Bidentate Research Articles

Thermodynamic Differentiation of the Two Sides of Azabuckybowl through Complexation with Square Planar Platinum(II).

The precise control of the two faces, concave/convex faces, is an attractive challenge to realizing novel dynamic molecular systems. Herein, we report the synthesis, X-ray crystal structure, and bowl-to-bowl inversion behavior of a platinum complex with azabuckybowl as a monodentate ligand. X-ray crystallography revealed that the azabuckybowl is orthogonally coordinated to the plane containing the Pt center and other ligands. One and two-dimensional NMR studies have also confirmed that this complex was observed as mixtures of two isomers, although the isomeric ratio was highly biased. Theoretical calculations indicate that the difference in thermodynamic stability of these isomers is due to the direction of the concave/convex face of an azabuckybowl ligand.

The Structural Features of Monomeric Octahedral Dioxocomplexes of d2-Rhenium(V) [ReO2(L)4] (L = Monodentate Ligands)

The Structural Features of Monomeric Octahedral Dioxocomplexes of d2-Rhenium(V) [ReO2(L)4] (L = Monodentate Ligands)

2-Hydroxychalcone as a Novel Natural Photosynthesis Inhibitor against Bloom-Forming Cyanobacteria.

The control of harmful cyanobacterial blooms has been becoming a global challenge. The development of eco-friendly algicides with strong specificity is urgently needed. The photosynthetic apparatus is a promising target site for algicides to minimize the possible harmful effects on animals and humans. In this study, biologically derived 2-hydroxychalcone efficiently inhibited the growth of bloom-forming M.aeruginosa by selectively interfering with photosynthesis. 2-Hydroxychalcone targeting Photosystem II (PSII) inhibited electron transfer between the primary and secondary electron acceptors (QA and QB) and the binding of plastoquinone (PQ) molecules to the QB binding pocket at the acceptor side of PSII, as revealed by polyphasic chlorophyll (Chl) a fluorescence induction and QA- reoxidation kinetics. Molecular docking for 2-hydroxychalcone to D1 protein and the proteomic responses of M.aeruginosa suggested that 2-hydroxychalcone formed a stable monodentate ligand with the nonheme iron in D1 protein, provoking significant modulation of PSII proteins. The unique binding mode of 2-hydroxychalcone with PSII differentiated it from classical PSII inhibitors. Furthermore, 2-hydroxychalcone down-regulated the expression of microcystin (MC) synthesis-related genes to restrain MC synthesis and release. These results indicated the potential application of 2-hydroxychalcone as an algicide or a template scaffold for designing novel derivatives with superior algicidal activity.

A theory-driven synthesis of symmetric and unsymmetric 1,2-bis(diphenylphosphino)ethane analogues via radical difunctionalization of ethylene

1,2-Bis(diphenylphosphino)ethane (DPPE) and its synthetic analogues are important structural motifs in organic synthesis, particularly as diphosphine ligands with a C2-alkyl-linker chain. Since DPPE is known to bind to many metal centers in a bidentate fashion to stabilize the corresponding metal complex via the chelation effect originating from its entropic advantage over monodentate ligands, it is often used in transition-metal-catalyzed transformations. Symmetric DPPE derivatives (Ar12P−CH2−CH2−PAr12) are well-known and readily prepared, but electronically and sterically unsymmetric DPPE (Ar12P−CH2−CH2−PAr22; Ar1≠Ar2) ligands have been less explored, mostly due to the difficulties associated with their preparation. Here we report a synthetic method for both symmetric and unsymmetric DPPEs via radical difunctionalization of ethylene, a fundamental C2 unit, with two phosphine-centered radicals, which is guided by the computational analysis with the artificial force induced reaction (AFIR) method, a quantum chemical calculation-based automated reaction path search tool. The obtained unsymmetric DPPE ligands can coordinate to several transition-metal salts to form the corresponding complexes, one of which exhibits distinctly different characteristics than the corresponding symmetric DPPE–metal complex.

