Role Of Coordination Chemistry Research Articles

Pyrazole and Benzimidazole Derivatives: Chelating Properties Towards Metals Ions and their Applications

Abstract: Due mainly to their structural diversities, pharmacological, electrochemical, and photophysical properties, the metal synthesis pyrazole and benzimidazole complexes were extensively designed and developed. The nitrogen-containing ligands playing an important role in coordination chemistry contain a wide variety of heterocyclic systems possessing one or more nitrogen atoms as electron donors, such as pyridine, isoxazole, pyrazole, 1,2,4-triazole, 1,3,5-triazine, quinoline, quinoxaline and benzothiazole. The structure of all ligands and the corresponding metal complexes are established using elemental analysis, infrared spectroscopy, NMR spectroscopy, mass spectrometry, single-crystal X-ray diffraction, thermogravimetric differential thermal analysis, static, magnetic susceptibility measurements, electron paramagnetic resonance spectroscopy (EPR), UV-Vis spectroscopy, and conductivity measurements.In this review, we report the synthesis and the chelating reactions of several heterocyclic ligands with various metals such as transition metals and lanthanides. The photophysical and photochemical properties of the metal complexes will also be presented and discussed.

Synthesis and Characterization of Bis(pyridylimino)isoindolide Alkali Metal Complexes in Three Redox States

AbstractNon‐innocent ligands (NILs) like bis(pyridylimino)isoindolide (BPI) play crucial roles in coordination chemistry, biosciences, catalysis and material sciences. Investigating the isolated redox states of NILs is inevitable for understanding their redox‐activity and fine‐tuning the properties of corresponding metal complexes. The limited number of fundamental studies on the coordination behavior and redox chemistry of reduced BPI species is suggested to hamper further applications of the title compounds. This work describes for the first time the isolation of alkali metal complexes of BPI and Me2BPI in three different oxidation states and their characterization by means of NMR or EPR spectroscopy, DFT calculations, and SC‐XRD studies. The latter revealed the connection between bond orders in the ligand scaffold and its oxidation state. The paramagnetic compound Me2BPI‐K2 was isolated as a coordination copolymer with 18‐crown‐6, which enabled the characterization of the dianionic BPI radical. Furthermore, the so‐far unknown trianionic state of BPI was reported by the isolation of BPI‐K3. This divulges an unprecedented bis(amidinato)isoindolide coordination mode.

Synthesis, spectroscopic and hydrogen storage studies of mono or bimercury(II) mixed ligand complexes of amines with 2-cyanoamino thiophenolate ligand

Organic heterocyclic compounds play a significant role in coordination chemistry due to their ability to act as donor atoms for coordinating with various metal or metal ions. In this study, particular attention was given to the conversion of the 2-aminobenzothiazole ligand into 2-cyanoaminothiophenolate (LH) through a ring-breaking reaction. This transformation was achieved by reacting 2-aminobenzothiazole with phenyl mercury(II) acetate in the presence of sodium hydroxide, resulting in the formation of the complex [pHHg(LH)]n. During this process, mono-deprotonation of 2-aminobenzothiazole occurred, accompanied by facial carbon-sulfur bond breaking. This complex was used as a synthon to prepare four new mononuclear and binuclear complexes, which were [pHHg(LH)(apmy)2] (apmy= 2-aminopyrimidine) and [PhHg(LH)(bipy)] and [pHHg(LH)(μ-Cl)2Hg(bipy)] and [pHHg(LH)(μ-Cl)2Hg(phen)]. The prepared complexes were characterized using melting point, elemental analysis, FTIR, 1HNMR and 13CNMR. The results showed that the 2-cyanoamino thiophenolate ligand exhibited a monodentate behavior across the thiol sulfur atom, while the nitrile group remained free. The complex [pHHg(LH)(μ-Cl)2Hg(phen)] was used to study its ability to store hydrogen at different temperatures in order to study the thermodynamic parameters (enthalpy and entropy). The study proved that the highest stored value was 1.92 wt.% H2. It was noted that this ratio can be stored at lower pressures as the temperature decreases, proving that the storage is of a physical type with the value of R2= 0.92602 for the Van't Hof plot. The enthalpy value was 0.1131118 (kJ/(mol H2) while the entropy value was 0.60649754 (J/mol H2. K).

