~ Pergamon 0277-5387(95)00472-6 Pohhedron Vol. 15. No 12~ pp. 1923 1930, 1996 Copyright ~ 1996 Elsevier Science Lid Printed in Great Britain. All rights reserved 0277 5387/96 $15.00+0.00 AQUA (IODO) (PYRIDINE- 1-OXIDE-2- CARBOXYLATE)CADMIUM(II), [Cd(C6H4NO3)I(H20)], A COMPOUND WITH BIDIMENSIONAL SUPRAMOLECULAR SELF-ORGANIZATION ELENA BERMEJO, ALFONSO CASTINEIRAS* and RICARDO DOM[NGUEZ Departamento de Qulmica Inorg/mica, Universidad de Santiago de Compostela, E-15706 Santiago de Compostela, Spain and JOACHIM STRAHLE and CACILIA MAICHLE-MOSSMER Institut far Anorganische Chemie der Universitfit Tfibingen, Auf der Morgenstelle 18, A9, D-72076 TObingen, Germany (Received 26 June 1995 accepted 27 September 1995) Abstract--The compound aqua(iodo) (pyridine- l-oxide-2-carboxylate)cadmium(l I), [Cd(C6H4NO3)I(H20)], which crystallizes in the monoclinic system, was prepared by reac- tion ofcadmium(II) iodide with picolinic acid N-oxide. This compound exists as a polymeric structure in layers along the bc plane forming a supramolecular association derived from the existence of Cd--O dative bonds [2.629(7) A], and in which each cadmium atom is coordinated to the iodide ligand (Cd--I, 2.814 ,~) and to the oxygen atoms of the water molecule, the carboxylate group [Cd--O, av. 2.333(8) /~] and the N--O, which acts as a bridge [Cd--O, 2.329(8) and 2.371 (7) ,~] in such a way that if all interactions are taken into account, the cadmium atom is hepta-coordinated with a distorted pentagonal bipyramidal geometry. The existence of a hydrogen bond between the water molecule and the carboxylate group helps to achieve a supramolecular self-organization. IR and NMR (~H and 13C) spectra have also been studied. Research in the field of supramolecular chemistry has advanced greatly in the past 20 years due to the interest in molecular recognition arising from specific molecular interactions and the relation between structure and bond sites. 1 This interest in molecular associations at the supramolecular level deals not only with the construction of pre-designed crystal structures using directional molecular inter- actions associated with hydrogen bonds,: but also the construction of coordination compounds in which molecular units are associated through secondary and/or dative bonds. This results from * Author to whom correspondence should be addressed. the tendency of the metal to increase its coor- dination number and from the ability of ligands containing oxygen, sulfur or halogen atoms with more than one electron pair capable of being donated, to act as bridging ligands. 34 However, the formation of supramolecular struc- tures, involving self-organization processes which go beyond a simple packing of molecules in the crystal lattice, can also be achieved using ligands derived from traditional organic compounds which contain several donor atoms which can be coor- dinated simultaneously to different metal centres, thereby behaving as bridging ligands. 56 Hence, under suitable conditions and if a suitable acceptor is chosen, it is possible to predict and obtain solid 1923