Transition Metal Coordination Complexes Research Articles

Conformation-dependent phosphorescence emission of individual mononuclear ruthenium-(ii)-bis-terpyridine complexes.

The potential of supramolecular transition metal coordination complexes to form robust, long-living, radiative charge transfer states makes this class of triplet state emitters ideal candidates for application as photosensitizes or in photonic devices. Antenna-enhanced phosphorescence experiments on single Ru2+-bis-terpyridine complexes incorporated into a thin PMMA film show that phosphorescence emission spectra can exhibit shifts depending on the local environment [J. F. Herrmann, P. S. Popp, A. Winter, U. S. Schubert and C. Höppener, ACS Photonics, 2016, 3, 1897-1906]. Here, we demonstrate that the environmentally altered spectral properties of individual dual-luminescent Ru2+-bis-terpyridine complexes in PMMA and acetonitrile can be reproduced by DFT-based vibrationally resolved Franck-Condon spectra, if the phosphorescent emission of different molecular conformations is taken into account. Furthermore, we demonstrate that the triplet emission of these complexes occurs from a metal-to-ligand charge transfer (MLCT) state.

Coordination Compounds with Photochromic Ligands: Ready Tunability and Visible Light-Sensitized Photochromism.

Photochromic compounds are well-known for their promising applications in many areas. In this context, many different photochromic families have been developed. As the early study of these photochromic compounds was mainly focused on the organic system, their photochromic reactivity was mainly derived from the singlet excited state. We hypothesized that the incorporation of the photochromic ligand to the transition metal complex and coordination complex systems would not only render the triplet state of the organic photochromic system more readily accessible due to the large spin-orbit coupling of the heavy metal center but also would lead to ready extension of the excitation wavelength to less destructive longer wavelength low-energy excitation. On the other hand, the long-lived triplet excited states of the metal complexes are also suitable for energy or electron transfer processes, which should lead to new photochromic behavior and photoswitchable functional properties. Through the incorporation of the stilbene-, azo-, spirooxazine-, and dithienylethene-containing ligands to transition metal complex systems with heavy metal centers and suitable excited states, triplet state photosensitized photochromism has been achieved. With the triplet state photosensitization, the photochromism of these compounds could be extended from the high energy UV region to the visible region. In the development of dithienylethene-containing ligands, we have adopted an alternative strategy, which involves the incorporation of nitrogen and sulfur heterocycles that directly form part of the dithienylethene framework as ligands to exert a much stronger perturbation and influence on the excited state properties of the photochromic unit by the metal center. On the basis of the new design, wide ranges of dithienylethene-containing ligands, including phenanthrolines, 2-pyridylimidazoles, N-pyridylimidazol-2-ylidenes, cyclometalating thienylpyridines, β-diketonates, and β-ketoiminates have been designed and incorporated into various coordination systems. Apart from the photosensitization, tuning of the closed form absorption and photochromic behavior based on the perturbation of the metal center, coordination-assisted planarization, modification of the ancillary ligands and introduction of various electronic excited states derived from the coordination system have been successfully demonstrated. This strategy can be used for developing NIR photochromic dithienylethenes. With the above effects observed upon the coordination to different transition metal centers and central atoms, this strategy offers a simple and effective way for the modification of the photochromic characteristics. Moreover, the emission and other functional properties of the coordination systems could also be photoswitched by the photochromic reactions.

Syntheses, crystal structures and photophysical properties of d10 transition-metal (Ag+, Cu+, Cd2+ and Zn2+) coordination complexes based on a thiophene-containing heterocyclic thioamide

Four d10 transition-metal coordination complexes 1–4 (1: [Ag2(TPT)2(TPTH)2]; 2: [Cu6(TPT)6]·2DMF; 3: [Cd(TPT)2(TPTH)]·CH3CH2OH, 4: [Zn(TPT)2]n) have been constructed from a newly designed heterocyclic thioamide ligand, TPTH (TPTH = 4-(thiophen-2-yl)-pyrimidine-2-thiol). All complexes have been structurally elucidated by single crystal X-ray diffraction analyses. Except for 4, which shows a one-dimensional (1-D) chain structure, 1–3 are all discrete coordination complexes featuring dinuclear, hexanuclear and mononuclear entities, respectively. Their photophysical properties have been evaluated in the solid state at room temperature by UV–vis diffuse reflectance and luminescence spectra. Among them, 2 exhibits a strong red luminescence (λem = 699 nm) with a remarkable red-shift of the maximum emission compared to that of the TPTH ligand (λem = 536 nm). The red emission observed with 2 is ascribed to a LMCT (ligand-to-metal charge transfer) transition which agrees with the DFT calculations.

