Search

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are primarily activated by voltage and further modulated by cAMP. While cAMP binding alone does not open the channel, its presence facilitates the action of voltage, increasing channel open probability. Functional results indicate that the membrane-based voltage sensor domain (VSD) communicates with the cytosolic cyclic nucleotide-binding domain (CNBD), and vice-versa. Yet, a mechanistic explanation on how this could occur in structural terms is still lacking. In this review, we will discuss the recent advancement in understanding the molecular mechanisms connecting the VSD with the CNBD in the tetrameric organization of HCN channels unveiled by the 3D structures of HCN1 and HCN4. Data show that the HCN domain transmits cAMP signal to the VSD by bridging the cytosolic to the membrane domains. Furthermore, a metal ion coordination site connects the C-linker to the S4–S5 linker in HCN4, further facilitating cAMP signal transmission to the VSD in this isoform.

A layered coordination polymer (CP) with the fine-tuned alignment of four diolefinic ligands has been designed by shifting the coordination site of the ligand. The trimeric and tetrameric cyclobutane derivatives were reversely achieved by the photoinitiated [2+2] cycloaddition of the CP due to the favorable Schmidt's distance. More interestingly, a dynamic fluorescence shift was observed during the photo-oligomerization and heat-cycloreversion of the CP system.

The reaction of 2,3,7,8,12,13,17,18-octaethylporphyrin with sodium nitrite in trifluoroacetic acid produced 5-nitro-2,3,7,8,12,13,17,18-octaethylporphyrin, 5,15-dinitro-2,3,7,8,12,13,17,18-octaethylporphyrin, and 5,10,15-trinitro-2,3,7,8,12,13,17,18-octaethylporphyrin. Reactions of octaethylporphyrin, mono-, di-, tri-, and tetranitro-substituted porphyrins coordination to cobalt(II) acetate in a chloroform–methanol mixture were studied. The corresponding Co(II) porphyrinates were obtained and identified. It was shown that, upon dissolution of Co(II) octaethylporphyrinates in dimethylformamide in the presence of NaOH, the Co(II)→Co(III) oxidation occurs in the coordination site of the macrocycle.

Postsynthetic modification (PSM) in metal–organic frameworks (MOFs) can introduce multiple functionalities and alter the structural function for the desired application. However, the PSM of the coo...

Cysteine dioxygenase (CDO) structurally resembles cupin enzymes that use a 3-His/1-Glu coordination scheme. However, the glutamate ligand is substituted with a cysteine (Cys93) residue, which forms a thioether bond with tyrosine (Tyr157) under physiological conditions. The reversion variant, C93E CDO, was generated in order to reestablish the more common 3-His/1-Glu metal ligands of the cupin superfamily. This variant provides a framework for testing the structural and functional significance of Cys93 and the cross-link in CDO. Although dioxygen consumption was observed with C93E CDO, it was not coupled with l-cysteine oxidation. Substrate analogues (d-cysteine, cysteamine, and 3-mercaptopropionate) were not viable substrates for the C93E CDO variant, although they showed variable coordinations to the iron center. The structures of C93E and cross-linked and non-cross-linked wild-type CDO were solved by X-ray crystallography to 1.91, 2.49, and 2.30 Å, respectively. The C93E CDO variant had similar overall structural properties compared to cross-linked CDO; however, the iron was coordinated by a 3-His/1-Glu geometry, leaving only two coordination sites available for dioxygen and bidentate l-cysteine binding. The hydroxyl group of Tyr157 shifted in both non-cross-linked and C93E CDO, and this displacement prevented the residue from participating in substrate stabilization. Based on these results, the divergence of the metal center of cysteine dioxygenase from the 3-His/1-Glu geometry seen with many cupin enzymes was essential for effective substrate binding. The substitution of Glu with Cys in CDO allows for a third coordination site on the iron for bidentate cysteine and monodentate oxygen binding.

The active site of [FeFe] hydrogenase features a binuclear iron cofactor Fe2ADT(CO)3(CN)2, where ADT represents the bridging ligand aza-propane-dithiolate. The terminal diatomic ligands all coordinate in a basal configuration, and one CO bridges the two irons leaving an open coordination site at which the hydrogen species and the competitive inhibitor CO bind. Externally supplied CO is expected to coordinate in an apical configuration. However, an alternative configuration has been proposed in which, due to ligand rotation, the CN– bound to the distal Fe becomes apical. Using selective 13C isotope labeling of the CN– and COext ligands in combination with pulsed 13C electron–nuclear–nuclear triple resonance spectroscopy, spin polarization effects are revealed that, according to density functional theory calculations, are consistent with only the “unrotated” apical COext configuration.