Effect of Subtle Changes on the Slow Relaxation Behavior of Co(II) Ions Based Metal-Organic Frameworks

Metal-organic framework (MOF) materials play an important role in coordination chemistry. Here, we report the synthesis, structure, and magnetic properties of a Co(II)-based MOF [Co(dps)2Cl2]n (1). Single-crystal diffraction analysis reveals that compound 1 has a two-dimensional (2D) layered structure. The magnetic properties studies indicate that compound 1 shows easy-plane anisotropy with positive D value, which is further proved by high-field electron paramagnetic resonance (HF-EPR). AC susceptibility measurements show that compound 1 is field-induced SMM governed by single Co(II) ion. The magnetic properties studies indicate that coordinate halogens have almost no effect on the slow magnetic relaxation time and effective energy barrier. However, the secondary coordination environment of packing pattern has a significant effect on the slow relaxation.

An Updated Review on Recent Advancements in the Diverse Biological Applications of Medicinally Privileged Scaffold: Chalcone and its derivatives

Fused heterocyclic compounds rank among the most significant systems in medicinal chemistry because of their wide-ranging biological effects. Among the various class of compounds, chalcones and their derivatives are found to be one of the important classes in the field of synthetic and pharmaceutical chemistry. These derivatives are mainly synthesized by means of Claisen-Schmidt condensation, Crossed Aldol condensation and Knoevenagel condensation reactions, which provides wider applications in the field of medicine. Due to the broader biological applications like antimicrobial, anticancer, antimalarial, antioxidant, anti-inflammatory, antitubercular, antidiabetic, antileishmanial, anti-vitiligo and neuroprotective properties, these derivatives extended their role in coordination chemistry and also act as intermediates for the synthesis of various organic derivatives containing isoxazole, pyrazole, pyrimidine, naphthalene, indole, polyamine and other moieties as hybrid molecules. The present review discusses the biological applications of various chalcone derivatives. Due to their easiest way of synthesis, nowadays, these types of derivatives were tried for various ailments and by means of implementing various greener chemistry approaches, novel and potent derivatives can be synthesized and applied for various applications. Thus, this review will be helpful for the design of potent chalcone derivatives for numerous applications in the future. Keywords: Chalcones, 1,3-diphenyl-2-propene-1-one, microbial properties, anticancer, antioxidant, neuroprotective and biological applications

Elucidating Solution-State Coordination Modes of Multidentate Neutral Amine Ligands with Group-1 Metal Cations: Variable-Temperature NMR Studies.

Multidentate neutral amine ligands play vital roles in coordination chemistry and catalysis. In particular, these ligands are used to tune the reactivity of Group-1 metal reagents, such as organolithium reagents. Most, if not all, of these Group-1 metal reagent-mediated reactions occur in solution. However, the solution-state coordination behaviors of these ligands with Group-1 metal cations are poorly understood, compared to the plethora of solid-state structural studies based on single-crystal X-ray diffraction (SCXRD) studies. In this work, we comprehensively mapped out the coordination modes with Group-1 metal cations for three multidentate neutral amine ligands: tridentate 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN), tetradentate tris[2-(dimethylamino)ethyl]amine (Me6Tren), and hexadentate N,N′,N″-tris-(2-N-diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN). The macrocycles in the Me3TACN and DETAN are identified as the rigid structural directing motif, with the sidearms of DETAN providing flexible “on-demand” coordination sites. In comparison, the Me6Tren ligand features more robust coordination, with the sidearms less likely to undergo the decoordinating–coordinating equilibrium. This work will provide a guidance for coordination chemists in applying these three ligands, in particular, the new DETAN ligand to design metal complexes which suit their purposes.

