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Issue 41, 2010
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Thermal spin-crossover in the [M3Zn6Cl6L12] (M = Zn, FeII; L = 5,6-dimethoxy-1,2,3-benzotriazolate) system: structural, electrochemical, Mössbauer, and UV-Vis spectroscopic studies

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Abstract

Fusion of pentanuclear Kuratowski-type coordination units leads to homo- and heterononanuclear coordination compounds, two of which are presented, having structural formulae [Zn9Cl6(OMe2bta)12]·DMF (1), and [FeII3Zn6Cl6(OMe2bta)12]·DMF (2), respectively; (OMe2btaH = 5,6-dimethoxy-1,2,3-benzotriazole; DMF = N,N′-dimethylformamide). Single crystal X-ray structure analyses reveal the presence of {M3Zn6L12}6+ cores (M = Zn or FeII; L = 5,6-dimethoxy-1,2,3-benzotriazolate) in which the MII ions are bridged by μ3-OMe2bta ligands. In both compounds, the six peripheral Zn ions are tetracoordinated, whereas the remaining three metal ions M are hexacoordinated. The charge of each {M3Zn6L12}6+ moiety is balanced by six chloride anions that are monodentately bound to the peripheral Zn ions. Based on differences in experimental Fe–N-donor bond lengths (deduced from single crystal data of 2 recorded at 223 K), two out of three FeII ions are found in a high-spin (HS) state, whereas one FeII ion shows a low-spin (LS) state. The assignment of different energetic ground states of FeII ions is corroborated by spectroscopic studies: Both solid-state and solution UV-Vis spectra of 2 (at ambient temperature) display absorption bands owing to the presence of both HS and LS FeII ions. Removal of occluded DMF molecules from the crystal lattices of 1 and 2 in high vacuum leads to fully desolvated powders, termed hereafter 1a and 2a, respectively. Mössbauer studies on 2a show that all three FeII ions are in HS state at 160 K, and upon cooling to 7 K, the central FeII ion undergoes a HS→LS transition while the HS states of the other FeII ions remains unchanged. The cyclic voltammogram of 2 (chloroform solution) exhibits a single reversible oxidation regardless of different FeII spin states in the nonanuclear core of 2.

Graphical abstract: Thermal spin-crossover in the [M3Zn6Cl6L12] (M = Zn, FeII; L = 5,6-dimethoxy-1,2,3-benzotriazolate) system: structural, electrochemical, Mössbauer, and UV-Vis spectroscopic studies

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Supplementary files

Article information


Submitted
26 May 2010
Accepted
27 Jul 2010
First published
14 Sep 2010

Dalton Trans., 2010,39, 9851-9859
Article type
Paper

Thermal spin-crossover in the [M3Zn6Cl6L12] (M = Zn, FeII; L = 5,6-dimethoxy-1,2,3-benzotriazolate) system: structural, electrochemical, Mössbauer, and UV-Vis spectroscopic studies

S. Biswas, M. Tonigold, H. Kelm, H. Krüger and D. Volkmer, Dalton Trans., 2010, 39, 9851
DOI: 10.1039/C0DT00556H

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