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Issue 102, 2004

A critical look on the nature of the intra-molecular interligand π,π-stacking interaction in mixed-ligand copper(II) complexes of aromatic side-chain amino acidates and α,α′-diimines

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Abstract

The mixed ligand complexes {[Cu(4Cl-Phe)(bpy)(H2O)]Cl·[Cu(4Cl-Phe)(bpy)Cl]·2H2O} (1) and [Cu(4HPG)(bpy)]·2H2O (2) were synthesized and their crystal structures determined by X-ray crystallography (4Cl-Phe = D,L-4-chlorophenylalaninato, 4HPG = D-4-hydroxyphenylglycinato, bpy = 2,2′-bipyridine). The asymmetric unit of crystals of 1 consists of two slightly different Cu(II) complexes-one contains an axial water ligand, whereas the second one has a chloride anion at that position. By contrast, 2 exhibits two close similar molecules, both having axial chloride ligands, and non coordinated water. The geometrical parameters for π,π-stacking interactions were determined by an application of PLATON program. Intermolecular π,π-interaction between bpy ligands on adjacent Cu(II) moieties results in homo pairs of complexes in the case of 1. In addition, both species of compound 1 exhibit intramolecular interligand π,π-interaction between the 4Cl-phenyl ring of 4Cl-Phe and the metalloaromatic Cu–bpy chelate ring. In crystal 2, multi-stacked homo chains are formed. Analogous calculations for previously reported, related compounds, similar to those presented here, revealed that in most cases with intra-molecular interligand π,π-interaction there is an efficient “aryl–metal chelate ring” π,π-stacking instead of an aryl–aryl interligand π,π-interaction, which indeed is not observed. These findings let us to take a critical look at the nature of the intramolecular interligand π,π-stacking interaction in the referred copper(II) mixed-ligand complexes.

Graphical abstract: A critical look on the nature of the intra-molecular interligand π,π-stacking interaction in mixed-ligand copper(ii) complexes of aromatic side-chain amino acidates and α,α′-diimines

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Publication details

The article was received on 22 Nov 2004, accepted on 03 Dec 2004 and first published on 15 Dec 2004


Article type: Paper
DOI: 10.1039/B417707J
Citation: CrystEngComm, 2004,6, 627-632
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    A critical look on the nature of the intra-molecular interligand π,π-stacking interaction in mixed-ligand copper(II) complexes of aromatic side-chain amino acidates and α,α′-diimines

    U. Mukhopadhyay, D. Choquesillo-Lazarte, J. Niclós-Gutiérrez and I. Bernal, CrystEngComm, 2004, 6, 627
    DOI: 10.1039/B417707J

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