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16 pages, 9475 KiB

Open AccessArticle

The [(Bn-tpen)Fe^II]²⁺ Complex as a Catalyst for the Oxidation of Cyclohexene and Limonene with Dioxygen

by Katarzyna Rydel-Ciszek and Andrzej Sobkowiak

Molecules 2024, 29(16), 3755; https://doi.org/10.3390/molecules29163755 - 8 Aug 2024

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Abstract

[(Bn-tpen)Fe^II(MeCN)](ClO₄)₂, containing the pentadentate Bn-tpen–N-benzyl-N,N′,N′-tris(2-pyridylmethyl)-1,2-diaminoethane ligand, was studied in the oxygenation of cyclohexene and limonene using low-pressure dioxygen (0.2 atm air or 1 atm pure O₂) in [...] Read more.

[(Bn-tpen)Fe^II(MeCN)](ClO₄)₂, containing the pentadentate Bn-tpen–N-benzyl-N,N′,N′-tris(2-pyridylmethyl)-1,2-diaminoethane ligand, was studied in the oxygenation of cyclohexene and limonene using low-pressure dioxygen (0.2 atm air or 1 atm pure O₂) in acetonitrile. 2-Cyclohexen-1-one and 2-cyclohexen-1-ol are the main products of cyclohexene oxidations, with cyclohexene oxide as a minor product. Limonene is oxidized to limonene oxide, carvone, and carveol. Other oxidation products such as perillaldehyde and perillyl alcohol are found in trace amounts. This catalyst is slightly less active than the previously reported [(N4Py)Fe^II(MeCN)](ClO₄)₂ (N4Py–N,N-bis(2-pyridylmethyl)-N-(bis-2-pyridylmethyl)amine). Based on cyclic voltammetry experiments, it is postulated that [(Bn-tpen)Fe^IV=O]²⁺ is the active species. The induction period of approx. 3 h during cyclohexene oxygenation is probably caused by deactivation of the reactive Fe(IV)=O species by the parent Fe(II) complex. Equimolar mixtures of Fe(II) salt and the ligand (in situ-formed catalyst) gave catalytic performance similar to that of the synthesized catalyst. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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16 pages, 3210 KiB

Open AccessArticle

Triiron Complexes Featuring Azadiphosphine Related to the Active Site of [FeFe]-Hydrogenases: Their Redox Behavior and Protonation

by Ahmad Hobballah, Catherine Elleouet and Philippe Schollhammer

Molecules 2024, 29(14), 3270; https://doi.org/10.3390/molecules29143270 - 10 Jul 2024

Viewed by 740

Abstract

The design of iron clusters featuring a bimetallic core and several protonation sites in the second coordination sphere of the metal centers is important for modeling the activity of polymetallic active sites such as the H-cluster of [FeFe]-hydrogenases. For this purpose, the syntheses [...] Read more.

The design of iron clusters featuring a bimetallic core and several protonation sites in the second coordination sphere of the metal centers is important for modeling the activity of polymetallic active sites such as the H-cluster of [FeFe]-hydrogenases. For this purpose, the syntheses of complexes [Fe₃(CO)₅(κ²-P^Ph₂N^R₂)(μ-pdt)₂] (R = Ph (1), Bn (2)) and [Fe₃(CO)₅(κ²-P^Ph₂N^R₂)(μ-adt^Bn)(μ-pdt)] (R = Ph (3), Bn (4)) were carried out by reacting hexacarbonyl precursors [Fe₂(CO)₆(µ-xdt)] (xdt = pdt (propanedithiolate), adt^Bn (azadithiolate) with mononuclear complexes [Fe(κ²-pdt)(CO)₂(κ²-P^Ph₂N^R₂)] (P^Ph₂N^R₂ = (P^PhCH₂N^RCH₂)₂, R = Ph, Bn) in order to introduce amine functions, through well-known P^Ph₂N^R₂ diphosphine, into the vicinity of the triiron core. The investigation of the reactivity of these triiron species towards the proton (in the presence of CF₃SO₃H) and the influence of the pendant amines on the redox properties of these complexes were explored using spectroscopic and electrochemical methods. The protonation sites in such triiron clusters and their relationships were identified. The orientation of the first and second protonation processes depends on the arrangement of the second coordination sphere. The similarities and differences, due to the extended metal nuclearity, with their dinuclear counterparts [Fe₂(CO)₄(κ²-P^Ph₂N^R₂)(μ-pdt)], were highlighted. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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16 pages, 4422 KiB

Open AccessArticle

Porous Electropolymerized Films of Ruthenium Complex: Photoelectrochemical Properties and Photoelectrocatalytic Synthesis of Hydrogen Peroxide

by Hong-Ju Yin and Ke-Zhi Wang

Molecules 2024, 29(3), 734; https://doi.org/10.3390/molecules29030734 - 5 Feb 2024

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Abstract

The photoelectrochemical cells (PECs) performing high-efficiency conversions of solar energy into both electricity and high value-added chemicals are highly desirable but rather challenging. Herein, we demonstrate that a PEC using the oxidatively electropolymerized film of a heteroleptic Ru(II) complex of [Ru(bpy)(L) [...] Read more.