A series of silver coordination complexes (CCs) have been synthesized through self-assembly of five pyridine-substituted tetraphenylethylene stereoisomer ligands with silver ions (named Ag-TPE-2by-1-E, Ag-TPE-2by-2-E, Ag-TPE-2by-2-Z, Ag-TPE-2by-3-E, and Ag-TPE-2by-3-Z). These silver CCs show distinct topologies including beaded chain frameworks, linear structures, and discrete metallacycles. The single-crystal analysis results reveal the critical role of the space distribution of the coordination site and stereoisomer ligands in controlling the silver CCs' geometry configuration and modulating the optical properties. Luminescent investigations revealed that Ag-TPE-2by-2-E, Ag-TPE-2by-2-Z, Ag-TPE-2by-3-E, and Ag-TPE-2by-3-Z possess obvious mechanocharomic behaviors, which can be achieved several reversible cycles through repeated grinding and methanol soaking processes. However, the Ag-TPE-2by-1-E showed tenacious stability toward mechanical grinding and temperature. Thus, these silver CCs provide a good platform to investigate the influence of the space distribution of the coordination site of ligands on their geometry and mechanocharomic properties.

By exploiting an established on-surface metallation strategy, we address the ability of the corrolic macrocycle to stabilise transition metal ions in high-valent (III) oxidation states in metal-supported molecular layers. This approach offers a route to engineer adsorbed metal complexes that cannot be easily fabricated by organic synthesis methods and bear a vacant axial coordination site for catalytic conversions.

The aim of the study was to evaluate the labeling yield of 44Sc-DOTATATE radiobioconjugate when the labeling is performed in the presence of various amounts of competing metallic impurities. In the case of Ca2+ and Al3+ the effect is irrelevant, which is understandable considering the low stability constant of Ca2+-DOTA and Al3+-DOTA complexes. However, the presence of Fe2+/3+, Zn2+ and Cu2+ cations very strongly influences the efficiency of the 44Sc-DOTATATE formation. Surprisingly, while the Zn2+-DOTA stability constants is the smallest, Zn2+ cations competes more strongly with Sc3+ than Fe2+,3+ and Cu2+ at the DOTATATE coordination site.

We report polymer-promoted cooperative catalysis of Cu for oxygen activation. A series of random copolymers containing dipicolylamine as binding motifs are designed to coordinate type-3 Cu sites. The Cu-copolymers show a 6–8-fold activity enhancement, compared to the molecular complex of Cu with an identical coordination site. Michaelis–Menten analysis demonstrates that the kinetic enhancement results from flexible polymer-promoted cooperative catalysis among multi-Cu sites despite the imposed thermodynamic barrier. These observations provide guidance for the bioinspired design of metallopolymers as soluble catalysts with high activity.

The potential of structured peptides has not been explored much in the design of metal-organic frameworks (MOFs). This is partly due to the difficulties in obtaining stable secondary structures from the short α-peptide sequences. Here we report the design, crystal conformations, coordination site dependent different silver coordinated frameworks of short α,γ-hybrid peptide 12-helices consisting of terminal pyridyl moieties and the utility of metal-helix frameworks in the adsorption of CO2 . Upon silver ion coordination the 12-helix terminated by the 3-pyridyl derivatives adopted a 2:2 macrocyclic structure, while the 12-helix terminated by the 4-pyridyl derivatives displayed remarkable porous metal-helix frameworks. Both head-to-tail intermolecular H-bonds of the 12-helix and metal ion coordination have played an important role in stabilizing the ordered metal-helix frameworks. The studies described here open the door to design a new class of metal-organic-frameworks from peptide foldamers.

A novel N-confused porphyrin (NCP) analogue bearing an external aza-dipyrrin-like coordination site was synthesized by a Schiff-base forming reaction of N-confused oxoporphyrin and 2-aminopyridine derivatives. The chimera molecule enhances the intrinsic NH tautomerism of NCP to enable four possible tautomeric structures, three of which were identified by metal coordination.

Aluminum is an important component for luminescence. However, the fluorescent aluminum complex with unambiguous structural information is still limited. Herein, we report a series of fluorescence aluminum oxo clusters (AlOCs). By introducing an additional coordination site to the aromatic conjugation ligand, cluster nuclearity increment and fluorescence variation are observed. Al8(OH)2(μ4-O)2(1-NA)2(OEt)16 (AlOC-41, 1-NA = 1-naphthoic acid, OEt = ethanol) is made up of two tetrahedral subunits. By introducing an additional coordination site to the aromatic conjugation ligand, we isolate a high nuclearity compound Al10(μ3-O)2(3-HNA)2(OEt)22 (AlOC-47, 3-HNA = 3-hydroxy-2-naphthoic acid). Correspondingly, their luminescence performance is different (blue fluorescence in AlOC-41 and green in AlOC-47). Present herein is a platform to illustrate the relationship between synthesis, structure, and fluorescence properties.

