Building two-dimensional silver(I) co-ordination polymers with dicarboxylate-like ligands: synthesis and crystal structures of polymeric complexes of silver nitrate and perchlorate with flexible double betaines

Abstract

Four novel two-dimensional silver(I) co-ordination polymers of two flexible double betaines with different quaternary ammonio side groups in the adipic acid skeleton, namely [{Ag₂(L¹)}_n][CIO₄]_2n1, [{Ag₂(L²)}_n][CIO₄]_2n·2nH₂O 2, [{Ag₂(L¹)(NO₃)₂}_n]3 and [{Ag₂(L²)(NO₃)₂}_n]4[L¹=meso-2,5-bis(trimethylammonio)adipate, ^–O₂CCH(N⁺Me₃)CH₂CH₂CH(N⁺Me₃)CO₂^–; L²=meso-2,5-bis(pyridinio)adipate, ^–O₂CCH(N⁺C₅H₅)CH₂CH₂CH(N⁺C₅H₅)CO₂^–], have been prepared and characterized by X-ray crystallography. Each complex contains dimeric subunits in which each pair of adjacent metal atoms is doubly bridged by coplanar syn-synµ-carboxylato-O,O′ groups. The dimeric subunits are extended into a step polymer through the linkage of each metal centre to a carboxylate group of an adjacent dimer. Such [Ag₂(carboxylate-O,O′)₂]_n chains are extended into sawtooth-wave layer structures in 1, 3 and 4, and an unusual corrugated layer in 2 by the cross-linkage of the adipic acid skeleton of the double-betaine ligands. The different ligation ability of the perchlorate and nitrate anions results in different co-ordination geometries about the silver(I) atoms. In 1 and 2, the silver(I) atom is co-ordinated by three carboxylato oxygen atoms in a T-shaped geometry, and the [Ag₂(carboxylate-O,O′)₂]_n chain exhibits the typical type D structure. The co-ordination geometry of the silver(I) atom in 3 is a distorted tetrahedron, and the [Ag₂(carboxylate-O,O′)₂]_n chain adopts a modified type D structure. The silver(I) atom in 4 exhibits unusual five-co-ordination in a square pyramid, and the dimer is converted into a novel paddlewheel-like structure, which is the first example found in silver(I) carboxylates.