The photoelectrochemical cells (PECs) performing high-efficiency conversions of solar energy into both electricity and high value-added chemicals are highly desirable but rather challenging. Herein, we demonstrate that a PEC using the oxidatively electropolymerized film of a heteroleptic Ru(II) complex of [Ru(bpy)(L)₂](PF₆)₂ Ru1 {bpy and L stand for 2,2′-bipyridine and 1-phenyl-2-(4-vinylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline respectively}, polyRu1, as a working electrode performed both efficient in situ synthesis of hydrogen peroxide and photocurrent generation/switching. Specifically, when biased at −0.4 V vs. saturated calomel electrode and illuminated with 100 mW·cm⁻² white light, the PEC showed a significant cathodic photocurrent density of 9.64 μA·cm⁻². Furthermore, an increase in the concentrations of quinhydrone in the electrolyte solution enabled the photocurrent polarity to switch from cathodic to anodic, and the anodic photocurrent density reached as high as 11.4 μA·cm⁻². Interestingly, in this single-compartment PEC, the hydrogen peroxide yield reached 2.63 μmol·cm⁻² in the neutral electrolyte solution. This study will serve as a guide for the design of high-efficiency metal-complex-based molecular systems performing photoelectric conversion/switching and photoelectrochemical oxygen reduction to hydrogen peroxide. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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12 pages, 13023 KiB

Open AccessArticle

An AIE Metal Iridium Complex: Photophysical Properties and Singlet Oxygen Generation Capacity

by Weijin Zhu, Shengnan Liu, Ziwei Wang, Chunguang Shi, Qiaohua Zhang, Zihan Wu, Guangzhe Li and Dongxia Zhu

Molecules 2023, 28(23), 7914; https://doi.org/10.3390/molecules28237914 - 3 Dec 2023

Cited by 1 | Viewed by 1580

Abstract

Photodynamic therapy (PDT) has garnered significant attention in the fields of cancer treatment and drug-resistant bacteria eradication due to its non-invasive nature and spatiotemporal controllability. Iridium complexes have captivated researchers owing to their tunable structure, exceptional optical properties, and substantial Stokes displacement. However, [...] Read more.

Photodynamic therapy (PDT) has garnered significant attention in the fields of cancer treatment and drug-resistant bacteria eradication due to its non-invasive nature and spatiotemporal controllability. Iridium complexes have captivated researchers owing to their tunable structure, exceptional optical properties, and substantial Stokes displacement. However, most of these complexes suffer from aggregation-induced quenching, leading to diminished luminous efficiency. In contrast to conventional photosensitizers, photosensitizers exhibiting aggregation-induced luminescence (AIE) properties retain the ability to generate a large number of reactive oxygen species when aggregated. To overcome these limitations, we designed and synthesized a novel iridium complex named Ir-TPA in this study. It incorporates quinoline triphenylamine cyclomethylated ligands that confer AIE characteristics for Ir-TPA. We systematically investigated the photophysical properties, AIE behavior, spectral features, and reactive oxygen generation capacity of Ir-TPA. The results demonstrate that Ir-TPA exhibits excellent optical properties with pronounced AIE phenomenon and robust capability for producing singlet oxygen species. This work not only introduces a new class of metal iridium complex photosensitizer with AIE attributes but also holds promise for achieving remarkable photodynamic therapeutic effects in future cellular experiments and biological studies. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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12 pages, 3117 KiB

Open AccessArticle

Enantiomeric Complexes Based on Ruthenium(III) and 2,2′-Biimidazole: X-ray Structure and Magnetic Properties

by Marta Orts-Arroyo, Joel Monfort, Nicolás Moliner and José Martínez-Lillo

Molecules 2023, 28(20), 7213; https://doi.org/10.3390/molecules28207213 - 22 Oct 2023

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Abstract

We have prepared and characterized two Ru(III) compounds based on the 2,2′-biimidazole (H₂biim) ligand, namely, a single complex of formula cis-[RuCl₂(H₂biim)₂]Cl·4H₂O (1) and a racemic mixture of formula {cis-[RuCl₂(H [...] Read more.

We have prepared and characterized two Ru(III) compounds based on the 2,2′-biimidazole (H₂biim) ligand, namely, a single complex of formula cis-[RuCl₂(H₂biim)₂]Cl·4H₂O (1) and a racemic mixture of formula {cis-[RuCl₂(H₂biim)₂]Cl}₂·4H₂O (2), which contains 50% of Ru(III) complex 1. Both compounds crystallize in the monoclinic system with space groups C2 and P2₁ for 1 and 2, respectively. These complexes exhibit the metal ion bonded to four nitrogen atoms from two H₂biim molecules and two chloride ions, which balance part of the positive charges in a distorted octahedral geometry. Significant differences are observed in their crystal packing, which leads to the observation of differences in their respective magnetic behaviors. Despite having imidazole rings in both compounds, π–π stacking interactions occur only in the crystal structure of 2, and the shortest intermolecular Ru···Ru separation in 2 is consequently shorter than that in 1. Variable-temperature dc magnetic susceptibility measurements performed on polycrystalline samples of 1 and 2 reveal different magnetic behaviors at low temperatures: while 1 behaves pretty much as a magnetically isolated mononuclear Ru(III) complex with S = 1/2, 2 exhibits the behavior of an antiferromagnetically coupled system with S = 0 and a maximum in the magnetic susceptibility curve at approximately 3.0 K. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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18 pages, 1488 KiB

Open AccessArticle

Oxidation of the Platinum(II) Anticancer Agent [Pt{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)] to Platinum(IV) Complexes by Hydrogen Peroxide

by Ruchika Ojha, Peter C. Junk, Alan M. Bond and Glen B. Deacon

Molecules 2023, 28(17), 6402; https://doi.org/10.3390/molecules28176402 - 1 Sep 2023

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Abstract

Pt^IV coordination complexes are of interest as prodrugs of Pt^II anticancer agents, as they can avoid deactivation pathways owing to their inert nature. Here, we report the oxidation of the antitumor agent [Pt^II(p-BrC₆F₄)NCH [...] Read more.

