Bidentate Coordination Mode Research Articles

Sulfuric Acid Solutions of [Pt(OH)4(H2O)2]: A Platinum Speciation Survey and Hydrated Pt(IV) Oxide Formation for Practical Use

The systematic study of the platinum speciation in sulfuric acid solutions of platinum (IV) hydroxide {[Pt(OH)4(H2O)2], HHPA} was performed with the use of a combination of methods. Depending on the prevailing Pt form, the three regions of H2SO4 concentration were marked: (1) up to 3 M H2SO4 forms unstable solutions gradually generating the PtO2·xH2O particles; (2) 4-12 M H2SO4, where the series of mononuclear aqua-sulfato complexes ([Pt(SO4)n(H2O)6-n]4-2n, where n = 0···4) dominate; and (3) 12 M and above, where, along with [Pt(SO4)n(H2O)6-n]4-2n species, the polynuclear Pt(IV) species and complexes with a bidentate coordination mode of the sulfato ligand are formed. For the first time, the salts of the aqua-hydroxo Pt(IV) cation [Pt(OH)2(H2O)4]SO4 (triclinic and monoclinic phases) were isolated and studied with a combination of methods, including the single-crystal X-ray diffraction. The formation of PtO2·xH2O particles in sulfuric acid solutions (1-3 M) of HHPA and their spectral characteristics and morphology were studied. The deposition of PtO2·xH2O was highlighted as a convenient method to prepare various Pt-containing heterogeneous catalysts. This possibility was illustrated by the preparation of Pt/g-C3N4 catalysts, which show an excellent performance in catalytic H2 generation under visible light irradiation with a quantum efficiency up to 5% and a rate of H2 evolution up to 6.2 mol·h-1 per gram of loaded platinum.

Luminescent and Sublimable Binaphthyl-Based Field-Induced Lanthanide Single-Molecule Magnets

The association of the [Ln(hfac)3(H2O)2] metallic building blocks with the new ligand [1,1’-binaphthalene]-8,8’-diylbis(diphenylphosphine oxide) (L) led to the formation of three mononuclear complexes of formula [Ln(hfac)3(L)] (LnIII = Eu (1), Dy (2) and Yb (3)). The mononuclear character of the compounds is due to the bidentate coordination mode adopted by L to link the metal. L allows the observation of the characteristic visible 5D0  7FJ (J = 0-4) EuIII- and near infrared 2F5/2  2F7/2 YbIII- emissions while 2 is only weakly emissive due to the mismatch between the energy positions of the triplet excited state of the ligand and DyIII emissive state. The magnetic data reveal a field-induced Single-Molecule Magnet (SMM) behavior for 2 and 3 with an efficient suppression of the Quantum Tunneling of the Magnetization (QTM). The slow magnetic relaxation occurs through a Raman process while the Orbach contribution is discarded as confirmed by the correlation with the MJ states energy splitting provided by the luminescence spectrum of 3.

Conversion of monodentate benzoylthiourea palladium(II) complex to bidentate coordination mode: Synthesis, crystal structure and catalytic activity in the Suzuki-Miyaura cross-coupling reaction

Trans-dichloro bis[N,N-dibutyl-N'-(4-chloro-benzoyl)thioureato-κS]palladium(II) complex (Trans-[PdIICl2(HBTU-κS)2]) is formed by reaction between PdCl2 and N,N-dibutyl-N'-(4-chlorobenzoyl)thiourea (BTU) in acetonitrile. Cis-bis[N,N-dibutyl-N'-(4-chlorobenzoyl) thioureato-κ2O,S]palladium(II) (cis-[PdII(BTU-κ2S,O)2]) is obtained by recrystallization of trans-[PdIICl2(HBTU-κS)2] in ethanol:dichloromethane solvent mixture. The prepared ligand coordinates with Pd(II) ion in monodentate coordination mode for trans-[PdIICl2(HBTU-κS)2] and in bidentate coordination mode for cis-[PdII(BTU-κ2S,O)2]. Both Pd(II) complexes have been characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, and UV-Vis techniques. The detail structural formulations of trans-[PdIICl2(HBTU-κS)2] and cis-[PdII(BTU-κ2S,O)2] have been defined by X-ray single-crystal diffraction. The palladium complexes were also applied as an efficient catalyst for the Suzuki-Miyaura cross-coupling reaction of aryl halides with aryl boronic acids at 110°C using a very high substrate/catalyst ratio.

