Synthesis, Characterization and Molecular Structures of someBismuth(III) Complexes with Thiosemicarbazones andDithiocarbazonic Acid Methylester Derivatives with Activityagainst Helicobacter Pylori

Abstract

The reactions of bismuth(III) nitrate pentahydrate and bismuth(III) chloride with heterocyclic thiosemicarbazones and derivatives of dithiocarbazonic acid methylester were used to synthesize the respective bismuth(III) complexes, which could be divided into five groups D-H because of their stoichiometrical properties and their molecular structures. The molecular structure and the near coordination sphere of the bismuth(III) central atom of four representative compounds were determined by single-crystal X-ray studies. Bis[1-azepanyl-4-(2-pyridyl)-2,3-diazapenta-1,3-diene-1-thiolato-N′,N3,S]bismuth(III) nitrate (5) belongs to group D. The two tridentate ligands and the nitrate ion surround the bismuth atom. The best description of the coordination sphere appears to be that of a distorted trigonal dodecahedron with one position occupied by the lone pair of the bismuth atom. Bis[1-azepanyl-4-(2-thienyl)-2,3-diazapenta-1,3-diene-1-thiolato-N3,S]bismuth(III) nitrate (9) is assigned to complex type E. Here, two deprotonated ligand molecules are coordinated to the bismuth(III) central atom as bidentate ligands. The structure of this complex can best be described as a distorted trigonal antiprism with a five-coordinated central atom. The two triangular faces are formed by the atoms S(4), N(6), O(11) and S(3), N(4) and the lone pair of the central atom. The two chelate rings are almost perpendicular to each other. Complex molecules of group F form dimeric units with bichloro-bridged bismuth atoms. The structure of di-μ-chlorobis[1-azepanyl-4-(2-pyridyl)-2,3-diazapenta-1,3-diene-1-thiolato-N′,N3,S-chloro]dibismuth(III) (15) can be described as two six-coordinated bismuth atoms, which are bound together via two bridging chlorine atoms. The two bismuth atoms Bi(1) and Bi(1a) and the two bridging chlorine atoms Cl(2) and Cl(2a) form the Bi2Cl2 plane. The two tridentate ligand molecules coordinate via the same atoms as shown in complex 5. In addition, they form two parallel planes, which are perpendicular to the Bi2Cl2 plane. With regard to the center of the Bi(1)-Bi(2) axis they are central point symmetrical, i.e. one pyridine ring lies above and the other beneath the Bi2Cl2 plane. Bismuth(III) chloride and pyridine-2-carboxaldehydethiosemicarbazone 1 b or 2-acetylpyridine-thiosemicarbazone 1 c form complexes of group G. Three chlorine atoms and a bidentate ligand are coordinated to the bismuth(III) central atom. The bidentate ligand bound to the central atom through the N(3) atom and the sulfur atom of the thioketo group. The structure of 18 is completely different from the structures of the bismuth(III) complexes discussed so far and was therefore assigned to group H. The bismuth central atom is coordinated with two ligands, which are bound in different ways. One of them is deprotonated. This ligand is bound to the central atom via the sulfur atom S(3) of the thiolate group and the N(5) atom. An interaction between the sulfur atom of the thiophene ring and the bismuth atom is not possible.The other ligand molecule is not de...

Syntheses, crystal structures and antimicrobial activities of monomeric 8-coordinate, and dimeric and monomeric 7-coordinate bismuth(III) complexes with tridentate and pentadentate thiosemicarbazones and pentadentate semicarbazone ligands

“…In fact, two geometries for the bismuth(III) complexes with the pentadentate dapt 2À ligand (H 2 dapt ¼ 2,6-diacetylpyridine bis(2-thenoylhydrazone)) have been proposed; one is the 7-coordinate pentagonal bipyramid [22,24] and the other is the 6-coordinate pentagonal pyramid [25][26][27]. KepplerÕs group has counted an electron pair (6s 2 ) of the bismuth(III) atom as one of the coordination numbers [22,24], whereas BattagliaÕs group did not [25][26][27]. Since an electron pair of the bismuth(III) atom is reactioninert, but forces steric pressure on the coordination interaction between the ligand and the bismuth(III) atom, i.e., stereochemically active, it can be counted in the coordination number of the bismuth(III) complexes [22,24].…”

“…KepplerÕs group has counted an electron pair (6s 2 ) of the bismuth(III) atom as one of the coordination numbers [22,24], whereas BattagliaÕs group did not [25][26][27]. Since an electron pair of the bismuth(III) atom is reactioninert, but forces steric pressure on the coordination interaction between the ligand and the bismuth(III) atom, i.e., stereochemically active, it can be counted in the coordination number of the bismuth(III) complexes [22,24]. If an electron pair is not taken into account in the coordination number, a specific reason why the pentagonal pyramid is more stable than the octahedron for the 6-coordinate complex is required.…”

“…The biological activities of thiosemicarbazones are considered to be due to their ability to form chelates with heavy metals [11][12][13][14]. Biological activities of the metal complexes differ from those of either the ligand or the metal ion itself, and increased and/or decreased biological activities are reported for several transition metal complexes such as copper(II) and nickel(II) [6,7].…”

“…In a separate account, the discovery and design of bioactive bismuth compounds, and the interactions of bismuth compounds with biomolecules and pharmaceutical agents have been recently reviewed [20][21][22][23][24][25][26][27][28]. Generally, the bismuth(III) atom with a larger ionic radius (1.16 A) [29] has one inert electron pair (6s 2 ) and forms the complexes of the non-transition metal center with higher coordination numbers.…”

“…Generally, the bismuth(III) atom with a larger ionic radius (1.16 A) [29] has one inert electron pair (6s 2 ) and forms the complexes of the non-transition metal center with higher coordination numbers. Derivatives of bismuth(III) thiosemicarbazones and dithiocarbazonic acid methylester are now numerous, allowing for comparison of the relationships between specific structural features and the bioactivity [24][25][26][27].…”