ISSN:
1432-2234
Keywords:
Mössbauer spectroscopy
;
Thermogravimetry
;
Di-imidazolato iron(II)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The polymeric system di-imidazolato iron(II) is synthesized from the reaction of either ferrocene or cyclopentadienyl-irondicarbonyl with imidazole. From Mössbauer measurements in the temperature range 4.2 K⩽T⩽448 K we find two different iron sites in the compound, denoted byA andB, respectively with ratio [A]/[B] = 1.79±0.03. From the isomer shift values we conclude that both Fe A and Fe B are in the ferrous high-spin state. Below 13.95±0.10 K both subspectra are considerably broadened due to magnetic ordering. From the analysis of the magnetic spectra we derive for the main componentV zz of the electric field gradient tensorV zz A 〉0 andV zz B 〈0. Additionally, we investigate the thermal decomposition of the compound by thermogravimetry in the temperature range 20 °C⩽T⩽ 750 °C and by Mössbauer spectroscopy in the temperature range 20 °C⩽T⩽505 °C. The decomposition takes place in four steps. The first step between 20 °C and 190 °C is due to the loss of imidazole nonbonded to iron(II). Comparing the amount of iron with that of pure imidazolato iron(II) we find the formula FeIz2+0.70 (±0.02) IzH, with Iz standing for doubly deprotonated and IzH for deprotonated imidazole. Step 2 (193 °C〈T〈235 °C) and step 3 (400 °C〈T〈500 °C) are found from both methods. Step 4 is above 500 °C. Heat treatment and vacuum conditions affect the thermal decomposition products. Isomer shifts δ A and δ B , and temperature dependent quadrupole splittings ΔE Q A and ΔE Q B are explained using a simple ligand field picture for orbital splittings and occupancies of quasi-tetrahedrally (A) and quasi-octahedrally (B) coordinated ferrous high-spin compounds. Using finally the experimental ratio [A]/[B] = 1.79 we derive for the over-all chemical formula (1.79 Fe A Iz4/2+Fe B Iz4/2+2 IzH) n = (FeIz2+0.71 Iz) −n in agreement with the result which we derived from investigating the thermal decomposition of our compound.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01151957
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