(Electro)chemical and antimicrobial characterization of novel Ru(II) bipyridine complexes with acetylpyridine analogs

Three ruthenium-bipyridine complexes (1–3) carrying acetylpyridine ligand unit were synthesized in methanol via the reaction of [RuCl2(bpy)2] with corresponding acetylpyridine (2-, 3-, and 4-acpy). Obtained complexes were characterized by (1H and 13C) NMR and IR spectroscopy, MS spectrometry, UV‒vis spectrophotometry, and cyclic voltammetry. Their structural characterization revealed bidentate coordination mode for 2-acpy while 3- and 4-acpy acted as monodentate ligands. The electrochemical profile of newly synthesized compounds was investigated by cyclic voltammetry which confirmed their electrochemical activity. Voltammetric responses within the −1.20 < Ep < 1.50 V range of potentials were summarized in two major events: Ru(II)→Ru(III) oxidation spotted at app. ΔEp = 0.65 V and successive reductions of bpy units located from ‒0.79 V to 0.47 V (vs. Ag/AgCl (3 M) electrode). The DNA-binding activity of the complexes was evaluated by both UV‒vis spectrophotometry and cyclic voltammetry indicating DNA-intercalation with a slight contribution of electrostatic interactions. Furthermore, antimicrobial activity was tested against bacterial and fungal strains, for which moderate activity was observed. Assessment of in vitro toxicity against freshly hatched nauplii of Artemia salina as well as radical scavenging capacity was evaluated. The test compounds showed neither toxicity nor antioxidant activity.

Synthesis, Characterization, Biological Activity and Molecular Docking Studies of Novel Organotin(IV) Carboxylates.

Four new carboxylates complexes with general formula R2SnL2 and R3SnL, where R = n-butyl (1, 3), methyl (2, 4) and L = 4-Chlorophenoxyacetate, were synthesized in significant yields. FT-IR analysis revealed a chelating (1 and 2) and a bridging bidentate (3 and 4) coordination modes for the carboxylate ligand in solid state which was further confirmed by the single crystal X-ray analysis of complex 4. The NMR data (1H, 13C and 119Sn) revealed a higher coordination number around the tin center in R2SnL2 (1 and 2) compared to R3SnL (3 and 4). A close matching was observed between the experimental and calculated structures (obtained at B3LYP/6-31G* + LANL2DZ basis set). Quantum chemical analysis indicates that the carboxylate moiety has the major contribution in the formation of filled and unfilled orbitals as well as in ligand to ligand intramolecular charge transfer during the electronic transitions. The cytotoxicity data of the screened compounds evaluated against lung cancer cell line (A549) and normal lung fibroblast cell line (MRC-5) revealed that 1, 3 and 4 have shown dose dependent cytotoxic effects while HL and 2 have shown steady and low cytotoxic activities. The antibacterial activity of complexes 1–4 is higher than that of HL. Molecular docking study showed an intercalation binding mode for complex 3 with DNA (docking score = −3.6005) involving four polar interactions. Complex 3 docking with tubulin (PDB ID 1SA0) with colchicine as a target protein resulted in three polar interactions (docking score −5.2957). Further, the docking analysis of the HL and 1–4 has shown an adequate interactions with the coronavirus SARS-CoV-2 spike protein, nucleocapsid protein and human angiotensin converting enzyme (ACE2).

