3d Transition Metal Complexes Research Articles

Correlation between the M←OH2 Bond Force Constants, Energies, and Lengths and Magnetic Moments of the Metal Atoms in Isostructural Nitrilotris(methylenephosphonic) Complexes [MII(H2O)3μ-NH(CH2PO3H)3] (MII = Cr-Zn)

The isostructural 3d transition metal complexes [MII(H2O)3μ-NH(CH2PO3H)3] (MII = Cr-Zn) were studied by X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. In order to gain more in-depth knowledge about the chemical bonds in coordination compounds, correlation analysis was carried out between the force constants and energies of the M←OH2 coordination bonds and the magnetic moments of transition metal atoms. The correlation of the force constants of the M←OH2 bonds with the M-O(w) interatomic distances was in line with the known empirical Badger’s rule. The double linear regression between the bond energy and reciprocal of M-O(w) interatomic distances and atomic magnetic moments shows a close relationship between the M←OH2 bond energy and the spin magnetic moment of 3d-metal atoms. The results account for the stability of Fe-containing heterometallic polymeric NTP complexes and high efficiency of NTP complexes as corrosion inhibitors for iron alloys in aqueous media.

Complexation of free-base and 3d transition metal(II) phthalocyanines with endohedral fullerene Sc3N@C80

Abstract We performed systematic theoretical analysis of noncovalent interactions of free-base phthalocyanine H2Pc and its 3d transition metal(II) complexes (MnPc, singlet and triplet FePc, CoPc, NiPc, CuPc and ZnPc) with endohedral fullerene Sc3N@Ih–C80. In terms of the optimized geometries and variability of bonding pattern, electrostatic potential plots, frontier orbital features and spin density distribution, the calculated characteristics of noncovalent MPc + Sc3N@C80 conjugates are generally more similar to the corresponding properties of MPc + C60 than of MPc + C80 dyads studied previously. However, the magnitude of binding strength for MPc + Sc3N@C80 dyads matches more closely the interaction strength in MPc + C80 series than the one for MPc + C60 dyads.

Synthesis and characterization of d10 transition metal complexes in bulk and nano scales: DNA binding, molecular docking and anticancer activity against MCF-7 cell line

Three d10 transition metal complexes including [Zn (tptz) Cl2] (1), [Cd(tptz)Cl2] (2) and [Hg(tptz)I2] (3) [tptz = 2,4,6-Tri(2-pyridyl)-s-triazine] have been synthesized and characterized by elemental, IR, 1HNMR and X-ray single-crystal analysis.The DNA-binding properties of the complexes (1–3) in bulk and nano-size were investigated by spectrophotometric method and viscosity measurements. Experimental results indicated that each complex can effectively intercalate into DNA. Binding constants of all complexes in nano and bulk scales with mdr1 gene were calculated using UV spectroscopy. Also, molecular docking studies showed that ligand and complexes (1–3) interact with DNA through its minor groove with hydrogen bonding, vander Waal’s and hydrophobic interactions. In vitro cytotoxic activities of the complexes in bulk and nano forms against MCF-7 cell line were evaluated by MTT method. IC50 value ranges are from 2.2 ± 0.1 to 28.6 ± 0.6 μM. Totally, these findings suggested that our synthesized complexes in both nano and balk forms can be introduced as an effective anticancer agents.

Probing through-space and through-bond magnetic exchange couplings in a new benzotriazinyl radical and its metal complexes.

