Solid-state 111 Cd NMR studies on cadmium(II)-2,x-pyridinedicarboxylates. Crystal structure of 2,4-pyridinedicarboxylato triaqua cadmium(II) hemihydrate: [Cd(II)(2,4-pydc)(H 2 O) 3 ] Æ 1/2H 2 O Guillermo Mendoza-Dı ´az a, * , Graciela Rigotti b , Oscar E. Piro b , Elsa E. Sileo c a Universidad de Guanajuato, Facultad de Quı ´mica, Noria Alta s/n, Guanajuato, Gto. 36050, Mexico b Departamento de Fı ´sica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata and and Instituto de Fı ´sica de La Plata (CONICET), C. C. 67, 1900 La Plata, Argentina c Departamento de Quı ´mica Inorga ´ nica, Analı ´tica y Quı ´mica Fı ´sica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabello ´ n II, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina Received 30 September 2004; accepted 2 February 2005 Available online 13 April 2005 Abstract The synthesis and characterisation by solid-state 111 Cd NMR of Cd(2,3-), Cd(2,4-), Cd(2,5-) and Cd(2,6-pyridinedicarboxy- lato) Æ xH 2 O is reported. Results indicate that the 111 Cd NMR signal is very sensitive to the relative position of both carboxylates. Similar shifts (at 54.0 and 55.4 ppm) are found for the 2,4- and the 2,6-isomers where the carboxylates groups are meta to each other. For the 2,3- and 2,5-derivatives (carboxylates in ortho and para positions), the signals are detected at 119.6 and 84.2 ppm. The crys- tal and molecular structure of the seven-coordinated cadmium complex, [Cd(2,4-pyridinedicarboxylato)(H 2 O) 3 ] Æ 1/2H 2 O is also reported. This data allows a correlation between Cd–O and Cd–N coordination and geometry with 111 Cd chemical shifts. Additional coupling between 111 Cd and 14 N in 2,3- (also found in 2,4-pydc) suggests only one N is coordinated to Cd. The anisotropy magni- tude, Dr, and the asymmetry parameter, g, are also analysed. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Solid-state 111 Cd NMR; Pyridinedicarboxylate; Lutidinate; Crystal structure 1. Introduction Metal pyridinedicarboxylates have interesting prop- erties in biological systems [1–4], and their presence seems to be related with metal-transport and cell mem- brane protection in some microorganisms [5,6]. These compounds are derived from pyridinedicarboxylic acids (H 2 pydc) that form a series that includes the 2,3-, 2,4-, 2,5- and 2,6-pyridinedicarboxylic isomers. Cadmium forms 1:1 complexes with all four isomers and it may ex- hibit various coordination modes, depending on the rel- ative position of the donor sites: the oxygen atoms from the two carboxylic groups and the nitrogen atom from the pyridinic ring. Because of the donor sites and the variety in relative positions, metal pyridinedicarboxy- lates may provide excellent models for less characterised samples of biological interest. 111 Cd NMR (more commonly 113 Cd NMR) spectros- copy is a sensitive probe of the Cd environment as the number and type of coordinating groups and the geome- try around the metal ion can be correlated with the 111 Cd chemical shift. This signal is highly sensitive to oxygen 0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2005.02.007 * Corresponding author. Tel.: +52 473 7320006; fax: +52 473 7330177. E-mail address: mendozag@quijote.ugto.mx (G. Mendoza-Dı ´az). www.elsevier.com/locate/poly Polyhedron 24 (2005) 777–783