Comparison of the molecular structure of solid metal 2,5- and 2,6-pyridindicarboxylates

E. E. SILEO; G. E. RIGOTTI; O. E. PIRO ; M. A. BLESA

Viña del Mar, Valparaíso

Congreso; SOLIDOS 2009; 2009

SÓLIDOS 2009

The family of pyridindicarboxylic (pdc) acids is composed of six positional isomers, and offers a rich and varied coordination chemistry. Several variables are easily recognized as important in defining the structure of solid metal pyridindicarboxylates: the coordination polyhedron adopted by the metal ion, the position in the ring of the three potentially coordinating groups of pdc, the metal to ligand ratio and the charge balance requirements. These features define the basic building blocks of the structure (discrete molecules, cyclic arrangements, extended 1D, 2D or 3D chains). Some examples are found in our previous work [1]-[4]. Except for 3D polymers, the crystal structure itself usually results from weaker interactions between the basic building units: hydrogen bonding and ð-ð stacking interactions. The interaction of pdc with metals is of importance in several fields, all related to the socalled Metal Organic Frameworks (MOFs): the rational design of materials with specific architectures, the sequestering of metal ions from aqueous media, etc. This paper reports the structure of a Gd(III) salt of 2,5-H2pdc. [Gd(III)(2,5-pdc)(2,5-pdcH)(H2O)5]·4H2O crystallizes in the monoclinic space group C2/c, with a=13.844(2), b=9.622(4), c=32.913(5) Å, â =93.37(2)°, and Z=8. The structure was solved employing 2193 independent X-ray reflections with I >2ó(I) by Patterson and Fourier methods and refined by full-matrix least-squares to R1=0.060. The compound is isostructural with the analogous Eu salt [5], although interesting differences in the cell dimensions are observed. The structure of this compound is compared with that of reported Ln(III) salts of 2,6-H2pdc. The objective is to assess the importance of the various types of interactions in the determination of the crystal structure of nine-coordinated lanthanide pdc’s. In particular, the possibility of 2,6-pdc2- to form three-dentate complexes contrasts with the limitation to bidenticity in the case of 2,5-pdc2-. The second carboxylate coordinates another lanthanide ion, and the overall motif is determined also by bridging carboxylates, by hydrogen bonds and by ð-ð stacking interactions. The octahedrally coordinated salts of Zn(II): {Zn(2,5-pdc)(H2O)n} (n= 2.5 or 3), reported earlier by us, and Zn(2,6-Hpdc)2·3H2O [6] are also compared, and the same ideas are seen to apply. References [1] E.E. Sileo, M.F. Quinteros-Rivero, B.E. Rivero, G. Rigotti and M.A. Blesa, Solid State Ionics 73, 153-159 (1994). [2] E.E. Sileo, M.A. Blesa, G. Rigotti, B.E. Rivero and E.E. Castellano, Polyhedron 15, 4531-4540 (1996). [3] E.E. Sileo, D. Vega, R. Baggio, M.T. Garland and M.A. Blesa, Austr. J. Chem. 52, 205-212 (1999). [4] E.E. Sileo, O.E. Piro, G.Rigotti, M.A. Blesa, A.S. de Araujo and E.E. Castellano. Struct. Chem. 19 (4), 651-657 (2008). [5] Y. Song, B. Yan and Zh. Chen, J. Coord. Chem. 58, 811–816 (2005). [6] N. Okabe and N. Oya, Acta Cryst., C56, 305±307 (2000).