The synthesis and characterization of a new chelating benzotriazinyl radical (Rad2) are described. Crystallographic studies coupled with SQUID magnetometry on Rad2 reveal the presence of discrete radical pairs which are antiferromagnetically coupled. The reaction of Rad2 with the 3d transition metal complexes M(hfac)2·xH2O (hfac- = hexafluoroacetylacetonate) led to mononuclear metal complexes of general formula M(hfac)2(Rad2) [M = Zn(ii) (1); Ni(ii) (2) and Co(ii) (3)] whose structures have been determined by single crystal X-ray diffraction. Compounds 1-3 are isostructural and crystallize in the monoclinic space group P21/n with two molecules in the asymmetric unit. In the case of the Zn(ii) complex (1) through-space intermolecular radicalradical antiferromagnetic exchange interactions viaπ*π* contacts are observed, whereas strong intramolecular through-bond metal-radical ferromagnetic interactions [J = +59.3(9) cm-1] are observed for the Ni(ii) complex (2). For the Co(ii) complex (3), computational and magnetic studies reveal substantial zero field splitting and ferromagnetic metal-radical interactions.

2,2‐Bis(5‐tetrazolyl)propane as Ligand in Energetic 3d Transition Metal Complexes

This contribution covers the preparation and characterization of 2,2‐bis(5‐tetrazolyl)propane (5‐DTP) (1). The bridged bitetrazole is used as a neutral nitrogen‐rich ligand in 3d transition metal(II) based complexes for the first time and can be synthesized via [2+3] cycloaddition from sodium azide and dimethylmalononitrile. The combination with different anions (e.g., perchlorate, nitrate, sulfate, and chloride) yields materials with widely varying physicochemical properties. The obtained coordination compounds were characterized using low‐temperature single‐crystal X‐ray diffraction (except 14), IR spectroscopy, elemental analysis, and DTA (except 16). The sensitivities toward external stimuli (impact and friction) were determined according to the Bundesamt für Materialforschung und ‐prüfung (BAM) standard methods together with its sensitivities against electrostatic discharge (except 16). Complexes 10 and 14 were characterized in laser ignition experiments. For determination of the compounds' deflagration to detonation transition (DDT) capability, hot plate and hot needle tests were performed for the zinc(II) and copper(II) perchlorate complexes.

Approach to the Mechanism of Hydrogen Evolution Electrocatalyzed by a Model Co Clathrochelate: A Theoretical Study by Density Functional Theory.

The hydrogen evolution reaction (HER) has attracted much attention within the scientific community because of increasing demands of modern society for clean and renewable energy sources. Molecular complexes of 3d-transition metals, such as cobalt, hold potential to replace platinum for the HER in acidic media. Among these, cage complexes such as tris-glyoximate metal clathrochelates, have demonstrated promising catalytic properties towards the HER. However, it is not clear whether the catalytic activity of this molecule stems from metal-centered activation of H+ , due to a low oxidation state of the metal stabilized by the surrounding organic cage, or if it is the organic cage playing a further cooperative role in bringing protons together. Herein, we report on a density functional theory study of two possible mechanisms for the HER catalyzed by a model Co clathrochelate. To assess the putative ligand involvement in the mechanism, several combinations of single and double protonation sites were investigated. The structural and energetic analysis of relevant intermediates suggests that the electrocatalytic mechanism is not based on the cooperation between the ligand and the metal. Instead, it is mainly due to the activation of H+ by the Co metallocenter. Our calculations further suggest that the last step in the mechanism is a proton coupled electron transfer step.

Computational Study of Methane C-H Activation by Diiminopyridine Nitride/Nitridyl Complexes of 3d Transition Metals and Main-Group Elements.

The C-H bond activation of methane using Ph,MePDI-M≡N [Ph,MePDI = 2,6-(PhN═CMe)2C5H3N] (M = V, Mn, Fe, Co, Ni, Al, or P) has been studied via three reaction pathways: [2σ + 2π] addition, hydrogen atom abstraction (HAA), and direct insertion. The activating ligand is a nitride/nitridyl (N), with diiminopyridine (PDI) as the supporting ligand. Calculations show reasonable C-H activation barriers for Co, Ni, Al, and P Ph,MePDI nitrides, complexes that favor an HAA pathway. Electrophilic Ph,MePDI nitride complexes of the earlier metals with a nucleophilic actor ligand-V, Mn, Fe-follow a [2σ + 2π] addition pathway for methane activation. Free energy barriers for methyl migration, Ph,MePDI-M(CH3)═NH → Ph,MePDI-M-N(H)CH3, are also interesting in the context of alkane functionalization; discriminating factors in this mechanistic step include the strengths of the σ-bond and metal-actor ligand π-bond that are broken and the electrophilicity of the actor ligand to which methyl migrates.

