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Issue 48, 2010
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Synthesis and characterization of a trinuclear CuII3 complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions

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Abstract

The synthesis and characterization of the extended phloroglucinol-ligand H3felden based on the trialdehyde 2,4,6-triformylphloroglucinol and its trinuclear CuII3 complex [(felden){Cu(bpy)}3](ClO4)3 is presented. This study is motivated to optimize analogous extended phloroglucinol-ligands based on the triketone 2,4,6-triacetylphloroglucinol, which transmit ferromagnetic interactions by the spin-polarization mechanism between three CuII ions and have therefore been applied as the central ligand backbone for a class of heptanuclear single-molecule magnets in a supramolecular approach. A detailed NMR spectroscopic study reveals that the ligand H3felden is not in the usually anticipated enol-imine form but in the tautomeric keto-enamine form. The presence of a C3h and a Cs symmetric isomer results in a set of four different signals for each proton. In conjunction with FTIR, electronic absorption spectroscopy, and bond length considerations, it also appears that the complex [(felden){Cu(bpy)}3](ClO4)3 must be considered as a resonance hybrid of an enolate-imine and a keto-enamine form. A strong contribution of the keto-enamine resonance structure with loss of the central π system explains the weak but ferromagnetic interactions between the CuIIS = 1/2 spins. This detailed analysis identifies the strong resonance with unsaturated groups in 2,4,6-position of phloroglucinol as the main source for the low ferromagnetic couplings by the spin-polarization mechanism in these ligands. This provides a synthetic handle to improve the spin-polarization mechanism in these ligands by replacing the imine with amine functions.

Graphical abstract: Synthesis and characterization of a trinuclear CuII3 complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions

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Article information


Submitted
04 Aug 2010
Accepted
24 Sep 2010
First published
05 Nov 2010

Dalton Trans., 2010,39, 11675-11685
Article type
Paper

Synthesis and characterization of a trinuclear CuII3 complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions

B. Feldscher, A. Stammler, H. Bögge and T. Glaser, Dalton Trans., 2010, 39, 11675
DOI: 10.1039/C0DT00961J

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