LANTHANIDE COORDINATION POLYMERS WITH DICARBOXYLATE-LIKE LIGANDS - CRYSTAL-STRUCTURES OF POLYMERIC NEODYMIUM(III) AND ERBIUM(III) COMPLEXESWITH FLEXIBLE DOUBLE BETAINES

Four novel two-dimensional lanthanide(III) coordination polymers of tw o flexible double betaines with different numbers of methylene groups bridging two quaternary nitrogen atoms, namely [{Nd(L(2))(2)(H2O)(2)}( n)][ClO4](3n) (1), [{Nd(L(2))(2)(H2O)(2)}(n)][ClO4](3n). nH(2)O (2), [ {Er(L(1))(2)(H2O)(2)}(n)][ClO4](3n). nH(2)O (3) and [{Er(L(2))(2)(H2O) }(n)][ClO4](3n). nH(2)O (4) [L(1) = 2)CCH(2)N(+)Me(2)-(CH2)(3)-N(+)Me( 2)CH(2)CO(2)(-); L(2) = )CCH(2)N(+)Me(2)-(CH2)(4)-N(+)Me(2)CH(2)CO(2)( -)], have been prepared and characterized by X-ray crystallography. Ea ch complex contains a centrosymmetric paddle-wheel-like dimeric subuni t in which each pair of adjacent metal atoms is bridged by four syn-sy n mu-carboxylato-O,O' groups that are oriented nearly perpendicular to each other about the metal-metal axis. The dimeric subunits are exten ded into a polymeric chain through the linkage of each metal centre to carboxylato groups of an adjacent dimer. Such infinite chains are ext ended into a plane wave-like layer structure by cross-linkage of the m olecular skeletons of double betaine ligands. The neodymium(III) atom is (1) is surrounded, in a distorted monocapped square-antiprismatic g eometry, by seven carboxylato oxygen atoms and two aqua ligands, and t he carboxylato groups are involved in three different coordination mod es: the common bidentate bridging, unidentate and unusual tridentate b ridging. In (2), (3) and (4), the lanthanide(III) atom exhibits eight coordination in a distorted square antiprism, and the carboxylato grou ps in the dimeric subunits adopt the common unidentate and bidentate b ridging modes. In addition, the uncommon bidentate chelate mode of car boxylato groups also occurs in (4). Copyright (C) 1996 Elsevier Scienc e Ltd