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Recent Advances in Coordination Chemistry of Metal Complexes

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Inorganic Chemistry".

Deadline for manuscript submissions: 31 August 2024 | Viewed by 9110

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Guest Editor
School of Chemistry and Pharmaceutical Science, Guangxi Normal University, Guilin, China
Interests: high-nuclear Ln(III) cluster; molecular magnetism; assembly mechanism; assembly process; crystal structure
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The sustainable development of metal complexes is an interesting and significant topic, attracting increasing attention due to the complexes’ aesthetically pleasing structures and unique electronic and stereochemical properties. Their sustainable development has been successfully applied in the fields of solid-state lighting, biological diagnosis treatment, molecular magnetism, catalysis, adsorption, and intelligent sensing, and is gradually moving towards emerging fields. In addition, metal complexes contain both inorganic and organic substances. Therefore, the unique physical and chemical properties of both inorganic and organic compounds are of great significance for the development of a new generation of multifunctional materials, and various multifunctional metal complexes have emerged. However, chemists prefer to select specific organic ligands and metal ions to synthesize metal complexes with certain specificity, in particular, the design and synthesis of finite high-nuclear metal complexes with specific structural connections, beautiful topologies, and rich properties. In recent years, high-nuclear metal complexes have attracted intense interest, which can be attributed to their wide application value in emerging fields such as luminescent materials, chemical sensors, biosensors, catalysis, and smart materials. With the development of science and technology, focus on metal complexes has become more and more specific and scientific, which provides valuable opportunities for their cross-application in different fields.

Dr. Huahong Zou
Guest Editor

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Keywords

  • high-nuclear complexes
  • magnetism
  • catalysis
  • fluorescence
  • adsorption

Published Papers (10 papers)

