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The preparation and characterization of two novel europium–azobenzene complexes that demonstrate the effectiveness of this ligand for stabilizing reactive, redox-active metals are reported. With the family of rare earth metals receiving attention due to their potential as catalysts, critical components in electronic devices, and, more recently, in biomedical applications, a detailed understanding of factors contributing to their coordination chemistry is of great importance for customizing their stability and reactivity. This study introduces azobenzene as an effective nonprotic ligand system that provides novel insights into rare earth metal coordination preferences, including factors contributing to the coordinative saturation of the large, divalent europium centers. The two compounds demonstrate the impact of the solvent donors (tetrahydrofuran (THF) and dimethoxyethane (DME)) on the overall coordination chemistry of the target compounds. Apart from the side-on coordination of the doubly-reduced azobenzene and the anticipated N-N bond elongation due to decreased bond order, the two compounds demonstrate the propensity of the europium centers towards limited metal-π interactions. The target compounds are available by direct metallation in a straightforward manner with good yields and purity. The compounds demonstrate the utility of the azobenzene ligands, which may function as singly- or doubly-reduced entities in conjunction with redox-active metals. An initial exploration into the computational modeling of these and similar complexes for subsequent property prediction and optimization is performed through a methodological survey of structure reproduction using density functional theory. [ABSTRACT FROM AUTHOR]

The coordination chemistry of 2-pyridyl ketoximes continues to attract the interest of many inorganic chemistry groups around the world for a variety of reasons. Cadmium(II) complexes of such ligands have provided models of solvent extraction of this toxic metal ion from aqueous environments using 2-pyridyl ketoxime extractants. Di-2-pyridyl ketone oxime (dpkoxH) is a unique member of this family of ligands because its substituent on the oxime carbon bears another potential donor site, i.e., a second 2-pyridyl group. The goal of this study was to investigate the reactions of cadmium(II) halides and dpkoxH in order to assess the structural role (if any) of the halogeno ligand and compare the products with their zinc(II) analogs. The synthetic studies provided access to complexes {[CdCl2(dpkoxH)∙2H2O]}n (1∙2H2O), {[CdBr2(dpkoxH)]}n (2) and {[CdI2(dpkoxH)]}n (3) in 50–60% yields. The structures of the complexes were determined by single-crystal X-ray crystallography. The compounds consist of structurally similar 1D zigzag chains, but only 2 and 3 are strictly isomorphous. Neighboring CdII atoms are alternately doubly bridged by halogeno and dpkoxH ligands, the latter adopting the η1:η1:η1:μ (or 2.0111 using Harris notation) coordination mode. A terminal halogeno group completes distorted octahedral coordination at each metal ion, and the coordination sphere of the CdII atoms is {CdII(η1 − X)(μ − X)2(Npyridyl)2(Noxime)} (X = Cl, Br, I). The trans-donor–atom pairs in 1∙2H2O are Clterminal/Noxime and two Clbridging/Npyridyl; on the contrary, these donor–atom pairs are Xterminal/Npyridyl, Xbridging/Noxime, and Xbridging/Npyridyl (X = Br, I). There are intrachain H-bonding interactions in the structures. The packing of the chains in 1∙2H2O is achieved via π-π stacking interactions, while the 3D architecture of the isomorphous 2 and 3 is built via C-H∙∙∙Cg (Cg is the centroid of one pyridyl ring) and π-π overlaps. The molecular structures of 1∙2H2O and 2 are different compared with their [ZnX2(dpkoxH)] (X = Cl, Br) analogs. The polymeric compounds were characterized by IR and Raman spectroscopies in the solid state, and the data were interpreted in terms of the known molecular structures. The solid-state structures of the complexes are not retained in DMSO, as proven via NMR (1H, 13C, and 113Cd NMR) spectroscopy and molar conductivity data. The complexes completely release the coordinated dpkoxH molecule, and the dominant species in solution seem to be [Cd(DMSO)6]2+ in the case of the chloro and bromo complexes and [CdI2(DMSO)4]. [ABSTRACT FROM AUTHOR]