Mono- and Dinuclear Aluminium Complexes Derived from Biguanide and Carbothiamide Ligands

Dianionic N,N-chelating ligands play a crucial role in coordination chemistry, but reports on related complexes remain limited to certain types of ligands. In here, the reactions of two diprotic ligands, i.e., a biguanide and a carbothiamide, with trimethylaluminium, are reported, which give rise to mono- and dinuclear aluminium(III) complexes. In addition, single deprotonation of the diprotic biguanide using potassium bis(trimethylsilyl)amide gives rise to a one-dimensional coordination polymer. All complexes have been fully characterized, and their solid-state structures were determined by single crystal X-ray diffraction analysis.

Role of Anions and Mixtures of Anions on the Thermochromism, Vapochromism, and Polymorph Formation of Luminescent Crystals of a Single Cation, [(C6H11NC)2Au].

Noncoordinating anions, which generally play a subordinate role in coordination chemistry, alter the structure, the luminescence, as well as the thermochromic and vapochromic behaviors of salts of the two-coordinate cation, [(C6H11NC)2Au]+. Thus whereas the yellow polymorphs of [(C6H11NC)2Au](PF6) and [(C6H11NC)2Au](AsF6) contain single chains of cations and are vapochromic, yellow [(C6H11NC)2Au](SbF6) does not form the same polymorph and is not vapochromic but contains two distinct chains of cations connected through aurophilic interactions. Mixed crystals such as [(C6H11NC)2Au](PF6)0.50(AsF6)0.50 have been prepared by adding diethyl ether to a dichloromethane solution containing equimolar amounts of [(C6H11NC)2Au](PF6) and [(C6H11NC)2Au](AsF6). The initial (kinetic) product for the three combinations of anions ((PF6)-/(AsF6)-, (PF6)-/(SbF6)-, and (AsF6)-/(SbF6)-) was a precipitate of fine yellow needles with a green emission, which were gradually transformed at rates that depended on the anions present into colorless crystals with a blue emission. Whereas neither polymorph of [(C6H11NC)2Au](PF6) nor [(C6H11NC)2Au](SbF6) is thermochromic, the colorless mixed crystal [(C6H11NC)2Au](PF6)0.50(SbF6)0.50 is thermochromic and converts from blue-emitting to green-emitting at 87-95 °C. The temperature required to transform a crystal of the type [(C6H11NC)2Au](PF6)n(AsF6)1-n from colorless (blue-emitting) to yellow (green-emitting) increases as the fraction of hexafluorophosphate ion in the crystal increases. The yellow crystals of [(C6H11NC)2Au](PF6)0.75(AsF6)0.25, [(C6H11NC)2Au](PF6)0.50(AsF6)0.50, and [(C6H11NC)2Au](PF6)0.25(AsF6)0.75 are vapochromic, whereas the yellow crystals of [(C6H11NC)2Au](PF6)0.50(SbF6)0.50 and [(C6H11NC)2Au](AsF6)0.50(SbF6)0.50 are not.

Novel Chemotherapeutic Agents - The Contribution of Scorpionates.

The development of safe and effective chemotherapeutic agents is one of the uppermost priorities and challenges of medicinal chemistry and new transition metal complexes are being continuously designed and tested as anticancer agents. Scorpionate ligands have played a great role in coordination chemistry, since their discovery by Trofimenko in the late 1960s, with significant contributions in the fields of catalysis and bioinorganic chemistry. Scorpionate metal complexes have also shown interesting anticancer properties, and herein, the most recent (last decade) and relevant scorpionate complexes reported for application in medicinal chemistry as chemotherapeutic agents are reviewed. The current progress on the anticancer properties of transition metal complexes bearing homo- or hetero- scorpionate ligands, derived from bis- or tris-(pyrazol-1-yl)-borate or -methane moieties is highlighted.

