Combined M枚ssbauer Spectral and Density Functional Study of an Eight-Coordinate Iron(II) Complex
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- 作者：Gary J. Long ; Fernande Grandjean ; Todd C. Harrop ; Heather M. Petroccia ; Georgia C. Papaefthymiou
- 刊名：Inorganic Chemistry
- 出版年：2015
- 出版时间：September 8, 2015
- 年：2015
- 卷：54
- 期：17
- 页码：8415-8422
- 全文大小：328K
- ISSN：1520-510X
文摘
The iron-57 M枚ssbauer spectra of the eight-coordinate complex, [Fe(LN4)2](BF4)2, where LN4 is the tetradentate N1(E),N2(E)-bis[(1-methyl-1H-imidazol-2-yl)methylene]-1,2-benzenediimine ligand, have been measured between 4.2 and 295 K and fit with a quadrupole doublet. The fit at 4.2 K yields an isomer shift, 未Fe, of 1.260(1) mm/s and a quadrupole splitting, 螖EQ, of 3.854(2) mm/s, values that are typical of a high-spin iron(II) complex. The temperature dependence of the isomer shift yields a M枚ssbauer temperature, 螛M, of 319(27) K and the temperature dependence of the logarithm of the M枚ssbauer spectral absorption area yields a Debye temperature, 螛D, of 131(6) K, values that are indicative of high-spin iron(II). Nonrelativistic single point density functional calculations with the B3LYP functional, the full 6-311++G(d,p) basis set, and the known X-ray structures for [Mn(LN4)2]2+, [Mn(LN4)2](ClO4)2, 1, [Fe(LN4)2]2+, and [Fe(LN4)2](BF4)2, 2, yield small electric field gradients for the manganese(II) complexes and electric field gradients and s-electron densities at the iron-57 nuclide that are in good to excellent agreement with the M枚ssbauer spectral parameters. The structure of 2 with a distorted square-antiprism C1 iron(II) coordination symmetry exhibits four different Fe鈥揘imid bonds to the imidazole nitrogens with an average bond distance of 2.253(2) 脜 and four different Fe鈥揘imine bonds to the benzenediimine nitrogens, with an average bond distance of 2.432(2) 脜; this large difference yields the large observed 螖EQ. An optimization of the [Fe(LN4)2]2+ structure leads to a highly symmetric eight-coordination environment with S4 symmetry and four equivalent Fe鈥揘imid bond distances of 2.301(2) 脜 and four equivalent Fe鈥揘imine bond distances of 2.487(2) 脜. In contrast, an optimization of the [Mn(LN4)2]2+ structure leads to an eight-coordination manganese(II) environment with D2d symmetry and four equivalent Mn鈥揘imid bond distances of 2.350(3) 脜 and four equivalent Mn鈥揘imine bond distances of 2.565(3) 脜.