Pt^IV coordination complexes are of interest as prodrugs of Pt^II anticancer agents, as they can avoid deactivation pathways owing to their inert nature. Here, we report the oxidation of the antitumor agent [Pt^II(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)], 1 (py = pyridine) to dihydroxidoplatinum(IV) solvate complexes [Pt^IV{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(OH)₂(py)].H₂O, 2·H₂O with hydrogen peroxide (H₂O₂) at room temperature. To optimize the yield, 1 was oxidized in the presence of added lithium chloride with H₂O₂ in a 1:2 ratio of Pt: H₂O_2, in CH₂Cl₂ producing complex 2·H₂O in higher yields in both gold and red forms. Despite the color difference, red and yellow 2·H₂O have the same structure as determined by single-crystal and X-ray powder diffraction, namely, an octahedral ligand array with a chelating organoamide, pyridine and chloride ligands in the equatorial plane, and axial hydroxido ligands. When tetrabutylammonium chloride was used as a chloride source, in CH₂Cl₂, another solvate, [Pt^IV{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(OH)₂(py)].0.5CH₂Cl_2,3·0.5CH₂Cl₂, was obtained. These Pt^IV compounds show reductive dehydration into Pt^II [Pt{(p-BrC₆F₄)NCH=CHNEt₂}Cl(py)], 1H over time in the solid state, as determined by X-ray powder diffraction, and in solution, as determined by ¹H and ¹⁹F NMR spectroscopy and mass spectrometry. 1H contains an oxidized coordinating ligand and was previously obtained by oxidation of 1 under more vigorous conditions. Experimental data suggest that oxidation of the ligand is favored in the presence of excess H₂O₂ and elevated temperatures. In contrast, a smaller amount (1Pt:2H₂O₂) of H₂O₂ at room temperature favors the oxidation of the metal and yields platinum(IV) complexes. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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18 pages, 5610 KiB

Open AccessArticle

H(N3)dap (Hdap = 2,6-Diaminopurine) Recognition by Cu₂(EGTA): Structure, Physical Properties, and Density Functional Theory Calculations of [Cu₄(μ-EGTA)₂(μ-H(N3)dap)₂(H₂O)₂]·7H₂O

by Homa Mousavi, María Eugenia García-Rubiño, Duane Choquesillo-Lazarte, Alfonso Castiñeiras, Luis Lezama, Antonio Frontera and Juan Niclós-Gutiérrez

Molecules 2023, 28(17), 6263; https://doi.org/10.3390/molecules28176263 - 26 Aug 2023

Cited by 1 | Viewed by 1146

Abstract

Reactions in water between the Cu₂(µ-EGTA) chelate (EGTA = ethylene-bis(oxyethyleneimino)tetraacetate(4-) ion) and Hdap in molar ratios 1:1 and 1:2 yield only blue crystals of the ternary compound [Cu₄(μ-EGTA)₂(μ-H(N₃)dap)₂(H₂O)₂]·7H₂ [...] Read more.

Reactions in water between the Cu₂(µ-EGTA) chelate (EGTA = ethylene-bis(oxyethyleneimino)tetraacetate(4-) ion) and Hdap in molar ratios 1:1 and 1:2 yield only blue crystals of the ternary compound [Cu₄(μ-EGTA)₂(μ-H(N₃)dap)₂(H₂O)₂]·7H₂O (1), which has been studied via single-crystal X-ray diffraction and various physical methods (thermal stability, spectral and magnetic properties), as well as DFT theoretical calculations. In the crystal, uncoordinated water is disordered. The tetranuclear complex molecule also has some irrelevant disorder in an EGTA-ethylene moiety. In the complex molecule, both bridging organic molecules act as binucleating ligands. There are two distorted five- and two six-coordinated Cu(II) centers. Each half of EGTA acts as a tripodal tetradentate Cu(II) chelator, with a mer-NO2 + O(ether, distal) conformation. Hdap exhibits the tautomer H(N3)dap, with the dissociable H-atom on its less basic N-heterocyclic atom. These features favor the efficient cooperation between Cu-N7 or Cu-N9 bonds with appropriate O-EGTA atoms, as N6-H···O or N3-H···O interligand interactions, respectively. The bridging role of both organics determines the tetranuclear dimensionality of the complex. In this crystal, such molecules associate in zig-zag chains built by alternating π–π interactions between the five- or six-atom rings of Hdap ligands of adjacent molecules. DFT theoretical calculations (using two different theoretical models and characterized by the quantum theory of “atoms in molecules”) reveal the importance of these π–π interactions between Hdap ligands, as well as those corresponding to the referred hydrogen bonds in the contributed tetranuclear molecule. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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13 pages, 4434 KiB

Open AccessArticle

Three Iodoargentate-Based Hybrids Decorated by Metal Complexes: Structures, Optical/Photoelectric Properties and Theoretical Studies

by Minghui Liu, Xiaochen Ren, Weiyang Wen, Baohan Li, Jiaqi Li, Jun Li and Bo Zhang

Molecules 2023, 28(16), 6116; https://doi.org/10.3390/molecules28166116 - 18 Aug 2023

Cited by 5 | Viewed by 1153

Abstract

So far, the development of new iodoargentate-based hybrids, especially those compounds with metal complex cations, and the understanding of their structure–activity relationships have been of vital importance but full of challenges. Herein, using the in-situ-generated metal complex cations as structural directing agents, three [...] Read more.

So far, the development of new iodoargentate-based hybrids, especially those compounds with metal complex cations, and the understanding of their structure–activity relationships have been of vital importance but full of challenges. Herein, using the in-situ-generated metal complex cations as structural directing agents, three new iodoargentate-based hybrids, namely, [Co(phen)₃]Ag₂PbI₆ (phen = 1,10-phenanthroline; 1), [Ni(5,5-dmpy)₃]Ag₇I₉·CH₃CN (5,5-dmpy = 5,5-dimethyl-2,2-bipyridine; 2) and [Co(5,5-dmpy)₃]Ag₅I₈ (3), have been solvothermally prepared and then structurally characterized. Compound 1 represents one new heterometallic Ag–Pb–I compound characteristic of the chain-like [Ag₂PbI₆]_n²ⁿ⁻ anions. Compound 2 features the straight one-dimensional (1D) [Ag₇I₉]_n²ⁿ⁻ anionic moieties, while compound 3 contains infrequent two types of curved [Ag₅I₈]_n³ⁿ⁻ anions. Optical properties reveal that the title compounds exhibit interesting semiconductor behaviors with the band gaps of 1.59–2.78 eV, which endow them with good photoelectric switching performances under the alternate light irradiations. We also present their Hirshfeld surface analyses, and the theoretical studies (band structures, density of states (DOS) and partial density of states (PDOS)). Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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18 pages, 4941 KiB

