Dinuclear Complexes Research Articles

Visible light induced generation of nitric oxide from designed ruthenium nitrosyl complex and studies on antibacterial activity

In this article, a chloro-bridged dinuclear ruthenium complex Ru-(a) has been synthesized, which was employed for the synthesis of a photolabile NO liberating complex Ru-(b). A newly synthesized tridentate ligand 2-methyl-6-((2-phenyl-2-(pyridin-2-yl)hydrazineylidene)methyl)pyridine with three N-atoms as donating site was used to synthesize the complex Ru-(a). The molecular structure of Ru-(a) was investigated by single-crystal X-ray crystallography and, in solution was characterized by or ESI mass spectrometry. Several spectroscopic techniques were used for the characterization of the ligand as well as complexes. To understand the electronic structure of Ru-(a) and Ru-(b), DFT computations were utilized. By the utilization of visible light, photo-liberation experiments were examined. The amount of NO released during the photodissociation experiment was measured using the Griess reagent assay technique. The photodissociated NO was fruitfully transported to reduced myoglobin (Mb). The antibacterial activity against Escherichia coli was carried out with 31.2 μg/mL concentration of Ru-(b). In the final results, we detected considerable antibacterial activity against E. coli and showed >99 % inhibition of the bacterial cells after 120 min of the experiment on exposure to visible light. These investigations proposed that Ru-(b) could be employed to treat several topical deliveries of NO for treating various topical and bacterial infections.

Synthesis, Reactivity, and Complexation with Fe(0) of a Tight-bite Bis(N-heterocyclic silylene).

The synthesis, reactivity, and complexation with Fe(0) precursor of a tight-bite bis(N-heterocyclic silylene) (bis(NHSi)) ligand 1 are reported. The reaction of 1 with p-toluidine led to the activation of both N-H bonds across Si(II) atoms to afford a four-membered heterocyclic cyclodisilazane 2, with hydride substituents attached to five-coordinate Si atoms. A 1 : 2 reaction of 1 with Fe(CO)5 led to an intriguing dinuclear complex 3 featuring a five-membered (N-Si-Fe-Fe-Si) ring with a Fe-Fe bond distance of 2.6892(13) Å. All compounds (1-3) were thoroughly characterized by various spectroscopic methods and X-ray diffraction studies conclusively established their molecular structures. DFT calculations were carried out to shed light on bonding and energetic aspects in 1-3.

Design of New Bis(1,2,3-triazol-1-yl)methane-Based Nitrogen Ligands: Synthesis and Coordination Chemistry.

The reaction between bis(1,2,3-triazol-1-yl)methane derivatives and nBuLi and various aldehydes, yielded novel neutral ligand precursors incorporating alcohol functional groups. The resulting compounds exhibited distinct characteristics depending on the steric hindrance of the aldehyde employed. In instances where aromatic aldehydes were utilized, functionalization occurred at the methine group bridging both triazole rings. Conversely, the use of pivalic aldehyde prompted functionalization at the C5 position of the triazole ring. These compounds were subsequently employed as ligand precursors in the synthesis of organometallic aluminum and zinc complexes, yielding dinuclear complexes with high efficiency. The structural elucidation of all compounds was accomplished through spectroscopic methods and validated by X-ray crystallography. Preliminary catalytic investigations into the coupling reaction of cyclohexene oxide and CO2 revealed that aluminum and zinc complexes catalyzed the selective formation of polyether and polycarbonate materials, respectively.

Unprecedented Pyrazine‐Bridged Guanidinate Rare Earth Complexes Through a Bridge Splitting Reaction Path

AbstractThe development of reaction pathways and ancillary ligand scaffolds is essential in the pursuit of higher nuclearity rare earth metal clusters that are relevant in storage materials and catalysis. Guanidinate anions represent attractive ligands due to their high degree of customizability allowing for facile alterations of both their steric and electronic properties. Here, we demonstrate an unprecedented bridge splitting reaction that shifts chloride anions in favor of a bridging neutral pyrazine to give pyrazine‐bridged dinuclear guanidinate rare earth complexes, [{(Me3Si)2NC(NiPr)2}2RECl]2(μ‐pyz) (RE =Y (1) and Er (2), pyz=pyrazine). Each six‐coordinate metal center is ligated by two guanidinates, one chloride ligand, and one nitrogen atom from the bridging pyrazine unit. The molecules were characterized by X‐ray crystallography, IR, NMR, and UV‐Vis spectroscopy. DFT calculations conducted on 1 provide insight into both the bonding picture and the mechanism of complex formation. This type of reaction constitutes a seminal application of a bridge splitting mechanism to the rare earth metals.