K(Na,K)Na2[Cu2(SO4)4]: a new highly porous anhydrous sulfate and evaluation of possible ion migration pathways

Alkali copper sulfates form a rapidly developing family of inorganics. Herein, we report synthesis and crystal structure, and evaluate possible ion migration pathways for a novel Na-K-Cu anhydrous sulfate, K(Na,K)Na2[Cu2(SO4)4]. The CuO7 and SO4 polyhedra share common vertices and edges to form [Cu2(SO4)4]4− wide ribbons, which link to each other via common oxygen atoms forming the host part of the structure. Four guest alkali sites are occupied by solely K+, mixture of K+ and Na+, and solely Na+, which agrees well with the size of the cavities. The crystal structure of K(Na,K)Na2[Cu2(SO4)4] contains two symmetry-independent Cu sites with [4+1+(2)] coordination environments. The overall coordination polyhedra of Cu2+ can be considered as `octahedra with one split vertex'. A similar coordination mode was observed also in some other multinary copper sulfates, mostly of the mineral world. These coordination modes were reviewed and five types of CuO7 polyhedra are identified. CuO7 polyhedra are almost restricted to copper sulfates and phosphates. It was found that a larger amount of the smaller SO4 2− and PO4 3− anions can cluster around a single Cu2+ cation; in addition, for such relatively small anions, both mono (κ1) and bidentate (κ2) coordination modes to the Cu2+ are possible. The correlation between crystallographic characteristics and bond valence energies showed that the new copper sulfate framework, [Cu2(SO4)4]4−, contains one interconnected path suitable for Na+ mobility at tolerable activation energies and that K(Na,K)Na2[Cu2(SO4)4] can be considered as a potential candidate for novel Na-ion conductors.

Synthesis, spectroscopic characterization, density functional, thermal studies, and molecular docking simulation of rare earth element complexes

AbstractSix new complexes, namely, [ErH2L1Cl2H2O]Cl·5H2O, [YbH2L1Cl2H2O]Cl·5H2O, [LaH2L1Cl2H2O]Cl·4H2O, [ErHL2(H2O)4]Cl2·5H2O, [YbHL2(H2O)4]Cl2·4H2O, and [LaHL2Cl(H2O)3]Cl·5H2O, have been prepared under sufficient experimental conditions. The six complexes have been characterized by UV–visible tests, infrared (IR) spectroscopy, elemental analyses, and molar conductivity measurements. Thermal studies using thermogravimetric analysis demonstrated that the complexes decomposed in three to four steps within the temperature range 30–900°C and metal oxides left as residues. At the DFT/B3LYP/LANL2DZ level of theory, theoretical calculations including geometry optimization and some quantum chemical parameters were carried out. Time‐dependent density functional theory (TD‐DFT) measurements have also been conducted to allocate their electronic spectra. All the complexes exhibit molecular structure with the metal ions in six‐coordination geometry. According to the spectroscopic data, the investigated ligands coordinated to the metal ions in bidentate (H2L1) and tridentate (HL2) coordination mode. All complexes were tested for in vitro anticancer, antibacterial, and antifungal activities where they exhibited promising antibacterial and antifungal activity. Furthermore, the molecular docking study examined the possible ways to tie up Staphylococcus aureus' 50S‐RsfS complex with the crystal structure of Cryo‐EM (PDB ID: 6SJ6).

Photoinduced Trifluoromethylation of Arenes and Heteroarenes Catalyzed by High-Valent Nickel Complexes.

We describe a series of air-stable NiIII complexes supported by a simple, robust naphthyridine-based ligand. Access to the high-valent oxidation state is enabled by the CF3 ligands on the nickel, while the naphthyridine exhibits either a monodentate or bidentate coordination mode that depends on the oxidation state and sterics, and enables facile aerobic oxidation of NiII to NiIII . These NiIII complexes act as efficient catalysts for photoinduced C(sp2 )-H bond trifluoromethylation reactions of (hetero)arenes using versatile synthetic protocols. This blue LED light-mediated catalytic protocol proceeds via a radical pathway and demonstrates potential in the late-stage functionalization of drug analogs.