Open AccessArticle

The Copper(II)-Thiodiacetate (tda) Chelate as Efficient Receptor of N9-(2-Hydroxyethyl)Adenine (9heade): Synthesis, Molecular and Crystal Structures, Physical Properties and DFT Calculations of [Cu(tda)(9heade)(H₂O)]·2H₂O

by Carmen Rosales-Martínez, Antonio Matilla-Hernádez, Duane Choquesillo-Lazarte, Antonio Frontera, Alfonso Castiñeiras and Juan Niclós-Gutiérrez

Molecules 2023, 28(15), 5830; https://doi.org/10.3390/molecules28155830 - 2 Aug 2023

Cited by 1 | Viewed by 1336

Abstract

Considering that Cu(tda) chelate (tda: dithioacetate) is a receptor for adenine and related 6-aminopurines, this study reports on the synthesis, molecular and crystal structures, thermal stability, spectral properties and DFT calculations related to [Cu(tda)(9heade)(H₂O)]·2H₂O (1) [9heade: N9-(2-hydroxyethyl)adenine]. [...] Read more.

Considering that Cu(tda) chelate (tda: dithioacetate) is a receptor for adenine and related 6-aminopurines, this study reports on the synthesis, molecular and crystal structures, thermal stability, spectral properties and DFT calculations related to [Cu(tda)(9heade)(H₂O)]·2H₂O (1) [9heade: N9-(2-hydroxyethyl)adenine]. Concerning the molecular recognition of (metal chelate)-(adenine synthetic nucleoside), 1 represents an unprecedented metal binding pattern (MBP) for 9heade. However, unprecedentedly, the Cu(tda)-9heade molecular recognition in 1 is essentially featured in the Cu-N1(9heade) bond, without any N6-H⋯O(carboxyl tda) interligand interaction. Nevertheless, N1 being the most basic donor for N9-substituted adenines, this Cu-N1 bond is now assisted by an O2–water-mediated interaction (N6-H⋯O2 and O2⋯Cu weak contact). Also, in the crystal packing, the O-H(ol) of 9heade interacts with its own adenine moiety as a result of an O3–water-mediated interaction (O(ol)-H⋯O3 plus O3-H36⋯π(adenine moiety)). Both water-mediated interactions seem to be responsible for serious alterations in the physical properties of crystalline or grounded samples. Density functional theory calculations were used to evaluate the interactions energetically. Moreover, the quantum theory of atoms-in-molecules (QTAIM), in combination with the noncovalent interaction plot (NCIPlot), was used to analyze the interactions and rationalize the existence and relative importance of hydrogen bonding, chalcogen bonding and π-stacking interactions. The novelty of this work resides in the discovery of a novel binding mode for N9-(2-hydroxyethyl)adenine. Moreover, the investigation of the important role of water in the solid state of 1 is also relevant, along with the chalcogen bonding interactions demonstrated by the density functional theory (DFT) study. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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16 pages, 3749 KiB

Open AccessArticle

Mono-, Bis-, and Tris-Chelate Zn(II) Complexes with Imidazo[1,5-a]pyridine: Luminescence and Structural Dependence

by Valerio Cerrato, Giorgio Volpi, Emanuele Priola, Alessia Giordana, Claudio Garino, Roberto Rabezzana and Eliano Diana

Molecules 2023, 28(9), 3703; https://doi.org/10.3390/molecules28093703 - 25 Apr 2023

Cited by 7 | Viewed by 1985

Abstract

New mono-, bis-, and tris-chelate Zn(II) complexes have been synthesized starting from different Zn(II) salts and employing a fluorescent 1,3-substituted-imidazo[1,5-a]pyridine as a chelating ligand. The products have been characterized by single-crystal X-ray diffraction; mass spectrometry; and vibrational spectroscopy. The optical properties [...] Read more.

New mono-, bis-, and tris-chelate Zn(II) complexes have been synthesized starting from different Zn(II) salts and employing a fluorescent 1,3-substituted-imidazo[1,5-a]pyridine as a chelating ligand. The products have been characterized by single-crystal X-ray diffraction; mass spectrometry; and vibrational spectroscopy. The optical properties have been investigated to compare the performances of mono-, bis-, and tris-chelate forms. The collected data (in the solid state and in solution) elucidate an important modification of the ligand conformation upon metal coordination; which is responsible for a notable increase in the optical performance. An intense modification of the emission quantum yield along the series in the solid state is observed comparing mono-, bis-, and tris-chelate adducts; independently from the anionic ligand introduced by ionic exchange. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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13 pages, 2861 KiB

Open AccessArticle

Effect of Metal Complexing on Mn–Fe/TS-1 Catalysts for Selective Catalytic Reduction of NO with NH₃

by Yuanyuan Ma, Wanting Liu, Zhifang Li, Yuhang Sun, Mingyuan Shi, Zheng Nan, Ruotong Song, Liying Wang and Jingqi Guan

Molecules 2023, 28(7), 3068; https://doi.org/10.3390/molecules28073068 - 29 Mar 2023

Cited by 3 | Viewed by 1763

Abstract

TS-1 zeolite with desirable pore structure, an abundance of acidic sites, and good thermal stability promising as a support for the selective catalytic reduction of NO with NH₃ (NH₃-SCR). Herein, a series of Mn–Fe/TS-1 catalysts have been synthesized, adopting tetraethylenepentamine [...] Read more.

