Pt₄S₄ Clusters with Functionalized Thiosemicarbazones derived from 5‐Acetylbarbituric Acid

Abstract

Reaction of K 2 [PtCl 4 ] with thiosemicarbazones derived from 5-acetylbarbituric acid led to the isolation of the tetranuclear species [Pt(AcbM)] 4 · 2/2DMSO · 2DMSO · 5H 2 O (1) and [Pt(AcbE)] 4 · 4DMSO · 2H 2 O (2) (H 2 AcbM ϭ 5-acetylbarbituric-4N-methyl thiosemicarbazone and H 2 AcbE ϭ 5-acetylbarbituric-4N-ethyl thiosemicarbazone). Both of these compounds feature a Pt 4 S 4 cluster in which some of the PtϪPt distances suggest the existence of weak metal-metal interactions. Crystals of these tetranuclear species are stabilized by intermolecular π-π stacking interactions. The two compounds have almost equivalent molecular 2255 structures, differing only in the orientation of the substituent on the amine nitrogen atom of the thiosemicarbazone. The two tetranuclear complexes contain the thiosemicarbazone bonded as a terdentate ligand to the platinum atom through the thiolate sulfur atom, the azomethine nitrogen atom and the alcoholate oxygen atom of the 5-acetylbarbiturate function.

Neutral NiII, PdII and PtII ONS-pincer complexes of 5-acetylbarbituric-4N-dimethylthiosemicarbazone: synthesis, characterization and properties

“…The ν(CvS) band appears at 839 cm −1 in the ligand and at lower frequencies in the complexes, in keeping with coordination through sulphur. 8 Coordination by the carbonyl O, azomethine N and thiolate S is also supported by the location of the ν(M-O) modes at 226-278 cm −1 , the ν(M-N) modes at 467-476, and the ν(M-S) modes at 347-395 cm −1 . 10 The room temperature magnetic moment of the nickel(II) complex 1, 2.86 μ B , indicates that this centre is of the high-spin type.…”

“…Barbituric acids can coordinate through the deprotonated nitrogen atoms, the carbonyl oxygen atoms and the deprotonated CH 2 group ( pK a = 4), giving rise to a large number of metal complexes that can range from mononuclear to polynuclear. 7 However, 5-acetylbarbituric thiosemicarbazones are usually expected to bind to a metal centre as dianionic tridentate O,N,Sdonors (a binding mode we have observed in platinum complexes 8 ), as monoanionic tridentate O,N,S-donors following loss of the enolic barbituric proton, as thiolate ligands following dissociation of the hydrazinic N-H proton, or as neutral ligands. 9…”

Synthesis and Characterization of Some 5-Acetylbarbituric Based Thiosemicarbazone Derivatives

“…The 1 H NMR spectra of these synthesized compounds, showed two characteristic signals in the range of δ 2.5 to 2.6 ppm and 13.0 to 13.6 ppm due to C-CH3 and N2H protons, respectively. The 1 H NMR spectra of Acb4NDH and the N-monosubstituted thiosemicarbazones (1)(2)(3) show a signal in the range of 9.9-10.1 ppm due to the N3H proton, while in the spectra of the N-disubstituted thiosemicarbazones (4)(5)(6), this signal is absent, appearing a new signal at 2.45 ppm attributed to the proton C6H (Figure 1). This fact reflects the keto/exo-enol tautomerism present in solution (Scheme 2).…”

“…5-Acetylbarbituric acid (5-Acb) was prepared according to literature procedure [7]. The thiosemicarbazones (5-Acbtsc) were prepared by condensation reactions between 5-Acb and the unsubstituted/substituted thiosemicarbazides [1,6], as follows (Scheme 2): Scheme 2. Synthesis pathway of 5-acetylbarbituric acid and thiosemicarbazones and tautomeric behavior of 5-acetylbarbiturate.…”

“…Then, in the light of the above facts about thiosemicarbazones and barbituric acid derivatives, it is likely that the combination of both types of compounds may lead to new biologically active agents. For that reason, we have undertaken the reaction between such bioactive moieties, already tested previously [1,6].…”