Generation of coordination networks with dicarboxylate-like ligands: Synthesis and crystal structures of polymeric complexes of gadolinium(III) perchlorate with flexible double betaines

Abstract

Three novel gadolinium(III) co-ordination polymers containing three flexible double betaines with different numbers of metahylene bridges and a rigid tris(ethylene) bridge between two quaternary ntirogen atoms, namely [ sGd( L 1) 2(H 2O 2 s n ](ClO 4) 3 n · nH 2O ( 1),[ sGd( L 2) 2(H 2O) 2 s n ](ClO 4) 3 n · nH 2O ( 2) and [ sGd(L 3) 2 (H 2O) 2 s n ](ClO 4) 3 n · 8 nH 2O ( 3) (L 1 = N, N′-dicarboxymethyl- N, N, N′, N′-tetramethyl-1,3-propanediammonium, −O 2CCH 2N +Me 2-(CH 2) 3-N +Me 2CH 2CO 2 −; L 2 = N, N′-dicarboxymethyl- N, N′-dicarboxymethyl- N, N, N′, N′-tetramethyl-1,4-butanediammonium, −O 2CCH 2N +Me 2-(CH 2) 4-N +Me 2CH 2CO 2 −; L 3 = 1,4-diazoniabicyclo[2.2.2]octane-1,4- diacetate, −O 2CCH 2N +(CH 2CH 2) 3N +CH 2CO 2 −), have been prepared and characterized by X-ray crystallography. Each complex contains paddlewheel-like dimeric subunits in which each pair of adjacent metal atoms is bridged by four μ-carboxylato- O, O′ groups that are orientated nearly perpendicular to each other about the metal-metal axis. The dimeric subunits are extended into a polymeric chain through the linkage of each metal center to the carboxylato groups of an adjacent dimer. Such infinite chains are extended into a plane wave-like layer structure in ( 1) and ( 2), and a three-dimensional framework in ( 3) by the cross-linkage of the molecular skeletons of double betaine ligands. The formation of hydrogen bonds further leads to 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 groups in the dimeric subunits adopt the common syn-syn bidentate bridging and unidentate co-ordination modes in ( 1), ( 2) and ( 3). In addition, the carboxylato groups in ( 1) and ( 2) also coordinate the metal atoms in an unusual syn-skew μ- O, O′ bridging mode.