Syntheses, characterizations and crystal structures of two Ni(II) complexes [Ni2(neoc)4(H2O)(CO3)](NO3)2·3H2O and [Ni(bapa)2](NO3)2·H2O and magnetic properties of the carbonato complex

By the reaction of nickel(II) nitrate hexahydrate with 2,9-dimethyl-1,10-phenanthroline (neoc) and bis(3-aminopropyl)amine (bapa) two novel complexes were isolated, namely [Ni2(neoc)4(H2O)(CO3)](NO3)2·3H2O (1) and [Ni(bapa)2](NO3)2·H2O (2). Both structures are ionic and comprise hexacoordinated Ni(II) central atoms. Complex 1 is built up of dinuclear [Ni2(neoc)4(H2O)(CO3)]2+ complex cation, nitrate anions and water solvate molecules. The dinuclear complex cation is centrosymmetric and the two Ni(II) atoms are linked by a μ3-bridging-chelating carbonato ligand which, due to the presence of an inversion centre, exhibits two orientations with equal probability. The coordination sphere of Ni(II) atom is heteroleptic with an N4O2 donor set formed by two chelating neoc ligands and two O-donor atoms from bridging carbonato and aqua ligands. The carbonato ligand was formed by transformation of absorbed carbon dioxide from air (single crystals) or from dry ice (bulk sample). The crystal structure of 2 is formed by [Ni(bapa)2]2+ complex cation, nitrate anions and water solvate molecule. The coordination sphere of Ni(II) atom in 2 is homoleptic with N6 donor set. Both bapa ligands act as double chelating 3 N-donor ligands and are coordinated in mer-fashion. The study of the magnetic response of 1 in the temperature range 1.8–300 K revealed that the system can be considered as a system of antiferromagnetic S = 1 spin dimers with exchange interaction J/hc = -13.86 cm−1 (J/kB = -19.96 K) and axial single-ion anisotropy D/hc = -4.94 cm−1 (D/kB = -7.12 K). The experimental magnetic results were corroborated by ab initio and DFT calculations.

Conformational investigations on three large dinuclear triple helicates by single crystal X-ray diffraction

Three new dinuclear triple helicates were synthesised using a ditopic semi-rigid pyridylylimine ligand L, separated by a diphenoxy-biphenol spacer providing considerable length to the backbone. L and the new large dinuclear triple helicate complexes [Fe2L3](BF4)4 (1), [Ni2L3](BF4)4 (2) and [Zn2L3](BF4)4 (3) have been characterised in solution and solid state. Single crystal X-ray diffraction was used to investigate overall complex ion shape as the coordination sphere was modulated by metal ion selection. Small differences in complex shape were seen to arise due to subtle distortions in coordination sphere environments. This study sheds light on how the length and twist of dinuclear triple helicates can be tuned by selection of coordinating metal ion.

Air-Stable Dinuclear Complexes of Four-Coordinate ZnII and NiII Ions with a Radical Bridge: A Detailed Look at Redox Activity and Antiferromagnetic Coupling.

Air-stable dinuclear complexes [(bmsab)NiII(tmsab)NiII(bmsab)]3- and [(bmsab)ZnII(tmsab)ZnII(bmsab)]3- (bmsab = bis(methanesulfoneamido)benzene, tmsab = tetra(methanesulfonamido)benzene) were prepared via a synthetic route based on heteroleptic precursor complexes. The new complexes combine a distorted tetrahedral coordination environment with an open-shell bridging ligand. The ZnII species was subjected to a detailed investigation of the (spectro-)electrochemical processes. The NiII species is a rare example of a complex that combines strong exchange coupling (J > 440 cm-1) with pronounced positive zero-field splitting (D = +72 cm-1). Combining SQUID magnetometry and (HF)EPR spectroscopy with ab initio calculations allowed for accurate quantification of the exchange interaction.

Dynamic and relativistic effects on Pt-Pt indirect spin-spin coupling in aqueous solution studied by abinitio molecular dynamics and two- vs four-component density functional NMR calculations.

