Lanthanide coordination polymers with dicarboxylate-like ligands : crystal structures of polymeric neodymium(III) and erbium(III) complexes with flexible double betaines

Abstract

Four novel two-dimensional lanthanide(III) coordination polymers of two flexible double betaines with different numbers of methylene groups bridging two quaternary nitrogen atoms, namely [{Nd(L 2) 2(H 2O) 2} n][ClO 4] 3n ( 1), [{Nd(L 2) 2(H 20) 2} n][ClO 4] 3n·nH 2O ( 2), [{Er( 1) 2(H 2O) 2} n][ClO 4] 3n·nH 2O ( 3) and [{Er(L 2) 2(H 20)} n][ClO 4] 3n·nH 2O ( 4) [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,N′,N′-tetramethyl-1,4-butanediammonium : −O 2CCH 2N +Me 2 (CH 2), N +Me 2CH 2CO 2 −], have been prepared and characterized by X-ray crystallography. Each complex contains a centrosymmetric paddle-wheel-like dimeric subunit in which each pair of adjacent metal atoms is bridged by four syn-syn μ-carboxylato- O,O′ groups that are oriented 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 centre to carboxylato groups of an adjacent dimer. Such infinite chains are extended into a plane wave-like layer structure by cross-linkage of the molecular skeletons of double betaine ligands. The neodymium(III) atom is ( 1) is surrounded, in a distorted monocapped square-antiprismatic geometry, by seven carboxylato oxygen atoms and two aqua ligands, and the carboxylato groups are involved in three different coordination modes: the common bidentate bridging, unidentate and unusual tridentate bridging. In ( 2), ( 3) and ( 4), the lanthanide(III) atom exhibits eight coordination in a distorted square antiprism, and the carboxylato groups in the dimeric subunits adopt the common unidentate and bidentate bridging modes. In addition, the uncommon bidentate chelate mode of carboxylato groups also occurs in ( 4).