Methylsemicarbazide as a Ligand in Late 3d Transition Metal Complexes.

Most ignition and initiation systems nowadays still contain poisonous chemicals such as lead styphnate and lead azide but also chromates and other compounds of high concern. Therefore, methylsemicarbazide (1, MSC), which can be prepared in a one-step reaction and in an extraordinary high yield of 95 %, has been evaluated as ligand in energetic coordination compounds. For the first time 25 new transition metal complexes (Mn2+ , Ni2+ , Co2+ , Cu2+ , and Zn2+ ) using methylsemicarbazide (1) as the ligand were prepared and comprehensively analyzed by, for example, XRD, IR, EA, UV/Vis and DSC/DTA/TGA. Many show a strong energetic character, which can be tuned by using different anions such as Cl- , SO42- , NO3- , ClO4- , picrate or styphnate. Selected compounds were additionally evaluated as lead-free primary explosives in initiation tests (nitropenta filled detonators) and in laser ignition systems. Especially compound 7 showed very promising results during these tests and could be a potential candidate for future applications.

Study of distorted octahedral structure in 3d transition metal complexes using XAFS

Distortion in octahedral structure of 3d transition metal complexes (Mn, Fe, Co, Ni, Cu, Zn) has been studied using XAFS showing divergent nature of Cu complex. EXAFS analysis showed elongated metal-oxygen bonds for Cu complex leading to more distorted structure. Derivative XANES spectrum at Cu K-edge exhibits splitting of main edge which is correlated to elongated Cu-O bond length. Using these coordination geometry around metal centers, theoretical XANES spectra have been generated and features observed have been correlated to the corresponding metals p-DOS. It has been shown that distorted octahedral field in Cu complex is responsible for splitting of p-DOS.

New metal complex systems as electrode active components of ion selective electrode membranes

New donor-acceptor 3d-transition metal complexes were synthesized and the cobalt and nickel complexes were studied by X-ray diffraction; CIF files CCDC no. 1516693 (III(Ni)) and 1516694 (III(Co)). The crystal structure details of the reactants were discussed. The proposed compounds were tested as the active components of ion selective electrode membranes for determination of thiocyanate ions. The selectivity of the SCN-SE with metal complex-based membranes depends on the ligand structure and the central metal ion type. The proposed electrode is suitable for determination of thiocyanate ions in the presence of sulfate, chloride, nitrate, nitrite, bromide, and iodide ions.

Characterization of Rh:SrTiO3 photoelectrodes surface-modified with a cobalt clathrochelate and their application to the hydrogen evolution reaction

Water is a promising source of clean hydrogen. Besides water electrolysis, the direct photoelectrochemical dissociation of water that combines light absorption and electrochemical water splitting into a single device is actively investigated by the scientific community. We report results on the p-type rhodium-doped strontium titanate (Rh:SrTiO3) surface-modified by adsorption of a 3d-transition metal complex which is known to be a good catalyst of the hydrogen evolution reaction (HER) from water. The tris-dioximate cobalt hexachloroclathrochelate with an encapsulated cobalt(II) ion was selected as a surface HER co-catalyst for this study. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The kinetics of the photoelectrochemical water dissociation was studied using the open circuit photovoltage decay (OCPD) and photoelectrochemical impedance spectroscopy (PEIS) methods. Under open circuit conditions, the cobalt cage complex did not substantially affect the HER kinetics compared to the bare doped Rh:SrTiO3 semiconductor. But when a reverse bias was applied, a significant difference caused by presence of the clathrochelate was observed. The rate constants of the charge transfer and the recombination processes were both affected, leading to the conclusion that the macrobicyclic cobalt-encapsulated species not only increased the rate of charge transfer, but also played a role as recombination centers for photoexcited minority carriers. The space charge capacitance was determined under the inversion conditions. Only under strong reverse bias it was found that, whereas bulk Rh:SrTiO3 has a p-type conductivity, the surface of both bare Rh:SrTiO3 and the cobalt clathrochelate-covered Rh:SrTiO3 show the properties of a n-type semiconductor.

Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2'-bipyridine)2(CN)2

We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy)2(CN)2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy)2(CN)2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy)2(CN)2] complement prior measurement performed on [Fe(bpy)3]2+ and [Fe(bpy)(CN)4]2− in dimethylsulfoxide solution and help complete the chemical series [Fe(bpy)N(CN)6–2N]2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes.

Syntheses, Structures, and Catalytic Properties of Five Isomorphous 3D Transition Metal Complexes Derived from Formate

Five isomorphous 3D complexes of formates, namely, {Cu(HCOO)2·4H2O} n (1), {Co(HCOO)2·2H2O} n (2), {Mn(HCOO)2·2H2O} n (3), {Co(HCOO)2·DMF·H2O} n (4), and {Mn2(HCOO)6·0.5[HN(CH3)2]} n (5), were synthesized and characterized by microanalysis. The catalytic activities of these complexes for the oxidation of phenol by H2O2 to catechol (CAT) and hydroquinone (HQ) were investigated. Complex 1 showed the best performance by exhibiting a high conversion rate of 68.02% and a high selectivity for CAT with a maximum CAT/HQ ratio of 2.74.

Frontispiece: Iron(II), Cobalt(II), Nickel(II), and Zinc(II) Silylene Complexes: Reaction of the Silylene [iPrNC(NiPr2)NiPr]2Si with FeBr2, CoBr2, NiBr2⋅MeOCH2CH2OMe, ZnCl2, and ZnBr2

Donor-Stabilized Silylenes The chemistry of donor-stabilized silylenes has developed into one of the most actively studied research areas in molecular silicon chemistry. In their Full Paper on page 296 ff., R. Tacke et al report on the synthesis and characterization of novel transition-metal silylene complexes of FeBr2, CoBr2, NiBr2, ZnBr2, and ZnCl2 with the bis(guanidinato)silicon(II) complex [iPrNC(NiPr2)NiPr]2Si. These compounds represent very rare examples of carbonyl-free silylene complexes of 3d transition metals in the formal oxidation state +2.

Syntheses and Structure Investigations of 3d Transition Metal Complexes with a Flexible N4O2-Donor Hexadentate Schiff-Base Ligand

The syntheses and structure investigations of four new 3d transition metal complexes (1–4) with a flexible N4O2-donor hexadentate Schiff-base ligand are described; three complexes (1, 2, and 4) of FeIII, CoIII, and CuII metal ions have been investigated by UV-vis, FT-IR, high-resolution mass spectrometry (HR-MS), and scanning electron microscopy–electron dispersive spectroscopy, as well as single crystal X-ray diffraction. The X-ray structure of NiII complex 3 is also reported. The molecular structures of the complexes (1–3) demonstrate distorted octahedral coordination geometry, each exhibiting 1 : 1 (M : L) ratios and the CuII complex 4 shows a trinuclear structure with a CuII : L ratio of 3 : 2 in the solid state, which has been proven by X-ray diffraction. On the other hand, a mononuclear species of the CuII complex is formed in solution, which has been identified by electrospray ionization HR-MS.