Treating 195Pt nuclear magnetic resonance parameters in solution remains a considerable challenge from a quantum chemistry point of view, requiring a high level of theory that simultaneously takes into account the relativistic effects, the dynamic treatment of the solvent-solute system, and the dynamic electron correlation. A combination of Car-Parrinello molecular dynamics (CPMD) and relativistic calculations based on two-component zeroth order regular approximation spin-orbit Kohn-Sham (2c-ZKS) and four-component Dirac-Kohn-Sham (4c-DKS) Hamiltonians is performed to address the solvent effect (water) on the conformational changes and JPtPt1 coupling. A series of bridged PtIII dinuclear complexes [L1-Pt2(NH3)4(Am)2-L2]n+ (Am = α-pyrrolidonate and pivalamidate; L = H2O, Cl-, and Br-) are studied. The computed Pt-Pt coupling is strongly dependent on the conformational dynamics of the complexes, which, in turn, is correlated with the trans influence among axial ligands and with the angle N-C-O from the bridging ligands. The J-coupling is decomposed in terms of dynamic contributions. The decomposition reveals that the vibrational and explicit solvation contributions reduce JPtPt1 of diaquo complexes (L1 = L2 = H2O) in comparison to the static gas-phase magnitude, whereas the implicit solvation and bulk contributions correspond to an increase in JPtPt1 in dihalo (L1 = L2 = X-) and aquahalo (L1 = H2O; L2 = X-) complexes. Relativistic treatment combined with CPMD shows that the 2c-ZKS Hamiltonian performs as well as 4c-DKS for the JPtPt1 coupling.

Ligand‐field effect to harness the magnetic anisotropy in a series of mixed valence Co (III)–Co (II) dinuclear complexes

Three mixed valence dinuclear Co (III)–Co (II)‐based complexes having general formulae of [CoIICoIII (HL2)2(L1)] [L1H = 2‐hydroxy‐1‐naphthaldehyde (1), o‐vanillin (2), and salicylaldehyde (3)] have been synthesized successfully using Schiff base (LH4) ligand. The complexes were characterized by single‐crystal XRD, powder XRD, IR, and UV–Vis analyses. The CoII ion with elongated octahedral geometry conferred significant magnetic anisotropy with D values being 64.0(8), 71.1(7), and 52.1(3) cm−1 for 1, 2, and 3, respectively. These complexes exhibited single‐molecule magnet behavior with magnetic relaxation occurring mainly through Raman for 1 and 3 whereas direct and Raman for complex 2. The analysis of the static and dynamic magnetic properties was further supported by theoretical calculations using CASSCF/DLPNO‐NEVPT2.

NIR-II Emission from Cyclometalated Dinuclear Pt(III) Complexes.

Half-lantern Pt(II) dinuclear complexes [{Pt(C∧Npz)(μ-S∧NR)}2] (HC∧Npz = 1-naphthalen-2-yl-1H-pyrazole; R = H, HS∧N: 2-mercaptopyrimidine 1; R = CF3, HS∧NF: 4-(trifluoromethyl)-2-mercaptopyrimidine 2) were selectively obtained as single isomers with the C∧N groups in an anti-arrangement and rather short metallophilic interactions (dPt-Pt = 2.8684(2) Å for 2). They reacted with haloforms in the air and sunlight to obtain the corresponding oxidized diplatinum(III) derivatives [{Pt(C∧Npz)(μ-S∧NR)X}2] (X = Cl (1-Cl), Br (1-Br), I (1-I, 2-I)). The single-crystal X-ray structures exhibit Pt-Pt distances typical for the existence of a metal-metal bond, which evidence fairly well the influence of the axial ligand (X). The reactions of 1 and 2 with CHI3 in the dark afforded mixtures of [IPt(C∧Npz)(μ-S∧N)2Pt(C∧Npz)CHI2] and 1-I or 2-I, with the former being the major species under an Ar atmosphere, while the reactions of 1 with CHBr3 and CHCl3 need light to occur. These Pt2(III,III) complexes display low-energy absorptions and emissions that strongly depend on the axial ligand. In the solid state, they show a broad NIR emission ranging from 985 to 1070 nm at RT that suffers a hypsochromic shift when cooling down to 77 K. The photoemissive behavior of the dinuclear Pt(II) and Pt(III) systems is disclosed with the aid of density functional theory calculations.

Synthesis, Crystal Structures, Genotoxicity, and Antifungal and Antibacterial Studies of Ni(II) and Cd(II) Pyrazole Amide Coordination Complexes.

