Coordination polymers of 5,5′-dithiobis(2-nitrobenzoic acid): Synthesis, structure and topology

Abstract In this work we report on new coordination assemblies of the 5,5′-dithiobis(2-nitrobenzoic acid) acid (H 2 L) with Ce(III), La(III), Pr(III), Tb(III)) and Cd(II) metal ions. Two different secondary building units (SBUs) of di-nuclear metal clusters are observed in [Ce 2 (L) 3 (DMA) 3 (H 2 O) 4 ] n ·DMA ( 1 ; L = doubly deprotonated anion of H 2 L, DMA = N,N-dimethylacetamide), the structure of which represents a 2D coordination polymer. The reactions of H 2 L with La- and Pr-metal salts yielded two isomorphous structures of [Ln(L)(DMF)(H 2 O)(HCOO)] n , Ln = La ( 2 ), Pr ( 3 ) (DMF = N,N-dimethylformamide), characterized by coordination networking in two dimensions as well. In similar reaction conditions complexation of the organic ligand with Tb ions resulted in the formation of 1D polymeric chains of [Tb(L)(DMA) 2 (NO 3 )] n ·H 2 O ( 4 ). The conformation of the ligand in these structures is characterized by a ⩾90° dihedral angle about the central S–S bond. In the reaction of Cd ions with H 2 L in the presence of 4,4′-bipyridyl ( bpy ) a 2D coordination network of [Cd(L)( bpy )(H 2 O)] n ( 5 ) was obtained, revealing an acute C–S–S–C torsion angle of 83.3° about the central bond. Similar reaction in the absence of bpy yields yet a different product, [Cd(L ½ )(DMF)] n ( 6 ) (L ½  = dissociated 5-thio-2-nitrobenzoate moiety). Its formation involves breaking of the S–S bond, and coordination of the two separate thio-2-nitrobenzoate parts to the Cd ion through their S-sites. Compounds 1 – 6 have been analyzed by X-ray diffraction techniques and infrared spectroscopy, throwing light on the preferred molecular shape of this ligand and its coordination patterns with the various metal ions.