Bismuth Complexes Research Articles

The Emissive and Electrochemical Properties of Hypervalent Pyridine-Dipyrrolide Bismuth Complexes.

We present a series of six hypervalent bismuth complexes Bi(R1PDPR2)X bearing ligands characterized by the pyridine-2,6-bis(pyrrolide) (PDP) structural motif. While bismuth holds considerable potential for facilitating efficient intersystem crossing (ISC), reports on phosphorescent molecular bismuth complexes are still scarce and mostly based on systems that exhibit inter- or intraligand charge transfer character of their optical excitations. Herein, the UV/vis absorptive, luminescent, and electrochemical properties of complexes Bi(R1PDPR2)X are explored, where the substituents R1 and R2, as well as the halide ligand X are varied. These compounds are characterized by an intense HOMO→LUMO transition of mixed ligand-to-metal charge transfer (LMCT) and interligand charge transfer (LL'CT) character, as shown by time-dependent density functional theory (TD-DFT) calculations. At 77 K in a 2-MeTHF matrix, these compounds exhibit red, long-lived phosphorescence with lifetimes ranging from 479 to 14 μs. Cyclic voltammetry measurements and TD-DFT calculations show that the substituents influence HOMO and LUMO energies to almost equal extent, resulting in nearly constant emission wavelengths throughout this series. Single-crystal X-ray diffraction studies of four of the six complexes exemplify the inherent Lewis acidity of the coordinated Bi3+ ion, in spite of its hypervalency.

Activation and C-C Coupling of Aryl Iodides via Bismuth Photocatalysis.

Within the emerging field of bismuth redox catalysis, the catalytic formation of C-C bonds using aryl halides would be highly desirable; yet such a process remains a synthetic challenge. Herein, we present a chemoselective bismuth-photocatalyzed activation and subsequent coupling of (hetero)aryl iodides with pyrrole derivatives to access C(sp2)-C(sp2) linkages through C-H functionalization. This unique reactivity is the result of the bismuth complex featuring two redox state-dependent interactions with light, which 1) activates the Bi(I) complex for oxidative addition via MLCT, and 2) promotes the homolytic cleavage of aryl Bi(III) intermediates through a LLCT process.

Activation and C−C Coupling of Aryl Iodides via Bismuth Photocatalysis

AbstractWithin the emerging field of bismuth redox catalysis, the catalytic formation of C−C bonds using aryl halides would be highly desirable; yet such a process remains a synthetic challenge. Herein, we present a chemoselective bismuth‐photocatalyzed activation and subsequent coupling of (hetero)aryl iodides with pyrrole derivatives to access C(sp2)−C(sp2) linkages through C−H functionalization. This unique reactivity is the result of the bismuth complex featuring two redox state‐dependent interactions with light, which 1) activates the Bi(I) complex for oxidative addition via MLCT, and 2) promotes the homolytic cleavage of aryl Bi(III) intermediates through a LLCT process.

Establishing Composition of Solid Solution Based on Single Crystal and Powder X-ray Measurement: The Case of Halogenated Bismuth(III) Complexes with Acetophenone-4-methyl-3-thiosemicarbazone

New bismuth (III) complexes with acetophenone-4-methyl-3-thiosemicarbazone (L) and halogens (Cl and Br) in both bridging and terminal positions have been synthesized and structurally characterized using single-crystal X-ray diffraction. The pure complexes (Cl or Br) were found to be highly isostructural, which motivated our attempts to create solid solutions of these complexes. A series of such compounds was prepared using various procedures and stoichiometries. A method for determining the mutual concentrations of different halogens, based on the positions of selected peaks in powder diffraction patterns, was tested and compared with other methods.