We present a stepwise synthetic strategy for the preparation of the unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl2(CO)2}2(4′cisDPyP)(3′cisDPyP)] (5), in which two different 5,10-meso-dipyridylporphyrins, 4′cisDPyP [i.e., 5,10-bis(4′-pyridyl)-15,20-diphenylporphyrin] and 3′cisDPyP [i.e., 5,10-bis(3′-pyridyl)-15,20-diphenylporphyrin], are joined through equal 90°-angular Ru(II) connectors. The synthesis of 5 was accomplished through the preparation of a reactive ditopic intermediate in which one of the two pyridylporphyrins is linked to two neutral ruthenium fragments, each having one residual readily available coordination site (a dmso-O). Thus, compound 5 was obtained under mild conditions through two complementary routes: either by treatment of [{t,c,c-RuCl2(CO)2(dmso-O)}2(4′cisDPyP)] (3) with 1 equiv of 3′cisDPyP or, alternatively, by treatment of [{t,c,c-RuCl2(CO)2(dmso-O)}2(3′cisDPyP)] (4) with 1 equiv of 4′cisDPyP. Heteroleptic metallacycle 5 was isolated in pure form in acceptable yield and fully characterized. Spectroscopic data and a molecular model show that 5 has an L-shaped geometry, with the two porphyrins almost orthogonal to one another. The modular approach that we established is highly flexible and opens the way to several possible exciting developments., The unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl2(CO)2}2(4′cisDPyP)(3′cisDPyP)] (5), which features two different 5,10-meso-dipyridylporphyrins and has an L-shaped geometry, was isolated in pure form through a flexible stepwise synthetic approach.

Heterocycles, heteroaromatics and spirocyclic entities are ubiquitous components of a wide plethora of synthetic drugs, biologically active natural products, marketed pharmaceuticals and agrochemical targets. Recognizing their high proportion in drugs and rich pharmacological potential, these invaluable structural motifs have garnered significant interest, thus enabling the development of efficient catalytic methodologies providing access to architecturally complex and diverse molecules with high atom-economy and low cost. These chemical processes not only allow the formation of diverse heterocycles but also utilize a range of flexible and easily accessible building units in a single operation to discover diversity-oriented synthetic approaches. Alkynoates are significantly important, diverse and powerful building blocks in organic chemistry due to their unique and inherent properties such as the electronic bias on carbon–carbon triple bonds posed by electron-withdrawing groups or the metallic coordination site provided by carbonyl groups. The present review highlights the comprehensive picture of the utility of alkynoates (2007–2019) for the synthesis of various heterocycles (> 50 types) using transition-metal catalysts (Ru, Rh, Pd, Ir, Ag, Au, Pt, Cu, Mn, Fe) in various forms. The valuable function of versatile alkynoates (bearing multifunctional groups) as simple and useful starting materials is explored, thus cyclizing with an array of coupling partners to deliver a broad range of oxygen-, nitrogen-, sulfur-containing heterocycles alongside fused-, and spiro-heterocyclic compounds. In addition, these examples will also focus the scope and reaction limitations, as well as mechanistic investigations into the synthesis of these heterocycles. The biological significance will also be discussed, citing relevant examples of drug molecules highlighting each class of heterocycles. This review summarizes the recent developments in the synthetic methods for the synthesis of various heterocycles using alkynoates as readily available starting materials under transition-metal catalysis.

A polypyridyl monoruthenium complex with a dangling coordination site shows dual fluorescence/phosphorescence emissions at room temperature. The emission properties can be modulated by multiple stimuli including solvents, O2, and metal ions.

The research presented herein focuses on controlling the coordination environment of Mn, Fe, and Co in coordination complexes with the ligand N-2-pyridylimidoyl-2-pyridylamidine (Py2ImAm), which possesses both a bidentate and tridentate coordinating site. The synthesis and characterization of seven new metallic complexes are described, and these results indicate that the key factor dictating which coordination site of Py2ImAm the metal ion prefers is the presence (or absence) of a weak acid. More specifically, the presence of a weak acid directs the metal ion to the tridentate site of Py2ImAm, while neutral or basic conditions lead to coordination complexes in which the metal center is bound to the bidentate pocket.

