Versatile Chelating Behavior of Benzil Bis(thiosemicarbazone) in Zinc, Cadmium, and Nickel Complexes

Abstract

Reactions of benzil bis(thiosemicarbazone), LH(6), with M(NO(3))(2).nH(2)O (M = Zn, Cd, and Ni), in the presence of LiOH.H(2)O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule. Complexes of these metal ions with empirical formula [MLH(4)] were obtained, although they show different molecular structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a 1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as a bridge between the metal ions. However, in the nickel complex LH(6) acts as a N(2)S(2) ligand yielding a planar structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography, microanalysis, mass spectrometry, IR, (1)H, and (13)C NMR spectroscopies and for the cadmium complex by (113)Cd NMR in solution and in the solid state.

Reactivity of bisthiosemicarbazones with Sn(II) and Sn(IV): The synthesis and structure of an eight-coordinate complex with two bis(thiosemicarbazone) ligands

“…The coordination of the ligand affords six five-membered chelate rings. The TSC ligand shows a greater deviation from planarity than that observed for other bisthiosemicarbazone complexes [13,14], the sulphur atoms lying furthest from the mean plane. Within the two tetradentate ligands both branches are identical, which is not usual in bisthiosemicarbazone complexes, where the bond distances and angles are pretty similar but not exactly the same [13,15].…”

Structural Trends in Divalent Benzil Bis(thiosemicarbazone) Complexes

“…[27] The crystal structure of 1 consists of discrete molecules of [CuLH 4 ]. A perspective view of the complex, together with the atom-labelling scheme, is given in Figure 2 (the thermal ellipsoids are shown at 50 % probability) and selected bond lengths and angles are given in Tables 1 and 2, respectively.…”

“…The N-Cu-N bond angles are only 81.06°and 79.87°and the sulfur ends of the ligand arms are pushed outward well beyond the natural position that would be adopted by the planar ligand with 120°bond angles. For comparison, the Ni II complex with the same ligand shows a much better fit [27] as a result of the smaller ionic radius of nickel, with Ni-N and Ni-S distances of 1.86 and 2.157 Å, respectively, compared to 1.976 Å (N) and 2.235 Å (S) and 1.987 Å (N) and 2.24 Å (S) for complexes 1 and 2, respectively. All the angles at the nickel centre are significantly closer to the 90°p referred at the square-planar metal centre.…”

“…The brown solid formed was filtered off, washed with methanol and dried in vacuo. [26] A black solid (2) [28] A solution of zinc() nitrate hexahydrate (520 mg, 1.75 mmol) in ethanol (10 mL) was added to a suspension of LH 6 [27] Crystallography: Single crystals of complexes 1 and 3 were obtained by recrystallisation from DMSO and methanol, respectively, and crystals of 2 were isolated from the mother liquor of the reaction. Crystals of the compounds were mounted on a glass fibre and transferred to a Bruker SMART 6 K CCD area-detector three-circle diffractometer with a MAC Science Co., Ltd.…”

“…We report the X-ray structures of two copper complexes derived from LH 6 (Figure 1) whose reduction potential values are -0.550 and -0.520 V, [26] close to those of [Cu-(ATSM)], a related zinc complex, as well as the structure of a nickel complex for comparison. [27] We also discuss structural variations as a function of the ligand behaviour and/ or the metal ion. …”