Electrochemical and Spectroscopic Investigations of Bismuth(III) Pharmaceuticals with L-Glutathione

Due to the importance of L-cysteine in the human system, the interaction of metals with this amino acid are worthy of investigation by various methods. In this laboratory1, we have investigated the interaction of bismuth(III) compounds with L-cysteine by both cyclic voltammetry and UV-VIS spectroscopy in an attempt to understand the role of bismuth in treating gastrointestinal maladies.2 The addition of bismuth(III) compounds to solutions of L-cysteine causes a negative potential shift for bismuth(III) reduction as an indication of complex formation between bismuth(III) and L-cysteine. This interaction is also evident by the appearance of a UV-VIS spectroscopic band at 340 nm (Bi-sulfur bond). Even at low pH values (pH 1.0), electrochemical studies show evidence of some kind of interaction even when there is no 340 nm band. These investigations have been conducted at pH 1.00 and 3.00 to simulate conditions in the human stomach and at pH 7.40 MOPS [(3-N-morpholino)propanesulfonic acid] to simulate general physiological conditions, in particular the intestinal tract. Recent work has involved extension of this work to L-glutathione, a tripeptide incorporating L-cysteine, under similar conditions. As might be expected, these interactions are considerably more complicated than those involving L-cysteine. As an example, there is a considerable positive potential shift for the reduction of bismuth(III) citrate in the presence of L-glutathione on the first and second voltammetric sweeps at gold and glassy carbon electrodes. This behavior evidently reflects the rather long (several seconds) time required for the re-formation of the bismuth complex with L-glutathione after its reductive ligand (L-glutathione) loss during bismuth(III) reduction on the first sweep. In addition, there is evidence of a film buildup on the electrode surface as observed by peak current increases during multiple potential sweeps. These observations are planned for inclusion in this symposium presentation.References T. Cheek and D. Peña, J. Electrochem. Soc., 167, 155522 (2020)Li, R. Wang, and H. Sun, Acc. Chem. Res., 52, 216 (2019).

Transition Metal Mimetic π-Activation by Cationic Bismuth(III) Catalysts for Allylic C-H Functionalization of Olefins Using C═O and C═N Electrophiles.

The discovery and utilization of main-group element catalysts that behave similarly to transition metal (TM) complexes have become increasingly active areas of investigation in recent years. Here, we report a series of Lewis acidic bismuth(III) complexes that allow for the catalytic allylic C(sp3)-H functionalization of olefins via an organometallic complexation-assisted deprotonation mechanism to generate products containing new C-C bonds. This heretofore unexplored mode of main-group reactivity was applied to the regioselective functionalization of 1,4-dienes and allylbenzene substrates. Experimental and computational mechanistic studies support the key steps of the proposed catalytic cycle, including the intermediacy of elusive Bi-olefin complexes and allylbismuth species.

In vitro and In vivo anticancer activities of Bi(III) 2-thiazolecarboxaldehyde thiosemicarbazone complex

While the currently available platinum-based antitumor drugs have severe side effects, there is a need to develop highly efficient and low-toxicity metal agents. In this study, we synthesized four bismuth (Bi) complexes (C1–C4) derived from 2-thiazolecarboxaldehyde thiosemicarbazones. These Bi(III) complexes showed significant antitumor activity, with C4 exhibiting the highest efficacy in structure–activity relationship studies. Notably, C4 effectively inhibited tumor growth and produced fewer side effects in vivo. We further confirmed the antitumor mechanisms of the C4 complex, which include inducing apoptosis, arresting the cell cycle at the S phase, inducing mitochondrial and its DNA damage, and suppressing angiogenesis.

Simultaneous determination of lead and cadmium in water by metal oxide framework complex-modified glassy carbon electrodes

