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

• Coordination polymers of 5,5′-dithiobis(2-nitrobenzoic acid) with various Ln(III) ions and with Cd(II) have been obtained.
• La(III)-, Ce(III)- and Pr(III)-based polymers represent 2D nets, while that with the smaller Tb(III) ion extends in 1D.
• Preferential conformational features of the organic ligand (Ellman’s reagent) have been established.

In this work we report on new coordination assemblies of the 5,5′-dithiobis(2-nitrobenzoic acid) acid (H2L) 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 [Ce2(L)3(DMA)3(H2O)4]n·DMA (1; L = doubly deprotonated anion of H2L, DMA = N,N-dimethylacetamide), the structure of which represents a 2D coordination polymer. The reactions of H2L with La- and Pr-metal salts yielded two isomorphous structures of [Ln(L)(DMF)(H2O)(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(NO3)]n·H2O (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 H2L in the presence of 4,4′-bipyridyl (bpy) a 2D coordination network of [Cd(L)(bpy)(H2O)]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(L½)(DMF)]n (6) (L½ = 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.

Coordination complexes of the 5,5′-dithiobis(2-nitrobenzoic acid) linker with the Ce(III), La(III), Pr(III), Tb(III) and Cd(II) metal ions exhibit 1D and 2D polymeric assemblies. The organic moiety adopts an obtuse dihedral angle about the central C–S–S–C bond in the lanthanoid derivatives 1–4, but an acute value in the Cd-compound 5. The observed metallic nodes in an oxo- or carboxyl-bridged clusters are either dinuclear as in 1 and 4 or poly-nuclear as in 2, 3 and 6.Figure optionsDownload as PowerPoint slide