Coordination Chemistry of Polynitriles, Part XI. Influence of 4,4′-Bipyridine and Solvent on the Crystal and Molecular Structures of Alkaline Earth Pentacyanocyclopentadienides

The reaction of alkaline earth pentacyanocyclopentadienides with 4,4′-bipyridine in MeOH yielded undefined products of composition [M(PCC)2(Bipy)x(MeOH)y(H2O)z] (PCC = [C5(CN)5]−). Recrystallization from MeOH, EtOH, or n-BuOH gave crystals of [Mg(H2O)4(4,4′-bipy)2](PCC)2∙2BuOH (1), [Ca(H2O)4(4,4′-bipy)2](PCC)2∙(4,4′-bipy) (2), [Sr(MeOH)8](PCC)2∙3(4,4′-bipy) (3), [Sr2(H2O)4(BuOH)4(PCC)2(µ-PCC)2 (µ-4,4′-bipy)]∙4 (4,4′-bipy)∙0.29 (BuOH) (4), [Ba3(H2O)4(EtOH)10 (PCC)2(µ-PCC)2 (µ-4,4′-bipy)2(4,4′-bipy)](PCC)2 ∙3(4,4′-bipy)∙2EtOH∙H2O (5) and [Ba4(H2O)8(BuOH)6 (PCC)2(µ-PCC)6 (4,4′-bipy)6]∙3(4,4′-bipy) (6). 4,4′-Bipyridine functions either as monodentate or bidentate ligand and is present in all cases except for 2 as lattice guest. While in compounds 1 and 2 only water is present as O-donor, the alcohol coordinates in the other compounds either exclusively (3) or together with water (4–6). The pentacyanocyclopentadienide does not coordinate in 1–3, but is present as mono-, bi-, or tridentate ligand in 4–6. In all compounds, a more or less complicated interplay of hydrogen bridges and π–π stacking is observed.

A review on the chemistry of novel platinum chelates based on azo-azomethine ligands

Abstract Numerous platinum group metals (PGMs) complexes contain azo-azomethine-based ligands. Azo-azomethine ligands are N-donor ligands that have extended conjugated π-bonded systems and both azo (–N=N–) and aldimine (–C=N–) functions in their structure. Plenty of platinum (Pt) complexes with azo-imine ligands have been prepared and characterized. Various multidentate azo-imine ligands coordinated with different platinum metal substrates afforded structurally diverse platinum chelates. Nonetheless, many azo-imine-based platinum complexes demonstrated a wide range of biological activities, photo-switchable properties, and redox activities. The review encompasses a general overview of platinum complexes with versatile azo-azomethine ligands, their synthetic protocol, spectroscopic and structural features, chemical reactivity, and multipurpose applications in different areas.

Exploration of Variable Temperature Magnetism and Electrical Properties of a Pyridyl-isonicotinoyl Hydrazone Bridged Three-Dimensional Mn-Metal–Organic Framework with a Thiophene Dicarboxylato Link

In emerging trends in our technology-dependent society, the applicability of multifunctional coordination polymers (CPs) and metal–organic frameworks is highly stimulating. In search of such chemical compounds, a Mn(II), d5, based metal–organic framework (MOF), {[Mn2(tdc)2(pcih)2(EtOH)]n} (1), has been designed with the coordination of multidentate ligands tdc2– (2,5-thiophene dicarboxylato) and pcih (pyridine-4-carboxaldehyde isonicotinoylhydrazone). The structure determination by single crystal X-ray diffraction has revealed the formation of three-dimensional (3D) supramolecular architecture via the combined nearly perpendicular bridging of pcih and tdc2– ligands. A variable temperature magnetic measurement of 1 shows weak antiferromagnetism (χMT, 9.41 cm3 K mol–1 at 300 K) with two as good as “isolated” Mn(II) centers (S = 5/2 with g ≈ 2.07). Magnetic exchange is considered through 9/10 carboxylato bridged atoms inclusively spanning two Mn(II) centers at a distance of 4.114 Å. Interestingly, the 3D assembly of 1 exhibits electrical conductivity in the semiconducting region (band gap, 3.72 eV; barrier height, 0.65 eV; series resistance, 0.03 Ω). A Schottky barrier diode feature is recorded at a threshold potential of 0.19 V and follows a non-ohmic relation (I α V2), and the conductivity is 3.42 × 10–5 S m–1. A galvanostatic charge–discharge (GCD) experiment measures the moderate specific capacitance of 1 F/g at a 2 mV/s scan rate.