TS-1 zeolite with desirable pore structure, an abundance of acidic sites, and good thermal stability promising as a support for the selective catalytic reduction of NO with NH₃ (NH₃-SCR). Herein, a series of Mn–Fe/TS-1 catalysts have been synthesized, adopting tetraethylenepentamine (TEPA) as a metal complexing agent using the one-pot hydrothermal method. The introduced TEPA can not only increase the loading of active components but also prompts the formation of a hierarchical structure through decreasing the size of TS-1 nanocrystals to produce intercrystalline mesopores during the hydrothermal crystallization process. The optimized Mn–Fe/TS-1(R-2) catalyst shows remarkable NH₃-SCR performance. Moreover, it exhibits excellent resistance to H₂O and SO₂ at low temperatures. The characterization results indicate that Mn–Fe/TS-1(R-2) possesses abundant surface Mn⁴⁺ and Fe²⁺ and chemisorbed oxygen, strong reducibility, and a high Brønsted acid amount. For comparison, Mn–Fe/TiO₂ displays a narrower active temperature window due to its poor thermostability. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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15 pages, 2951 KiB

Open AccessArticle

Urea Decomposition Mechanism by Dinuclear Nickel Complexes

by Christian O. Martins, Leticia K. Sebastiany, Alejandro Lopez-Castillo, Rafael S. Freitas, Leandro H. Andrade, Henrique E. Toma and Caterina G. C. Marques Netto

Molecules 2023, 28(4), 1659; https://doi.org/10.3390/molecules28041659 - 9 Feb 2023

Cited by 1 | Viewed by 2917

Abstract

Urease is an enzyme containing a dinuclear nickel active center responsible for the hydrolysis of urea into carbon dioxide and ammonia. Interestingly, inorganic models of urease are unable to mimic its mechanism despite their similarities to the enzyme active site. The reason behind [...] Read more.

Urease is an enzyme containing a dinuclear nickel active center responsible for the hydrolysis of urea into carbon dioxide and ammonia. Interestingly, inorganic models of urease are unable to mimic its mechanism despite their similarities to the enzyme active site. The reason behind the discrepancy in urea decomposition mechanisms between inorganic models and urease is still unknown. To evaluate this factor, we synthesized two bis-nickel complexes, [Ni₂L(OAc)] (1) and [Ni₂L(Cl)(Et₃N)₂] (2), based on the Trost bis-Pro-Phenol ligand (L) and encompassing different ligand labilities with coordination geometries similar to the active site of jack bean urease. Both mimetic complexes produced ammonia from urea, (1) and (2), were ten- and four-fold slower than urease, respectively. The presence and importance of several reaction intermediates were evaluated both experimentally and theoretically, indicating the aquo intermediate as a key intermediate, coordinating urea in an outer-sphere manner. Both complexes produced isocyanate, revealing an activated water molecule acting as a base. In addition, the reaction with different substrates indicated the biomimetic complexes were able to hydrolyze isocyanate. Thus, our results indicate that the formation of an outer-sphere complex in the urease analogues might be the reason urease performs a different mechanism. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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17 pages, 4307 KiB

Open AccessArticle

Ruthenium(II) Complexes Coupled by Erianin via a Flexible Carbon Chain as a Potential Stabilizer of c-myc G-Quadruplex DNA

by Zhixiang Wang, Wentao Liu, Guohu Li, Jiacheng Wang, Bin Zhao, Peishan Huang and Wenjie Mei

Molecules 2023, 28(4), 1529; https://doi.org/10.3390/molecules28041529 - 4 Feb 2023

Cited by 2 | Viewed by 2143

Abstract

Herein, two novel ruthenium(II) complexes coupled by erianin via a flexible carbon chain, [Ru(phen)₂(L₁-(CH₂)₄-erianin)](ClO₄)₂ (L₁ = 2-(2-(tri-fluoromethyphenyl))-imidazo [4,5f][1–10]phenanthroline (1) and [Ru(phen)₂(L₂-(CH₂)₄-eria)](ClO [...] Read more.

Herein, two novel ruthenium(II) complexes coupled by erianin via a flexible carbon chain, [Ru(phen)₂(L₁-(CH₂)₄-erianin)](ClO₄)₂ (L₁ = 2-(2-(tri-fluoromethyphenyl))-imidazo [4,5f][1–10]phenanthroline (1) and [Ru(phen)₂(L₂-(CH₂)₄-eria)](ClO₄)₂ (L₂ = 2-(4-(tri-fluoromethyphenyl))-imidazo [4,5f][1,10]phenanthroline (2), have been synthesized and investigated as a potential G-quadruplex(G4) DNA stabilizer. Both complexes, especially 2, can bind to c-myc G4 DNA with high affinity by electronic spectra, and the binding constant calculated for 1 and 2 is about 15.1 and 2.05 × 10⁷ M⁻¹, respectively. This was further confirmed by the increase in fluorescence intensity for both complexes. Moreover, the positive band at 265 nm in the CD spectra of c-myc G4 DNA decreased treated with 2, indicating that 2 may bind to c-myc G4 DNA through extern groove binding mode. Furthermore, fluorescence resonance energy transfer (FRET) assay indicated that the melting point of c-myc G4 DNA treated with 1 and 2 increased 15.5 and 16.5 °C, respectively. Finally, molecular docking showed that 1 can bind to c-myc G4 DNA in the extern groove formed by base pairs G7–G9 and G22–A24, and 2 inserts into the small groove of c-myc G4 DNA formed by base pairs T19–A24. In summary, these ruthenium(II) complexes, especially 2, can be developed as potential c-myc G4 DNA stabilizers and will be exploited as potential anticancer agents in the future. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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13 pages, 1387 KiB

Open AccessArticle

Studies on the Complexation of Platinum(II) by Some 4-Nitroisoxazoles and Testing the Cytotoxic Activity of the Resulting Complexes

by Henryk Mastalarz, Agnieszka Mastalarz, Joanna Wietrzyk, Magdalena Milczarek, Andrzej Kochel and Andrzej Regiec

Molecules 2023, 28(3), 1284; https://doi.org/10.3390/molecules28031284 - 28 Jan 2023

Cited by 1 | Viewed by 2037

Abstract

Two novel platinum(II) complexes (1 and 2) were synthesized by the reaction of the appropriate 3,5-dimethyl-4-nitroisoxazole with K₂PtCl₄ and characterized by elemental analysis, ESI MS spectrometry, ¹H NMR and far-IR spectroscopy. The structure of trans complex 2 [...] Read more.

