Synthesis, Characterization, and Crystal Structures of Three New Divalent Metal Carboxylate−Sulfonates with a Layered and One-Dimensional Structure

Hydrothermal reactions of 5-sulfoisophthalic acid (HO3SC6H3-1,3-(CO2H)2, H3L) with M(II) carbonate (or oxide) and
4,4‘-bipyridine (4,4‘-bipy) (or 2,2‘-bipyridine, 2,2‘-bipy) resulted in three new metal carboxylate−sulfonate hybrids,
namely, [CdL(H-4,4‘-bipy)] (1) and [Cd3L2(2,2-bipy)4(H2O)2]·2H2O (2) with layered structures and [ZnL(H-4,4‘-bipy)(H2O)]·2H2O (3), whose structure features a one-dimensional double chain. The cadmium(II) ion in complex 1 is
seven-coordinated by five carboxylate oxygen atoms and one sulfonate oxygen atom from four ligands and a
unidentate 4,4‘-bipyridine. The interconnection of the cadmium(II) ions through bridging carboxylate−sulfonate ligands
resulted in the formation of a 〈002〉 double layer with the bipyridyl rings orientated toward the interlayer space.
Complex 2 has a different layered structure. Cd(1) is seven-coordinated by two bidentate chelating carboxylate
groups from two ligands, a bidentate chelating 2,2‘-bipy and an aqua ligand, and Cd(2) is octahedrally coordinated
by two bidentate chelating 2,2‘-bipy's, a sulfonate oxygen, and an aqua ligand. The coordination geometry around
Cd(3) is similar to that of Cd(1) with the aqua ligand being replaced by an oxygen atom from the sulfonate group.
The carboxylate−sulfonate ligand acts as pentadentate ligand, bridging with three cadmium(II) ions. The bridging
of cadmium(II) ions through the carboxylate−sulfonate ligands resulted in the formation of 〈006〉 and 〈003〉 layers;
the 2,2‘-bipy molecules and [Cd(2)(2,2‘-bipy)2(H2O)] cations are orientated to the interlayer space. Complex 3
features a 1D metal carboxylate−sulfonate double chain along the diagonal of the a- and b-axes. The zinc(II) ion
is octahedrally coordinated by four carboxylate O atoms from three ligands, a unidentate 4,4‘-bipy, and an aqua
ligand. Each pair of zinc(II) ions is bridged by two carboxylate groups from two ligands to form a dimer, and such
dimeric units are interconnected by bridging ligands to form a double chain. The sulfonate group of the carboxylate
sulfonate ligand remains noncoordinated and forms a number of hydrogen bonds with aqua ligands as well as
lattice water molecules.