Cobalt(II) Chloride Complexes with Acetonitrile, Isopropanol and Tetrahydrofuran Ligands: Considerations on Nuclearity, Reactivity and Synthetic Applications

Cobalt(II) chloride complexes with acetonitrile, isopropanol and tetrahydrofuran ligands: considerations on nuclearity, reactivity and synthetic applications

Danilo Stinghen,1 André Luís Rüdiger,1 Siddhartha O. K. Giese,1 Giovana G. Nunes,1 Jaísa F. Soares,1 David L. Hughes2 1 Departamento de Química, Universidade Federal do Paraná, Centro Politécnico, Jardim das Américas, 81530-900, Curitiba – PR, Brazil 2 School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK [email protected]

Since Olivier Kahn’s seminal work on molecular magnetism, synthetic chemists have sought ways to prepare new molecules with distinguished magnetic properties. A recently described class of compounds studied under the purview of molecular magnetism, called single-molecule magnets (SMM),1 attracted attention due to potential applications in the construction of information storage devices or as models to study magnetic interactions at the molecular level. Our research group has become interested in the synthesis of such compounds employing several transition metals in heterometallic complexes. The purpose of this work is to present the results of the preparation of cobalt(II) chloride adducts for use as potential precursors in the synthesis of SMMs. The structures of the complexes are found in Scheme 1. The compounds were characterized by single-crystal X-ray diffraction analysis and spectroscopic methods. Complex 1 was synthesized in 60% yield through the recrystallization of CoCl2 in thf:acetonitrile 1:1, layered with hexane (final solvent proportion 1:1:1). It is an ionic compound containing an octahedrally coordinated cobalt(II) cation, trans- 2+ [Co(thf)2(MeCN)4] , and the tetrahedral anion – [CoCl3(MeCN)] . The structure of 1 is nearly identical to that of another ionic compound prepared by Cotton et al.,2 which contains only Scheme 1 – Representation of the structure of the cobalt(II) complexes MeCN as a coordinating solvent bound to cobalt. Polymeric 2 was prepared in 68% yield by the dissolution of CoCl2 in toluene:isopropanol (2:1 ratio), followed by layering with hexane (final ratio 4:3:1.5 hexane:toluene:isopropanol). The structure of this complex is analogous to that of an 3 isopropanol adduct of FeCl2 that was previously reported by our research group. Complex 3 was obtained unexpectedly in an attempt to prepare a heterometallic vanadium(IV)- i i cobalt(II) compound. A reaction between [{V(OPr )3}2(-OPr )2] and two equivalents of CoCl2 in neat isopropanol was attempted and, after subsequent layering with hexane, a small amount of a blue microcrystalline solid was isolated. Recrystallization of that solid in tetrahydrofuran at –20 ºC led to the formation of 3. The resolution of the binuclear structure was a surprising result, since the recrystallization of CoCl2 from neat thf leads to the formation of the tetranuclear adduct 4 [Co4Cl8(thf)6], as reported by Sobota et al. Spectroscopic evidence points to the blue precursor to 3 having the same chemical nature as complex 2, possibly possessing the same structure. Attempts to reproduce the synthesis of 3 through recrystallization of 2 in thf and thf:hexane are underway to test this hypothesis. In conclusion, we have successfully synthesized three different cobalt(II) compounds with labile ligands, which may serve as precursors to the synthesis of heterometallic complexes in organic media, given the appropriate reaction conditions.

1 Gatteschi, D.; Sessoli, R.; Villain, J. (2006) Molecular Nanomagnets. Oxford University Press. 2 Cotton, F. A.; Daniels, L. M.; Jordan, I. V. (1998) Polyhedron, v. 17, p. 589. 3 Nunes, G. G. Bottini, R. C. R.; Reis, D. M.; Camargo, P. H. C.; Evans, D. J.; Hitchcock, P. B.; Leigh, G. J.; Sá, E. L.; Soares, J. F. (2004) Inorg. Chim. Acta, v. 357, p. 1219. 4 Sobota, P.; Olejnik, Z.; Utko, J.; Tadeusz, L. (1993) Polyhedron, v. 12, p. 613.

Financial support by CNPq, Capes, Fundação Araucária and UFPR is gratefully acknowledged.