In this study, we synthesized two coordination complexes based on pyrazole-based ligands, namely 1,5-dimethyl-N-phenyl-1H-pyrazole-3-carboxamide (L1) and 1,5-dimethyl-N-propyl-1H-pyrazole-3-carboxamide (L2), with the aim to investigate bio-inorganic properties. Their crystal structures revealed a mononuclear complex [Ni(L1)2](ClO4)2 (C1) and a dinuclear complex [Cd2(L2)2]Cl4 (C2). Very competitive antifungal and anti-Fusarium activities were found compared to the reference standard cycloheximide. Additionally, L1 and L2 present very weak genotoxicity in contrast to the observed increase in genotoxicity for the coordination complexes C1 and C2.

The performance and efficiency of twelve range-separated hybrid DFT functionals for calculation of the magnetic exchange coupling constants of di-nuclear first row transition metal complexes

The performance and efficiency of twelve range-separated hybrid functionals are compared with each other in calculating magnetic exchange coupling constant (J) data on eleven di-nuclear first-row transition metal complexes having di-copper (Cu) and di-vanadium (V) as their central atoms. The J values are then compared with the experimental findings. In addition to that we also computed the B3LYP results of these complexes. We compared them with the results obtained from range-separated functionals as well as with the experimental results to understand their performances in predicting the magnetic exchange coupling constant. When computing, we reoptimized all the structures of the complexes taken from the crystal data, and then the values of Js were determined. The performances are predicted in terms of four statistical error matrices, namely, the mean absolute error (MAE), mean fractional error (MFE), mean signed error (MSE), root mean square error (RMSE) in cm−1.

Nicotinamide, acetate and their two new complexes with Zn(II) and Cd(II)

Two new complexes of Zn(II) and Cd(II) with acetate and nicotinamide as mixed ligands were synthesized and characterized. The Zn(II) complex is mononuclear, [Zn(ac)2(NA)2] (1), while the Cd(II) is a dinuclear one, [Cd2(ac)4(NA)4].2H2O (2), where ac = acetate and NA = nicotinamide. The compounds were characterized by means of single-crystal X-ray diffraction, FTIR, 1H NMR, 13C NMR spectroscopy, thermal analysis and elemental analysis. The geometry of the metal ion is distorted tetrahedral for Zn(II) and distorted pentagonal bipyramid geometry for Cd(II). In the dinuclear complex, each metal ion is coordinated by three acetate groups, but there are two different types of coordination modes for the acetate ligands: bidentate chelating and bridging bidentate chelating.

Valence Tautomerism Induced Proton Coupled Electron Transfer:X-H Bond Oxidation with a Dinuclear Au(II) Hydroxide Complex.

We report the preparation and characterization of the dinuclear AuII hydroxide complex AuII 2(L)2(OH)2 (L=N,N'-bis (2,6-dimethyl) phenylformamidinate) and study its reactivity towards weak X-H bonds. Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton-coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au-Au σ-bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)-H bond cleavage. We thus describe the oxidation event as a valence tautomerism-induced PCET where the basicity of one reduced Au-OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical-type reactivity by a closed shell AuII complex.

Valence Tautomerism Induced Proton Coupled Electron Transfer:X−H Bond Oxidation with a Dinuclear Au(II) Hydroxide Complex

AbstractWe report the preparation and characterization of the dinuclear AuII hydroxide complex AuII2(L)2(OH)2 (L=N,N′‐bis (2,6‐dimethyl) phenylformamidinate) and study its reactivity towards weak X−H bonds. Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton‐coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au−Au σ‐bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)−H bond cleavage. We thus describe the oxidation event as a valence tautomerism‐induced PCET where the basicity of one reduced Au−OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical‐type reactivity by a closed shell AuII complex.

Synthesis and characterization of bis[(dimethylphosphanylethynyl)dimethylsilyl]methane-digold(I) dichloride

Abstract The reaction of chlorodimethylphosphane with dilithiated bis(ethynyldimethylsilyl)methane leads to the corresponding bis[(dimethylphosphanylethynyl)dimethylsilyl]methane (1) which reacts readily with chloroauric acid in the presence of a reductant to form its dinuclear chlorogold(I) complex (2). The terminal chloride units of this compound can be substituted by reaction with nucleophiles. Furthermore, the metallophilic host functionality of the dinuclear complex 2 towards metallophilic atoms such as copper, silver, and thallium was tested. The crystal structure of bis[(dimethylphosphanylethynyl)dimethylsilyl]methane-digold(I) dichloride (2) is presented, which shows chains of the molecules aggregated by intermolecular aurophilic contacts.

Ho(III)-coordination Complex: Fluorescence Performances and Combined with Captopril-Hydrogels against Glioma.

