The Raman spectra of iron(III) complexes with ethylenediaminetetraacetate were observed for the purpose of elucidating the structure of the complexes in solution. In a Raman spectral study on the solid complexes, the spectra in the 300–600 cm−1 region were found to be diagnostic to coordination geometry. Namely, the coordination number can be determined on the basis of the wavenumber difference of the two major bands observed in the 450–600 cm−1 region; the wavenumber differences observed for heptacoordinate complexes lie between 32 and 42 cm−1, while that for the hexacoordinate complex is 62 cm−1. Complexes containing a sexidentate edta exhibit a single intense band around 470 cm−1 in the 450–500 cm−1 region, while complexes containing a quinquedentate edta exhibit two intense bands in this region. These Raman spectral criteria were then applied for the determination of the solution structure. The Raman spectral features observed for solutions of Fe(III)-edta complexes indicate that the any alkali metal salts and acid salts of FeIII(edta)− give sexidentate heptacoordinate complex ions in water. The dimeric complex which is formed in an alkaline solution was characterized as being a dinuclear complex consisting of two quinquedentate hexacoordinate iron(III) moieties with a Fe–O–Fe bridging unit.

in HC1 should greatly reduce the stability of the HC1 antihydrogen-bonded complexes with respect to their HF analogues. This change in relative intensities of the vs and avs absorptions can play a key role in the band assignments of these weak complexes since the absorptions are in the same spectral region. Conclusions UF6 and HC1 interact in solid argon to form a well-defined 1:1 hydrogen-bonded complex, UF6-HC1. The band positions of the UF6-HC1 and the FC1-HC1 complexes were very comparable. As the HC1 aggregation increased, a 1:2 complex, UF6-(HC1)2, was observed and characterized by considering the perturbation of the second HC1 submolecule on the 1:1 complex. In contrast, the codeposition of WF6 and MoF6 with HC1 produced hydrogen-bonded 1:1 complexes and antihydrogen-bonded complexes.WF6 and MoF6 displayed little preference between the different structural arrangements. In addition, the HC1 in the hydrogenbonded and the antihydrogen-bonded complexes activated several WF6 and MoF6 modes that are normally infrared-inactive.

The Raman spectra of the ions Co(CO)4—, Fe(CO)42—, and HFe(CO)4— have been studied in aqueous solutions of the corresponding sodium salts. The spectra of Co(CO)4— and Fe(CO)42—, excited by the helium radiations 5875.6 and 6678.1 A are in full agreement with the expected Td symmetry of these ions; all observed frequencies were assigned to fundamental vibrational modes. A normal coordinate treatment was carried out under the assumption of a simplified valence force field model making use of only two interaction constants. The values of the fundamental frequencies of the tetrahedral ions, calculated by means of the potential constants of this model, were found to be in satisfactory agreement with the observed Raman shifts. The Raman spectrum of HFe(CO)4—, put in correlation with that of Fe(CO)42—, points strongly to a C3v symmetry of the former ion.

give a high noise level in data at higher k. Over this more limited range, three-wave fits of the first shell became impossible and correlation effects between Fe and other atoms in the second shell increased significantly, increasing the calculated number of Fe atoms. ConclusionsThis investigation has shown that EXAFS spectra of oxo-and hydroxo-bridged iron complexes 1-4 are highly sensitive to the presence or absence of a short µ-Fe-O distance and that this geometric feature can be unambiguously determined. This result provides further evidence in confirmation of the conclusions reached about the presence of such a short iron-oxo bridging distance in azidomethemerythrin.24,26 The ability of EXAFS spectroscopy to differentiate Fe-oxygen bridge bond lengths in the 1.78 vs. 1.95 Á distance ranges should prove to be valuable in assessing the stereochemistry of semimet forms of hemerythrin, of deoxyhemerythrin (cf. ref 25), and of the binuclear iron centers in ribonucleotide reductase and purple acid phosphatase. It has also been demonstrated that great care must be exercised in determining the second-shell contributions to the EXAFS, since the Fe-"Fe scattering can be severely influenced by the presence of C or other low Z atoms at the same distance range from Fe as Fe itself. This perturbation can affect especially the determination of the number of neighboring Fe atoms, a problem that is further exacerbated if the k range of data is more limited, as is often the case with EXAFS data for dilute metalloproteins. On the positive side, however, the dramatic improvement of the fit for the phosphate ester bridged complex 3 upon addition of the P(S) atom to the second shell augurs well for the potential utility of EXAFS spectroscopy to delineate structural details of iron phosphate centers in biology.Registry No. I, 86177-70-0; 2, 103835-68-3; 3, 96502-34-0; 4, 90886-30-9; ribonucleotide reductase, 9040-57-7; purple acid phosphatase, 9013-05-2.Supplementary Material Available: Listings of raw data for compounds 1-4 (20 pages). Ordering information is given on any current masthead page.

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