ISSN:
1432-2234
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract For the Fe-derivatives of 2-methyl-, 2-ethyl-, and 2-phenyl-imidazoles Mössbauer spectra are measured in the temperature range 4.2 K⩽T⩽300 K. Their computer analysis yields isomer shifts δ, quadrupole splittings gDE Q, asymmetry parameters η, line widths Γ, internal magnetic fieldsH int, sign of the main componentV zz of the electric field gradient tensor, and angle ζ between $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {H} ^{\operatorname{int} } $$ and $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {V} _{zz} $$ . We find that the substituents methyl, ethyl, and phenyl have significant influence upon these parameters, i.e. upon electronic structure and magnetic ordering; onlyV zz〉0 and η=0 are the same for all compounds. The δ- and ΔE Q-values indicate that the iron is in the ferrous high-spin state and tetrahedrally coordinated by imidazole nitrogens. The conclusion that the compounds are three-dimensional coordination polymers is drawn from their magnetic ordering at low temperatures. Transition temperatures areT methyl * =33.25±0.05 K,T ethyl * =30.5±0.05 K, andT phenyl * =25.7±0.05 K. Assuming a power-law dependence forH int of the formH int =H(4.2)D(1-T/T*)β we deriveD= 1.52±0.05 and β = 0.31±0.03 for the three compounds. From the discussion of the saturation value of the internal magnetic fieldH int (4.2 K) we derive for the methyl- and phenyl-compound ground state and first excited state single-electron wave function |n〉=a|x 2−y 2〉+b|xy〉+c|3z 2−r 2〉+d|xz〉+e|yz〉+lig. and |K〉=a′|x 2−y 2〉+b′xy〉+c ′|3z 2−r 2〉+d′|xz+e′|yz〉+lig, respectively, and energy separationsE k-E n, specified by: 0.88⩽b⩽0.92, 0.27⩽c⩽0.39, 0.55⩽a′⩽0.57, −0.32⩽b′⩽−0.22, 0.69=⩽c′⩽0.77,a =d=e =d′ =e′ = 0,E k-E n = 4000±500 cm−1 for the methyl compound, and 0.92⩽b⩽0.96, 0⩽c⩽0.27, 0.49 ⩽a′ ⩽0.52, 0.76 ⩽c′⩽0.84,a =d=e =b′ =d′ =e′ = 0,E k-E n = 4000±500 cm−1 for the phenyl compound. The coefficientsa, h.,e′ are approximate values mainly due to the assumption of isotropic covalency, due to the lack of better knowledge of the energy separationE k —E n, and due to the approximative procedure of estimating the orbital contribution toH int. The situation for the ethyl compound is less transparent because of the non-collinearity of $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {H} ^{\operatorname{int} } $$ and $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {V} _{zz} $$ in this case.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01151958
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