Facile process for surface metalization: Rational design of Ag nanoparticle/polymer brush toward high-efficiency electroless plating

In order to realize the convenient process of metalization on different materials and make electroless plating more efficient and fast, a multi-dentate ligand Ag complex (MLAg) was synthesized, which components include deionized water, 3-aminopropyl triethoxysilane, polyvinyl alcohol, and silver nitrate. It is worth noting that because the surface of MLAg contains a large number of -NH2 and -OH groups, it can be coated on different substrate surfaces through a process of rapid film formation (in situ film generation, brush coating, and dip coating) with a special structure (silver nanoparticles/polymer brush (Ag/PB) structure). Of note, we introduced polyvinyl alcohol as a structural optimization scheme to improve the structure of the Ag/PB interface (enhancing the Ag adsorption strength and electronic structure), which has a beneficial inhibitory effect on the growth of Ag grains. Of note, the MLAg/Ag interfacial force is a strong bond cooperation by means of covalent bond. The results show that the polyhedral Ag particles are composed of triangular (111) and square (100) crystal planes, and are evenly distributed on the surface of the substrate with outstanding film-forming performance, speed and catalytic ability. In the Cu chemical plating solution, HCHO exhibits an unstable free state and transforms into H-COOH, Ag d-orbitals and open orbitals donate their charge to Cu2+, enabling reduction to Cu atom, and thereby deposition on substrate surface. Furthermore, the excellent film-forming and catalytic capacity of as-fabricated MLAg make it suitable for a pre-treated material with a metallized surface.

Boosting CO2-to-CO selectivity and durability by metal-support interaction and encapsulated effect of Ni@C capsules

The thermocatalytic selective hydrogenation of CO2 to CO is significant for environment protection and artificial carbon cycling. Ni is a low-cost and promising candidate for CO2 hydrogenation. However, its CO selectivity and durability are still unsatisfactory. Here metal-support interaction (MSI) and encapsulation strategies are simultaneously introduced to one Ni-based material to suppress the commonly high CH4 production as well as enhance the CO selectivity, and the performance durability could be prolonged due to the sintering prevention of active Ni species by the encapsulation. Then, a sequential self-template method is designedly to synthesize well-dispersed Ni nanoparticles confined in hollow carbon capsules (Ni@C HCs). Ni@C HCs exhibit an outstanding CO selectivity of 91.30 % and good durability of over 72 h, greatly outperforming the corresponding impregnation-calcination derived Ni/SiO2 (CO selectivity: 12.73 %) and Ni/C (durability: < 4 h). Furthermore, the change of CO adsorption mode from the commonly polydentate ligand over Ni/SiO2 to easily desorbed monodentate ligand over Ni@C HCs confirmed by CO-TPD and in situ DRIFTS is revealed to be responsible for the enhanced CO selectivity of Ni@C HCs. Moreover, the positively charged Ni species in Ni@C HCs due to the MSI effect is experimentally and theoretically verified to be the in-depth reason for the alteration of the adsorption mode. Besides, the facile self-template method is suitable for synthesizing Co@C, NiCo@C, Ni3Fe@C, and NiCu3.8@C HCs, highlighting the potential of this methodology.

Analysis of Carrier Transport in Quantum Dot/Metal‐Oxide Phototransistors via Light‐Mediated Interfacial Modeling