Metalloenzymes make extensive use of manganese centers for oxidative catalysis, including water oxidation; the need to develop improved synthetic catalysts for these processes has long motivated the development of bioinspired manganese complexes. Herein, we report a series of bpy-(imidazole)n (n = 1 or 2) (bpy = 2,2′-bipyridyl) ligands and their Mn2+ complexes. Four Mn2+ complexes are structurally characterized using single-crystal X-ray diffraction, revealing different tridentate and tetradentate ligand coordination modes. Cyclic voltammetry of the complexes is consistent with ligand-centered reductions and metal-centered oxidations, and UV-vis spectroscopy complemented by TD-DFT calculations shows primarily ligand-centered transitions with minor contributions from charge-transfer type transitions at higher energies. In solution, ESI-MS studies provide evidence for ligand reorganization, suggesting complex speciation behavior. The oxidation of the complexes in the presence of water is probed using cyclic voltammetry, but the low stability of the complexes in aqueous solution leads to decomposition and precludes their ultimate application as aqueous electrocatalysts. Possible reasons for the low stability and suggestions for improvement are discussed. [ABSTRACT FROM AUTHOR]

Metallophthalocyanine (PcM) coordination complexes are well-known mediators of the electrochemical reduction of carbon dioxide (CO2). They have many properties that show promise for practical applications in the energy sector. Such properties include synthetic flexibility, a high stability, and good efficiencies for the reduction of CO2 to useful feedstocks, such as carbon monoxide (CO). One of the ongoing challenges that needs to be met is the incorporation of PcM into the heterogeneous materials that are used in a great many CO2-reduction devices. Much progress has been made in the last decade and there are now several promising approaches to incorporate PcM into a range of materials, from simple carbon-adsorbed preparations to extended polymer networks. These approaches all have important advantages and drawbacks. In addition, investigations have led to new proposals regarding CO2 reduction catalytic cycles and other operational features that are crucial to function. Here, we describe developments in the immobilization of PcM CO2 reduction catalysts in the last decade (2013 to 2023) and propose promising avenues and strategies for future research. [ABSTRACT FROM AUTHOR]

Since chemistry, materials science, and crystallography deal with three-dimensional structures, they use mathematics such as geometry and symmetry. In recent years, the application of topology and mathematics to material design has yielded remarkable results. It can also be seen that differential geometry has been applied to various fields of chemistry for a relatively long time. There is also the possibility of using new mathematics, such as the crystal structure database, which represents big data, for computational chemistry (Hirshfeld surface analysis). On the other hand, group theory (space group and point group) is useful for crystal structures, including determining their electronic properties and the symmetries of molecules with relatively high symmetry. However, these strengths are not exhibited in the low-symmetry molecules that are actually handled. A new use of mathematics for chemical research is required that is suitable for the age when computational chemistry and artificial intelligence can be used. [ABSTRACT FROM AUTHOR]

Within this work, we review the metal coordination effect on the photophysics of metal dipyrrinato complexes. Dipyrrinato complexes are promising candidates in the search for alternative transition metal photosensitizers for application in photodynamic therapy (PDT). These complexes can be activated by irradiation with light of a specific wavelength, after which, cytotoxic reactive oxygen species (ROS) are generated. The metal coordination allows for the use of the heavy atom effect, which can enhance the triplet generation necessary for generation of ROS. Additionally, the flexibility of these complexes for metal ions, substitutions and ligands allows the possibility to tune their photophysical properties. A general overview of the mechanism of photodynamic therapy and the properties of the triplet photosensitizers is given, followed by further details of dipyrrinato complexes described in the literature that show relevance as photosensitizers for PDT. In particular, the photophysical properties of Re(I), Ru(II), Rh(III), Ir(III), Zn(II), Pd(II), Pt(II), Ni(II), Cu(II), Ga(III), In(III) and Al(III) dipyrrinato complexes are discussed. The potential for future development in the field of (dipyrrinato)metal complexes is addressed, and several new research topics are suggested throughout this work. We propose that significant advances could be made for heteroleptic bis(dipyrrinato)zinc(II) and homoleptic bis(dipyrrinato)palladium(II) complexes and their application as photosensitizers for PDT. [ABSTRACT FROM AUTHOR]