Seven-coordinated chelate [Cd(SCZ)3·H2O](HTNR)2(H2O)2: Synthesis, crystal structure and energetic properties

ABSTRACTTo deepen the study on heptacoordinate transition metal coordination complexes, a novel seven-coordinated coordination compound [Cd(SCZ)3·H2O](HTNR)2(H2O)2 (1, SCZ = semicarbazide, H2TNR = styphnic acid) was synthesized and characterized by elemental analysis and FTIR spectroscopy. Single-crystal X-ray diffraction analysis revealed that 1 crystallizes in the triclinic space group P-1. The thermal decomposition mechanism of 1 was studied by differential scanning calorimetry (DSC). The non-isothermal kinetics parameters were calculated by the Kissinger's method and Ozawa-Doyle's method, respectively. Sensitivity tests revealed that 1 is insensitive to mechanical stimuli. The heat of combustion was measured by oxygen bomb calorimetry and the enthalpy of formation was calculated.

Transition metal complexes of 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol: Synthesis, characterization, crystal structures and anti-tuberculosis assay with docking studies

Transition metal coordination complexes of Co(II), Ni(II), Cu(II) and Zn(II) with a newly designed ligand, 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol have been synthesized and characterized using various spectro-analytical techniques. The molecular structures of Co(II), Cu(II) and Zn(II) complexes are determined by single-crystal X-ray diffraction method. The metal to ligand stoichiometry has been found to be 1:2 in the case of Cobalt(II), Nickel(II) and Zinc(II) whereas 1:1 in the case of Copper(II) complex. The newly synthesized ligand and complexes have been assessed for their growth inhibiting potencies against H37Rv strain of Mycobacterium tuberculosis. The copper and cobalt complexes have emerged to be potent in vitro growth inhibitors of H37Rv. All the complexes are inhibiting the growth of other tested common microbial flora to a significantly lesser extent, making them selective towards H37Rv in the preliminary analysis. The consensus scores obtained by the docking studies of the molecules to the target protein enoyl acyl carrier protein reductase of M. tuberculosis H37Rv are in good agreement with the obtained MIC values.

The synthesis and structural characterization of transition metal coordination complexes of coumarilic acid

The coumarilate (coum−) complexes of CoII(1), NiII(2) CuII(3) and ZnII(4) were synthesized and characterized by elemental analysis, magnetic susceptibility, solid-state UV–Vis, FTIR spectra, thermoanalytical TG–DTG/DTA and single-crystal X-ray diffraction methods. It was found that all of the complex structures have 2 mol (coum−) ligand bonded as monoanionic monodentate in the structures of 1 and 2 while they were coordinated to metal cations as monoanionic bidentate in the complexes 3 and 4. There was not any hydrate water in the metal complexes. The complexes of 1 and 2 have four moles of aqua ligand, and the other complexes have two moles. Thermal decomposition of each complex starts with dehydration, and then the decomposition of organic parts goes. The thermal dehydration of the complexes takes place in one (for the compounds of 2, 3, 4) or two (for the compound 1) steps. The decomposition mechanism and the thermal stability of the complexes under investigation were determined on the basis of their structures. Metal oxides were obtained as the final decomposition product.