A novel volatile Pt(II)β-iminoketonate complex is synthesized. β-Aminovinylketone H(i-ptac) = [CF3–C(O)–CH=C(NH2)–C(CH3)3] is used as a ligand. The XRD method is used to determine the structures of the ligand and the complex. The crystallographic data for C16H22F6N2O2Pt are as follows: a = 10.0716(4) A, b = 10.9572(4) A, c = 9.6322(4) A, β = 110.9010(10)°, space group С2/m, Z = 2, R = 0.011. The platinum atom has a square planar coordination with two oxygen and two nitrogen atoms of two bidentately linked ketoiminate ligands in trans-position; the PtO2N2 coordination site is formed.

Four new 3d–4f heterobinuclear complexes [Zn(L)Sm(Py)(NO3)3] (1), [Zn(L)Eu(OAc)(NO3)2] (2), [Zn(L)Tb(Py)(NO3)3] (3) and [Zn(L)Dy(OAc)(NO3)2] (4); Py = pyridine; H2L = 6,6′-dimethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) have been successfully prepared by the one-pot reaction of H2L with zinc(II) acetate, lanthanide(III) nitrate and a simple auxiliary ligand Py. Although the heterobinuclear complexes 1–4 are prepared in the same reaction condition, the auxiliary ligand Py doesn’t coordinate to the Zn(II) center of the complexes 2 and 4. Instead, the bridging µ-acetato ligand is present in the complexes 2 and 4. The coordination of the auxiliary ligand Py in the complexes 1 and 3 leads to the smaller distortion of square pyramidal coordination site of Zn(II), the higher coplanarity between the planes of ZnO(phenoxo)2 and LnO(phenoxo)2, and the longer Zn⋯Ln distance compared with the complexes 2 and 4. Moreover, the ligand (L)2− can selectively sensitize Sm(III) ion from among Sm(III), Eu(III), Tb(III) and Dy(III) ions, although these complexes would often exhibit f–f luminescence.

Luminescent lanthanide (Ln(III)) complexes with coumarin or carbostyril antennae were synthesized and their photophysical properties evaluated using steady-state and time-resolved UV-vis spectroscopy. Ligands bearing distant hydroxycoumarin-derived antennae attached through triazole linkers were modest sensitizers for Eu(III) and Tb(III), whereas ligands with 7-amidocarbostyrils directly linked to the coordination site could reach good quantum yields for multiple Ln(III), including the visible emitters Sm(III) and Dy(III), and the near-infrared emitters Nd(III) and Yb(III). The highest lanthanide-centered luminescence quantum yields were 35% (Tb), 7.9% (Eu), 0.67% (Dy), and 0.18% (Sm). Antennae providing similar luminescence intensities with 2-4 Ln-emitters were identified. Photoredox quenching of the carbostyril antenna excited states was observed for all Eu(III)-complexes and should be sensitizing in the case of Yb(III); the scope of the process extends to Ln(III) for which it has not been seen previously, specifically Dy(III) and Sm(III). The proposed process is supported by photophysical and electrochemical data. A FRET-type mechanism was identified in architectures with both distant and close antennae for all of the Lns. This mechanism seems to be the only sensitizing one at long distance and probably contributes to the sensitization at shorter distances along with the triplet pathway. The complexes were nontoxic to either bacterial or mammalian cells. Complexes of an ester-functionalized ligand were taken up by bacteria in a concentration-dependent manner. Our results suggest that the effects of FRET and photoredox quenching should be taken into consideration when designing luminescent Ln complexes. These results also establish these Ln(III)-complexes for multiplex detection beyond the available two-color systems.

Iridacycles are a group of cyclometalated metal complexes, which have recently been shown to be versatile catalysts for a range of reactions. This Feature Article provides an account of the work carried out by our groups. We start with an introduction to the variety of iridacycles and how they entered into catalysis. The following sections provide an overview of the discovery and applications in catalysis of the iridacycles originated from our labs, including transfer hydrogenation with formic acid, hydrogenation with H2, dehydrogenation and borrowing-hydrogen reactions. Where possible, mechanistic insight is also presented. A notable advantage of these iridacycles is their ease of preparation, stability to air and water and high modularity. With only one coordination site available for substrate activation, the iridacycles differ from most homogeneous catalysts structure-wise.