Photoinduced Trifluoromethylation of Arenes and Heteroarenes Catalyzed by High‐Valent Nickel Complexes

AbstractWe describe a series of air‐stable NiIII complexes supported by a simple, robust naphthyridine‐based ligand. Access to the high‐valent oxidation state is enabled by the CF3 ligands on the nickel, while the naphthyridine exhibits either a monodentate or bidentate coordination mode that depends on the oxidation state and sterics, and enables facile aerobic oxidation of NiII to NiIII. These NiIII complexes act as efficient catalysts for photoinduced C(sp2)−H bond trifluoromethylation reactions of (hetero)arenes using versatile synthetic protocols. This blue LED light‐mediated catalytic protocol proceeds via a radical pathway and demonstrates potential in the late‐stage functionalization of drug analogs.

Centro-symmetric paddlewheel copper(II) carboxylates: Synthesis, structural description, DNA-binding and molecular docking studies

The synthesis, structural characterization and biological relevance of three paddlewheel binuclear carboxylate copper(II) complexes with the formulae [Cu2(2-nitrophenylacetate)4(H2O)2]C2H5OH (1), [Cu2(diclofenate)4(acetone)2] (2) and [Cu2(4-bromophenylacetate)4(pyridine)2] (3) have been presented here. These complexes have been characterized using melting point, FTIR, absorption spectroscopy, electron spin resonance, cyclic voltammetry (CV) and single crystal XRD techniques, while their biological relevance was ascertained using molecular docking and DNA-binding studies. The FTIR spectra indicated all the important functionalities and the typical bridging bidentate coordination mode of the carboxylate moieties to the copper ion. Absorption spectroscopy yielded broad spectra corresponding to the 2B1g ground state and the singly occupied dx2–y2 orbital, typical of the copper(II) ion. This finding was confirmed by the ESR signals of complexes 1–3, with g values of 1.44353, 1.44317 and 1.44324, respectively. CV yielded redox couples typical of complexes with Cu2+ metal centers. XRD showed that the copper(II) ions in all three complexes are coordinated by four carboxylate ligands, constituting the square base of the square pyramid around each copper ion. The apical position is occupied by water (1), acetone (2) or pyridine (3) molecules. Owing to the structural differences, 1 and 3 have inter-molecular interactions and growth along all three axes, while 2 has such interactions only along the a-axis, leading to preferential growth along this axis. The structural parameters of the structures are different from each other and have been correlated mutually as well as with their literature analogues. Their supra-molecular synthons have been presented and explained. A computational study by molecular docking using MOE (molecular operating environment) software has yielded docking scores of −8.4098, −8.0453 and −9.4098, respectively for 1–3. The DNA-binding activity, explored via spectrophotometry and cyclic voltammetry, yielded intrinsic binding constant values of the order of 104 M−1 for all the complexes, showing excellent binding potency with DNA. The structural as well as biological importance of the complexes has been manifested.

Palladium complexes derived from benzoylthiourea ligands: Synthesis, crystal structure, and catalytic application in Suzuki C–C coupling reactions

Abstract[PdCl2(HL1‐κS)2] and [PdCl2(HL2‐κS)2] complexes were formed from neutral monodentate modes of HL1 and HL2 ligands, which are coordinated to the palladium(II) center, respectively. [Pd(L1‐κ2S,O)2] and [Pd(L2‐κ2S,O)2] complexes were obtained by recrystallization of corresponding [PdCl2(HL1‐κS)2] and [PdCl2(HL2‐κS)2] complexes as anionic bidentate coordination modes. All palladium(II) complexes were characterized by elemental analysis, FT‐IR, and NMR (1H and 13C) techniques. The molecular structure of [Pd(L1‐κ2S,O)2] and [Pd(L2‐κ2S,O)2] was also confirmed by single‐crystal X‐ray diffraction method. The roles and behaviors of the prepared four palladium(II) complexes in catalytic investigations for the Suzuki C–C coupling reaction were examined for the first time. The complexes acted as the excellent catalyst precursor and showed highly catalytic activity for the Suzuki C–C coupling reaction of various arylhalides with phenylboronic acid at low catalyst loading (0.01 mol%).

