Alkali Metal Ion Complexes with Pyrazinetetracarboxylate: Two- and Three-Dimensional Frameworks

Three novel polymeric assemblages have been obtained from alkali metal salts of pyrazinetetracarboxylic acid (H4PZTC). In the complexes [Na2(H2PZTC)(H2O)2] (1), [K(H3PZTC)] (2), and [Cs2(H2PZTC)] (3), the cations are chelated in the O,N,O site of one (1) or two ligands (2 and 3),and further carboxylic/ate complexation results in the formation of two- (1) or three-dimensional (2 and 3) compact assemblages with alternate rows or planes of cations and ligands. The H4−xPZTCx− ligand is bound to 6, 4, and 12 cations in 1−3, respectively, with four oxygen atoms in the last case being coordinated to as many as four cesium atoms each. The crystal structure of complex 3 is particularly remarkable, with the cesium cation having a coordination number of 12 and a hexagonal prismatic environment. The Cs···Cs contacts in this compound are among the shortest reported. These compounds further illustrate the potential of H4PZTC for the building of metal−organic frameworks.