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Diiron(III)–μ‐Fluoro Bisporphyrins: Effect of Bridging Ligand on the Metal Spin State
Author(s) -
Sil Debangsu,
Kumar Amit,
Rath Sankar Prasad
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201600786
Subject(s) - chemistry , crystallography , antiferromagnetism , metal , mössbauer spectroscopy , spectroscopy , ligand (biochemistry) , stereochemistry , organic chemistry , biochemistry , physics , receptor , quantum mechanics , condensed matter physics
A hitherto unknown family of diiron(III)–μ‐fluoro bisporphyrins has been synthesized and structurally characterized. Fluoride abstraction from SbF 6 − and BF 4 − resulted in the synthesis of the μ‐fluoro complexes of ethane‐ and ethene‐bridged diiron(III) bisporphyrins. Two such complexes were structurally characterized, which revealed a single fluoro bridge between two iron centers with a remarkably bent Fe‐F‐Fe unit. Although isoelectronic with the μ‐hydroxo complexes, the μ‐fluoro species are quite divergent in terms of the electronic structure and properties. UV/Vis spectroscopy of the μ‐fluoro complex exhibits a large redshift (ca. 18 nm) of the Soret band in comparison to their μ‐hydroxo analog. Combined analysis by single crystal X‐ray structure determination and Mössbauer and 1 H NMR spectroscopy revealed the presence of two equivalent iron(III) centers in the μ‐fluoro complexes in both solid and solution phases. In contrast, the iron(III) centers of the μ‐hydroxo complexes are known to be inequivalent. Variable‐temperature magnetic studies show a weak antiferromagnetic interaction between the iron(III) centers of the μ‐fluoro complexes with coupling constants ( J ) ranging from −33 to −40 cm −1 . The experimental results were further supported by DFT calculations.