Cyclic porphyrin dimers as hosts for coordinating ligands

Vaijayanthimala, G and Krishnan, V and Mandal, SK (2008) Cyclic porphyrin dimers as hosts for coordinating ligands. In: 10th National Symposium in Chemistry, FEB 01-03, 2008, Bangalore.

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Abstract

Bicovalently linked tetraphenylporphyrins bearing dioxypentane groups at the opposite (transoid, H4A) and adjacent (cisoid, H4B) aryl groups have been synthesised. Protonation of the free-base porphyrins leads to fully protonated species H8A4+/H8A4+ accompanied by expansion of cavity size of the bisporphyrins. The electrochemical redox studies of these porphyrins and their Zinc(II) derivatives revealed that the first ring oxidation proceeds through a two-electron process while the second ring oxidation occurs at two distinct one-electron steps indicating unsymmetrical charge distribution in the oxidized intermediate. The axial ligation properties of the Zinc(Il) derivatives of H4A/H4B with DABCO and PMDA investigated by spectroscopic and single crystal X-ray diffraction studies showed predominant existence of 1: I complex. The Zn2A.DABCO complex assumes an interesting eclipsed structure wherein DABCO is located inside the cavity between the two porphyrin planes with Zn-N distances at 2.08 and 2.22 Å. The Zn atoms are pulled into the cavity due to coordination towards nitrogen atoms of DABCO and deviate from the mean porphyrin plane by 0.35 Å. The electrochemical redox potentials of the axially ligated metal derivatives are found to be sensitive function of the relative coordinating ability of the ligands and the conformation of the hosts.

Item Type:	Conference Paper
Publisher:	Springer
Additional Information:	Copyright of this article belongs to Springer.
Keywords:	Crystal structure;cyclic porphyrin dimmers;host;guest complexes;solution conformation.
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	11 Mar 2010 07:55
Last Modified:	19 Sep 2010 05:56
URI:	http://eprints.iisc.ac.in/id/eprint/26091

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