Formation Of Transition Metal Complexes Research Articles

Theoretical Analysis of Coordination Geometries in Transition Metal-Histidine Complexes Using Quantum Chemical Calculations.

A theoretical investigation utilizing density functional theory (DFT) calculations was conducted to explore the coordination complexes formed between histidine (His) ligands and various divalent transition metal ions (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+). Conformational exploration of the His ligand was initially performed to assess its stability upon coordination. Both 1:1 and 1:2 of metal-to-ligand complexes were scrutinized to elucidate their structural features and the relative stability of the complexes. This study examined the ability of His to act as a bidentate or tridentate coordinating ligand, along with the differences in coordination geometry when solvent effects were incorporated. The reduced density gradient (RDG) analysis and local electron attachment energy (LEAE) analysis were employed to elucidate the interaction planes and the nucleophilic and electrophilic properties. The electronic properties were analyzed through electrostatic potential (ESP) maps and natural population analysis (NPA) of atomic charge distributions. This computational study provides valuable insights into the diverse coordination modes of His and its interactions with divalent transition metal ions, contributing to a better understanding of the role of this amino acid ligand in the formation of transition metal complexes. The findings can aid in the design and construction of self-assembled structures involving His-metal coordination.

Trans-IV restriction: a new configuration for metal bis-cyclam complexes as potent CXCR4 inhibitors.

The chemokine receptor CXCR4 is implicated in multiple diseases including inflammatory disorders, cancer growth and metastasis, and HIV/AIDS. CXCR4 targeting has been evaluated in treating cancer metastasis and therapy resistance. Cyclam derivatives, most notably AMD3100 (Plerixafor™), are a common motif in small molecule CXCR4 antagonists. However, AMD3100 has not been shown to be effective in cancer treatment as an individual agent. Configurational restriction and transition metal complex formation increases receptor binding affinity and residence time. In the present study, we have synthesized novel trans-IV locked cyclam-based CXCR4 inhibitors, a previously unexploited configuration, and demonstrated their higher affinity for CXCR4 binding and CXCL12-mediated signaling inhibition compared to AMD3100. These results pave the way for even more potent CXCR4 inhibitors that may provide significant efficacy in cancer therapy.

Experimental and theoretical evidences for the formation of transition metal complexes with five coplanar metal-carbon σ bonds.

The σ bond is an important concept in chemistry, and the metal-carbon (M-C) σ bond in particular is a central feature in organometallic chemistry. Synthesis of stable complexes with five coplanar M-C σ bonds is challenging. Here, we describe the synthesis of two different types of stable complexes with five coplanar M-C σ bonds, and examine the stability of such complexes which use rigid conjugated carbon chains to chelate with the metal center. Density functional theory (DFT) calculations show that the M-C σ bonds in these complexes have primarily a covalent character. Besides the σ nature, there are also a π conjugation component among the metal center and carbons, which causes delocalization. This work expanded the coplanar M-C σ bonds to five.

In Situ Multi-Modal Approach for Electrode-Electrolyte Interfacial Chemistryand Electrode and Electrolyte Aging Behavior Studies

Increasing demands for cost-effective electric vehicles and electrochemical energy storage systems require advanced secondary batteries with higher energy density, longer lifetime, and enhanced safety. Increase of the battery operating voltage is one realistic strategy to extend the energy density, but it is accompanied by irreversible structural changes to the electrodes and parasitic reactions within an electrode-electrolyte interphase resulting in capacity fading and subsequent battery failure. Therefore, a fundamental understanding of underlying electrochemical mechanisms in the electrodes during battery cycling is critical for the development of next-generation secondary batteries.Based on our previous studies utilizing in situ surface-enhanced Raman spectroscopy to monitor the evolution of the Si-electrolyte interphase1 and in situ ATR-FTIR to investigate the voltage dependent electrolyte solution structure changes at the interface, transition metal redox chemistry, and cathode/electrolyte interfacial layer evolution,2 recently we updated the in situATR-FTIR with a newly designed ‘full-cell’ that enables us to analyze the interfacial reactions and interactions on the surfaces of both electrodes that directly influence battery performance, lifetime, and safety. Specifically, we focus on transition metal complex formation and its effect on solid-electrolyte interphase (SEI) formation and evolution on the anode due to transition metal dissolution and crosstalk of Mn-rich cathodes at high voltages (≥4.4 V).In addition, using our multi-modal characterization—a combination of in situ gas chromatography with flame ionization detection (GC-FID) and in situ ATR-FTIR—(electro)chemical degradation of the electrolyte is correlated with gas evolution in the battery. For example, GC-FID measures increasing amounts of ethylene gas until the end the first charging cycle of a LiNiO2//Graphite cell with Gen2 electrolyte (LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC), 3:7 wt.%). Concurrently, in situ ATR-FTIR shows decreasing concentration of EC solvent, as calculated from the FTIR intensity of EC vibrational absorption. Ethylene is a known by-product of ethylene carbonate electrochemical reduction and is produced during SEI formation.3 Quantifying multiphase reactions occurring during battery operation is critical to understanding and mitigating battery degradation pathways, and developing next-generation battery materials systems.