Lead (Pb) and cadmium (Cd) are pervasive environmental pollutants known for their significant biological toxicity. The traditional methods for detecting these ions often necessitate large-scale instruments and complex procedures. In contrast, electrochemical detection methods offer advantages such as rapidity, portability, and sensitivity, making them suitable for the simultaneous detection of heavy metals. Metal-organic frameworks (MOFs), characterized by their exceptional adsorption and enrichment capabilities for heavy metal ions, have shown promise in this regard. Nevertheless, the poor conductivity of most MOFs has limited their electrochemical applications. In this study, glassy carbon electrodes (GCEs) were modified using the MOF ZIF-8, in combination with a bismuth complex and carboxylated multi-walled carbon nanotubes, resulting in the fabrication of Bi@ZIF-8/CMWCNTs/GCE electrochemical sensors. Leveraging the porous nature and large specific surface area of ZIF-8, the lead and cadmium ion adsorption by bismuth akin to mercury, and the conductivity of carboxylated multi-walled carbon nanotubes, the sensor developed in this study exhibits excellent capability for simultaneous detection of lead and cadmium ions in water. Under optimized conditions, Pb2+ and Cd2+ showed good linear relationships with the peak current in the concentration range of 2.0–50.0 μg/L. In the concentration range studied, the regression equations for Pb2+ and Cd2+ were determined as follows: y = 0.2982x + 0.4553 (r = 0.9962) for Pb2+ and y = 0.3631x + 0.1242 (r = 0.9949) for Cd2+. The detection limits for Pb2+ and Cd2+ were 0.76 μg/L and 0.87 μg/L, respectively. The relative standard deviations (RSDs) for 50 μg/L mixed standard solution of Pb and Cd were 1.89 % and 1.23 %, respectively. Furthermore, the RSDs for the same modified electrode tested with 50 μg/L Pb2+ and Cd2+ mixed standard solution over seven consecutive days were 2.27 % and 1.42 %, respectively, under identical conditions. In practice, the lead and cadmium concentrations of a lake were found to range from 4.42 μg/L to 5.60 μg/L, while the lead and cadmium concentrations of effluent from a wastewater plant ranged from 11.83 μg/L to 14.49 μg/L. This research not only describes a new electrochemical platform for the simultaneous determination of lead and cadmium in water but also provides a new method for the simultaneous determination of lead and cadmium in water. This research is valuable for promoting the application of MOFs in the field of electrochemistry.

Synthesis, crystal and electronic structures of two novel tunnel bismuth oxychlorides Bi18O22Cl8.5(BO3)0.5 and Bi18O22Cl8Se

Single crystals of two new quaternary bismuth oxychlorides, Bi18O22Cl8.5(BO3)0.5(1) and Bi18O22Cl8Se (2), have been serendipitously produced in syntheses starting from bismuth borate or oxyselenide and oxychloride. The crystal structure of 1 represents a high symmetry analog of the PbBi17O22Cl9 type structure, formed by double aliovalent (Pb2+ → Bi3+, 0.5Cl– → 0.5BO33−) substitution at the two respective cationic and anionic sites, while 2 is a full structural analog of PbBi17O22Cl9. Overall, their structures can be described as sequences of thick (16 Å) slabs (2D “host” structure) comprised of litharge–like layers and ribbons formed by edge-sharing oxocentered OBin, polyhedra (n = 4 and 5). The chloride anions fill the 7.6 Å channels with the triangular cross-section inside the slabs as well as the interlayer space wherein they are partially substituted by disordered BO33− groups or Se2− anions. Compound 1 is just the second example of a mixed halide–borate occupancy among bismuth compounds while 2 illustrates much broader perspectives of mixed oxyhalide–oxychalcogenide approach to construction of novel complex bismuth compounds. Both compounds make new contributions to the family of tunnel structures of anion-centered tetrahedra featuring wide trigonal channels filled by halide anions or more complex metal–halide “salt inclusions”.

Experimental and Theoretical Approaches to Monitor the Behavior of Bovine Liver Catalase in Interaction with a Binuclear Bismuth Complex.

Here, the antioxidant potency of a binuclear Bi(III) complex {[Bi2(μ-ox)(dipic)2(H2O)2 (taa)2].H2O, where ox2- = oxalato, dipic2- = pyridine 2,6-dicarboxylato, and taa = thiourea} was evaluated using the •DPPH assay. It was demonstrated that the Bi complex exhibited a high ability to inhibit DPPH free radicals. The binding mechanism of the complex with bovine liver catalase (BLC) was also investigated, revealing structural and activity changes in the enzyme in the presence of the complex. The catalase activity in the decomposition of hydrogen peroxide increased in the presence of the Bi complex, reaching 39.8% higher than its initial activity at a concentration of 7.77 × 10-6 M. The complex exhibited a relatively high affinity for BLC, with K b values of 3.98, 0.13, and 0.09 × 105 M-1 at 303, 310, and 317 K, respectively. The mechanisms involved in the interaction were hydrogen bonding and van der Waals interactions, as validated through molecular docking simulations. Synchronous fluorescence showed that tryptophan was more affected by enzyme-complex interactions than tyrosine. In addition, a cell viability test using the MTT method revealed that at its highest concentration, the Bi complex caused a decrease in the number of cells below 50% compared to the control, while cisplatin showed negative effects at all concentrations. These findings suggest that the Bi complex has the potential to be developed as a promising candidate for BLC-related therapeutic target therapy.

