray structures, and magnetochemical properties are reported for two new hexanuclear ferric complexes, [Fe6(M3-0)2(M2-OH)2(M2-02CCH3)io(C7HnN20)2]4CH2Cl2 (9-4CH2Cl2) and [Fee0*3-0)2(C6H6N0)8C14](C104)24MeCN (KMMeCN). The ligand C7HnN20-is the anion of 2-(7V-methylimidazol-2yl)-2-hydroxypropane and C6H6NO™ is the anion of 2-pyrididylcarbinol. The reaction of [Fe3G(OAc)6(py)3] C104 in acetonitrile with 2-(iV-methylimidazol-2-yl)-2-hydroxypropane gives a brown oil which can be crystallized via vapor diffusion of CH2C12 with hexanes to give complex 94CH2Cl2• The reaction of FeCl3-6H20 and 2-pyridylcarbinol in acetonitrile gives, upon addition of NaC104, complex KMMeCN. Complex 9 has six high-spin Fem ions and can be viewed as two trinuclear /i3-oxo-bridged subunits bridged by two M2-hydroxo and M2-acetato ligands. Complex 10 can also be viewed as two asymmetric triangular ß3-µ3-subunits bridged together by alkoxo groups. However, in complex 9 there is a planar array of six Fem ions, whereas in complex 10 the six high-spin Fem ions are arranged in a chair conformation. Variable temperature DC magnetic susceptibility data measured at 10.0 kG are presented for both complexes. For complex 9-3/2CH2Cl2 Meff/molecule was found to be 9.10 mb at 300.0 K, and as the temperature is decreased, this value increases to a maximum of 10.55 mb at 30.0 K, whereupon there is a decrease to 9.77 mb at 5.00 K. Complex 10-MeCN in a 10.0 kG field gives MCff/molecule = 8.82 mb at 320.0 K. In contrast to 9, the Mefr/ molecule for complex 10-MeCN decreases with decreasing temperature to 6.08 mb at 5.01 K. Least-squares Fitting of the reduced magnetization (M/ µb) versus H/T data for paraffin-embedded complex 9-3/2CH2Cl2 in the range of 5.00-50.0 kG external field and 2.0-30.0 K clearly shows that complex 9 has a well isolated Sj = 5 ground state. Reduced magnetization versus H/T data are also presented for a parafilm-embedded sample of complex 10-MeCN in external fields of 0.50-50 kG at temperatures of 2-30 K. Fitting the high-Field data suggests the presence of a ST = 3 ground state. However, the fit of the low-field data is not good for just an isolated St = 3 ground state. Theoretical calculations were carried out for two of the known Fem6 complexes. The energies of all of the 4332 different spin states of a Fenl6 complex were calculated, taking into account the pairwise magnetic exchange interactions within µ3-bridged Fem3 triangular subunits (parameters J\, /2, and /3) and the interaction (J4) between iron ions in two Fe30 triangular subunits. The 20-320 K data measured at 10.0 kG for complex 5 (isostructural to 9) could be Fit well with a theoretical calculation where J¡ = -5.6(5) cm-1, /2 = /3 = -38(1) cm-1, and J4 = -7.5(1) cm-1. In agreement with experimental data, a well-isolated St = 5 ground state is predicted. The theoretical fit of 20-320 K data for complex 10-MeCN in a 10.0 kG Field gives fitting parameters of J¡ = 72 = -18(1) cm-1, /j = -52(2) cm-1, and J4 = -3(2) cm-1.Even though all pairwise exc...
The synthesis, structure, and magnetic properties of [Mn40~(0A~)7(bipy)2](C104)~3H20, bipy = 2,2'-bipyridine) are reported; this complex is the first tetranuclear oxide-bridged manganese(rii) species and represents the best available model for the photosynthetic water oxidation centre.
ChemInform Abstract The mixed-valence title complex is prepared from Mn3O(O-CO-Ph)6(Py)2(H2O) in MeCN by addition of solid salicylic acid (3 equiv.) with a yield of 35-40%. It crystallizes in C2/c with Z=4. The structure consists of two butterfly-like Mn4(µ3-O)2 units, ontaining octahedral Mn(III) ions, linked together by a bridging Mn(sal)4 central unit, containing an eight-coordinate Mn(II) ion. The linking salicylate groups have a rare µ3-η3-bridging mode. A detailed theoretical model has been derived by the Kambe vector coupling odel to interpret magnetic susceptibility data measured for the cluster in the range of 5.0-300.9 K.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.