Four 3d–4f heteronuclear complexes, [(ZnL)2La(OAc)2]·ClO4·2CHCl3 (1), [(ZnL)2La(OAc)2]·CF3SO3·H2O (2), [ZnNd(L)(Py)(NO3)3] (3), and [ZnGd(L)(OAc)(NO3)2] (4) (Py = pyridine; H2L = 6,6′-dimethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), have been prepared by one-pot reaction of H2L with zinc(II) acetate, lanthanide(III) ions and Py. Although the heterobinuclear complexes 1–4 are prepared in the same reaction condition, the Py does not coordinate to Zn(II) of 1, 2, and 4. Instead, the bridging μ-acetato ligand is present. The coordination of the Py in 3 leads to smaller distortion of square pyramidal coordination site of Zn(II), the higher coplanarity between the planes of ZnO(phenoxo)2 and LnO(phenoxo)2, and the longer Zn⋯Ln distance compared with 4. The luminescence properties of 1–4 have been discussed. The ligand (L2−) can sensitize NIR luminescence of Nd(III) ions.

The heterometallic chromium-manganese carbonyl nitrosyls CrMn(NO)(CO)n (n = 9, 8) have been investigated by density functional theory. The lowest energy CrMn(NO)(CO)9 structures have unbridged staggered conformations with a ~2.99 &Aring, Cr&ndash, Mn single bond similar to the experimental and lowest energy structures of the isoelectronic Mn2(CO)10 and Cr2(NO)2(CO)8. A significantly higher energy CrMn(NO)(CO)9 isomer has a nearly symmetrical bridging nitrosyl group and a very weakly semibridging carbonyl group. The two lowest energy structures of the unsaturated CrMn(NO)(CO)8 have a five-electron donor bridging &eta, 2-&micro, NO nitrosyl group or a four-electron donor bridging &eta, CO group, as well as a Cr&ndash, Mn single bond of length ~2.94 &Aring, The next higher energy CrMn(NO)(CO)8 structure has exclusively terminal CO and NO ligands and a shorter Cr&ndash, Mn single bond of ~2.85 &Aring, suggesting an 18-electron configuration for the manganese atom and a 16-electron configuration for the chromium atom indicated by a vacant coordination site nearly perpendicular to the Cr&ndash, Mn bond.

Cyclic alkyl amino carbene (CAAC) anchored [FeFe]-hydrogenase model complex featuring rotated conformation at one of the iron centers are found to be promising candidate for effective production of dihydrogen. A stepwise comparison of the complete mechanism using the CAAC stabilized model complex [1]0 has been performed with that of an experimentally isolated one ([2]0). Interestingly, the reduction events involved in the catalytic cycles are found to be more favorable than those previously reported for a similar experimentally known system. Furthermore, the computed ΔpKa values indicate that the distal iron center with a vacant coordination site is more basic compared to the amino nitrogen atom of the azadithiolate bridge. We also made an attempt to determine the oxidation states of the iron centers for the intermediates involved in the catalytic cycles on the basis of the computed Mossbauer isomer shift and Mulliken spin density values.

Hemilabile tris( -butoxy)silanolate ligands allow stabilizing a mononuclear octahedral Mo( ) complex without quenching its reactivity towards small molecules (N , CO , N O)., Coordinatively unsaturated Mo( ) complexes have been identified as highly reactive species able to activate dinitrogen without the need for a sacrificial reducing agent. Here, we report a coordinatively saturated octahedral Mo( ) complex stabilized by κ -tris( -butoxy)silanolate ligands, which is yet highly reactive towards dinitrogen and small molecules. The combined high stability and activity are ascribed to the dual binding mode of the tris( -butoxy)silanolate ligands that allow unlocking a coordination site in the presence of reactive small molecules to promote their activation at low temperatures.

Aminopyridines are among the classes of heterocyclic compounds that have been extensively studied in the last few decades owing to their interesting biological activities. They exist in three isomeric forms: 2-aminopyridine, 3-aminopyridine and 4-aminopyridine. The diversity in their pharmacological activities has attracted the attention of many researchers to explore the reasons for their wide potential. This study examines recent advances related to the efficient procedure for synthesizing different types of aminopyridine derivatives, its coordination site with metals and biological activities using systematic literature review and content analysis. Other important concepts of aminopyridines discussed are basicity, electric hindrance as related to percentage yield of isomeric forms and spectra updates on the characterization of aminopyridines. The findings from this study also reveal the array of solvents used for purification processes; ideas on isomers that have not been used in the synthesis of aminopyridine derivatives and their respective biological activities. The significance of this study is on the various synthetic methods revealed, which may be helpful to the development of newer compounds with aminopyridines moieties that could offer high bioactivity and lesser toxicity.