Unlocking Arene Phosphorescence in Bismuth-Organic Materials.

Three novel bismuth-organic compounds, with the general formula [Bi2(HPDC)2(PDC)2]·(arene)·2H2O (H2PDC = 2,6-pyridinedicarboxylic acid; arene = pyrene, naphthalene, and azulene), that consist of neutral dinuclear Bi-pyridinedicarboxylate complexes and outer coordination sphere arene molecules were synthesized and structurally characterized. The structures of all three phases exhibit strong π-π stacking interactions between the Bi-bound PDC/HPDC and outer sphere organic molecules; these interactions effectively sandwich the arene molecules between bismuth complexes and thereby prevent molecular vibrations. Upon UV irradiation, the compounds containing pyrene and naphthalene displayed red and green emission, respectively, with quantum yields of 1.3(2) and 30.8(4)%. The emission was found to originate from the T1 → S0 transition of the corresponding arene and result in phosphorescence characteristic of the arene employed. By comparison, the azulene-containing compound displayed very weak blue-purple phosphorescence of unknown origin and is a rare example of T2 → S0 emission from azulene. The pyrene- and naphthalene-containing compounds both display radioluminescence, with intensities of 11 and 38% relative to bismuth germanate, respectively. Collectively, these results provide further insights into the structure-property relationships that underpin luminescence from Bi-based materials and highlight the utility of Bi-organic molecules in the realization of organic emission.

Synthesis, crystal structure, and in vitro biological evaluation of bismuth (III) complexes incorporating pyrazinohydrazide‐derived Schiff bases

Two new Schiff‐base bismuth (III) complexes were prepared by an equivalent reaction between Schiff‐base ligand and Bi (NO3)3•5H2O with the assistance of Mannitol. The chemical structures of the two complexes were characterized by spectroscopic studies (FT‐IR, NMR, and MS), elemental analysis, and single‐crystal X‐ray diffraction. The ligand‐to‐metal ion ratio was found to be 1:1 in the complexes. During the formation of the complexes, Schiff bases changed from the amidic forms to the iminol forms, and the resulting tautomers could coordinate with bismuth (III) ions to produce dinuclear BiIII complexes(1a and 2a). Structural analyses showed that each Bi (III) ion held a distorted capped octahedron geometry with a seven‐coordinate mode in two complexes. Screening in vitro biological activities revealed that two bismuth (III) complexes exhibited much higher antimicrobial and cytotoxic activity than their parent ligands. The cytotoxic activity of the complex(1a) was close to that of the known anticancer drug (Doxorubicin) by evaluating against SGC7901 cells, with the IC50 value 0.59 μM. The complex(1a) could effectively induce SGC7901 cell apoptosis and its oral acute toxicity for LD50 value was found to be 576 mg kg−1. The content of bismuth (III) in mitochondria was higher than that in the nucleus.

Evaluation of DFT methods for predicting geometries and NMR spectra of Bi(III) dithiocarbamate complexes with antitumor properties.

Bismuth complexes with dithiocarbamate ligands have attracted attention because of their biological applications, such as antimicrobial, antileishmanial, and anticancer properties. These complexes have high cytotoxic activity against cancer cells, being more active than the standard drugs cisplatin, doxorubicin, and tamoxifen. In the present study, we investigated the ability of some DFT methods to reproduce the geometries and NMR spectra of the Bi(III) dithiocarbamate complexes, selected based on their proven antitumor activity. Our investigation revealed that the M06-L/def2-TZVP/ECP/CPCM method presented good accuracy in predicting geometries, while the TPSSh/def2-SVP/ECP/CPCM method proved effective in analyzing the 13C NMR spectra of these molecules. In general, all examined methods exhibited comparable performance in predicting 1H NMR signals. Calculations were performed with the Gaussian 09 program using the def2-SVP and def2-TZVP basis sets, employing relativistic effective core potential (ECP) for Bi and using the CPCM solvent model. The exchange-correlation functionals BP86, PBE, OLYP, M06-L, B3LYP, B3LYP-D3, M06-2X, TPSSh, CAM-B3LYP, and ωB97XD were used in the study. Geometry optimizations were started from crystallographic structures available at the Cambridge Structural Database. The theoretical results were compared with experimental data using the mean root-mean-square deviation (RMSD), mean absolute deviations (MAD), and linear correlation coefficient (R2).

