2-hydroxy-1,4-naphthoquinone(lawsone) is a natural henna dye extracted from Lawsonia alba and Lawsonia inermis. Versatile applications of this dye include from ‘body art to anticancer agents. Lawsone is also a versatile ligand in coordination chemistry that can coordinate to metal ions in monodentate, bidentate, tridentate, and bridging forms. Complexes that are formed are of the type [M(L)2(S)2], where S = solvent, varying the experimental conditions of the synthesis of metal complexes, the arrangement of the ligand around metal ions resulted into cis, cis-[M(L)2(S)2] or trans, trans-[M(L)2(S)2]. The lawsone ligand is noninnocent can be reduced by one electron (naphthosemiquinone) and two electrons (catechol). In this investigation, two series of metal complexes of a few first-row transition metal ions are synthesized at 0 °C (with sodium metal as reductant) and 26 °C in this investigation. The X-ray crystal structure reveals the arrangement of the lawsone ligands around metal ions is cis, cis to the complexes synthesized at 0 °C and trans, trans at 26 °C. The trans, trans complexes show polymeric chains formed via C-H---O and O-H---O hydrogen bonding interactions. Molecular packing In the cis, cis-[Cu(Lawsone)2(H2O)(CH3OH)] complex, the two coordinated lawsone ligands differ in their bond distances and the molecular interactions, and the plane of the ligands make an angle of 73.95° to one another. The carbonyl bond distances found at ~1.27 Å and 1.24 Å these bond distances suggest the naphthosemiquinone coordination of the ligand. The trans, trans-[Cu(L)2(H2O)(py)] complex, two lawsone ligands make an angle of 17.04°, and the carbonyl bond distance is ~1.23 Å. This investigation will discuss the electrochemical behavior and anticancer activity of all complexes.

Transition metal complexes of henna dye; 2-hydroxy-1,4-naphthoquinone: Molecular structures and electrochemical behavior

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