New Perspectives for Aminotroponiminates: Coordination Chemistry, Redox Behavior, Cooperativity, and Catalysis

Aminotroponiminates (ATIs) are monoanionic ligands with an N,N‐binding pocket and a rigid, planar, unsaturated, C7‐ring as a ligand backbone. Recent findings show that this ligand backbone can play an active role in coordination chemistry, redox reactions, and ligand‐centered reactivity of ATI complexes. Based on these results, ATIs have been recognized as redox‐active and cooperative ligands, which has implications for existing and potential future applications of ATI compounds in synthesis, catalysis, and materials science. The catalytic applications of ATI complexes are summarized in this Microreview, including results from the fields of hydroamination, epoxidation, cyanosilylation, ε‐caprolactone‐, olefin‐, epoxide‐, and epoxide/CO2 (co‐)polymerization as well as electron transfer catalysis. Furthermore, recent advances in the use of ATI ligands for stabilizing heavy analogs of carbon oxo compounds are showcased.

A Review on 4, 5-Imidazoledicarboxylic Acid: Their Chemistry and Coordination Potentials

As part of heterocyclic imidazole interest to explore new receptors for anion; 4,5-imidazoledicarboxylic acid and their derivatives have great roles in coordination chemistry. This review, was also update the application and behaviour of 4,5-imidazoledicarboxylic acid (H3IMDC) as a potential motif for coordination compound in supramolecular structure activity. H3IMDC contains one imidazole NH and two COOH protons which could be donated for hydrogen bonding to the anions. Due to the electronic properties of carboxyl group oxygens, coordination to metal ions can occur in different modes. In situ ligand synthesis is of growing interest as a new approach for the synthesis of coordination polymers. The main reason for interesting of 4,5-imidazoledicarboxylic acid (H3IMDC) and its derivatives in coordination polymers of metal-organic framework is because it has six potential donor atoms: two imidazole nitrogens and four carboxylate oxygen atoms, and can remove one to three hydrogen atoms forming H3-nIMDCn- (n=1,2 or 3) species. The six donors may show various coordination modes and construct beautiful structures. In present review, the chemistry of 4,5-imidazoledicarboxylic acid and its coordination potential in coordination and supramolecular chemistry, which are uses as input for medicinal and drug synthesis, pharmacological actions and as biological activity; where reviewed based on the coordination potentials of imidazole derived heterocyclic molecules in metal-organic frameworks.

The wonderful world of pyridine-2,6-dicarboxamide based scaffolds.

The present perspective focusses on a variety of scaffolds based on a pyridine-2,6-dicarboxamide fragment and their noteworthy roles in coordination chemistry, stabilization of reactive species, synthetic modelling of some metalloenzyme active sites, catalytic organic transformations, and sensing as well as recognition applications. These examples illustrate the significance of synthetic scaffolds based on the pyridine-2,6-dicarboxamide fragment in synthetic chemistry in general and coordination chemistry in particular.

Infrared Spectroscopic Investigations of Effect of Strong Resonance Stabilized Intramolecular Hydrogen Bonding in 1-(1-Hydroxy-2-naphthyl)-3-(phenyl or Substituted phenyl)-prop-2-en-1-ones and on their Complexation with Some Transition Metals

Some copper(II), nickel(II) and cobalt(II) complexes of naphthalene analogues of 2'-hydroxychalcones have been synthesized and characterized. The complexes have the general formula ML2.XH2O (X=2 or 0) where, L is the deprotonated ligand, the naphthyl chalcone and M is the divalent metal ion. The present paper deals with the effect of strong resonance stabilized intramolecular hydrogen bonding on the IR spectral properties of the naphthalene analogues of 2'- hydroxychalcones as mentioned above and also on their complexation with transition metals such as Cu(II), Ni(II) and Co(II). The conjugated chelation alters considerably the IR spectral properties of these compounds and plays a prominent role in coordination chemistry. IR spectroscopy is the most sensitive and direct method for the study of hydrogen bonding.