METHANE PRODUCTION FROM COW MANURE IN THE PRESENCE OF Bi(III) COMPLEX OF SULFAMIC ACID

The present study examines the process of biomethanization of cow manure in an anaerobic environment, in the presence of small amounts of Bi(III) complex of sulfamic acid. Since this complex has good antimicrobial activity, the purpose of adding the complex is to determine its effect on biogas and methane production. The reference samples (cow manure only) and mixtures of cow manure + 10 mg and cow manure + 20 mg of bismuth complex with a composition [Bi6O4(OH)4](NH2SO3)6 are subjected to biodegradation under the following conditions – duration of 33 days, nitrogen atmosphere and temperature of 34.5 ± 1°C. During the process, the volume of biogas and the percentage content of methane in biogas are measured in 2 - 3 days as well. The analyses performed reveal that until the 10th day, the amount of biogas produced increases constantly and is comparable both for the control samples and for the mixtures. Further, until the end of the experiment, a significant and constant increase in the volume of biogas produced by the mixtures is observed compared to the control samples.Regarding the percentage of methane produced by the reference samples and the mixtures, comparable relative amounts are found by the 7th day. From the 8th day to the 33rd day, the percentage of methane released by the mixtures is visibly greater than that by the reference samples.

Coordination environment dependence of anticancer activity in cyclometalated bismuth(III) complexes with C,O-chelating ligands

In this paper, a series of cyclometalated bismuth(III) complexes bearing C,O-bidentate ligands were synthesized and characterized by techniques such as UV–vis, NMR, HRMS, and single crystal X-ray diffraction. Meanwhile, their cytotoxicities against various human cell lines, including colon cancer cells (HCT-116), breast cancer cells (MDA-MB-231), lung cancer cells (A549), gastric cancer cells (SGC-7901), and normal embryonic kidney cells (HEK-293) were assessed in vitro. Compared with the clinical cisplatin, most of the synthesized complexes possessed significantly higher degrees of anticancer activity and selectivity, giving a selectivity index of up to 71.3. The structure-activity relationship study revealed that the anticancer performance of these bismuth(III) species depends on the factors of coordination environment surrounding the metal center, such as coordination number, coordination bonding strength, lone 6s2 electron pair stereoactivity. The Annexin V-FITC/PI double staining assay results suggested that the coordination environment-dependent cytotoxicity is ascribable to apoptosis. Western blot analysis confirmed the proposal, as evidenced by the down-regulating level of Bcl-2 and the activation of caspase-3. Furthermore, the representative complexes Bi1, Bi4, Bi6, and Bi8 exhibited relatively lower inhibitory efficiency on human ovarian cancer cells (A2780) than on its cisplatin-resistant daughter cells (A2780/cis), thus demonstrating that such compounds are capable of circumventing the cisplatin-induced resistance. This investigation elucidated the excellent anticancer performance of C,O-coordinated bismuth(III) complexes and established the correlation between cytotoxic activity and coordination chemistry, which provides a practical basis for in-depth designing and developing bismuth-based chemotherapeutics.

Fusing Bismuth and Mercaptocarboranes: Design and Biological Evaluation of Low-Toxicity Antimicrobial Thiolato Complexes.

This study proposes an innovative strategy to enhance the pharmacophore model of antimicrobial bismuth thiolato complex drugs by substituting hydrocarbon ligand structures with boron clusters, particularly icosahedral closo-dicarbadodecaborane (C2B10H12, carboranes). The hetero- and homoleptic mercaptocarborane complexes BiPh2L (1) and BiL3 (2) (L=9-S-1,2-C2B10H11) were prepared from 9-mercaptocarborane (HL) and triphenylbismuth. Comprehensive characterization using NMR, IR, MS, and XRD techniques confirmed their successful synthesis. Evaluation of antimicrobial activity in a liquid broth microdilution assay demonstrated micromolar to submicromolar minimum inhibitory concentrations (MIC) suggesting high effectiveness against S. aureus and limited efficacy against E. coli. This study highlights the potential of boron-containing bismuth complexes as promising antimicrobial agents, especially targeting Gram-positive bacteria, thus contributing to the advancement of novel therapeutic approaches.