First-principles analysis of X-ray magnetic circular dichroism for transition metal complex oxides

X-ray magnetic circular dichroism (XMCD) is widely used for the characterization of magnetism of materials. However, information from XMCD related to the atomic, electronic, and magnetic structures is not fully utilized due to the lack of reliable theoretical tools for spectral analysis. In this work, the first-principles configuration interaction (CI) calculations for X-ray absorption spectra developed by the author were extended for the calculation of XMCD, where the Zeeman energy was taken into the Hamiltonian of the CI to mimic magnetic polarization in the solid state. This technique was applied to interpret the L2,3 XMCD from 3d transition metal complex oxides, such as NiFe2O4 and FeTiO3. The experimental XMCD spectra were quantitatively reproduced using this method. The oxidation states as well as the magnetic ordering between transition metal ions on crystallographically different sites in NiFe2O4 can be unambiguously determined. A first-principles analysis of XMCD in FeTiO3 revealed the presence of Fe3+ and Ti3+ ions, which indicates that the charge transfer from Fe to Ti ions occurs. The origin of magnetic polarization of Ti ions in FeTiO3 was also discussed.

Theoretical Study of Two Possible Side Reactions for Reductive Functionalization of 3d Metal–Methyl Complexes by Hydroxide Ion: Deprotonation and Metal–Methyl Bond Dissociation

A DFT study of two possible competitive reactions for reductive functionalization (RF) of metal–methyl complexes ([MII(diimine)2(CH3)(Cl)], MII = VII through CuII) was performed to understand the factors that lower the selectivity of C–O bond forming reactions. One of the possible side reactions is deprotonation of the methyl group, which leads to formation of a methylene complex and water. The other possible side reaction is metal–methyl bond dissociation, which was assessed by calculating the bond dissociation free energies of M–CH3 bonds. Deprotonation was found to be competitive kinetically for most of the first-row transition-metal–methyl complexes (except for CrII, MnII, and CuII) but less favorable thermodynamically in comparison to reductive functionalization for all of the studied first-row transition metals. Metal–carbon bond dissociation was found to be less favorable than the RF reactions for most 3d transition-metal complexes studied. Therefore, this study suggests that Earth-abundant catalys...

3d transition metal complexes with a julolidine–quinoline based ligand: structures, spectroscopy and optical properties

Five new complexes of a julolidine–quinoline based ligand with 3d transition metals have been synthesised and structurally characterised.

Control of Metal Arrays Based on Heterometallics Masquerading in Heterochiral Aggregations of Chiral Clothespin‐Shaped Complexes

Heterometal arrays in molecular aggregations were obtained by the spontaneous and ultrasound-induced gelation of organic liquids containing the chiral, clothespin-shaped trans-bis(salicylaldiminato) d8 transition-metal complexes 1. Heterometallic mixtures of complexes 1 a (Pd) and 1 b (Pt) underwent strict heterochiral aggregation entirely due to the organic shell structure of the clothespin shape, with no effect of the metal cores. This phenomenon provides an unprecedented means of generating highly controlled heterometallic arrangements such as alternating sequences [(+)-Pd(-)-Pt(+)-Pd(-)-Pt⋅⋅⋅] as well as a variety of single metal-enriched arrays (e.g., [(+)-Pt(-)-Pd(+)-Pd(-)-Pd(+)-Pd(-)-Pd⋅⋅⋅] and [(+)-Pd(-)-Pt(+)-Pt(-)-Pt(+)-Pt(-)-Pt⋅⋅⋅]) upon the introduction of an optically active masquerading unit with a different metal core in the heterochiral single-metal sequence. The present method can be applied to form various new aggregates with optically active Pd and Pt units, to allow 1) tuning of the gelation ultrasound sensitivity based on the different hearing abilities of the metal units; 2) aggregation-induced chirality transfer between heterometallic species; and 3) aggregation-induced chirality enhancement. A mechanistic rationale is proposed for these molecular aggregations based on the molecular structures of the units and the morphologies of the aggregates.

Light-Emitting Self-Assembled Materials Based on d(8) and d(10) Transition Metal Complexes.

Light-Emitting Self-Assembled Materials Based on d(8) and d(10) Transition Metal Complexes.