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Research

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20 pages, 7706 KiB  
Article
Magnetic Ion-Imprinted Materials for Selective Adsorption of Cr(VI): Adsorption Behavior and Mechanism Study
by Shunfei Li, Siqing Ye, Weiye Zhang, Hongxing He, Yi Zhang, Mingyang Xiong, Yuhan Chen, Mingqiu Wang and Zhifeng Nie
Molecules 2024, 29(9), 1952; https://doi.org/10.3390/molecules29091952 - 24 Apr 2024
Viewed by 385
Abstract
With the increase of hexavalent Cr(VI) wastewater discharged from industrial production, it seriously pollutes water bodies and poses a risk to human health. Adsorption is used as an effective means to treat Cr(VI), but its effectiveness is affected by pH, and the adsorption [...] Read more.
With the increase of hexavalent Cr(VI) wastewater discharged from industrial production, it seriously pollutes water bodies and poses a risk to human health. Adsorption is used as an effective means to treat Cr(VI), but its effectiveness is affected by pH, and the adsorption performance decreases when acidity is strong. Furthermore, research on the mechanism of Cr(VI) adsorption using DFT calculations needs to be developed. This study focuses on the development of magnetically responsive core–shell nano-ion imprinted materials (Fe3O4@GO@IIP) through magnetic separation and surface imprinting techniques. Characterization techniques including FT-IR, XRD, and EDS confirmed the core–shell nanostructure of Fe3O4@GO@IIP. Batch adsorption experiments and model simulations demonstrated the exceptional adsorption capacity of Fe3O4@GO@IIP for Cr(VI) in strongly acidic solutions (pH = 1), reaching a maximum of 89.18 mg/g. The adsorption mechanism was elucidated through XPS and DFT calculations, revealing that Fe3O4@GO@IIP operates through electrostatic interactions and chemical adsorption, with charge transfer dynamics quantified during the process. This research provides new insights for addressing Cr(VI) treatment in highly acidic environments. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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20 pages, 4077 KiB  
Article
Investigating Ligand Sphere Perturbations on MnIII–Alkylperoxo Complexes
by Samuel A. Brunclik, Elizabeth N. Grotemeyer, Zahra Aghaei, Mohammad Rasel Mian and Timothy A. Jackson
Molecules 2024, 29(8), 1849; https://doi.org/10.3390/molecules29081849 - 18 Apr 2024
Viewed by 704
Abstract
Manganese catalysts that activate hydrogen peroxide carry out several different hydrocarbon oxidation reactions with high stereoselectivity. The commonly proposed mechanism for these reactions involves a key manganese(III)-hydroperoxo intermediate, which decays via O–O bond heterolysis to generate a Mn(V)–oxo species that institutes substrate oxidation. [...] Read more.
Manganese catalysts that activate hydrogen peroxide carry out several different hydrocarbon oxidation reactions with high stereoselectivity. The commonly proposed mechanism for these reactions involves a key manganese(III)-hydroperoxo intermediate, which decays via O–O bond heterolysis to generate a Mn(V)–oxo species that institutes substrate oxidation. Due to the scarcity of characterized MnIII–hydroperoxo complexes, MnIII–alkylperoxo complexes are employed to understand factors that affect the mechanism of the O–O cleavage. Herein, we report a series of novel complexes, including two room-temperature-stable MnIII–alkylperoxo species, supported by a new amide-containing pentadentate ligand (6Medpaq5NO2). We use a combination of spectroscopic methods and density functional theory computations to probe the effects of the electronic changes in the ligand sphere trans to the hydroxo and alkylperoxo units to thermal stability and reactivity. The structural characterizations for both MnII(OTf)(6Medpaq5NO2) and [MnIII(OH)(6Medpaq5NO2)](OTf) were obtained via single-crystal X-ray crystallography. A perturbation to the ligand sphere allowed for a marked increase in reactivity towards an organic substrate, a modest change in the distribution of the O–O cleavage products from homolytic and heterolytic pathways, and little change in thermal stability. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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15 pages, 2719 KiB  
Article
DFT Studies of Dimethylaminophenyl-Substituted Phthalocyanine and Its Silver Complexes
by Martin Breza
Molecules 2024, 29(6), 1344; https://doi.org/10.3390/molecules29061344 - 18 Mar 2024
Viewed by 497
Abstract
The dimethylaminophenyl-substituted silver phthalocyanine [dmaphPcAg] can be used as a UV-vis photoinitiator for in situ preparation of a silver/polymer nanocomposite. To verify early steps of the supposed mechanism of radical polymerization, we performed quantum chemical calculations of m[dmaphPcAg]q complexes with charges [...] Read more.
