ARTICLE DOI: 10.1002/zaac.200800313 Organotin Complexes of Alizarin and Purpurin Adriana T. de Sousa, [a] Karl E. Bessler, [a] * Sebastia ˜o S. Lemos, [a] Javier Ellena, [b] and Claudia C. Gatto [a] Keywords: Organotin dyes; Alizarin; Purpurin Abstract. Five novel organotin complexes with the anthraquinone dyes alizarin (1,2-dihydroxyanthraquinone) and purpurin (1,2,4- trihydroxyanthraquinone) were synthesized and characterized by elemental analyses, FTIR and NMR spectroscopy ( 1 H, 13 C and 119 Sn). The crystal and molecular structures of four complexes were determined by X-ray diffraction on single crystals: [Bu 2 Sn(aliz)(H 2 O)] · C 2 H 5 OH (A1 · EtOH), [Bu 2 Sn(aliz)(dmso)] 2 (A3), [(Bu 2 Sn) 3 O(Hpurp) 2 ](P1) and [Bu 2 Sn(Hpurp)(dmso)] 2 (P2), where H 2 aliz = alizarin and H 3 purp = purpurin. The coordination Introduction Alizarin (1,2-dihydroxyanthraquinone), and purpurin (1,2,4-trihydroxyanthraquinone) are the main components of the natural dye extracted from madder root (Rubia tinctorum). Metal salts of the madder extract, the so-called lakes, have been used since antiquity in textile dyeing and as pigments in painting. Alizarin was the first natural dye to be synthesized (Graebe , Liebermann and Caro 1868). After the development of an improved synthesis by Perkin in 1871, alizarin has been produced in industrial scale until about 1930, when it was displaced by modern synthetic dyes. The constitution of the calcium-aluminium complexes of alizarin and purpurin, which represent the main compo- nents of the historic lake pigments, remained unknown until 1993, when their crystal and molecular structures were re- solved from crystalline water/DMF solvates [1-3]. Both complexes have analogous dimeric structures of the general composition [AlCa(OH)L 2 ] 2 . Alizarin and purpurin act as dianionic tridentate ligands, involving the quinoid 9-oxygen and its neighboured deprotonated 1,2-oxygen atoms in co- ordination. Each ligand establishes an Al-O-Ca link via its 2-oxygen atom. The OH ions exhibit μ 3 -bridging func- tion forming additional Al-O-Ca and Al-O-Al connec- * Prof. Dr. K. E. Bessler Fax.: +55-61-2734149 E-Mail: bessler@unb.br [a] Instituto de Quı ´mica Universidade de Brası ´lia BR-70904-970 Brası ´lia DF, Brazil [b] Sa ˜o Carlos SP / Brazil, Instituto de Fı ´sica de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, Sa ˜o Paulo, Brazil 106  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2009, 635, 106-111 mode of the ligands is identical to that found in their Al/Ca com- plexes, where they act as dianionic tridentate ligands forming five and six-membered fused chelate rings. The coordination to the tin atoms occurs exclusively via the 1,2- phenolate oxygen and the ad- jacent quinoid oxygen atoms. The complexes A1, A3 and P1 are dimers with hepta-coordinated tin atoms in form of a slightly dis- torted pentagonal bipyramid. The trinuclear complex P2 contains two pentacoordinated and one heptacoordinated tin atoms. tions. H 2 O and DMF molecules complete the coordination sphere of the metal cations. Scheme 1. Common coordination modes of alizarin and purpurin. A variety of deeply colored metal complexes with alizarin or purpurin has been synthesized and analytically charac- terized [4-8]. In most of the studied complexes the alizarin or purpurin are considered to act as bidentate ligand, ac- cording to scheme 1(a) or (b). However, besides the case related above, very few of these complexes had their crystal and molecular structure determined. For instance, the structure of a ruthenium carbonyl complex is reported, where the alizarin behaves as bidentate uninegative ligand, like scheme 1(a) [8]. The purpose of this work was to ex- plore the coordination behaviour of hydroxyanthraquinone dyes to organotin centers. The oxophilic nature of organo- tin(IV) moities together with their ability to form complexes with various coordination numbers (5, 6 or 7) promised the finding of interesting structures in their compounds with multidentate O-donors like hydroxyanthraquinones. Results and Discussion Preparation and Characterization The equimolar reaction of (H 2 aliz) and dibutyltin oxide (Bu 2 SnO) in refluxing ethanol afforded a deep purple crys-