A quantum chemical model for a series of self-assembled nanocages: the origin of stability behind the coordination-driven formation of transition metal complexes up to [M12L24]24.

Herein, we present a systematic computational model to study the electronic states and free energies of a self-assembled multi-metal complex series. By combining the previously developed model Hamiltonian approach for transition-metal complexes and the generalized Born model, the thermodynamics, optimized geometries, and electronic states of the [Pd12L24]24+ nanocage are revealed, together with [PdnLm]2n+ complex series. The effective model Hamiltonian is a theoretical method to obtain the d-electron wavefunction and potential energy including interaction energy between the transition-metal and ligands. In the present improvement, the electronic state on each transition-metal center is focused as a building unit and solved under the whole electronic field of the assembling system. We realize a reliable and systematic treatment of multi-transition-metal complexes with different sizes and charges. Consequently, our model could reproduce binding energies of the [PdnLm]2n+ complex series quantitatively as compared to density functional theory (DFT). Regarding free energy, we revealed that the assembling solute becomes unstable due to the electrostatic interaction, and effects of the solvent and counter anions mainly compensated it. Optimized geometries were also analysed. The local square-planar coordination structures around the palladium centres were characterized in the complex series. The relationships between the entire symmetrical geometries and the local coordination structures are also discussed. Finally, electronic structures of the [Pd12L24]24+ nanocage were well characterized as a single-determinant, where only dx2-y2 is unoccupied due to the ligand-field effect. We also found that the solvent polarized the electronic states of the Pd ions, whereas the counter anion suppressed the polarization. The present method realizes size-independent reliable and rapid computations, and therefore can be expected to further application studies on self-assembly dynamics.

Pd(II) and Rh(III) Complexes with Isoquinoline Derivatives Induced Mitochondria-Mediated Apoptotic and Autophagic Cell Death in HepG2 Cells

Nonplatinum metal complexes of [Pd(L1)Cl2] (C1), [Rh(L1)Cl3(DMSO)] (C2), [Pd(L2)Cl2] (C3), and [Rh(L3)Cl3(DMSO)] (C4) with isoquinoline derivatives have been prepared and characterized. C1–C4 exhib...

Evaluation of Octaethyl-7,17-dioxobacteriochlorin as a Ligand for Transition Metals

The propensity of octaethyl-7,17-dioxobacteriochlorin toward the formation of transition metal complexes was evaluated. A variety of MII ions (M = Co, Ni, Cu, Zn, Pd, Ag, and Cd) and Fe(III) could be inserted using standard methodologies or, more often, using more forcing conditions. The stable products were spectroscopically characterized. The solid-state structures of the Ni(II), Cu(II), Pd(II), and Ag(II) complexes could also be determined by single crystal X-ray diffractometry, whereby the [7,17-dioxobacteriochlorinato] chromophore was found to be largely planar in all cases. The rate of Zn(II) insertion into octaethyl-7,17-dioxobacteriochlorin was less than half that into the corresponding 7-oxochlorin, which itself was about half the rate into the parent octaethylporphyrin. These rate differences reflect the relative decreased basicity of the β-oxo-substituted chromophores and possibly also their decreased conformational flexibility. We compare the basicity of the dioxobacteriochlorin to that of a range of related products of varying reduction state (porphyrin, chlorin, bacteriochlorin), an isomer, and the absence or presence of oxo-functionality, like oxochlorin, chlorin, oxobacteriochlorins, and bacteriochlorin, quantifying the effects of these macrocycle modifications. The work rationalizes earlier reports of the inability of tolyporphin A, a natural product possessing a 7,17-dioxobacteriochlorin chromophore, to form metal complexes and provide a more quantitative understanding of the degree of modulation that β-oxo groups have on the coordination properties of porphyrinoids.