Comparison of thallium(I) complexes with mesityl-substituted tris(pyrazolyl)hydroborate ligands, [Tl{HB(3-Ms-5-Mepz)3}] and [Tl{HB(3-Ms-5-Mepz)2(3-Me-5-Mspz)}

Tris(pyrazolyl)borate (scorpionate) ligands can be considered as the most prolific ligands in contemporary coordination chemistry due to the availability of various steric and electronic substituents at the pyrazolyl rings that allow fine-tuning of the open-coordination site for metal centres. The thallium(I) complexes of anionic tridentate-chelating scorpionate ligands, namely [tris(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN2)hydroborato]thallium(I) monohydrate, [Tl(C39H46BN6)]·H2O, (I), and [bis(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN2)(5-mesityl-3-methyl-1H-pyrazol-1-yl-κN2)hydroborato]thallium(I), [Tl(C39H46BN6)], (II), show a {TlIN3} coordination, with average TlI-N bond lengths of 2.53 and 2.55 Å in (I) and (II), respectively. The overall TlI coordination geometry is distorted trigonal pyramidal, with the average N-TlI-N angle being approximately 73° for both. The dihedral angle between the planes of the pyrazolyl and benzene rings of the mesityl group is 82° in (I), while the corresponding angles in (II) are in the range 64-104°. The structural differences between the two ligands are expected to contribute to the different reactivities of the transition metal coordination complexes towards activation of small molecules such as dioxygen and ethylene.

Antenna-Enhanced Triplet-State Emission of Individual Mononuclear Ruthenium(II)-Bis-terpyridine Complexes Reveals Their Heterogeneous Photophysical Properties in the Solid State

The ability of supramolecular transition metal coordination complexes to form stabilized, long-living, radiative charge-separated states has drawn interest to employ these triplet-state emitters for the design of photonic devices. Their applicability as photosensitizers of electron transfer in molecular photonic systems is directly coupled to fundamental studies of their rich and highly versatile photochemical and photophysical properties. Here, we demonstrate that the properties of individual dual-luminescent Ru2+-bis-terpyridine complexes can be addressed with excellent sensitivity in single-complex antenna-enhanced phosphorescence investigations. This sensitivity enables studying environmentally imposed alterations of their photophysical properties, e.g., in thin film applications. In contrast to ensemble averaging investigations in solution, single-complex antenna-enhanced phosphorescence investigations corroborate the existence of Ru2+-bis-terpyridine complexes with spectrally shifted emission peaks ...

Studies of Earth Abundant Metal Complexes for Near Neutral Aqueous Redox Flow Battery (RFB) for Grid Storage

Among the many options available for Large-Scale Grid Energy Storage, Redox Flow Batteries (RFB) are leading candidates because of the decoupled design of power and energy1 which offers tremendous design flexibility and modularity. As part of the Department of Energy’s Office of Electricity (OE) energy storage program at Sandia National Laboratories, we are investigating earth abundant transition metal coordination complexes for aqueous redox flow batteries at close to pH 7. The aqueous-based systems offer complete freedom from the thermal instabilities that plague non-aqueous systems, such as lithium-ion. Furthermore, the use of neutral pH electrolytes engenders intrinsic safety and low/no corrosion, unlike the highly corrosive and toxic electrolytes used for the vanadium redox flow battery or the zinc-bromine systems. In this abstract we discuss the electrochemical properties of some of the complexes under development, and the performance of full cells containing the optimized redox couples will be presented at the meeting. Performance of Fe(2+)(tris-BPY)Cl2-0.4M Na2SO4 We have performed dc and ac voltammetry to characterize a number of iron coordination complexes, and Figure 1 shows the dc voltammetry curves at a 10 mV/s scan rate of one of these. As seen, the peak separation is ~60 mV, close to the theoretical value. We have also performed DC voltammetry at different scan rates up to 200 mV/s, and the peak separation varies between 60 and 64 mV which clearly demonstrate highly reversible behavior as well. Additionally, this couple exhibits higher redox voltage which will assure a RFB with a higher cell voltage and energy when appropriately configured with another redox couple. Figure 2 shows a plot of redox peak potentials vs. square root of scan rate. The linear increase of peak value vs. square root of san rate indicates that this couple is highly reversible. We also performed AC voltammetry, which is more sensitive than the DC measurement, just to make sure that there are no other redox peaks buried around the solvent decomposition voltage. We observed only one reversible peak (Figure 3) which corroborates the DC measurement. Similar observations were observed for other couples and will be described in detail at the meeting. Reference: B. Dunn, B., H. Kamath, H. & Tarascon, J.-M. “Electrical energy storage for the grid: a battery of choices” Science 334, 928–935(2011). Acknowledgment: Sandia Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation for the U. S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL 85000. The authors would like to thank Dr. Imre Gyuk of the DOE Office of Electricity for the support. Figure 1

Visualizing, Rather than Deriving, Russell–Saunders Terms: A Classroom Activity with Quantum Numbers

A 1 h classroom activity is presented, aimed at consolidating the concepts of microstates and Russell–Saunders energy terms in transition metal atoms and coordination complexes. The unconventional approach, based on logic and intuition rather than rigorous mathematics, is designed to stimulate discussion and enhance familiarity with quantum numbers in classes of chemistry undergraduate students.