Two novel platinum(II) complexes (1 and 2) were synthesized by the reaction of the appropriate 3,5-dimethyl-4-nitroisoxazole with K₂PtCl₄ and characterized by elemental analysis, ESI MS spectrometry, ¹H NMR and far-IR spectroscopy. The structure of trans complex 2 was additionally confirmed by X-ray diffraction. The cytotoxicity of the investigated compounds was examined in vitro on three human cancer cell lines (MCF-7 breast, ES-2 ovarian and A-549 lung adenocarcinomas) in both normoxia and hypoxia conditions. LogPs of complexes were measured using the shake-flask method. The trans complex 2 showed much better cytotoxic activity than cisplatin for all the tested cancer cell lines. Cis complex 1 was inferior to its trans isomer against all the cancer lines tested in normoxia conditions but proved superior to the reference cisplatin against the MCF-7 and A549 lines, and showed similar activity to cisplatin against the ES-2 line. To gain additional information that may facilitate the explanation of the pharmacological activity of the tested compounds, cellular platinum uptake and stability in L-glutathione solution were determined for both compounds 1 and 2. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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15 pages, 4825 KiB

Open AccessArticle

Exploring the Co-Crystallization of Kojic Acid with Silver(I), Copper(II), Zinc(II), and Gallium(III) for Potential Antibacterial Applications

by Renren Sun, Lucia Casali, Raymond J. Turner, Dario Braga and Fabrizia Grepioni

Molecules 2023, 28(3), 1244; https://doi.org/10.3390/molecules28031244 - 27 Jan 2023

Cited by 7 | Viewed by 2240

Abstract

Co-crystallization of kojic acid (HKA) with silver(I), copper(II), zinc(II), or gallium(III) salts yielded three 1D coordination polymers and one 0D complex in which kojic acid was present as a neutral or anionic terminal or bridging ligand. All reactions were conducted mechanochemically via ball [...] Read more.

Co-crystallization of kojic acid (HKA) with silver(I), copper(II), zinc(II), or gallium(III) salts yielded three 1D coordination polymers and one 0D complex in which kojic acid was present as a neutral or anionic terminal or bridging ligand. All reactions were conducted mechanochemically via ball milling and manual grinding, or via slurry. All solids were fully characterized via single-crystal and/or powder X-ray diffraction. As kojic acid is a mild antimicrobial compound that is widely used in cosmetics, and the metal cations possess antibacterial properties, their combinations were tested for potential antibacterial applications. The minimal inhibition concentrations (MICs) and minimal biocidal concentrations (MBCs) for all compounds were measured against standard strains of the bacteria P. aeruginosa, S. aureus, and E. coli. All compounds exerted appreciable antimicrobial activity in the order of silver, zinc, copper, and gallium complexes. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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14 pages, 2277 KiB

Open AccessArticle

Remote Steric Control of the Tetrahedral Coordination Geometry around Heteroleptic Copper(I) Bis(Diimine) Complexes

by Jordan L. Appleton, Christophe Gourlaouen and Romain Ruppert

Molecules 2023, 28(3), 983; https://doi.org/10.3390/molecules28030983 - 18 Jan 2023

Cited by 4 | Viewed by 2560

Abstract

In this study, a series of new heteroleptic copper(I) bis(diimine) complexes are described. Using one highly hindered phenanthroline ligand and a second less-hindered diimine ligand led to unexpected results. Following a two-step one-pot method to obtain heteroleptic copper(I) complexes, an almost perfect tetrahedral [...] Read more.

In this study, a series of new heteroleptic copper(I) bis(diimine) complexes are described. Using one highly hindered phenanthroline ligand and a second less-hindered diimine ligand led to unexpected results. Following a two-step one-pot method to obtain heteroleptic copper(I) complexes, an almost perfect tetrahedral coordination geometry around the copper(I) ion was obtained in several cases, despite the fact that at least one ligand was not sterically encumbered near the coordination site (at the position α to the nitrogen atoms of the ligand). This was demonstrated in the solid state by resolution of crystal structures, and these findings, corroborated by calculations, showed that the non-covalent interactions between the two diimine ligands present in these complexes were governing these structural features. The electronic properties of all complexes were also determined and the fluorescence lifetimes of two complexes were compared. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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29 pages, 5229 KiB

Open AccessArticle

N-Heterocyclic Carbene-Iridium Complexes as Photosensitizers for In Vitro Photodynamic Therapy to Trigger Non-Apoptotic Cell Death in Cancer Cells

by Xing Wang, Chen Zhang, Ryma Madji, Camille Voros, Serge Mazères, Christian Bijani, Céline Deraeve, Olivier Cuvillier, Heinz Gornitzka, Marie-Lise Maddelein and Catherine Hemmert

Molecules 2023, 28(2), 691; https://doi.org/10.3390/molecules28020691 - 10 Jan 2023

Cited by 5 | Viewed by 3368

Abstract

A series of seven novel iridium complexes were synthetized and characterized as potential photosensitizers for photodynamic therapy (PDT) applications. Among them, four complexes were evaluated in vitro for their anti-proliferative activity with and without irradiation on a panel of five cancer cell lines, [...] Read more.