A series of ((pyridinyl)-1H-pyrazolyl)pyridine (pypzpy) ligands in which the pyrazolyl ring at 1- and 3-positions is modified by two 2-, 3-, or 4-pyridyl groups were prepared. Reaction of CuI with 2-(1-(pyridin-2-yl)-1H-pyrazolyl)pyridine (2,2′-pypzpy) in MeCN at room temperature or solvothermal reaction of the same components at 120 °C afforded one binuclear complex [{(2,2′-pypzpy)Cu}(μ-I)]2 (1). Treatment of CuI with 3-(1-(pyridin-2-yl)-1H-pyrazolyl)pyridine (3,2′-pypzpy) at room temperature or at 120 °C produced one-dimensional (1D) polymer [{Cu3(μ3-I)3}(μ-3,2′-pypzpy)]n (2) and one two-dimensional (2D) polymer [{Cu2(μ-I)(μ3-I)}2(3,2′-pypzpy)2]n (3), respectively. Similar reactions of CuI with 4-(1-(pyridin-2-yl)-1H-pyrazolyl)pyridine (4,2′-pypzpy) at room temperature or at 150 °C yielded one 1D polymeric complex [{Cu(μ3-I)}2(4,2′-pypzpy)2{Cu(μ-I)}2]n (4). Complexes [{Cu3(μ3-I)3}(μ-2,3′-pypzpy)]n (5), [(CuI)(μ-2,3′-pypzpy)]2 (6), [(Cu2I2)(3,3′-pypzpy)] (7), [(CuI)(4,3′-pypzpy)] (8), [{Cu(μ3-I)}2(μ-2,4′...

The hydride complexes [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] (1) and [RuH{κ3(N,N,N)-Tpms}(pta)2] (3) [Tp = hydridotris(pyrazol-1-yl)borate, Tpms = tris(pyrazol-1-yl)methanesulfonate, pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane] reacted with alkynes to form the corresponding neutral alkenyl complexes through insertion reactions. The addition of HBF4 to the hydride complex [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] (1) led to a coordinatively unsaturated complex through the loss of hydrogen. The free coordination site can be occupied by different groups, such as BF4 or NCMe.

New chiral cluster complexes containing (S)-mandelate and (S)-phenyllactate ligands, [Mo3S4(dtp)3(μ-(S)-mandelate)(py)] (1) and [Mo3S4(dtp)3(μ-(S)-phenyllactate)(py)], were prepared from [Mo3S4(dtp)3(μ-dtp)(H2O)] (dtp = (EtO)2PS2) by ligand substitution. The crystal structures of 1 and 2 were determined by X-ray diffraction. Detailed variable-temperature 31P{1H} and 1H NMR studies of solutions of 1 and 2 in non-coordinating solvents (CDCl3, CD2Cl2) demonstrated three dynamic processes at the Mo–Py coordination site: diastereomer interconversion [(PS) to (MS)] which is inhibited at low temperatures; pyridine rotation around the Mo–py bond (180°-flip), and pyridine exchange in the presence of added pyridine. Activation parameters for all exchange processes have been estimated.

A new type of IrIII metalloligands containing an unsaturated nitrogen coordination site, [Ir(H)2(PPh3)2(pprd)]BF4·2CHCl3 (1), [Ir(H)2(PPh3)2(Me2bpm)]BF4·CHCl3 (2), {[Ir(H)2(PPh3)2(Me2bpm)]PF6·CHCl3}4 (3), [Ir(H)2(PPh3)2(biqz)]BF4·2CHCl3 (4), and [Ir(H)2(PPh3)2(biqz)]PF6 (5), have been prepared by reaction of [Ir(H)2(PPh3)2(Me2CO)2]X (X = BF4 or PF6) with 4-(2-pyridyl)pyrimidine (pprd), 6,6′-dimethyl-4,4′-bipyrimidine (Me2bpm), or 4,4′-biquinazoline (biqz). Subsequently, three novel heterometallic AgI–IrIII hydride coordination polymers, {[Ir(H)2(μ-pprd)(PPh3)2Ag(η-CF3COO)]BF4·Me2CO}n (6), {[Ir(H)2(μ-biqz)(PPh3)2Ag2(μ-CF3COO)3]·Me2CO}n (7), and {[Ir(H)2(μ-Me2bpm)(PPh3)2Ag2(μ-CF3COO)2]PF6·2Me2CO}n (8) have been constructed by reaction of the IrIII metalloligands 1, 3, and 5 with AgCF3COO. In coordination polymer 6, the [Ir(H)2(PPh3)2(pprd)]3+ units are linked through the AgI atoms to form a 1D zigzag chain structure. In coordination polymer 7, the dinuclear [Ag2(μ-CF3COO)3]– units are linked through the terminal N atoms of biqz in two different [Ir(H)2(PPh3)2(biqz)]3+ units to form a 1D zigzag chain structure. In coordination polymer 8, the [Ag2(μ-CF3COO)2] frameworks are linked through the terminal N atoms of Me2bpm and the IrIII atom in two different [Ir(H)2(PPh3)2(Me2bpm)]3+ units to form a waved rectangular cavity. These waved rectangular cavities are connected to each other to afford a unique 2D sheet structure.