Synthesis and Electrochemical Properties of Two Transition Metal Coordination Complexes Based on 4-Pyridyl-Substituted TTF Ligand

The synthesis, crystal structures, and electrochemical properties of two transition metal coordination complexes, Co(acac)2•(EDO-TTF-4-py)2•2CH3CN 1, and ZnBr2•(EDO-TTF-4-py)2 2, are reported, where acac = acetylacetonate and EDO-TTF-4-py, L1 (EDO-TTF = ethylenedioxotetrathiafulvalene; py = pyridine). In complex 1, two N atoms from L1 are coordinated in the trans configuration to the Co(II) ion of Co(acac)2 to form an octahedral Co complex. And in complex 2, the Zn(II) atom is tetrahedral by two N atoms from L1 and two Br ions. Cyclic voltammetry measurements for both complexes show a sizable interaction involving the electroactive L1 ligand and the metal ion.

Coordination Complexes of Transition Metals (M = Mo, Fe, Rh, and Ru) with Tin(II) Phthalocyanine in Neutral, Monoanionic, and Dianionic States.

The ability of tin atoms to form stable Sn-M bonds with transition metals was used to prepare transition metal complexes with tin(II) phthalocyanine in neutral, monoanionic, and dianionic states. These complexes were obtained via the interactions of [Sn(IV)Cl2Pc(3-)](•-) or [Sn(II)Pc(3-)](•-) radical anions with {Cp*Mo(CO)2}2, {CpFe(CO)2}2, {CpMo(CO)3}2, Fe3(CO)12, {Cp*RhCl2}2, or Ph5CpRu(CO)2Cl. The neutral coordination complexes of Cp*MoBr(CO)2[Sn(II)Pc(2-)]·0.5C6H4Cl2 (1) and CpFe(CO)2[Sn(II)Pc(2-)]·2C6H4Cl2 (2) were obtained from [Sn(IV)Cl2Pc(3-)](•-). On the other hand, the coordination of transition metals to [Sn(II)Pc(3-)](•-) yielded anionic coordination complexes preserving the spin on [Sn(II)Pc(3-)](•-). However, in the case of {cryptand[2,2,2](Na(+))}{CpFe(II)(CO)2[Sn(II)Pc(4-)]}(-)·C6H4Cl2 (4), charge transfer from CpFe(I)(CO)2 to [Sn(II)Pc(3-)](•-) took place to form the diamagnetic [Sn(II)Pc(4-)](2-) dianion and {CpFe(II)(CO)2}(+). The complexes {cryptand[2,2,2](Na(+))}{Fe(CO)4[Sn(II)Pc(3-)](•-)} (5), {cryptand[2,2,2](Na(+))}{CpMo(CO)2[Sn(II)Pc(2-)Sn(II)Pc(3-)(•-)]} (6), and {cryptand[2,2,2](Na(+))}{Cp*RhCl2[Sn(II)Pc(3-)](•-)} (7) have magnetic moments of 1.75, 2.41, and 1.75 μ(B), respectively, owing to the presence of S = 1/2 spins on [Sn(II)Pc(3-)](•-) and CpMo(I)(CO)2 (for 6). In addition, the strong antiferromagnetic coupling of spins with Weiss temperatures of -35.5 -28.6 K was realized between the CpMo(I)(CO)2 and the [Sn(II)Pc(3-)](•-) units in 6 and the π-stacking {Fe(CO)4[Sn(II)Pc(3-)](•-)}2 dimers of 5, respectively. The [Sn(II)Pc(3-)](•-) radical anions substituted the chloride anions in Ph5CpRu(CO)2Cl to form the formally neutral compound {Ph5CpRu(II)(CO)2[Sn(II)Pc(3-)]} (8) in which the negative charge and spin are preserved on [Sn(II)Pc(3-)](•-). The strong antiferromagnetic coupling of spins with a magnetic exchange interaction J/k(B) = -183 K in 8 is explained by the close packing of [Sn(II)Pc(3-)](•-) in the π-stacked {Ph5CpRu(II)(CO)2[Sn(II)Pc(3-)](•-)}2 dimers.