The dimethylaminophenyl-substituted silver phthalocyanine [dmaphPcAg] can be used as a UV-vis photoinitiator for in situ preparation of a silver/polymer nanocomposite. To verify early steps of the supposed mechanism of radical polymerization, we performed quantum chemical calculations of m[dmaphPcAg]q complexes with charges q = +1 to −2 in the two lowest spin states m, of a free ligand and its dehydrogenated/deprotonated products m[dmaphPcHn]q, n = 2 to 0, q = 0, −1 or −2, in the lowest spin states m. The calculated electronic structures and electron transitions of all the optimized structures in CHCl3 solutions are compared with experimental EPR and UV-vis spectra, respectively. The unstable 3[dmaphPcAg]+ species deduced only from previous EPR spin trap experiments was identified. In addition to 2[dmaphPcAg]0, our results suggest the coexistence of both reaction intermediates 1[dmaphPcAg] and 3[dmaphPcAg] in reaction solutions. Silver nanoparticle formation is a weak point of the supposed reaction mechanism from the energetic, stereochemistry, and electronic structure points of view. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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21 pages, 3284 KiB  
Article
New Copper Complexes with N,O-Donor Ligands Based on Pyrazole Moieties Supported by 3-Substituted Acetylacetone Scaffolds
by Jo’ Del Gobbo, Carlo Santini, Alessandro Dolmella, Zhenzhen Li, Miriam Caviglia and Maura Pellei
Molecules 2024, 29(3), 621; https://doi.org/10.3390/molecules29030621 - 28 Jan 2024
Viewed by 919
Abstract
The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1H-pyrazol-1-yl)methyl)pentane-2,4-dione (HLacPz) and 3-((3,5-dimethyl-1H-pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HLacPzMe), were synthesized and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae [Cu(HLacX)2(LacX) [...] Read more.
The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1H-pyrazol-1-yl)methyl)pentane-2,4-dione (HLacPz) and 3-((3,5-dimethyl-1H-pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HLacPzMe), were synthesized and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae [Cu(HLacX)2(LacX)2] and [Cu(PPh3)2(HLacX)]PF6 (X = Pz (pyrazole) or PzMe (3,5-dimethylpyrazole)), respectively. In the syntheses of the Cu(I) complexes, the triphenylphosphine coligand (PPh3) was used to stabilize copper in the +1 oxidation state, avoiding oxidation to Cu(II). All compounds were characterized by CHN analysis, 1H-NMR, 13C-NMR, FT-IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The ligands HLacPz (1) and HLacPzMe (2) and the copper complex [Cu(PPh3)2(HLacPz)]PF6 (3) were also characterized by X-ray crystallography. The reactivity of these new compounds was investigated and the new compounds 4-phenyl-4-(1H-pyrazol-1-yl)butan-2-one (7) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-4-phenylbutan-2-one (8) were obtained in basic conditions via the retro-Claisen reaction of related 3-monosubstituted acetylacetone, providing efficient access to synthetically useful ketone compounds. Compound 8 was also characterized by X-ray crystallography. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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14 pages, 2746 KiB  
Article
Luminescent Behavior of Zn(II) and Mn(II) Halide Derivatives of 4-Phenyldinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine 4-Oxide and Single-Crystal X-ray Structure Determination of the Ligand
by Valentina Ferraro, Jesús Castro and Marco Bortoluzzi
Molecules 2024, 29(1), 239; https://doi.org/10.3390/molecules29010239 - 1 Jan 2024
Viewed by 860
Abstract
The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1′-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr2 afforded complexes having [...] Read more.
The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1′-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr2 afforded complexes having the general formula [ZnBr2{O=PPh(BINOL)}2] that showed intense fluorescence centered in the near-UV region rationalized on the basis of TD-DFT calculations. The corresponding Mn(II) complexes with the general formula [MnX2{O=PPh(BINOL)}2] (X = Cl, Br) exhibited dual emission upon excitation with UV light, with the relative intensity of the bands dependent upon the choice of the halide. The highest energy transition is comparable with that of the Zn(II) complex, while the lowest energy emission falls in the red region of the spectrum and is characterized by lifetimes in the hundreds of microseconds range. Although the emission at lower energy can also be achieved by direct excitation of the metal center, the luminescence decay curves suggest that the band in the red range is possibly derived from BINOL-centered excited states populated by intersystem crossing. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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14 pages, 1635 KiB  
Article
Synthesis and Characterization of Iridium(III) Complexes with Substituted Phenylimidazo(4,5-f)1,10-phenanthroline Ancillary Ligands and Their Application in LEC Devices
by Bárbara Vásquez, Max Bayas, Paulina Dreyse, Juan Luis Palma, Alan R. Cabrera, Elena Rossin, Mirco Natali, Cesar Saldias and Iván González-Pavez