2,2′-bipyridine-functionalized single-walled carbon nanotubes: The formation of transition metal complexes and their charge transfer effects

There is presently a great interest in the development of versatile nanohybrid systems that are based on the covalent functionalization of carbon nanotubes. Covalent functionalization of the single walled carbon nanotubes (SWCNTs) enhances their processability and functionality, allowing them to be further used in different applications. However, at the same time this leads to a disturbance of the nanotube π-network, thus reducing its intrinsically distinct physical and chemical properties of nanotubes. In the optimal situation, covalently functionalized SWCNT nanohybrid materials could be formed in a way where both of these wanted properties would exist; Good processability and the electronic properties nanotubes had before the functionalization. In this work, we describe the formation of nanohybrid materials by covalently grafting bipyridyl ligands directly onto the sidewall of the SWCNT. This is followed by addition of several different transition metals to form organometallic complexes. The systems we describe here does not utilize linker molecules between the ligands and the nanotubes allowing a better electronic communication between them. The covalent addition of the ligand onto the sidewall first causes p-type doping which is reversed to n-type doping after the addition of a transition metal. This technique offers a possibility to tune the electronic properties through reversing doping in charge transport between substrates and SWCNT. All new nanotube hybrids were fully characterized with the help of FTIR, XPS, Raman spectroscopy and HRTEM.

Sterically protected organophosphorus compounds of unusual structures

Abstract The character of bis(2,4,6-tri-tert-butylphenyl)diphosphene is described experimentally and theoretically. The diphosphene is stabilized by steric protection and the structure can be characterized by spectroscopic as well as crystallographic analyses. Theoretical calculation on the diphosphene strongly suggests that the P=P bond is an isolated double bond and that the P–C bonds are single covalent bond. The reactivity has been investigated including photolysis, oxidation, sulfurization, selenation, transition-metal complex formation, and carbene addition. Plausible mechanistic scheme for the reaction of the diphosphene with 3,4,5,6-tetrachlorocyclohexa-3,5-diene-1,2-dione (or tetrachloro-o-benzoquinone) to a pentavalent spiro product is discussed based on the product analysis.

The role of inner- and outer-sphere ligands in pivalate and cymantrenecarboxylate complexes of transition metals

The formation of transition metal complexes with pivalate and cymantrenecarboxylate ligands in the presence of axial cyclopentadienyl and α-substituted pyridine ligands is discussed. The latter present steric hindrances due to repulsion from the O atoms of the carboxylate bridges. Particular emphasis is placed on the role of outer-sphere ammonium cations: their hydrogen bonding to fluoride bridges limits the growth of cyclic chromium(III) complexes with the pivalate and fluoride ligands that possess the properties of molecular magnets.

ChemInform Abstract: Mechanistic Information on Some Inorganic and Bioinorganic Reactions from Volume Profile Analysis

AbstractReview: 166 refs.

Effective Modulation of DNA Duplex Stability by Reversible Transition Metal Complex Formation in the Minor Groove

Herein we describe the reversible changing of DNA duplex thermal stability by exploiting transition metal complexation phenomena. A terpyridine ligand was conjugated to the N2'-atoms of 2'-amino-2'-deoxyuridine and its locked counterpart 2'-amino-LNA, and these metal-complexing monomers were incorporated into oligodeoxyribonucleotides. Upon addition of varying amounts of transition metal ions, the thermal stability of DNA duplexes containing these terpyridine-functionalized units in different constitutions was affected to different degrees (DeltaTm values = -15.5 to +49.0 degrees C, relative to the unmodified duplex). The most pronounced effects were observed when two complexing monomers were positioned in opposite strands. Addition of 1 equiv of Ni2+ to such a system induced extraordinary duplex stabilization. Molecular modeling studies suggest, as an explanation for this phenomenon, formation of nickel-mediated interstrand linkages in the minor groove. Addition of an excess of metal ions resulted in largely decreased Tm values. Alternating addition of metal ions and EDTA demonstrated reversibility of metal ion-induced changes in hybridization strength, proving that the described approach provides an efficient method for duplex stability modulation.