We report the synthesis and characterization of a μ-hydroxo NiRu complex as a model for the active site of (Ni–SIr)I of [NiFe]hydrogenase. This is the first example of the (Ni–SIr)I model with a bridging hydroxo ligand between dimetal centers and an available coordination site on Ni center cis to the bridging hydroxo ligand. We have determined the structure of the (Ni–SIr)I model complex by X-ray analysis and reported reversible switching between the catalytically inactive (Ni–SIr)I and a catalytically active (Ni–SIr)II models.

A series of dinuclear and tetranuclear first-row transition metal complexes were synthesized with the dinucleating ligand 2,7-bis(di(2-pyridyl)fluoromethyl)-1,8-naphthyridine (DPFN). The coordination pocket and rigidity of the DPFN ligand enforces pseudo-octahedral geometries about the metal centers that contain chloro, hydroxo, and aqua bridging ligands forming a "diamond" shaped configuration with metal-metal distances varying from 2.7826(5) to 3.2410(11) Å. Each metal center in the dinuclear complexes has an additional open coordination site that accommodates terminal ligands in a syn geometry of particular interest in catalyst design. The complexes are characterized by electronic spectroscopy, electrochemistry and potentiometric titration methods.

Lanthanide( iii ) ions situated in a coordination site of phthalocyanine macrocycle as molecular paramagnets with a large magnetocaloric effect at the temperatures close to room are presented for the first time on the examples of gadolinium and thulium.

International audience; The canonical CysXXXCysXXCys motif is the hallmark of the Radical-SAM superfamily. This motif is responsible for the ligation of a [4Fe-4S] cluster containing a free coordination site available for SAM binding. The five enzymes MoaA, TYW1, MiaB, RimO and LipA contain in addition a second [4Fe-4S] cluster itself bound to three other cysteines and thus also displaying a potentially free coordination site. This review article summarizes recent important achievements obtained on these five enzymes with the main focus to delineate the role of this additional [4Fe-4S] cluster in catalysis.

The vital contribution of Mg2+ ions to RNA biology is challenging to dissect at the experimental level. This calls for the integrative support of atomistic simulations, which at the classical level are plagued by limited accuracy. Indeed, force fields intrinsically neglect nontrivial electronic effects that Mg2+ exerts on its surrounding ligands in varying RNA coordination environments. Here, we present a combined computational study based on classical molecular dynamics (MD) and Density Functional Theory (DFT) calculations, aimed at characterizing (i) the performance of five Mg2+ force field (FF) models in RNA systems and (ii) how charge transfer and polarization affect the binding of Mg2+ ions in different coordination motifs. As a result, a total of ~2.5 ?s MD simulations (100/200 ns for each run) for two prototypical Mg2+-dependent ribozymes showed remarkable differences in terms of populations of inner-sphere coordination site types. Most importantly, complementary DFT calculations unveiled that differences in charge transfer and polarization among recurrent Mg2+-RNA coordination motifs are surprisingly small. In particular, the charge of the Mg2+ ions substantially remains constant through different coordination sites, suggesting that the common philosophy of developing site-specific Mg2+ ion parameters is not in line with the physical origin of the Mg2+-RNA MD simulations inaccuracies. Overall, this study constitutes a guideline for an adept use of current Mg2+ models and provides novel insights for the rational development of next-generation Mg2+ FFs to be employed for atomistic simulations of RNA.

cited By 0; International audience; The active site of the [NiFe]-hydrogenase contains a pentacoordinated iron atom; therefore, a vacant coordination site is available for substrate binding. Nonetheless, most organometallic models of the [NiFe]-hydrogenase failed to reproduce this key feature of the active site. In order to rationalize such behavior, quantum chemical calculations were carried out on a series of [Fe(CN)2(CO)n(dithiolate)]2- n = 1,2 complexes, where dithiolate denotes the ligands (CF3)2C2S2 2-, (CO2Me)2C2S2 2-, Ph2C2S2 2-, C6Cl2H2S2 2-, C6H4S2 2-, C2H4S2 2-, and C3H6S2 2-. Structural and energetic features are discussed, and a topological analysis based on two scalar fields, the one-electron density and the electron localization function (ELF), has been attempted to describe the nature of the metal-ligand bonds. The present approach contributes to better understand the ability of noninnocent dithiolene to strongly labilize one CO whereas innocent dithiolate cannot. The methodology developed throughout the paper could be useful in the field of the CO-releasing molecules. © 2017 American Chemical Society.