AbstractQuantum dot (QD) hybrid phototransistors based on high‐mobility channel semiconductors have attracted great interest due to their outstanding photonic characteristics with diverse and broadband optoelectronic functionalities. However, difficulties for precise control of electronic coupling between QD particles and lack of QD/semiconductor interface analysis have limited the use of these platforms into practical optoelectronic applications. Here, the authors report a new strategy to high‐performance phototransistors based on CdSe QD/amorphous oxide semiconductor heterostructures using trap‐reduced chelating chalcometallate surface ligands by optimizing the QD layer thickness and interface engineering to enhance photogenerated charge transfer properties. Furthermore, based on performance parameters extracted from experimental structure and electrical characteristics, Technology Computer‐Aided Design (TCAD) modeling reveals carrier flow between the QDs in the semiconductor layer in agreement with various spectroscopic data. These modeling results indicate that interface engineering of QD with chalcometallate ligand results in very efficient photo‐induced charge transfer characteristics. Thus, high‐performance chalcometallate ligand QD‐based phototransistors are successfully realized with enhanced responsivity (2.12 × 104 A W−1) and photodetectivity (2.74 × 1016 Jones) compared with conventional monodentate ligand functionalized (SCN−) QD‐based devices (8.79 × 103 A W−1 and 8.8 × 1010 Jones, respectively). This is the demonstration of systematic analysis of QD‐based hetero‐structured phototransistors with light‐mediated interfacial physical modeling and electrochemical measurement.

Synthesis and Electrochemical Properties of Mixed‐Metal Triangular Complexes Based on Ferrocene‐Based Ligands and Dinuclear Arene Ruthenium Building Blocks

Six mixed-metal trinuclear complexes, [(p-cymene)2Ru2(μ-L)(μ-LFc)](OTf)2 (LFc=1,2-di(4-pyridylthio)ferrocene), were synthesized from a ferrocene-based ligand and a diruthenium building block. Crystallographic analyses revealed triangular structures with the ferrocene-based ligand linking the two ruthenium centers of the building blocks. The redox potentials of the trinuclear complexes depended on the type of L.

Atom-Precise Chiral Lanthanide-Silver(I) Heterometallic Clusters Ln3Ag5.

Three pairs of chiral Ln-Ag(I) clusters d/l-Ln3Ag5 with C3 symmetry were prepared by d/l-penicillamine as multidentate ligand bridged Ln3+ and Ag(I) ions. The chiral ligand induced the molecular cluster to be chiral, and the CD spectra of the chiral compounds d/l-Ln3Ag5 were slightly blue-shifted due to the lanthanide contraction. The studies of optical properties indicated that tunable photoluminescence from {AgS}-to-Ln3+ was achieved by introducing Ln3+ ions with different emission bands or regulating various excitation light.

Copper-Catalyzed Ligand-Controlled Selective Borocarbonylation of α-Substituted Styrenes Toward β-Boryl Aldehydes and Cyclopropyl Boronate Esters

Copper-Catalyzed Ligand-Controlled Selective Borocarbonylation of α-Substituted Styrenes Toward β-Boryl Aldehydes and Cyclopropyl Boronate Esters

Np(V) dicyanamide complexes with electroneutral N-donor ligands

Abstract Three new complexes of Np(V) dicyanamide with electroneutral N-donor ligands have been synthesized and structurally characterized: two with terpyridine derivatives: [(NpO2)(Cl-Terpy)(DMA)(N(CN)2)]·0.5DMA (1), [(NpO2)(TPTZ)(N(CN)2)(H2O)]·2H2O·CH3OH (2) and a dimeric complex with bipyridine [(NpO2)(Bipy)(N(CN)2)(H2O)]2·2(CH3OH) (3). In compounds 1–3, the coordination polyhedra of Np atoms are pentagonal bipyramids with “yl” oxygen atoms in apical positions. The equatorial plane of the bipyramids is formed by nitrogen atoms of the anions [N(CN)2]− and N-donor electroneutral ligands (Cl-Terpy, TPTZ, Bipy) and the oxygen atom of water molecule (1, 3) or DMA (2). In compounds 1 and 2, the [N(CN)2]− anions manifest themselves as monodentate ligands, and in compound 3 dicyanamide is a bidentate-bridging ligand.