Molecules 2024, 29(1), 53; https://doi.org/10.3390/molecules29010053 (registering DOI) - 21 Dec 2023
Viewed by 1262
Abstract
In this work, we report on the synthesis and characterization of six new iridium(III) complexes of the type [Ir(C^N)2(N^N)]+ using 2-phenylpyridine (C13) and its fluorinated derivative (C46) as cyclometalating ligands (C^N) and [...] Read more.
In this work, we report on the synthesis and characterization of six new iridium(III) complexes of the type [Ir(C^N)2(N^N)]+ using 2-phenylpyridine (C13) and its fluorinated derivative (C46) as cyclometalating ligands (C^N) and R-phenylimidazo(4,5-f)1,10-phenanthroline (R = H, CH3, F) as the ancillary ligand (N^N). These luminescent complexes have been fully characterized through optical and electrochemical studies. In solution, the C46 series exhibits quantum yields (Ф) twice as high as the C13 series, exceeding 60% in dichloromethane and where 3MLCT/3LLCT and 3LC emissions participate in the phenomenon. These complexes were employed in the active layer of light-emitting electrochemical cells (LECs). Device performance of maximum luminance values of up to 21.7 Lx at 14.7 V were observed for the C2 complex and long lifetimes for the C13 series. These values are counterintuitive to the quantum yields observed in solution. Thus, we established that the rigidity of the system and the structure of the solid matrix dramatically affect the electronic properties of the complex. This research contributes to understanding the effects of the modifications in the ancillary and cyclometalating ligands, the photophysics of the complexes, and their performance in LEC devices. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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10 pages, 1630 KiB  
Communication
Russian Doll-like 3d–4f Cluster Wheels with Slow Relaxation of Magnetization
by Lan Liu, Panpan Yang, Zhihui Qiu, Kai Wang, Dongcheng Liu, Yuning Liang, Huancheng Hu, Huahong Zou, Fupei Liang and Zilu Chen
Molecules 2023, 28(15), 5906; https://doi.org/10.3390/molecules28155906 - 6 Aug 2023
Viewed by 1096
Abstract
The solvothermal reactions of LnCl3·6H2O and MCl2·6H2O (M = Co, Ni) with 2,2′-diphenol (H2L1) and 5,7-dichloro-8-hydroxyquinoline (HL2) gave three 3d–4f heterometallic wheel-like nano-clusters [Ln7M6(L1 [...] Read more.
The solvothermal reactions of LnCl3·6H2O and MCl2·6H2O (M = Co, Ni) with 2,2′-diphenol (H2L1) and 5,7-dichloro-8-hydroxyquinoline (HL2) gave three 3d–4f heterometallic wheel-like nano-clusters [Ln7M6(L1)6(L2)6(µ3-OH)6(OCH3)6Cl(CH3CN)6]Cl2·xH2O (Ln = Dy, M = Co, x = 3 for 1; Ln = Dy, M = Ni, x = 0 for 2; Ln = Tb, M = Ni, x = 0 for 3) with similar cluster structure. The innermost Ln(III) ion is encapsulated in a planar Ln6 ring which is further embedded in a chair-conformation M6 ring, constructing a Russian doll-like 3d–4f cluster wheel Ln(III)⸦Ln6⸦M6. 2 and 3 show obvious slow magnetic relaxation behavior with negligible opening of the magnetic hysteresis loop. Such a Russian doll-like 3d–4f cluster wheel with the lanthanide disc isolated by transition metallo-ring is rarely reported. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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12 pages, 2170 KiB  
Article
Synthesis and Characterization of Iron Bispyridine Bisdicyanamide, Fe[C5H5N]2[N(CN)2]2
by Laura Henrich, Peter C. Müller, Jan Hempelmann, Markus Mann, Jan van Leusen, Simon Steinberg and Richard Dronskowski
Molecules 2023, 28(13), 4886; https://doi.org/10.3390/molecules28134886 - 21 Jun 2023
Viewed by 1058
Abstract
Fe[C5H5N]2[N(CN)2]2 (1) was synthesized from a reaction of stoichiometric amounts of NaN(CN)2 and FeCl2·4H2O in a methanol/pyridine solution. Single-crystal and powder diffraction show that 1 crystallizes in [...] Read more.
Fe[C5H5N]2[N(CN)2]2 (1) was synthesized from a reaction of stoichiometric amounts of NaN(CN)2 and FeCl2·4H2O in a methanol/pyridine solution. Single-crystal and powder diffraction show that 1 crystallizes in the monoclinic space group I2/m (no. 12), different from Mn[C5H5N]2[N(CN)2]2 (P21/c, no. 14) due to tilted pyridine rings, with a = 7.453(7) Å, b = 13.167(13) Å, c = 8.522(6) Å, β = 114.98(6)° and Z = 2. ATR-IR, AAS, and CHN measurements confirm the presence of dicyanamide and pyridine. Thermogravimetric analysis shows that π-stacking interactions of the pyridine rings play an important role in structural stabilization. Based on DFT-optimized structures, a chemical bonding analysis was performed using a local-orbital framework by projection from a plane-wave basis. The resulting bond orders and atomic charges are in good agreement with the expectations based on the structure analysis. SQUID magnetic susceptibility measurements show a high-spin state FeII compound with predominantly antiferromagnetic exchange interactions at lower temperatures. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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Review