Syntheses, Crystal Structures, Thermal and Photoluminescent Properties of Four Coordination Complexes with a Hetero­cyclic Thioether Carboxylate Ligand

AbstractA series of transition metal coordination complexes, {[Cu(3‐Sptta)2]·1/2H2O}n (1), {[Cd(3‐Sptta)2]·1/2H2O}n (2), [Zn(3‐Sptta)2(H2O)4] (3), and [Co(3‐Sptta)2(H2O)4] (4) were synthesized under solvothermal and solvent evaporation conditions using the newly designed heterocyclic N/NS carboxylate ligand [2‐(3‐pyridyl)‐1,3,4‐thiadiazole‐5‐]‐thio‐acetate (3‐Sptta) as a main building block. Their structures were determined by single‐crystal X‐ray diffraction analyses and further characterized by elemental analyses and IR spectroscopy. The four complexes exhibit structural diversity: complexes 1 and 2 exhibit similar 2D “wave‐like” double‐layer framework with two shares of mutually parallel left‐handed and right‐handed helical chains, whereas 3 and 4 present mononuclear structures. Moreover, the thermal stabilities of complexes 1–4 were investigated. The luminescent properties of complexes 2, 3 and the free ligand were also studied.

Communication: Does a single CH3CN molecule attached to Ru(bipy)3(2+) affect its absorption spectrum?

Tris(bipyridine)ruthenium(II) (Ru(bipy)3 (2+)) is a prototypical transition metal coordination complex whose photophysical properties have attracted considerable attention. A much debated issue is whether the metal-to-ligand charge transfer (MLCT) transition that accounts for the complex's beautiful red color is fully delocalized across all three bipyridine ligands or located on just one ligand. Here, we show based on gas-phase action spectroscopy that attachment of a single acetonitrile molecule does not change the absorption spectrum from that of the bare ions, which is indicative of a delocalized state. However, the gas-phase spectra of the bare and one solvent molecule complexes are significantly blueshifted relative to that obtained in bulk acetonitrile, which suggests that in solution the polarizability of many solvent molecules working together can localize the MLCT state. Our data clearly show that more than one solvent molecule is needed to break the symmetry of the MLCT excited state and reproduce its solution-phase characteristics.

((1H-tetrazol-5-yl) methyl) pyridine-based metal coordination complexes: in situ tetrazole synthesis, crystal structures, luminescence properties

Six novel transition metal coordination complexes based on pyridyltetrazole ligands have been hydrothermally in situ synthesized.

D7 /d8 Metal Complexes Constructed from 2,6-Bis(2-benzimidazolyl)pyridyl or 2,6-Di-(pyrazol-3-yl)pyridine Derivatives: Synthesis, Structure, Characterization, and Photocatalytic Activity.

By introducing 2,6-bis(2-benzimidazolyl)pyridyl and 2,6-di-(pyrazol-3-yl)pyridine derivatives as ligand in the reaction system, three new transition-metal coordination complexes have been successfully synthesized, namely, [Co(HL1 )2 ] (1), [Ni(HL1 )2 ] (2), and [Ni3 (H2 L2 )2 ⋅(HL2 )2 ]⋅(OH)3 ⋅(Ac)⋅H2 O (3) (H2 L1 =2,6-bis(benzimidazol-2-yl)pyridine and H2 L2 =2,6-di-(5-phenyl-1H-pyrazol-3-yl)pyridine). They are all characterized by elemental analysis, IR spectroscopy, UV absorption spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. Structural analysis shows that the structures of complexes 1 and 2 are similar. They are constructed from one metal (Co, Ni) atom and two 2,6-bis(benzimidazol-2-yl)pyridine ligands (HL1 - ); the HL1 - ligand is in the tridentate coordination mode with N3 donors. Complex 3 is a trinuclear Ni complex with four 2,6-di-(5-phenyl-1H-pyrazol-3-yl)pyridine (H2 L2 ) ligands, in which the H2 L2 possesses two coordination fashions: terminal tridentate and bridging tetradentate. In addition, the surface photovoltage spectroscopy and photocatalytic activities of complexes 1-3 were investigated in detail. The results reveal that complex 3 possesses higher photocatalytic activity.