Synthesis via microwave irradiation, structural characterization, and antibacterial activities of new complexes of bismuth(III) with thiosemicarbazones

Five derivatives of thiosemicarbazide, classified as thiosemicarbazone type ligands (L1-L5), were synthesized along with their respective bismuth(III) complexes (1–5), the latter using microwave irradiation. The ligands and complexes were characterized using various spectroscopic techniques, including IR, Raman, UV–Vis, 1H NMR, 13C NMR, EA, and ESI-mass. X-ray diffraction was also conducted to determine the crystal structures of ligands L1, L2, L4, and L5 and bismuth complexes LBi1 and LBi4. All complexes displayed an octahedral geometry, with a single bismuth atom coordinating with the ligands via the sulfide atoms. Ligands L1-L5 and their complexes were evaluated against the Gram-negative species Salmonella spp. and the Gram-positive species Staphylococcus aureus using the Inhibition Zone (IZ) method to assess their antimicrobial potential. The results indicated that the synthesized bismuth(III) complexes exhibited promising inhibitory effects on the growth of Salmonella spp.

Exploring Bismuth (III) Sulpha Drugs Schiff Base Coordination Complexes: Design, Synthesis, Structural, Spectroscopic Characterization, and Biological Evaluations

The present study aimed to prepare and then evaluate the tetra and coordinated Bismuth (III) complexes [BiCl2 (L)] (LH = N, O donor Schiff base employed by the condensation of 1-acetyl-2-naphthol and 2-acetyl-1-naphthol using sulpha drugs as ligand) were derived by the reaction of bismuth (III) trichloride and sodium salt of an N, O donor Schiff base ligand and characterized. The authenticity of all the synthesized ligands and their Bi (III) complexes had been identified by microanalysis, various spectroscopic techniques like FT-IR, 1H NMR, and elemental analysis. The spectral evidence of the complexes has revealed the bidentate complexing nature of the Schiff base through phenolic oxygen and azomethine nitrogen atoms. The Schiff base ligand and Bismuth (III) complexes were assessed for antimicrobial activity. Assessment of antimicrobial activity against Gram-negative & Gram-positive bacteria and fungi has demonstrated that the complex (III) was more active than the Schiff base.

Is bismuth(III) able to inhibit the activity of urease? Puzzling results in the quest for soluble urease complexes for agrochemical and medicinal applications.

Bismuth(III) complexes have been reported to act as inhibitors of the enzyme urease, ubiquitously present in soils and implicated in the pathogenesis of several microorganisms. The general insolubility of Bi(III) complexes in water at neutral pH, however, is an obstacle to their utilization. In our quest to improve the solubility of Bi(III) complexes, we selected a compound reported to inhibit urease, namely [Bi(HEDTA)]·2H2O, and co-crystallized it with (i) racemic DL-histidine to obtain the conglomerate [Bi2(HEDTA)2(μ-D-His)2]·6H2O + [Bi2(HEDTA)2(μ-L-His)2]·6H2O, (ii) enantiopure L-histidine to yield [Bi2(HEDTA)2(μ-L-His)2]·6H2O, and (iii) cytosine to obtain [Bi(HEDTA)]·Cyt·2H2O. All compounds, synthesised by mechanochemical methods and by slurry, were characterized in the solid state by calorimetric (DSC and TGA) and spectroscopic (IR) methods, and their structures were determined using powder X-ray diffraction (PXRD) data. All compounds show an appreciable solubility in water, with values ranging from 6.8 mg mL-1 for the starting compound [Bi(HEDTA)]·2H2O to 36 mg mL-1 for [Bi2(HEDTA)2(μ-L-His)2]·6H2O. The three synthesized compounds as well as [Bi(HEDTA)]·2H2O were then tested for inhibition activity against urease. Surprisingly, no enzymatic inhibition was observed during in vitro assays using Canavalia ensiformis urease and in vivo assays using cultures of Helicobacter pylori, raising questions on the efficacy of Bi(III) compounds to counteract the negative effects of urease activity in the agro-environment and in human health.

Geminal bimetallic coordination of a carbone to main-group and transition metals.

The non-bonding carbone lone pair in geometrically-constrained antimony and bismuth carbodiphosphorane complexes readily complexed AuCl to afford rare examples of geminal bimetallic carbone coordination featuring a main-group metal.