In this study, a novel dinuclear lanthanide complex, denoted as [Ho2(L)2(acac)2(CH3OH)2]·CH3OH (1) (where H2L is 2-[((4-methyl)-2-(carboxyl)-imino)]methyl]-8-hydroxyquinoline, and Hacac is acetylacetonate), was successfully synthesized and characterized using single-crystal and elemental analysis, with the auxiliary ligand β-diketonate and the 8-hydroxyquinoline Schiff base derivative serving as the foundation. Through ligand-to-metal charge transfer, Compound 1 demonstrated remarkable green fluorescence properties, showcasing potential applications in green fluorescence materials and fluorescence sensing. Additionally, Hyaluronic Acid (HA)/Carboxymethyl Chitosan (CMCS) hydrogels were synthesized through a chemical method. Utilizing captopril as a drug model, a novel metal gel granule of captopril was developed and assessed for its inhibitory activity against glioma cells. Molecular docking simulations revealed that only the methanol group in the Ho complex could contribute a polar atom for the formation of binding interactions.

New polypyridine Ru(II) dinuclear complex capable of catalyzing the water oxidation reaction

AbstractIn natural and artificial photosynthesis, the water oxidation reaction is the bottleneck for the conversion of solar energy into chemical energy. In this work, we report the syntheses and physicochemical characterization of two new dinuclear Ru(II) complexes, with molecular formula [{Ru(tpy)Cl}2(μ‐dpp)](PF6)2 (1) and [{Ru(tpy)(H2O)}2(μ‐dpp)](PF6)4 (2) (with tpy=2,2’ : 6’,2”‐terpyridine and dpp=2,3‐bis(2‐pyridyl)pyrazine). Chloro‐complex (1) was used as a precursor for the aquo‐complex (2) which can act as an active water oxidation reaction catalyst using Ce(IV) in CF3COOH 0.1 M as sacrificial oxidant. The mechanism and rate constants were explored by combining conventional mixing and stopped‐flow experiments with spectrophotometric monitoring in the UV‐visible region. DFT and TD‐DFT calculations were done to support the assignments of the experimental data. From the kinetic and theoretical data obtained, we propose‐ that (2) catalyses water oxidation via a nucleophillic water attack mechanism (WNA). Besides, catalytic activity for (2) was evaluated from reported values of turnover frequency (TOF) and turnover number (TON) values at pH=1.

Preparative and Catalytic Properties of MoVI Mononuclear and Metallosupramolecular Coordination Assemblies Bearing Hydrazonato Ligands.

A series of polynuclear, dinuclear, and mononuclear Mo(VI) complexes were synthesized with the hydrazonato ligands derived from 5-methoxysalicylaldehyde and the corresponding hydrazides (isonicotinic hydrazide (H2L1), nicotinic hydrazide (H2L2), 2-aminobenzhydrazide (H2L3), or 4-aminobenzhydrazide (H2L4)). The metallosupramolecular compounds obtained from non-coordinating solvents, [MoO2(L1,2)]n (1 and 2) and [MoO2(L3,4)]2 (3 and 4), formed infinite structures and metallacycles, respectively. By blocking two coordination sites with cis-dioxo ligands, the molybdenum centers have three coordination sites occupied by the ONO donor atoms from the rigid hydrazone ligands and one by the N atom of pyridyl or amine-functionalized ligand subcomponents from the neighboring Mo building units. The reaction in methanol afforded the mononuclear analogs [MoO2(L1-4)(MeOH)] (1a-4a) with additional monodentate MeOH ligands. All isolated complexes were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP) as an oxidant in water. The impact of the structure and ligand lability on the catalytic efficiency in homogeneous cyclooctene epoxidation was elucidated based on theoretical considerations. Thus, dinuclear assemblies exhibited better catalytic activity than mononuclear or polynuclear complexes.

Preparation of a Compound with a SiII -SiIV -SiII Bonding Arrangement.

Herein, we report the synthesis of a rare bis-silylene, 1, in which two SiII atoms are bridged by a SiIV atom. Compound 1 contains an unusual SiII -SiIV -SiII bonding arrangement with SiII -SiIV bond distances of 2.4212(8) and 2.4157(7) Å. Treatment of 1 with Fe(CO)5 afforded a dinuclear Fe0 complex 2 with two unusually long Si-Si bonds (2.4515(8) and 2.4488(10) Å). We have also carried out a detailed computational study to understand the nature of the Si-Si bonds in these compounds. Natural bond orbital (NBO) and energy decomposition analysis-natural orbital for chemical valence (EDA-NOCV) analyses reveal that the Si-Si bonds in 1 and 2 are of an electron-sharing nature.