A Review on “4, 5-Imidazoledicarboxylic Acid”: Their Chemistry and Coordination Potentials

As part of heterocyclic imidazole interest to explore new receptors for anion; 4,5-imidazoledicarboxylic acid and their derivatives have great roles in coordination chemistry. This review, was also update the application and behaviour of 4,5-imidazoledicarboxylic acid (H3IMDC) as a potential motif for coordination compound in supramolecular structure activity. H3IMDC contains one imidazole NH and two COOH protons which could be donated for hydrogen bonding to the anions. Due to the electronic properties of carboxyl group oxygens, coordination to metal ions can occur in different modes. In situ ligand synthesis is of growing interest as a new approach for the synthesis of coordination polymers. The main reason for interesting of 4,5-imidazoledicarboxylic acid (H3IMDC) and its derivatives in coordination polymers of metal-organic framework is because it has six potential donor atoms: two imidazole nitrogens and four carboxylate oxygen atoms, and can remove one to three hydrogen atoms forming H3-nIMDCn- (n=1,2 or 3) species. The six donors may show various coordination modes and construct beautiful structures. In present review, the chemistry of 4,5-imidazoledicarboxylic acid and its coordination potential in coordination and supramolecular chemistry, which are uses as input for medicinal and drug synthesis, pharmacological actions and as biological activity; where reviewed based on the coordination potentials of imidazole derived heterocyclic molecules in metal-organic frameworks.

Impact of divalent metal cations on the catalysis of peptide bonds: a DFT study

Within the ATP-grasp family of enzymes, divalent alkaline earth metals are proposed to chelate terminal ATP phosphates and facilitate the formation of peptide bonds. Density functional theory methods are used to explore the impact of metal ions on peptide bond formation, providing an insight into experimental metal substitution studies. Calculations show that alkaline earth and transition metal cations coordinate with an acylphosphate reactant and aid in the separation of the phosphate leaving group. The critical biochemical reaction is proposed to proceed through the formation of a six-membered transition state in the relatively nonpolar active site of human glutathione synthetase, an ATP-grasp enzyme. While the identity of the metal ion has a moderate impact on the thermodynamics of peptide bond formation, kinetic differences are much sharper. Simulations indicate that several transition metal ions, most notably Cu2+, may be particularly advantageous for catalysis. The detailed mechanistic study serves to elucidate the vital role of coordination chemistry in the formation of peptide bonds.

Poly(pyrrole) films efficiently electrodeposited using new monomers derived from 3-bromopropyl-N-pyrrol and dihydroxyacetophenone—Electrocatalytic reduction ability towards bromocyclopentane

Three monomers 6-[3′-N-pyrrolpropoxy]-2-hydroxyacetophenone (1), 5-(3′-N-pyrrol propoxy)-2-hydroxyacetophenone (2) and 4-(3′-N-pyrrolpropoxy)-2-hydroxyacetophenone (3) were synthesized and their poly(pyrrole) films were electrodeposited on glassy carbon (GC) and Indium tin oxide (ITO) conductive electrodes by anodic oxidation in acetonitrile solutions containing n-Bu)4N+ClO4− (TBAP 0.1M). These films, currently called modified electrodes (noted ME), were obtained by the successive cycling at the appropriate potentials. These films contain chelating sites such as carbonyl group bearing the phenolic function which could play an important role in coordination chemistry. The electrodeposited poly(pyrrole) films on the ITO conductive glass electrodes offer some analytical advantages as the optical and electronic properties. Consequently, these new materials of electrodes were characterized by cyclic voltammetry while the morphology of these films was studied by FT-IR spectroscopy, scanning electron microscopy (SEM), dispersive energy X-ray spectroscopy and atomic force microscopy (AFM). The AFM studies show that the morphology of polypyrrole (PPy) films, electrodeposited on ITO surface, depends on the specific structure of the compound deriving from the monoalkylated dihydroxyacetophenone 1, 2 and 3. The coordination of copper was performed by electroreduction reaction in presence of ligand (3) and copper acetate salt. The resulting electrode material was tested towards the electrocatalytic activity in the reduction of bromocyclopentane.

