%0 Journal Article
%T Structural and Spectroscopic Properties of Two New Isostructural Complexes of Lapacholate with Cobalt and Copper
%A R. A. Farf¨¢n
%A J. A. Esp¨ªndola
%A M. I. Gomez
%A M. C. L. de Jim¨¦nez
%A M. A. Mart¨ªnez
%A O. E. Piro
%A E. E. Castellano
%J International Journal of Inorganic Chemistry
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/973238
%X The molecular structures of two isostructural complexes of lapacholate (Lap) anion and dimethylformamide (DMF), M(Lap)2(DMF)2 with M: Co Cu, were determined by X-ray diffraction methods. The substances crystallize in the triclinic space group with one molecule per unit cell and cell constants (3), (3), (4) £¿, (2), (2), and (2)¡ã for the Co complex and (2), (4), (4), (2), (2), and (2)¡ã for the Cu complex. The structures were solved from 2933 (Co) and 2888 (Cu) reflections with (I) and refined by full matrix least squares to agreement R1-factors of 0.041 (Co) and 0.033 (Cu). The metal M(II) ion is sited on a crystallographic inversion center in a MO6 distorted octahedral environment. This ion is coordinated equatorially to two lapacholate anions through their adjacent carbonyl and phenol oxygen atoms [M¨CO bond distances of 2.134(1) and 2.008(1) £¿ (Co) and 2.301(1) and 1.914(1) £¿ (Cu)] and axially to two DMF molecules through oxygen atoms [M¨CO bond lengths of 2.143(1) £¿ (Co) and 2.069(1) £¿ (Cu)]. The solid state IR transmittance and solution electronic absorption spectra of both Co and Cu compounds are also reported and compared to each other and to the corresponding spectra of other members of the lapacholate metal family of complexes. 1. Introduction Lapachol (LapH), [2-hydroxy-3(3-methyl-2-butenyl)-1,4-naphthoquinone] is a yellow pigment present in several plant species, including the Lapacho tree Tabebuia ipe (shredded wood) from which it is extracted. This extract is also used as alternative medicine for different illness such as cancer, Chagas, and various skin diseases [1¨C6]. A tea extract from the inner bark of the Lapacho tree has been used as a folk remedy against many diseases in South America since the time of the Incas [7]. Lapachol presents pharmacological activity similar to acetonaphthonates, flavonates, and hydroxypyronates [8]. Several patents involving pharmaceutical applications of Lapachol have been filed in the last few years; for example, in 2008 alone there were granted 13 related patents [7]. The quest for improving this activity prompted renewed work during the last 10 years on the synthesis, physicochemical characterization, and pharmacological properties of Lapachol complexes with transition metal ions, including the Zn, Ni, and Mn lapacholates [7, 9, 10]. In alkaline medium, LapH loses a proton. This gives rise to a lapacholate anion (Lap) and turns into a bidentate ligand (Lap) to divalent metal ions through its phenolic and quinonic oxygen atoms located at positions 1 and 2 (see Scheme 1). Scheme 1: Molecular structure of
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