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Stereochemical effects on the spin-state transition shown by salts of [FeL<SUB>2</SUB>]2+ [L = 2,6-di(pyrazol-1-yl)pyridine]

Authors :
Holland, Joanne M.
McAllister, Judith A.
Kilner, Colin A.
Thornton-Pett, Mark
Bridgeman, Adam J.
Halcrow, Malcolm A.
Source :
Journal of the Chemical Society, Dalton Transactions; February 7, 2002, Vol. 2002 Issue: 4 p548-554, 7p
Publication Year :
2002

Abstract

The syntheses of [Fe(L&lt;superscript&gt;1&lt;/superscript&gt;H)&lt;SUB&gt;2&lt;/SUB&gt;]X&lt;SUB&gt;2&lt;/SUB&gt; (L&lt;superscript&gt;1&lt;/superscript&gt;H = 2,6-di(pyrazol-1-yl)pyridine [L&lt;superscript&gt;1&lt;/superscript&gt;H]; X&lt;superscript&gt;−&lt;/superscript&gt; = BF&lt;SUB&gt;4&lt;/SUB&gt;&lt;superscript&gt;−&lt;/superscript&gt;, PF&lt;SUB&gt;6&lt;/SUB&gt;&lt;superscript&gt;−&lt;/superscript&gt;) are described. Solvent-free [Fe(L&lt;superscript&gt;1&lt;/superscript&gt;H)&lt;SUB&gt;2&lt;/SUB&gt;][BF&lt;SUB&gt;4&lt;/SUB&gt;]&lt;SUB&gt;2&lt;/SUB&gt; shows an approximately D&lt;SUB&gt;2d&lt;/SUB&gt;-symmetric metal centre in the crystal, and undergoes an unusual abrupt spin-state transition centered at 261 K in the solid, or at 248 K in acetone solution. A solvated phase [Fe(L&lt;superscript&gt;1&lt;/superscript&gt;H)&lt;SUB&gt;2&lt;/SUB&gt;][BF&lt;SUB&gt;4&lt;/SUB&gt;]&lt;SUB&gt;2&lt;/SUB&gt;&#183;2.9CH&lt;SUB&gt;3&lt;/SUB&gt;NO&lt;SUB&gt;2&lt;/SUB&gt;&#183;0.25H&lt;SUB&gt;2&lt;/SUB&gt;O can be grown at 240 K, which undergoes an irreversible spin-state transition between 260 and 265 K. In contrast, solid [Fe(L&lt;superscript&gt;1&lt;/superscript&gt;H)&lt;SUB&gt;2&lt;/SUB&gt;][PF&lt;SUB&gt;6&lt;/SUB&gt;]&lt;SUB&gt;2&lt;/SUB&gt; adopts an unusual C&lt;SUB&gt;2&lt;/SUB&gt;-symmetric coordination geometry, reflecting a ca. 28&#176; twist of one L&lt;superscript&gt;1&lt;/superscript&gt;H ligand with respect to each other. This salt is high-spin in the range 10–330 K. DFT calculations have rationalised this unusual structure as a Jahn–Teller distortion of the &lt;superscript&gt;5&lt;/superscript&gt;E ground state of the six-coordinate Fe(ii) ion. This distortion is favoured by the restricted bite-angle of the L&lt;superscript&gt;1&lt;/superscript&gt;H ligands.

Details

Language :
English
ISSN :
03009246
Volume :
2002
Issue :
4
Database :
Supplemental Index
Journal :
Journal of the Chemical Society, Dalton Transactions
Publication Type :
Periodical
Accession number :
ejs2008495

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