Single-crystal X-ray and Mössbauer Effect Study of Iron(III) Crown Ether Complexes


An investigation of the complexes formed between iron and crown ethers has led to the isolation of the microcrystalline complexes (FeCl4)3[Fe(H2O)6](18-6) 3(H2O)2, H[FeBr4(18-6)(H2O)2], FeCl3(15-5)(H2O)2, and FeBr3(15-5)(H2O)2 and to single crystals of H[FeBr4(18-6)2(H2O)2.3], where (18-6) represents the cyclic 18-crown-6 ether and (15-5) represents the cyclic 15-crown-5 ether. The structure of the single crystals has been determined at 295 and 120 K and reveals a cubic crystal with space group Fdi3, No. 203, a Z of 8, and a lattice parameter a of 20.600 (4) Å at 295 K and 20.475 (1) Å at 120 K. The structure contains tetrahedral FeBr4 anions that have no bonding interaction with the 18-crown-6 ether. The crown ether, which serves as a dielectric medium to separate the anions, has the expected D3d symmetry and a longer than typical carbon-carbon bond. The Mössbauer effect spectral and magnetic properties of all the complexes reveal high-spin iron(III) in either a tetrahedral or octahedral coordination environment. Only one iron environment is found in all the complexes except (FeCl3)4(18-6)3(H2O)8, which has two different iron(III) sites in the ratio of 3:1, that corresponded to tetrahedral and octahedral sites, respectively, and may be formulated as (FeCl4)3-[Fe(H2O)6](18-6) 3(H2O)2. This complex undergoes facile decomposition induced by either heat or ultraviolet radiation in a variety of atmospheres to yield methane, carbon monoxide, and mixtures of hydrates of iron(II) chloride. The decomposition, under a variety of conditions, has been monitored by the Mössbauer effect of the iron-containing products. Similar results are obtained for the H[FeBr4(18-6)(H2O)2] complex. © 1987 American Chemical Society.



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© 1987 American Chemical Society (ACS), All rights reserved.

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01 Jan 1987