Extended NMR study of spin-crossover compounds [Fe(1-alkyl-1H-tetrazole)(6)](BF4)(2) and their Zn-II analogs

Marek, Tamás and Bokor, Mónika Zsuzsanna and Tompa, Kálmán and Vértes, Attila and Süvegh, Károly (2003) Extended NMR study of spin-crossover compounds [Fe(1-alkyl-1H-tetrazole)(6)](BF4)(2) and their Zn-II analogs. STRUCTURAL CHEMISTRY, 14 (4). pp. 349-368. ISSN 1040-0400

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A systematic NMR study was performed on several alkyl-tetrazole complexes of iron(II) and zinc(II) in the 10-300 K temperature range. The experiments were designed to separate the electronic and reorientational phase transitions caused by the spin crossover of the iron compounds from those independent of unpaired electrons. The F-19 spectral data on the propyl-tetrazole compounds show that the electronic spin-transition has a strong effect on the spectra, and their behavior can be explained as a combined response to molecular reorientations and the spin transition. For these complexes, second-moment calculations revealed the strength of the interaction between resonant and nonresonant nuclei. Both of the applied NMR methods show irregularities at the temperature region between 70 and 120 K, suggesting the presence of a phase transition. The data also suggest two kinds of reorientational behavior for the BF4- counter ions. In the iron-ethyl-tetrazole compound, unlike in the propyl-tetrazole complex, a significant amount of unpaired electrons remains in their original high-temperature HS state. Above their effect, the behavior of the nuclear spins of the iron compound is basically governed by the same structural factors as in its zinc analog. The two-exponential behavior of the H-1-T-1 in case of the zinc-methyl-tetrazole compound can be explained on the basis of cross relaxation with the 19F nuclei due to the low H-1/F-19 ratio. The presence of the two types of methyl reorientation is assumed to be the sign of the two different lattice sites known to be present in the FeII compound. The single-exponential T-1 above T-c in the case of [Fe(mtz)(6)](BF4)(2) is consistently the sign of the strength of the paramagnetic relaxation observed in the ethyl and propyl compounds.

Item Type: Article
Uncontrolled Keywords: Inorganic compounds; NMR spectroscopy
Subjects: Q Science / természettudomány > QC Physics / fizika
Q Science / természettudomány > QD Chemistry / kémia
Depositing User: MTMT SWORD
Date Deposited: 18 Jun 2014 06:04
Last Modified: 18 Jun 2014 06:05

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