A series of seven novel iridium complexes were synthetized and characterized as potential photosensitizers for photodynamic therapy (PDT) applications. Among them, four complexes were evaluated in vitro for their anti-proliferative activity with and without irradiation on a panel of five cancer cell lines, namely PC-3 (prostate cancer), T24 (bladder cancer), MCF7 (breast cancer), A549 (lung cancer) and HeLa (cervix cancer), and two non-cancerous cell models (NIH-3T3 fibroblasts and MC3T3 osteoblasts). After irradiation at 458 nm, all tested complexes showed a strong selectivity against cancer cells, with a selectivity index (SI) ranging from 8 to 34 compared with non-cancerous cells. The cytotoxic effect of all these complexes was found to be independent of the anti-apoptotic protein Bcl-xL. The compound exhibiting the best selectivity, complex 4a, was selected for further investigations. Complex 4a was mainly localized in the mitochondria. We found that the loss of cell viability and the decrease in ATP and GSH content induced by complex 4a were independent of both Bcl-xL and caspase activation, leading to a non-apoptotic cell death. By counteracting the intrinsic or acquired resistance to apoptosis associated with cancer, complex 4a could be an interesting therapeutic alternative to be studied in preclinical models. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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21 pages, 26672 KiB

Open AccessArticle

Rhenium(I) Block Copolymers Based on Polyvinylpyrrolidone: A Successful Strategy to Water-Solubility and Biocompatibility

by Kristina S. Kisel, Vadim A. Baigildin, Anastasia I. Solomatina, Alexey I. Gostev, Eugene V. Sivtsov, Julia R. Shakirova and Sergey P. Tunik

Molecules 2023, 28(1), 348; https://doi.org/10.3390/molecules28010348 - 1 Jan 2023

Cited by 4 | Viewed by 2046

Abstract

A series of diphosphine Re(I) complexes Re1–Re4 have been designed via decoration of the archetypal core {Re(CO)₂(N^N)} through the installations of the phosphines P⁰ and P¹ bearing the terminal double bond, where N^N = 2,2′-bipyridine (N^N1 [...] Read more.

A series of diphosphine Re(I) complexes Re1–Re4 have been designed via decoration of the archetypal core {Re(CO)₂(N^N)} through the installations of the phosphines P⁰ and P¹ bearing the terminal double bond, where N^N = 2,2′-bipyridine (N^N1), 4,4′-di-tert-butyl-2,2′-bipyridine (N^N2) or 2,9-dimethyl-1,10-phenanthroline (N^N3) and P⁰ = diphenylvinylphosphine, and P¹ = 4-(diphenylphosphino)styrene. These complexes were copolymerized with the corresponding N-vinylpyrrolidone-based Macro-RAFT agents of different polymer chain lengths to give water-soluble copolymers of low-molecular p(VP-l-Re) and high-molecular p(VP-h-Re) block-copolymers containing rhenium complexes. Compounds Re1–Re4, as well as the copolymers p(VP-l-Re) and p(VP-h-Re), demonstrate phosphorescence from a ³MLCT excited state typical for this type of chromophores. The copolymers p(VP-l-Re#) and p(VP-h-Re#) display weak sensitivity to molecular oxygen in aqueous and buffered media, which becomes almost negligible in the model physiological media. In cell experiments with CHO-K1 cell line, p(VP-l-Re2) and p(VP-h-Re2) displayed significantly reduced toxicity compared to the initial Re2 complex and internalized into cells presumably by endocytic pathways, being eventually accumulated in endosomes. The sensitivity of the copolymers to oxygen examined in CHO-K1 cells via phosphorescence lifetime imaging microscopy (PLIM) proved to be inessential. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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22 pages, 3364 KiB

Open AccessArticle

Synthesis and Characterization of Late Transition Metal Complexes of Mono-Acetate Pendant Armed Ethylene Cross-Bridged Tetraazamacrocycles with Promise as Oxidation Catalysts for Dye Bleaching

by Tuyet Hoang, Somrita Mondal, Michael B. Allen, Leslie Garcia, Jeanette A. Krause, Allen G. Oliver, Timothy J. Prior and Timothy J. Hubin

Molecules 2023, 28(1), 232; https://doi.org/10.3390/molecules28010232 - 27 Dec 2022

Cited by 3 | Viewed by 1842

Abstract

Ethylene cross-bridged tetraazamacrocycles are known to produce kinetically stable transition metal complexes that can act as robust oxidation catalysts under harsh aqueous conditions. We have synthesized ligand analogs with single acetate pendant arms that act as pentadentate ligands to Mn, Fe, Co, Ni, [...] Read more.

Ethylene cross-bridged tetraazamacrocycles are known to produce kinetically stable transition metal complexes that can act as robust oxidation catalysts under harsh aqueous conditions. We have synthesized ligand analogs with single acetate pendant arms that act as pentadentate ligands to Mn, Fe, Co, Ni, Cu, and Zn. These complexes have been synthesized and characterized, including the structural characterization of four Co and Cu complexes. Cyclic voltammetry demonstrates that multiple oxidation states are stabilized by these rigid, bicyclic ligands. Yet, redox potentials of the metal complexes are modified compared to the “parent” ligands due to the pendant acetate arm. Similarly, gains in kinetic stability under harsh acidic conditions, compared to parent complexes without the pendant acetate arm, were demonstrated by a half-life seven times longer for the cyclam copper complex. Due to the reversible, high oxidation states available for the Mn and Fe complexes, the Mn and Fe complexes were examined as catalysts for the bleaching of three commonly used pollutant model dyes (methylene blue, methyl orange, and Rhodamine B) in water with hydrogen peroxide as oxidant. The efficient bleaching of these dyes was observed. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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19 pages, 7967 KiB

Open AccessArticle

Coordination Polymers Based on Rhenium Octahedral Chalcocyanide Cluster Anions and Ag⁺ Cations with Bipyridine Analogs

by Yulia M. Litvinova, Yakov M. Gayfulin, Taisiya S. Sukhikh, Konstantin A. Brylev and Yuri V. Mironov

Molecules 2022, 27(22), 7684; https://doi.org/10.3390/molecules27227684 - 9 Nov 2022

Cited by 2 | Viewed by 1931

Abstract

A series of six coordination polymers based on octahedral cluster anions [Re₆Q₈(CN)₆]⁴⁻ (Q = S or Se) and Ag⁺ cations coordinated by bipyridine analogs were synthesized under solvothermal conditions. Their structures have been characterized by [...] Read more.