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14 pages, 6281 KiB  
Review
Metal Complexes of Redox Non-Innocent Ligand N,N′-Bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine
by Ari Lehtonen
Molecules 2024, 29(5), 1088; https://doi.org/10.3390/molecules29051088 - 29 Feb 2024
Cited by 1 | Viewed by 704
Abstract
Redox non-innocent ligands react with metal precursors to form complexes where the oxidation states of the ligand and thus the metal atom cannot be easily defined. A well-known example of such ligands is bis(o-aminophenol) N,N′-bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine, previously [...] Read more.
Redox non-innocent ligands react with metal precursors to form complexes where the oxidation states of the ligand and thus the metal atom cannot be easily defined. A well-known example of such ligands is bis(o-aminophenol) N,N′-bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine, previously developed by the Wieghardt group, which has a potentially tetradentate coordination mode and four distinct protonation states, whereas its electrochemical behavior allows for five distinct oxidation states. This rich redox chemistry, as well as the ability to coordinate to various transition metals, has been utilized in the syntheses of metal complexes with M2L, ML and ML2 stoichiometries, sometimes supported with other ligands. Different oxidation states of the ligand can adopt different coordination modes. For example, in the fully oxidized form, two N donors are sp2-hybridized, which makes the ligand planar, whereas in the fully reduced form, the sp3-hybridized N donors allow the formation of more flexible chelate structures. In general, the metal can be reduced during complexation, but redox processes of the isolated complexes typically occur on the ligand. Combination of this non-innocent ligand with redox-active transition metals may lead to complexes with interesting magnetic, electrochemical, photonic and catalytic properties. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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40 pages, 14175 KiB  
Review
Advances for Triangular and Sandwich-Shaped All-Metal Aromatics
by Miaomiao Wang and Yanlan Wang
Molecules 2024, 29(4), 763; https://doi.org/10.3390/molecules29040763 - 7 Feb 2024
Viewed by 1009
Abstract
Much experimental work has been contributed to all-metal σ, π and δ-aromaticity among transition metals, semimetallics and other metals in the past two decades. Before our focused investigations on the properties of triangular and sandwich-shaped all-metal aromatics, A. I. Boldyrev presented general [...] Read more.
Much experimental work has been contributed to all-metal σ, π and δ-aromaticity among transition metals, semimetallics and other metals in the past two decades. Before our focused investigations on the properties of triangular and sandwich-shaped all-metal aromatics, A. I. Boldyrev presented general discussions on the concepts of all-metal σ-aromaticity and σ-antiaromaticity for metallo-clusters. Schleyer illustrated that Nucleus-Independent Chemical Shifts (NICS) were among the most authoritative criteria for aromaticity. Ugalde discussed the earlier developments of all-metal aromatic compounds with all possible shapes. Besides the theoretical predictions, many stable all-metal aromatic trinuclear clusters have been isolated as the metallic analogues of either the σ-aromatic molecule’s [H3]+ ion or the π-aromatic molecule’s [C3H3]+ ion. Different from Hoffman’s opinion on all-metal aromaticity, triangular all-metal aromatics were found to hold great potential in applications in coordination chemistry, catalysis, and material science. Triangular all-metal aromatics, which were theoretically proved to conform to the Hückel (4n + 2) rule and possess the smallest aromatic ring, could also play roles as stable ligands during the formation of all-metal sandwiches. The triangular and sandwich-shaped all-metal aromatics have not yet been specifically summarized despite their diversity of existence, puissant developments and various interesting applications. These findings are different from the public opinion that all-metal aromatics would be limited to further applications due to their overstated difficulties in synthesis and uncertain stabilities. Our review will specifically focus on the summarization of theoretical predictions, feasible syntheses and isolations, and multiple applications of triangular and sandwich shaped all-metal aromatics. The appropriateness and necessities of this review will emphasize and disseminate their importance and applications forcefully and in a timely manner. Full article
(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)
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