The side-on end-on dinitrogen hydride complex [{Na(dme)}2{(O3)Nb}2(μ-η1:η2-N2)(μ-H)2] (3-Na, [O3]3− = [(3,5-tBu2-2-O-C6H2)3CH]3−) was observed to undergo facile elimination of H2 and cleavage of the N–N bond in the presence of 9-borabicyclo[3.3.1]nonane (9-BBN), AlMe3, and ZnMe2. Treatment of 3-Na with 9-BBN and ZnMe2 afforded the nitride complex [{K(dme)2}2{(O3)Nb}2(μ-N)2] (2-Na). The reaction of 3-Na with AlMe3 afforded [{Na(dme)}2{(O3)AlMe}2(NbMe2)2(μ-N)2] (5). The nitride complex 2-Na was treated with 9-BBN and AlMe3 to form [{Na(dme)}2{(O3)Nb}(μ-NH)(μ-NBC8H14){Nb(O3C)}] (4) and 5, respectively. Complex 2-Na, 4, and 5 were structurally characterized. [ABSTRACT FROM AUTHOR]

A series of coinage metal complexes asymmetrically substituted 2,5-diaryl phosphole ligands is reported. Structure, identity, and purity of all obtained complexes were corroborated with state-of-the-art techniques (multinuclear NMR, mass spectrometry, elemental analysis, X-ray diffraction) in solution and solid state. All complexes obtained feature luminescence in solution as well as in the solid state. Additionally, DOSY-MW NMR estimation experiments were performed to achieve information about the aggregation behavior of the complexes in solution allowing a direct comparison with their structures observed in the solid state. [ABSTRACT FROM AUTHOR]

New well-defined, paramagnetic nickel complexes have been prepared and characterized by X-ray crystallography. The complexes were found to be active for the cross-coupling of alkyl electrophiles (especially ethyl 2-bromobutyrate) with alkyl Grignard reagents. The ligand architecture in these new complexes could potentially be rendered chiral, opening up future possibilities for performing asymmetric cross-coupling reactions. [ABSTRACT FROM AUTHOR]

Fourteen new fosmidomycin analogues with altered metal chelating groups were prepared and evaluated for inhibition of E. coli Dxr, M. tuberculosis Dxr and the growth of P. falciparum K1 in human erythrocytes. None of the synthesized compounds showed activity against either enzyme or the Plasmodia. This study further underlines the importance of the hydroxamate functionality and illustrates that identifying effective alternative bidentate ligands for this target enzyme is challenging. [ABSTRACT FROM AUTHOR]

The present work describes the reactions of CdI2 with 2-pyridyl aldoxime (2paoH), 3-pyridyl aldoxime (3paoH), 4-pyridyl aldoxime (4paoH), 2-6-diacetylpyridine dioxime (dapdoH2) and 2,6-pyridyl diamidoxime (LH4). The primary goal was to contribute to understanding the molecular basis of the very good liquid extraction ability of 2-pyridyl ketoximes with long aliphatic chains towards toxic Cd(II) and the inability of their 4-pyridyl isomers for this extraction. Our systematic investigation provided access to coordination complexes [CdI2(2paoH)2] (1), {[CdI2(3paoH)2]}n (2), {[CdI2(4paoH)2]}n (3) and [CdI2(dapdoH2)] (4). The reaction of CdI2 and LH4 in EtOH resulted in a Cd(II)-involving reaction of the bis(amidoxime) and isolation of [CdI2(L'H2)] (5), where L'H2 is the new ligand 2,6-bis(ethoxy)pyridine diimine. A mechanism of this transformation has been proposed. The structures of 1, 2, 3, 4·2EtOH and 5 were determined by single-crystal X-ray crystallography. The complexes have been characterized by FT-IR and FT-Raman spectra in the solid state and the data are discussed in terms of structural features. The stability of the complexes in DMSO was investigated by 1H NMR spectroscopy. Our studies confirm that the excellent extraction ability of 2-pyridyl ketoximes is due to the chelating nature of the extractants leading to thermodynamically stable Cd(II) complexes. The monodentate coordination of 4-pyridyl ketoximes (as confirmed in our model complexes with 4paoH and 3paoH) seems to be responsible for their poor performance as extractants. [ABSTRACT FROM AUTHOR]