Six-coordinate ruthenium water oxidation catalysts bearing equatorial polypyridinedicarboxylato and axial phosphine ligands

Ruthenium catalysts for water oxidation combining multidentate ligands [2,2′:6′,2″-terpyridine]-6,6″-dicarboxylato (tda) and 2,2′-bipyridine-6,6′-dicarboxylato (bda) with apical phosphine ligands have been prepared. These new complexes were fully characterized by standard spectroscopic and single-crystal X-ray crystallography analyses, and their redox properties were evaluated by electrochemistry. Specifically, [RuII(tda)(tris(2-furyl)phosphine)2] displayed two reversible redox waves that were assigned to the RuII/III and RuIII/IV transitions, respectively. The number of turnovers in CeIV-driven water oxidation reached 258 for the bda analog, and for the tda analog, early reaction rates were first order in initial catalyst concentration. The effects of adding fractional equivalents of CeIV were studied using UV–vis spectroscopy. Steric and electronic changes in the axial phosphine ligand can exert their effects on the properties and catalytic activity of the resulting complexes, which may be useful when exploring other chemistry of these complexes.

Chemistry of azo-imine based palladium complexes: a brief review

Abstract This paper provides a general overview of palladium complexes incorporating numerous multidentate azo-imine ligands, their structural diversity, synthetic protocol, interesting properties such as redox properties, biological activity and their further application on C – N coupling reactions, C – C cross-coupling reactions (e.g., Suzuki and Heck) and catalytic activity on different organic transformations. A detailed literature survey revealed that no brief review has yet been published on the azo-azomethine-based palladium complex. Therefore, the present review incorporates the research undertaken on the synthetic strategies and coordinating behaviour of various azo-imine ligands with palladium metal centre and a few important properties of metal complexes.

Effect of Surface Functionalization on the Magnetization of Fe3O4 Nanoparticles by Hybrid Density Functional Theory Calculations.

Surface functionalization is found to prevent the reduction of saturation magnetization in magnetite nanoparticles, but the underlying mechanism is still to be clarified. Through a wide set of hybrid density functional theory (HSE06) calculations on Fe3O4 nanocubes, we explore the effects of the adsorption of various ligands (containing hydroxyl, carboxylic, phosphonic, catechol, and silanetriol groups), commonly used to anchor surfactants during synthesis or other species during chemical reactions, onto the spin and structural disorder, which contributes to the lowering of the nanoparticle magnetization. The spin-canting is simulated through a spin-flip process at octahedral Fe ions and correlated with the energy separation between O2– 2p and FeOct3+ 3d states. Only multidentate bridging ligands hamper the spin-canting process by establishing additional electronic channels between octahedral Fe ions for an enhanced ferromagnetic superexchange interaction. The presence of anchoring organic acids also interferes with structural disorder, by disfavoring surface reconstruction.

Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand

Chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone, caH2) as a bidentate ligand for Nb(V) as a metal center is presented. The different coordination behavior of caH2 is well illustrated by a monomeric (Et4N)cis-[NbO(ca)2(H2O)OPPh3]·3H2O.THF (5) and a novel tetranuclear compound (Et4N)4[Nb4O4(ca)2(μ2-O)2Cl8]·2CH3CN (6) via self-assembly, respectively. These were obtained in &gt;80% yields and characterized by IR, UV/Vis and NMR (1H, 13C{1H}, 31P{1H}) spectroscopy and single crystal X-ray diffraction, and they included a systematic assessment of the solid-state behavior. The anionic metal complexes showed different coordination modes at the Nb(V): [Nb4O4(ca)2(μ2-O)2Cl8]4− (6a; distorted octahedral) and cis-[NbO(ca)2(H2O)(OPPh3)]− (5a; D5h distorted pentagonal bipyramidal), respectively. The tetranuclear complex 6a is substitution inert, while cis-[NbO(ca)2(H2O)OPPh3]− (5a) allowed a systematic ligation kinetic evaluation. The substitution of the coordinated triphenylphosphine oxide by a range of pyridine-type entering nucleophiles, 4-N,N-dimethyl-aminopyridine (DMAP), pyridine (py), 4-methylpyridine (4Mepy), 3-chloropyridine (3Clpy) and 3-bromopyridine (3Brpy) in acetonitrile at 31.2 °C was carefully evaluated. The subtle interplay between the main group ligand systems and the hard, early transition metal Nb(V) complex (5a) was well illustrated. The entering monodentate ligands showed a 15-fold reactivity range increase in the order 3Brpy &lt; 3Clpy &lt; 4Mepy &lt; py &lt; DMAP in broad agreement with the Brønsted-donating ability of the nucleophiles. The activation parameters determined for the reaction of 5a with DMAP as the entering ligand yielded ΔH≠kf = 52 ± 1 kJ mol−1 and ΔS≠kf = −108 ± 3 J K−1 mol−1 for the enthalpy and entropy of activation, respectively, indicating an associative substitution mechanism. The study presents an important contribution to the structure/reactivity relationships in Nb(V) complexes stabilized by chloranilic acid as a bidentate ligand.