An enantioselective carbonyl-ene reaction of glyoxylate esters with 1,1-disubstituted alkenes catalyzed by chiral cationic dirhodium(II,III) carboxamidates is described. The paddlewheel dirhodium(II,III) carboxamidates having one open coordination site at each rhodium smoothly catalyze the carbonyl-ene reaction to afford homoallylic alcohol products in good isolated yields with high enantioselectivities.

Two hybrid materials based on Keggin-type polyoxometalate, [Ag4(mtrz)4(H2O)2(SiW12O40)] (1), [Ag4(mtez)5(SiW12O40)]·H2O (2), (mtrz = 1-methyl-1,2,4-triazole, mtez = 1-methyl-1,2,3,4-tetrazole), have been hydrothermally synthesized and structurally characterized. Through the use of the azole ligands mtrz and mtez, compounds 1 and 2 with totally different metal–organic units are obtained. In 1, the mtrz ligands with N atoms in meta-positions induced the formation of chain-like metal–organic units, while in 2, the mtez ligands with adjacent N atoms induced the assembly of tetranuclear units. The SiW12 anions act as bridging linkers to evolve the structural dimensionality of the two title compounds into 2D network and 3D framework, respectively.

We describe the successful synthesis of Fe2(dobdc) (dobdc4−=2, 5-dioxido-1, 4-benzenedicarboxylate), which has an open metal coordination site Fe(II), and investigate the adsorption properties of three important molecules CO2, CH4 and N2 on Fe2(dobdc) and an oxidized analog, Fe2(O2)(dobdc). We found that CO2 adsorption isotherm of Fe2(dobdc) at 10 bar was very different from Fe2(O2)(dobdc), with the capacities of 144.5 cm3 g−1 and 98.1 cm3 g−1, respectively. The adsorption capacities for CH4 were 75.8 cm3 g−1 and 36.8 cm3 g−1, respectively, at 10 bar in these materials. Using ideal adsorbed solution theory (IAST), we obtain the adsorption selectivity for CO2 using equimolar mixtures of CO2/CH4 and CO2/N2 with Fe2(dobdc) and Fe2(O2)(dobdc) as a function of pressure. Fe2(dobdc) has a higher, more stable separation factor.

Sublimed layers of 5-(pyridin-4-yl)-10,15,20-triphenylporphyrinato)cobalt(II) and 5-(pyridin-3-yl)-10,15,20triphenylporphyrinato)cobalt(II) ({Co(M4PyTPP)} (I) and {Co(M3PyTPP)} (II), respectively) form coordination oligomers upon standing. Interaction of NO(15NO) gas with these systems results in the formation of pentaand hexacoordinated nitrosyl complexes, the sixth coordination site of which is occupied by pyridyl group of adjacent molecule in the layer. The FTIR spectral data demonstrate that the long-term exposure of these systems under O2 results in oxidation of the nitrosyl complexes with formation of hexacoordinated nitrato complexes and the reaction proceeds predominantly with hexacoordinated nitrosyls. Мechanism of oxidation more likely includes the dissociation of NO from the hexacoordinated complex followed by O2 trapping of resulting (-4(3)Py)Co(M4(3)PyTPP) to give (4(3)Py) Co(M4(3)PyTPP)(O2), which then reacts rapidly with NO by the nitric oxide dioxygenation reaction.

A dinuclear zinc complex containing both a σ-dimerized 7,7,8,8-tetracyanoquinodimethane (TCNQ) ligand ([TCNQ-TCNQ](2-)) and TCNQ(-) was synthesized for the first time. This is the first instance of a single molecular complex with a bridging [TCNQ-TCNQ](2-) ligand. Each zinc center is coordinated with two 2,2'-bipyrimidines and one TCNQ(-), and the remaining coordination site is occupied by a [TCNQ-TCNQ](2-) ligand, which bridges the two zinc centers. The complex facilitates π-stacking of TCNQ(-) ligands when crystallized, which gives rise to a near-IR charge-transfer transition and strong antiferromagnetic coupling.

The simulation model for determining the maximum length of the queued vehicles at the adjacent towards the coordination intersection is proposed, which is written in the Objective-C programming language. The paper considers the process of the model development, which is based on analytical studies of the process of forming the queued vehicles at the adjacent intersection. Its adequacy is verified, and the results are compared with the values, obtained from VISSIM. The simulation model is implemented in such a way that the user can easily change the terms of the study due to the changes in input parameters. It can be run both on the PC, and portable devices (mobile phone, tablet computer). However, it is suitable for coordinated street sites with two lanes in one or both directions, where the main and secondary approaches are isolated, and the cycle duration at both adjacent intersections is equal.