One- and two-photon characterizations of a series of hetero- and homoleptic [RuL3-n(bpy)n]2+ (n = 0, 1, 2) complexes carrying bipyridine π-extended ligands (L), have been carried out. These π-extended D−π−A−A−π−D-type ligands (L), where the electron donor units (D) are based on diphenylamine, carbazolyl, or fluorenyl units, have been designed to modulate the conjugation extension and the donating effect. Density functional theory calculations were performed in order to rationalize the observed spectra. Calculations show that the electronic structure of the π-extended ligands has a pronounced effect on the composition of HOMO and LUMO and on the metallic contribution to frontier MOs, resulting in strikingly different nonlinear properties. This work demonstrates that ILCT transitions are the keystone of one- and two-photon absorption bands in the studied systems and reveals how much MLCT and LLCT charge transfers play a decisive role on the two-photon properties of both hetero- and homoleptic ruthenium complexes through cooperative or suppressive effects. [ABSTRACT FROM AUTHOR]

Nitriles (N≡CR) are ubiquitous in coordination chemistry, yet literature studies on metal–nitrile bonding based on a multi-technique approach are rare. We selected an easily-available di-organoiron framework, containing both π-acceptor (CO, aminocarbyne) and donor (Cp = η5−C5H5) ligands, as a suitable system to provide a comprehensive description of the iron–nitrile bond. Thus, the new nitrile (2–12)CF3SO3 and the related imine/amine complexes (8–9)CF3SO3 were synthesized in 58–83% yields from the respective tris-carbonyl precursors (1a–d)CF3SO3, using the TMNO strategy (TMNO = trimethylamine-N-oxide). The products were fully characterized by elemental analysis, IR (solution and solid state) and multinuclear NMR spectroscopy. In addition, the structures of (2)CF3SO3, (3)CF3SO3, (5)CF3SO3 and (11)CF3SO3 were ascertained by single crystal X-ray diffraction. Salient spectroscopic data of the nitrile complexes are coherent with the scale of electron-donor power of the R substituents; otherwise, this scale does not match the degree of Fe → N π-back-donation and the Fe–N bond energies, which were elucidated in (2–7)CF3SO3 by DFT calculations. [ABSTRACT FROM AUTHOR]

The interaction of hafnium(IV) salts (oxide-dichloride, chloride, and bromide) with nitrilotriacetic acid (NTA), diethylenetriamminepentaacetic acid (DTPA), 1,2-diaminocyclohexanetetraacetic acid (CDTA), 1,3-dipropylmino-2-hydroxy N,N,N′,N′-tetraacetic acid (dpta), and N-(2-hydroxyethyl)ethylenediamine triacetic acid (HEDTA) has been studied. The corresponding complexes Na2[Hf(NTA)2]·3H2O (1), Na[HfDTPA]·3H2O (2), [HfCDTA(H2O)2] (3), and Na[Hf2(dpta)2]·7.5H2O·0.5C2H5OH (4) have been isolated and characterized and their structures have been determined by single crystal X-ray diffraction. Biological studies of [HfCDTA(H2O)2] have shown that in 5% glucose solution this complex has low toxicity and good contrasting ability. [ABSTRACT FROM AUTHOR]

Fast and selective analytical methods help to ensure the chemical identity and desired purity of the prepared complexes before their medical application, and play an indispensable role in clinical practice. Mass spectrometry, despite some limitations, is an integral part of these methods. In the context of mass spectrometry, specific problems arise with the low ionization efficiency of particular analytes. Chemical derivatization was used as one of the most effective methods to improve the analyte's response and separation characteristics. The Schotten–Baumann reaction was successfully adapted for the derivatization of ESI hardly ionizable Re(VII) bis(catechol) oxochlorocomplex. Various alkyl and halogen p-substituted anilines as possible derivatization agents were tested. Unlike the starting complex, the reaction products were easily ionizable in electrospray, providing structurally characteristic molecular and fragment anions. DFT computer modeling, which proposed significant conformation changes of prepared complexes within their deprotonation, proved to have a close link to MS spectra. High-resolution MS and MS/MS measurements complemented with collision-induced dissociation experiments for detailed specification of prepared complexes' fragmentation pathways were used. The specified fragmentation schemes were analogous for all studied derivatives, with an exception for [Re(O)(Cat)2PIPA]. [ABSTRACT FROM AUTHOR]

