Solid- and Solution-State Studies of the Novel μ-Dicyanamide-Bridged Dinuclear Spin-Crossover System {[(Fe(bztpen)]2[μ-N(CN)2]}(PF6)3⋅n H2O
✍ Scribed by Norma Ortega-Villar; Amber L. Thompson; M. Carmen Muñoz; Víctor M. Ugalde-Saldívar; Andrés E. Goeta; Rafael Moreno-Esparza; José A. Real
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 318 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The mononuclear diamagnetic compound {Fe(bztpen)[N(CN)~2~]}(PF~6~)CH~3~OH (1) (bztpen = N‐benzyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethylenediamine) has been synthesized and its crystal structure studied. Complex 1 can be considered to be the formal precursor of two new dinuclear, dicyanamide‐bridged iron(II) complexes with the generic formula {[(Fe(bztpen)]~2~[μ‐N(CN)~2~]}(PF~6~)~3~⋅n H~2~O (n = 1 (2) or 0 (3)), which have been characterized in the solid state and in solution. In all three complexes, the iron atoms have a distorted [FeN~6~] octahedral coordination defined by a bztpen ligand and a terminal (1) or a bridging dicyanamide ligand (2 and 3). In the solid state, 2 and 3 can be considered to be molecular isomers that differ by the relative position of the phenyl ring of the two {Fe(bztpen)[N(CN)~2~]}^+^ halves (cis and trans, respectively). Depending on the texture of the sample, 2 exhibits paramagnetic behavior or displays a very incomplete spin transition at atmospheric pressure. Complex 3 undergoes a gradual two‐step spin transition with no observed hysteresis in the solid state. Both steps are approximately 100 K wide, centered at ≈200 K and ≈350 K, with a plateau of approximately 80 K separating the transitions. The crystal structure of 3 has been determined in steps of approximately 50 K between 400 K and 90 K, which provides a fascinating insight into the structural behavior of the complex and the nature of the spin transition. Order–disorder transitions occur in the dicyanamide bridge and the PF~6~^−^ ions simultaneously, with the spin‐crossover behavior suggesting that these transitions may trigger the two‐step character. In solution, 2 and 3 display very similar continuous spin conversions. Electrochemical studies of 2 and 3 show that the voltammograms are typical of dimeric systems with electronic coupling of the metals through the dicyanamide ligand.