FULL PAPER DOI: 10.1002/ejic.200700075 Thiodiacetate and Oxydiacetate Cobalt Complexes: Synthesis, Structure and Stereochemical Features Abdessamad Grirrane, [a,b] Antonio Pastor, [a] Eleuterio Álvarez, [b] Carlo Mealli, [c] Andrea Ienco, [c] Patrick Rosa, [d,e] and Agustín Galindo* [a] Keywords: Cobalt / Thiodiacetate / Oxydiacetate / Tridentate Ligands / Coordination modes A series of cobalt complexes containing the dianionic ligands X(CH 2 COO) 2 2– (X = S, tda; or X = O, oda) is reported. The complexes [Co(tda)(bipy)(H 2 O)]·4H 2 O(2), which was charac- terised by X-ray crystallography, [Co(tda)(phen)(H 2 O)] (3), [Co(tda){(MeO) 2 bipy}(H 2 O)]·2H 2 O (4) and [Co(tda)(dpp)- (H 2 O)]·2H 2 O(5) are obtained by reaction of the precursor complex [Co(tda)(H 2 O)] n (1a) with the bidentate N-donor li- gands 2,2'-bipyridine (bipy), o-phenanthroline (phen), 4,4'- dimethoxy-2,2'-bipyridine [(MeO) 2 bipy] and 2,3-bis(2-pyr- idyl)pyrazine (dpp), respectively. The reaction of 1a with di(2-pyridyl) ketone unexpectedly displaces tda from the co- ordination sphere and leads to the Co III species [Co{OC(OH)- (2-pyridyl) 2 } 2 ] + [Htda] – ·3H 2 O(6), as confirmed by an X-ray analysis. Three new oxydiacetate complexes of cobalt are also synthesised by treating the known complex [{Co(oda)- (H 2 O) 2 }·H 2 O] n with 4,4'-di-tert-butyl-2,2'-bipyridine (tBu 2 - bipy), 2,3-bis(2-pyridyl)pyrazine (dpp) and 4,4'-bipyridine Introduction The thiodiacetate (tda) and oxydiacetate (oda) dianions X(CH 2 COO) 2 2– (X = S and O, respectively) are versatile ligands that have been widely explored as multidentate and chelating units for one or more metals of a different nature. They contain five atoms that are potential donors, four of which come from two carboxylate groups and one from the thioether or ether function. These ligands can bind a single [a] Departamento de Química Inorgánica, Universidad de Sevilla, Aptdo 1203, 41071 Sevilla, Spain Fax: +34-95-455-7153 E-Mail: galindo@us.es [b] Instituto de Investigaciones Químicas, CSIC-Universidad de Sevilla, Avda. Américo Vespucio 49, 41092 Sevilla, Spain [c] ICCOM, CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy [d] LAMM, Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy [e] Institut de Chimie de la Matière Condensée de Bordeaux ICMCB-CNRS, Université Bordeaux, Groupe de Sciences Mo- leculaires, 87 Av. Dr. A. Schweitzer, 33608 PESSAC Cedex, France Supporting information for this article is available on the WWW under http://www.eurjic.org or from the author. Eur. J. Inorg. Chem. 2007, 3543–3552 © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3543 (4,4'-bipy). The complexes [Co(oda)(tBu 2 bipy)(H 2 O)]·1.5H 2 O (7), [Co(oda)(dpp)(H 2 O)]·2H 2 O(8) and [{Co(oda)(H 2 O) 2 } 2 (μ- 4,4'-bipy)]·2H 2 O(9) are structurally characterised (8 as a methanol solvate). Complex 9 is binuclear, in contrast to 7 and 8 (mononuclear), and magnetic susceptibility measure- ments down to 2 K for this complex show high-spin non- correlated Co II ions with a typical Curie–Weiss behaviour. The Co(oda) fragment in 7–9 adopts a planar (mer) rather than a folded (fac) conformation, the latter of which is com- mon to all the M(tda) complexes but is only occasionally ob- served in the M(oda) ones. In the final section of the paper, the key geometric parameters that control the stereochemis- try of the two ligands are determined from a statistical analy- sis based on the structurally characterised Co(oda) and Co(tda) complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) metal in a tridentate manner, with the two “exo” oxygen donor atoms of the carboxylate groups being capable of additional coordination of another metal or external elec- trophiles. This permits the formation of homo- and hetero- metallic extended solids or the formation of stabilizing hy- drogen bonds. The chemistry of thiodiacetate transition metal com- plexes is comparatively less developed than that of the re- lated oxydiacetate complexes. As a matter of fact, the number of X-ray characterised metal derivatives is smaller for tda than for oda derivatives (160 and 55 hits for the O(CH 2 COO) 2 2– and S(CH 2 COO) 2 2– fragments, respec- tively [1] ). Due to our interest in this area of chemistry, [2,3] we started to explore the behaviour of thiodiacetate toward cobalt as no structure of tda-Co complexes had been re- ported and there were only references in the literature to the solution behaviour of tda-Co II species. [4] The first structural characterisation of a tda-Co II complex was simultaneously presented by us [5] and by Zhu and co-workers [6] (complex [Co(tda)(phen)(H 2 O)]). Some additional examples, namely [Co(tda)(N-N)(H 2 O)]·2H 2 O and [Co(tda)(N) 3 ]·2H 2 O, where N and N-N are nitrogen ligands, were published soon afterwards by Xu and co-workers. [7] In this paper we present a complete report of our studies together with the synthesis and properties of new cobalt