The functionalization of the arsenic transfer reagent [Cp″2Zr(η1:1-As4)] (1) focuses on modifying its properties and enabling a broader scope of reactivity. The coordination behavior of 1 towards different Lewis-acidic transition metal complexes and main group compounds is investigated by experimental and computational studies. Depending on the steric requirements of the Lewis acids and the reaction temperature, a variety of new complexes with different coordination modes and coordination numbers could be synthesized. Depending on the Lewis acid (LA) used, a mono-substitution in [Cp″2Zr(µ,η1:1:1:1-As4)(LA)] (LA = Fe(CO)4 (4); B(C6F5)3 (7)) and [Cp″2Zr(µ,η3:1:1-As4)(Fe(CO)3)] (5) or a di-substitution [Cp″2Zr(µ3,η1:1:1:1-As4)(LA)2] (LA = W(CO)5 (2); CpMn(CO)2 (3); AlR3 (6, R = Me, Et, iBu)) are monitored. In contrast to other coordination products, 5 shows an η3 coordination in which the butterfly As4 ligand is rearranged to a cyclo-As4 ligand. The reported complexes are rationalized in terms of inverse coordination. [ABSTRACT FROM AUTHOR]

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO3)3·nH2O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln2(O2CMe)4(NO3)2(mepaoH)2] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the LnIII—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)3·4H2O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy2(O2CMe)6(mepaoH)2] (6). Treatment of 6 with one equivalent of HNO3 gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two LnIII centers are bridged by two bidentate bridging (η1:η1:μ2) and two chelating-bridging (η1:η2:μ2) acetate groups. The LnIII atoms are each chelated by a N,N'-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate LnIII centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the TbIII atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular GdIII...GdIII exchange interactions in 3; the J value is −0.09(1) cm−1 based on the spin Hamiltonian Ĥ = −J(ŜGd1·ŜGd2). [ABSTRACT FROM AUTHOR]

The first fifty years of the chemistry of 2,2′-bipyridine are reviewed from its first discovery in 1888 to the outbreak of the second global conflict in 1939. The coordination chemistry and analytical applications are described and placed in the context of the increasingly sophisticated methods of characterization which became available to the chemist in this time period. Many of the "simple" complexes of 2,2′-bipyridine reported in the early literature have been subsequently shown to have more complex structures. [ABSTRACT FROM AUTHOR]

The Cu2+, Mn2+, and Fe3+ complexes of a 14 membered macrocycle were synthesized and their antioxidant capacities were evaluated against ABTS and DPPH radicals, with the objective of collecting insights into the biomimetic role of the central metal ions. The macrocycle, abbreviated as H2L14, is a derivative of EDTA cyclized with 1,4-diamine, and the moderately flexible macrocyclic frame permits the formation of [ML14·H2O] chelates with octahedral coordination geometries common among the metal ions. The metal complexes were characterized by electrospray-ionization mass spectrometry, Fourier transform infrared spectroscopy, and Raman and X-ray photoelectron spectroscopic methods, as well as thermogravimetric analysis; the octahedral coordination geometries with water coordination were optimized by DFT calculations. The antioxidant assays showed that [FeL14·H2O]+ was able to scavenge synthetic radicals with moderate capacity, whereas the other metal chelates did not show significant activity. The Raman spectrum of DPPH in solution suggests that interaction was operative between the Fe3+ chelate and the radical so as to cause scavenging capability. The nature of the central metal ions is a controlling factor for antioxidant capacity, as every metal chelate carries the same coordination geometry. [ABSTRACT FROM AUTHOR]

The goal of this work is to model the nature of the chemical species [CdCl2(extractant)2] that are formed during the solvent (or liquid-liquid) extraction of the toxic cadmium(II) from chloride-containing aqueous media using hydrophobic 2-pyridyl ketoximes as extractants. Our coordination chemistry approach involves the study of the reactions between cadmium(II) chloride dihydrate and phenyl 2-pyridyl ketoxime (phpaoH) in water-containing acetone. The reactions have provided access to complexes [CdCl2(phpaoH)2]∙H2O (1∙H2O) and {[CdCl2(phpaoH)]}n (2); the solid-state structures of which have been determined by single-crystal X-ray crystallography. In both complexes, phpaoH behaves as an N,N'-bidentate chelating ligand. The complexes have been characterized by solid-state IR and Raman spectra, and by solution 1H NMR spectra. The preparation and characterization of 1∙H2O provide strong evidence for the existence of the species [CdCl2(extractant)2] that have been proposed to be formed during the liquid-liquid extraction process of Cd(II), allowing the efficient transfer of the toxic metal ion from the aqueous phase into the organic phase. [ABSTRACT FROM AUTHOR]