Charge Density Analysis and Bond Characterization of 3d‐Transition Metal Complexes

AbstractChemical bond, which makes molecules from independent atoms, is a very important concept in understanding the molecular behavior. Bond characterization is therefore becoming ever needed for predicting the physical and chemical properties of the molecule and the material. Combined experimental and molecular orbital calculation studies have been used for such purpose in terms of deformation density distribution, natural bond orbital analysis and the topological analysis on the total electron density. These analyses provide not only the distribution of density accumulation and density depletion, but also the information such as bond order, bond type etc. Atom domain in molecule or compound can be defined uniquely. Therefore the combined quantum mechanical calculation and high resolution X‐ray crystallography studies will be extremely useful for characterizing the chemical bond precisely. Bonding in 3d‐transition metal complexes is a major topic in coordination chemistry. The complexity of the 3d orbital splittings subjected in the ligand field is well known and this makes the bonding characterization more interesting and challenging. Charge density analysis on a series of Cr compounds, which contain a Cr‐L multiple bond, will be presented. Detail characterization of Cr‐nitrido, ‐oxo, ‐imido, ‐carbyne and ‐carbene bonds will be described. Metal squarates of late 3d transition elements have been investigated systematically. The valence shell charge concentration (VSCC) around metal ion will be demonstrated by the Laplacian topology, which provides the physical basis for the Lewis structure and valence shell electron pair repulsion (VSEPR). The metal‐metal bond is extremely important for metal clusters; the metal‐metal quintuple bond is rare and a detail analysis will be described. Electronic configurations of the 3d metal ion play important role in coordination chemistry; taking the advantage of the x‐ray absorption spectroscopy available in synchrotron radiation facility, the exact electronic configuration can be monitored. The great recent improvements on both experiment and theory have made the charge density analysis more accessible to even more complicated system, for example, the excited state or the meta‐stable states.

Improved Synthesis of 2,9-Dichloro-1,10-phenanthroline

1,10-Phenanthroline is a classic ligand that plays an important role in coordination chemistry and continues to be of considerable interest as a versatile starting material in organic, inorganic an...

The role of coordination chemistry in the development of innovative gallium-based bioceramics: the case of curcumin

Curcumin, an active ingredient in the traditional Ayurvedic herbal remedy [Curcuma longa L.], is nowadays also employed in western medicine for its pleiotropic activities, ranging from anticancer to its free radical scavenger ability. These features are related to curcumin's function as a metal chelator, especially being selective for hard Lewis acids, such as Ga3+ which has interesting pharmacological activities. We report the synthesis and characterization of bioactive gel and mesoporous Ga-containing phospho-silicate glasses loaded with curcumin, in which, for the first time, the design of novel drug delivery systems takes advantage of coordination chemistry. In particular, it was found that: (i) there is a direct correlation between the external surface area and the amount of loaded curcumin; (ii) the presence of Ga3+ species on the surface increases the quantity of drug molecules uploaded and slows down their release in the biological medium (SBF), hinting a coordination-like interaction between curcumin and the surface metal ions; (iii) curcumin molecules released in the SBF solution stabilize Ga3+ ions, avoiding their precipitation.

Interaction of cyanide with enzymes containing vanadium, manganese, non-heme iron, and zinc.

Since the early discovery of Prussian Blue, cyano transition metal complexes have played a fundamental role in coordination chemistry. They represent important compounds with fascinating chemical and physical properties which turn them into valuable tools for both chemists and biologists. HCN as a precursor in prebiotic chemistry has gained interest in view of its polymers being involved in the formation of amino acids, purines, and orotic acid, a biosynthetic precursor of uracil. Clearly, the rapid formation of adenine by aqueous polymerization of HCN is one of the key discoveries in these experiments. The cyanide anion is usually toxic for most aerobic organisms because of its inhibitory effects on respiratory enzymes, but as a substrate it is an important source of carbon and nitrogen for microorganisms, fungi and plants. Most interestingly, the cyanide anion is a ligand of important metal-dependent biomolecules, such as the hydrogenases and the cobalt site in vitamin B(12).