Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions

Feldscher B, Stammler A, Bögge H, Glaser T (2010)
Dalton Transactions 39(48): 11675-11685.

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Abstract
The synthesis and characterization of the extended phloroglucinol-ligand H(3)felden based on the trialdehyde 2,4,6-triformylphloroglucinol and its trinuclear Cu-3(II) 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 Cu-II 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 H(3)felden is not in the usually anticipated enol-imine form but in the tautomeric keto-enamine form. The presence of a C-3h and a C-s 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 p system explains the weak but ferromagnetic interactions between the Cu-II S = 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.
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Feldscher B, Stammler A, Bögge H, Glaser T. Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions. Dalton Transactions. 2010;39(48):11675-11685.
Feldscher, B., Stammler, A., Bögge, H., & Glaser, T. (2010). Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions. Dalton Transactions, 39(48), 11675-11685.
Feldscher, B., Stammler, A., Bögge, H., and Glaser, T. (2010). Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions. Dalton Transactions 39, 11675-11685.
Feldscher, B., et al., 2010. Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions. Dalton Transactions, 39(48), p 11675-11685.
B. Feldscher, et al., “Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions”, Dalton Transactions, vol. 39, 2010, pp. 11675-11685.
Feldscher, B., Stammler, A., Bögge, H., Glaser, T.: Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions. Dalton Transactions. 39, 11675-11685 (2010).
Feldscher, Bastian, Stammler, Anja, Bögge, Hartmut, and Glaser, Thorsten. “Synthesis and characterization of a trinuclear Cu-3(II) complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions”. Dalton Transactions 39.48 (2010): 11675-11685.
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Spin-polarization in 1,3,5-trihydroxybenzene-bridged first-row transition metal complexes
GLASER, Comptes Rendus Chimie 11(10), 2008

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