Ligand‐Template Directed Assembly: An Efficient Approach for the Supramolecular Encapsulation of Transition‐Metal Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Spectroscopic characterization of coordination complexes based on dichlorocopper(II) and poly(4-vinylpyridine): Application in catalysis

The formation of transition metal complexes between dichlorocopper(II) and a poly(4-vinylpyridine)/divinylbenzene(2%) polymeric matrix is described in this contribution. The nitrogen atom of the pyridine groups of the organic polymer is coordinatively bonded to the Cu center as suggested by X-ray photoelectron spectroscopy (XPS), UV–vis/diffuse reflectance (UV–vis/DR), electron paramagnetic resonance (EPR), differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) techniques. The immobilized catalyst was also characterized by DTA-TGA analysis and the morphology and elemental analysis of this copper/poly(4-vinylpyridine) complex were studied by the scanning electron microscopy/energy dispersive X-ray (SEM/EDX) technique. This material catalyzes the water gas shift reaction as well as the reduction of nitrobenzene to aniline and azobenzene.

P−B Adducts of 3,4‐Dimethyl‐1‐phosphaferrocene with Bromoboranes

AbstractThe crystalline adducts FcP−BBr3 (2) and FcP−BBr2Fc (3), which are very rare examples of P‐bonded complexes between phosphaferrocene and a main‐group metal atom, were obtained by the reaction of 3,4‐dimethyl‐1‐phosphaferrocene (FcP) with BBr3 and FcBBr2 (Fc: ferrocenyl). According to X‐ray crystallography, the Fe−P bond length in 2 is 0.085 Å shorter than in the parent phosphaferrocene. All structural changes resulting from P−B acid−base pairing follow the same qualitative trend, but are significantly larger than those occurring from the formation of transition metal complexes of phosphaferrocene. In contrast to 2, NMR spectroscopy reveals 3 to be almost completely dissociated in CDCl3 solution at room temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Neutral and anionic transition metal complexes supported by decafluorodiphenylamido ligands: X-ray crystal structures of {Na(THF) 2}{Ti[N(C 6F 5) 2] 4}, {K(η 6-C 6H 5Me) 2}{ZrCl 2[N(C 6F 5) 2] 3}, K{VCl[N(C 6F 5) 2] 3}, Fe[N(C 6F 5) 2] 2(THF) 2 and Co[N(C 6F 5) 2] 2(py) 2

Reaction of MN(C 6F 5) 2 (M=Na, K) with transition metal halides results in the formation of transition metal complexes incorporating decafluorodiphenylamido ligands. TiCl 3(THF) 3 reacts with 3 equiv. NaN(C 6F 5) 2 to yield the ‘metallate’ complex {Na(THF) 2}{Ti[N(C 6F 5) 2] 4} ( 1). Single crystal X-ray diffraction studies reveal a tetrahedral titanium center complexed by four decafluorodiphenylamido ligands; while two THF ligands and four fluorine atoms coordinate the sodium cation. ZrCl 4 reacts with 3 equiv. KN(C 6F 5) 2 to give {K(η 6-C 7H 8) 2}{ZrCl 2[N(C 6F 5) 2] 3} ( 2). The 19F NMR spectrum of 2 reveals phenyl resonances in a 2:1 ratio, consistent with a trigonal bipyramidal structure being maintained in solution. The crystal structure of 2 reveals a pseudo-octahedral structure, with the sixth-coordination site being completed by a weak ZrF interaction with a pentafluorophenyl group of an amido ligand. The potassium counterion interacts in an η 6 fashion with two toluene rings in addition to a fluorine atom arising from one of the pentafluorophenyl groups. The reaction of VCl 3 with 3 equiv. KN(C 6F 5) 2 generates the ‘metallate’ complex K{VCl[N(C 6F 5) 2] 3} ( 3); the solid state structure of 3 reveals a distorted trigonal bipyramid with the coordination sphere being completed by a weak V–F interaction with the ortho-fluorine of one of the fluorophenyl amido ligands. Exposure of FeCl 3 to 3 equiv. KN(C 6F 5) 2 results in reduction of the metal center and the formation of the Fe(II) species Fe[N(C 6F 5) 2] 2(THF) 2 ( 4). Compound 4 is tetrahedral in the solid state with none of the weak MF contacts observed for 1, 2, 3 and 5. CoI 2 reacts with 2 equiv. NaN(C 6F 5) 2 in the presence of pyridine to produce the expected product Co[N(C 6F 5) 2] 2(py) 2 ( 5); X-ray crystallography reveals a five-coordinate species in the solid state which is additionally stabilized by a weak CoF interaction.