A Series of Transition-metal Coordination Complexes Assembled from 3-Nitrophthalic Acid and Thiabendazole: Synthesis, Structure and Properties

In order to explore new coordination frameworks with novel designed 3-nitrophthalic acid and the same N-donor ancillary ligand, a series of novel coordination complexes, namely, (1), (2), (3), (4) (3- = 3-nitrophthalic acid), have been hydrothermally synthesized through the reaction of 3-nitrophthalic acid with divalent transition-metal salts in the presence of N-donor ancillary coligand (TBZ = thiabendazole). As a result of various coordination modes of the versatile 3- and the coligand TBZ, these complexes exhibit structural diversity. X-ray structure analysis reveals that 1 and 2 are 0D molecular rings, while 3 and 4 are one-dimensional (1D) infinite chain polymers. And the weak O-HO hydrogen bonds and C-HO nonclassical hydrogen bonds as well as stacking also play important roles in affecting the final structure where complexes 1, 3 and 4 have 3D supramolecular architectures, while complex 2 has a 2D supramolecular network. Also, IR spectra, fluorescence properties and thermal decomposition process of complexes 1-4 were investigated.

An organometallic complex revealing an unexpected, reversible, temperature induced SC–SC transformation

A reversible, temperature driven phase transformation that takes place at ca. 180 K, in a single-crystal to single-crystal manner, has been observed for a monometallic transition metal coordination complex based on a fac-Re(CO)3 core, with a chelated 2,2′-bipyridine unit and a halogenated N-(4-iodophenyl)nicotinamide axial co-ligand.

Syntheses, Crystal Structure, and Properties of Cu(II) and Zn(II) Complexes with EDO-TTF-3-py

The syntheses, crystal structures, and electrochemical of the transition metal coordination complexes, Cu(acac)2(EDO-TTF-3-py)2 (2) and Zn(acac)2(EDO-TTF-3-py)2 (3) are reported, where acac = acetylacetonate; EDO-TTF-3-py (L1) = 4,5-ethylenedioxy-3′-(3′-pyridyl)-tetrathiafulvalene). In the complexes 2 and 3, the ligand L1 is coordinated to the metal atom through pyridine nitrogen. The similarly oxidation potentials were observed for the ligand L1 and 2 and 3, indicating the negligible interaction between the ligand and the metal in solution.

Two new coordination polymers constructed by naphthalene-1,4-dicarboxylic acid and 2,4-diamino-6-methyl-triazine

Two new transition metal coordination complexes, {[MnO(nda)](H2dmt)(H2O)}n (1), [Ag5(nda)2.5(dmt)]n (2), (H2nda=naphthalene-1,4-dicarboxylic acid, dmt=2,4-diamine-6-methyl-1,3,5-triazine) have been hydrothermally synthesized by the reactions of H2nda and dmt with the homologous MnCl2·4H2O and AgNO3, respectively, and characterized by single-crystal X-ray diffraction, IR spectra, elemental analysis, thermogravimetric analysis (TGA). The compound 1 exhibits a 3D network comprising 1D metal chain {MnO(CO2)2}n connected by the ligand nda2−, featuring a four-connected uninodal diamond -like topology. In compound 2, it is firstly observed that decanuclear silver units as secondary building units to construct 3D network by the ligands dmt and nda2−, with a rare 2-nodal (3,8)-connected tfz-d topology ({43}2{46.618.84}). The interactions within each Mn(II)—Mn(II) pair of compound 1 are antiferromagnetic (g=2.07, J=−1.42(1) cm−1, zj′=−0.73(2) cm−1). In addition, compound 2 exhibits photoluminescent property at about 472 nm (λex=394 nm).