Synthesis, Characterization and Molecular Structures of someBismuth(III) Complexes with Thiosemicarbazones andDithiocarbazonic Acid Methylester Derivatives with Activityagainst Helicobacter Pylori
Authors: Diemer Rolf , Dittes Uwe , Nuber Bernhard , Seifried Volker , Opferkuch Wolfgang , Keppler Bernhard K. 
Published: March 2007

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 deprotonated. This ligand is bound to the bismuth(III) cation
merely via the sulfur atom S(1) of the thioketo group. The best description of the coordination
sphere of the bismuth atom is that of a distorted square bipyramidal polyhedron. The square
face is formed by the atoms S(3), N(5), Cl(1), the lone pair and the bismuth atom within. The
axial positions are occupied by the atoms S(1) and Cl(2). The bond angle between S(1), Bi(1)
and Cl(2) differs by about eight degrees from the value determined for a regular square
bipyramidal polyhedron of 180 degrees.

Some of the newly synthesized bismuth complexes and three ligands have been tested
against several strains of Helicobacter pylori bacteria in an agar dilution test. Almost all of the
listed bismuth complexes show excellent inhibitory properties with regard to growth of H. pylori already at low concentrations.