"Tree"-like Multidentate Ligand-Assisted Synthesis of Polymolybdate-Based Architectures with Multinuclear Metal Clusters: Supercapacitor and Electrochemical Sensing Performances.

In this work, aiming for constructing multinuclear metal cluster-modified polymolybdate-based architectures with novel conformation, the "tree"-like multidentate ligand 5-(3-pyridyl)-1H-tetrazole) (3-ptzH) is introduced into the polymolybdate reaction system. Three new polymolybdate-based architectures with various multinuclear metal clusters, H4[Cu6(μ3-OH)2(3-ptz)6(γ-Mo8O28) (H2O)2]·2H2O (BOHU-1), H2[Ag4(3-ptz)2(Mo8O26)] (BOHU-2), and H4[Cu5(3-ptzH)2(3-ptz)2(MnMo9O32)2(H2O)4] (BOHU-3) (BOHU = Bohai University), have been prepared via the hydrothermal method and structurally characterized. In BOHU-1, a kind of pentanuclear copper cluster unit: [Cu5(μ3-OH)2(3-ptz)6]2+ is formed, which connects to construct a one-dimensional (1D) cluster-based chain. The 1D chains are extended to a two-dimensional (2D) layer via the Cu ions, which are further linked by the 4-connected [γ-Mo8O28]8- anions to build a three-dimensional (3D) framework. In BOHU-2, when a AgI ion was used as the central metal, the 3-ptz adopts different coordination modes to link the Ag ions, forming hexanuclear [Ag6(3-ptz)4]2+ cluster and finally 1D chains. These 1D cluster-based chains are connected by the 6-connected [γ-Mo8O26]4- anions to establish a 2D layer, which is further extended by [Mo8O26]n4n- 1D chains to a 3D framework. For BOHU-3, the chiral [MnMo9O32]6- anions are introduced and coordinated with the Cu ions to build left- and right-handed 1D chains, which are connected via the [Cu3(3-ptz)4]2+ cluster to form a 1D ladder-like chain. The effects of 3-ptz on the formation of multinuclear clusters, as well as the metals and polymolybdates on the multinuclear clusters and final structures of BOHU-1∼3, are discussed. The electrochemical performances of BOHU-1∼3 as electrode materials for supercapacitors and electrochemical sensors are investigated.

Co-operation between multidentate ligand and inorganic salts: preparation of solvent-free primary explosives based on 4-amino-1,2,5-oxadiazole-3-carbohydrazide

Using the furazan skeleton and hydrazide group with coordination potentiality as targets, the ligand 4-Amino-1,2,5-oxadiazole-3-carbohydrazide (AOCA, 4) with multiple coordination sites was designed and synthesized. According to the different coordination abilities of Ag(I) and Cu(II), four kinds of ECPs were prepared by different crystallization methods, and their structures were confirmed by X-ray single-crystal diffraction, IR, and elemental analysis. In addition, the physicochemical properties test results show that the 1D structure ECPs-6 ([Ag(AOCA)ClO4]n) has the best performance (Tted = 255 °C, D = 7.6 km s−1,IS = 10 J, FS = 40 N). The test results of detonation performance show that ECPs-8 (Cu(AOCA)2(ClO4)2) with 0D structure is the best. In particular, only ECPs-6 and ECPs-8 can be directly detonated by laser, and the energy of the laser detonating for ECPs-8 is the smallest (P = 6 W, τ = 10 ms, E = 60 mJ). In addition, the interrelationship of “DSC-MS-DP-IM” was also explored.