A series of six coordination polymers based on octahedral cluster anions [Re₆Q₈(CN)₆]⁴⁻ (Q = S or Se) and Ag⁺ cations coordinated by bipyridine analogs were synthesized under solvothermal conditions. Their structures have been characterized by single crystal X-ray diffraction. Compounds 1 and 2 described by the general formula [{Ag(phen)}₄Re₆Q₈(CN)₆] (Q = Se (1), S (2); phen = 1,10-phenanthroline) exhibit layered structures assembled into a supramolecular network by CH…π contacts. At the same time, compounds [{Ag(bipym)}₂Ag₂Re₆Se₈(CN)₆] (bipym = 2,2′-bipyrimidine) (3), [{Ag₂(bipy)}Ag₂Re₆Se₈(CN)₆]·CH₃CN (bipy = 4,4′-bipyridine) (4) and [{Ag(dpbp)}₄Re₆Q₈(CN)₆]·2H₂O·2CH₃CN (Q = Se (5), S (6); dpbp = 4,4′-Di(4-pyridyl)biphenyl)) evince framework structures. In 1, 2, 5 and 6 weak Ag⋯Ag interactions are observed. All the compounds show luminescence in the red region. The luminescence quantum yields and lifetimes were found to be notably higher than those for most of the coordination polymers based on the octahedral rhenium cluster complexes. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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7 pages, 1079 KiB

Open AccessArticle

Reactions of a Dioxidomolybdenum(VI) Complex with Thionation Reagents—Formation of Mo(IV) Species with Sulfur Donors

by Esko Salojärvi, Anssi Peuronen, Narhari Sapkota and Ari Lehtonen

Molecules 2022, 27(21), 7154; https://doi.org/10.3390/molecules27217154 - 22 Oct 2022

Viewed by 1332

Abstract

Molecular molybdenum complexes with sulfur donor ligands are generally studied as soluble model compounds for molybdenum enzymes essential for life. The dioxidomolybdenum(VI) complex with tetradentate aminobisphenolate ligand undergoes a reaction with thionation reagent P₂S₅ or its organic derivative, Lawesson’s reagent, [...] Read more.

Molecular molybdenum complexes with sulfur donor ligands are generally studied as soluble model compounds for molybdenum enzymes essential for life. The dioxidomolybdenum(VI) complex with tetradentate aminobisphenolate ligand undergoes a reaction with thionation reagent P₂S₅ or its organic derivative, Lawesson’s reagent, to yield stable Mo(IV) aminobisphenolate complexes, where pristine oxido ligands have been replaced by bidentate sulfur donors tetrasulfide, S₄²⁻ or (4-methoxyphenyl)phosphonotrithioate residue derived from Lawesson’s reagent. This is in contrast to the behaviour of analogous dioxidotungsten(VI) complex, which, under similar conditions, yields W(VI) S₂ systems. The overall cis,trans,cis geometry of the parent dioxidomolybdenum(VI) aminobisphenolate is retained, namely, the neutral nitrogen donors are in cis positions, phenolate oxygens are trans to each other and sulfur donors are cis. Although formally Mo(IV), thus d² system, the studied complexes have diamagnetic singlet electron configurations as a result of the axially compressed octahedral structures. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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12 pages, 1677 KiB

Open AccessArticle

Synthesis and Application of New Salan Titanium Complexes in the Catalytic Reduction of Aldehydes

by Joana Hipólito, Ana M. Martins and Luis G. Alves

Molecules 2022, 27(20), 6821; https://doi.org/10.3390/molecules27206821 - 12 Oct 2022

Cited by 3 | Viewed by 1618

Abstract

Complexes of formula [(H₂N₂O₂)TiCl₂] and [(H₂N₂O₂)Ti(OⁱPr)₂] (H₂N₂O₂H₂ = HOPh’CH₂NH(CH₂)₂NHCH₂Ph’OH, where [...] Read more.

Complexes of formula [(H₂N₂O₂)TiCl₂] and [(H₂N₂O₂)Ti(OⁱPr)₂] (H₂N₂O₂H₂ = HOPh’CH₂NH(CH₂)₂NHCH₂Ph’OH, where Ph’ = 2,4-(CMe₂Ph)C₆H₂) were synthesized by the reaction of the salan ligand precursor H₂N₂O₂H₂ with TiCl₄ and Ti(OⁱPr)₄, respectively, in high yields. The dichlorido complex [(H₂N₂O₂)TiCl₂] revealed to be an efficient catalyst for the reduction of benzaldehyde in toluene. Full conversion was observed after 24 h at 55 °C in THF. The same catalyst also converted phenylacetaldehyde and hydrocinnamaldehyde into the corresponding alkanes quantitatively. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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35 pages, 19729 KiB

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Iron(II) Mediated Supramolecular Architectures with Schiff Bases and Their Spin-Crossover Properties

by Dawit Tesfaye, Wolfgang Linert, Mamo Gebrezgiabher, Yosef Bayeh, Fikre Elemo, Taju Sani, Nandakumar Kalarikkal and Madhu Thomas

Molecules 2023, 28(3), 1012; https://doi.org/10.3390/molecules28031012 - 19 Jan 2023

Cited by 9 | Viewed by 2741

Abstract

Supramolecular architectures, which are formed through the combination of inorganic metal cations and organic ligands by self-assembly, are one of the techniques in modern chemical science. This kind of multi-nuclear system in various dimensionalities can be implemented in various applications such as sensing, [...] Read more.

Supramolecular architectures, which are formed through the combination of inorganic metal cations and organic ligands by self-assembly, are one of the techniques in modern chemical science. This kind of multi-nuclear system in various dimensionalities can be implemented in various applications such as sensing, storage/cargo, display and molecular switching. Iron(II) mediated spin-crossover (SCO) supramolecular architectures with Schiff bases have attracted the attention of many investigators due to their structural novelty as well as their potential application possibilities. In this paper, we review a number of supramolecular SCO architectures of iron(II) with Schiff base ligands exhibiting varying geometrical possibilities. The structural and SCO behavior of these complexes are also discussed in detail. Full article

(This article belongs to the Special Issue Synthesis and Applications of Transition Metal Complexes)

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