GENERATION OF COORDINATION NETWORKS WITH DICARBOXYLATE-LIKE LIGANDS -SYNTHESIS AND CRYSTAL-STRUCTURES OF POLYMERIC COMPLEXES OF GADOLINIUM(III) PERCHLORATE WITH FLEXIBLE DOUBLE BETAINES

Three novel gadolinium(III) co-ordination polymers containing three fl exible double betaines with different numbers of methylene bridges and a rigid tris(ethylene) bridge between two quaternary nitrogen atoms, namely [{Gd(L-1)(2)(H2O)(2)}(n)](ClO4)(3n). nH(2)O (1), [{Gd(L-2)(2)(H 2O)(2)}(n)](ClO4)(3n). nH(2)O (2) and [{Gd(L-3)(2)(H2O)(2)}(n)](ClO4)( 3n). 8nH(2)O (3) (L-1 = ethyl-N,N,N',N'-tetramethyl-1,3-propanediammon ium, -O2CCH2N+Me2-(CH2)(3)-N+Me2,CH2CO2-; L-2 = ethyl-N,N,N',N'-tetram ethyl-1,4-butane-diammonium, -O2CCH2N+Me2-(CH2)(4)-N+Me2CH2CO2-; L-3 = 1,4-diazoniabicyclo[2.2.2]octane-1,4-diacetate, -O2CCH2N+(CH2CH2)(3)N +CH2CO2-), have been prepared and characterized by X-ray crystallograp hy. Each complex contains paddlewheel-like dimeric subunits in which e ach pair of adjacent metal atoms is bridged by four mu-carboxylato-O,O ' groups that are orientated nearly perpendicular to each other about the metal-metal axis. The dimeric subunits are extended into a polymer ic chain through the linkage of each metal center to the carboxylato g roups of an adjacent dimer. Such infinite chains are extended into a p lane wave-like layer structure in (1) and (2), and a three-dimensional framework in (3) by the cross-linkage of the molecular skeletons of d ouble betaine ligands. The formation of hydrogen bonds further leads t o a three-dimensional network in (1). The gadolinium(III) atom in each complex is surrounded in a distorted square-antiprismatic geometry by six carboxylato oxygen atoms and two aqua ligands. The carboxylato gr oups in the dimeric subunits adopt the common syn-syn bidentate bridgi ng and unidentate co-ordination modes in (1), (2) and (3). In addition , the carboxylato groups in (I) and (2) also coordinate the metal atom s in an unusual syn-skew, mu-O,O' bridging mode. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.