Solvent-free mechanochemical synthesis of two Pt complexes: cis-(Ph3P)2PtCl2 and cis-(Ph3P)2PtCO3.

Cis-(Ph3P)2PtCl2 and cis-(Ph3P)2PtCO3 were prepared mechanochemically from solid reactants in the absence of a solvent; cis-(Ph3P)2PtCl2 was obtained in 98% yield after ball-milling of polycrystalline PtCl2 and Ph3P; the mechanically induced solid-state reaction of cis-(Ph3P)2PtCl2 with an excess of anhydrous K2CO3 produced cis-(Ph3P)2PtCO3 in 70% yield; the formation of transition metal complexes as a result of mechanochemical solvent-free reactions has been confirmed by means of solid-state 31P MAS NMR spectroscopy, X-ray powder diffraction and differential thermal analysis.

In situ synthesis of the first C 7 cumulene (Fc) 2CCCCCCC(Fc) 2 via deprotonation of its conjugate acid [(Fc) 2C 7H(Fc) 2] +BF 4− (Fc=ferrocenyl)

Copper-mediated cross-coupling of diferrocenyl propargylic and homopropargylic C 3 and C 4 building blocks yields an α,ω-dimethoxy-tetraferrocenyl C 7 cumulene precursor together with a C 8 homo-coupled byproduct. Subsequent acid-promoted twofold elimination of methanol gives access to tetraferrocenylheptapentaenylium tetrafluoroborate which can be deprotonated by non-nucleophilic strong bases to cumulene (Fc) 2C 7(Fc) 2. Although this compound can be handled in solution only, UV–vis spectroscopic evidence and trapping experiments (hydrolysis and transition metal complex formation) support the existence of this first compound containing seven cumulated carbons.

Schrock type transition metal complex formation of push–pull substituted phosphanyl-carbenes, a quantum chemical investigation by density-functional methods

The formation of coordination compounds of phosphanyl carbenes with a transition metal in a high oxidation state (Schrock type) is evaluated by density functional theory. In the Schrock type carbene complexes the transition metalcarbon bond possesses a multiple bond character. If one of the ligands at the carbene center possesses a leaving ability, e.g. as the diaminophosphenium unit, a facile distortion to a new type of an anionic metallaalkylidene donor-acceptor complex with a diaminophosphenium cation is predicted.

Synthesis and Characterization of Bivalent Copper and Palladium Complexes of Tetraaza Macrocycles Bearing Polyamide Groups

The template condensation of methyl acetoacetate and ethyl acetoacetate with 1, 2-diaminoethane in the presence of copper and palladium salts resulted in the formation of transition metal complexes of an interesting 14-membered macrocyclic ligand, N4L. The geometry and the mode of bonding of the resulting coloured complexes have been inferred from IR, 1H NMR, mass, EPR and electronic spectral studies. On the basis of magnetic and molar conductance data an octahedral geometry around the copper ion is suggested for the [Cu(N4L)(NO3)2] complex and a square planar geometry is proposed in the case of [Pd(N4(L)]Cl2 complex.