Synthetic approaches and supramolecular properties of 2,2′:n′,m″-terpyridine domains (n = 3,4,5,6; m = 2,3,4) based on the 2,2′-bipyridine core as ligands with k2N-bidentate coordination mode

• Main synthetic strategies for 2,2′:6′,2″-terpyridine domain have been discussed. • Other 2,2′:n′,m″-terpyridine domains (n = 4,5,6; m = 2,3,4) were also mentioned. • Ligand properties of these terpyridines were discussed. • Photophysical properties of 2,2′:n′,m″-terpyridine domains have been disclosed. Despite almost a century-long history of studying the potential of 2,2′:6′,2″-terpyridine in various fields, the development of synthetic atom-economic “one-pot” approaches/techniques/methods (meeting the requirements of “green chemistry”) of the “parent” 2,2′:6′,2″-tpy domain and its derivatives remains a strategic challenge for synthetic chemists. However, considering modern requirements for ligands in supramolecular chemistry, the development of alternative 2,2′:n′,m″-terpyridine domains (n = 3,4,5,6; m = 2,3,4) based on the 2,2′-bipyridine core, sometimes representing “competitive” minor products of the “parent” tpy synthesis, is dictated by time itself as well as the systematization of such information. The transition metal complexes with 2,2′:6′,2″-tpy and the related tpy ligands in the bidentate coordination modes of k 2 N,N′ and k 2 N,N″ have attracted much attention as promising photoluminescent materials and photocatalysts. In this review article we analyzed classical and modern methods for the synthesis and functionalization of both the terpyridine prototypes and other 2,2′:n′,m″-terpyridines and their supramolecular properties as ligands with the k 2 N-bidentate coordination mode as non-classical hypodentate coordination mode. Also, most significant examples of terpyridine-based metallocomplexes as well as biologically active terpyridines/metallocomplexes have been presented.

Synthesis, characterization, in-vitro anti-inflammatory and antimicrobial screening of metal(II) mixed diclofenac and acetaminophen complexes

Mixed ligand complexes derived from diclofenac potassium salt (Kdc) and acetaminophen (ace) has been synthesized and proposed to have a general formula [MB] where M = Co2+, Ni2+, Cu2+ and Zn2+and B = (ace)(dc)(H2O)2 except for Mn2+ complex which exists as [Mn(ace)(dc)OH2]. The complexes were characterized by solubility, melting point, conductivity, elemental analyses, UV-Vis, FT-IR spectroscopy, X-ray powder diffraction (XRPD) study and magnetic susceptibility measurement. Electronic absorption spectra data are characteristic of octahedral structures for [MB]. The IR spectra revealed a bidentate coordination mode. In acetaminophen, the nitrogen and carbonyl-O atoms of the amide group were involved while the carboxylate oxygen atoms of potassium diclofenac were used; typical of a carboxylic acid derivative. The compounds were screened for in-vitro anti-inflammatory activity by inhibition of albumin denaturation assay and antimicrobial activity against bacteria strains: Bacillus subtilis, Bacillus anthrax, Escherichia coli, Salmonella typhi and a fungus Aspergillus niger. Some of the tested compounds showed moderate anti-inflammatory activity when compared to the standard drug diclofenac potassium salt. The in-vitro antimicrobial screening revealed an increased activity of the complexes against the bacteria isolates compared to the free ligands.&#x0D; &#x0D; KEY WORDS: Metal(II) ion, NSAIDs, Anti-inflammatory activity, Diclofenac potassium salt, XRPD, Antimicrobial activity&#x0D; &#x0D; Bull. Chem. Soc. Ethiop. 2021, 35(1), 77-86.&#x0D; DOI: https://dx.doi.org/10.4314/bcse.v35i1.6

Structural elucidation of chiral (imino)pyridine/phosphine palladium(II) complexes and their applications as catalysts in methoxycarbonylation of styrene

Treatment of ligands (S)-1-phenyl-N-(1-(pyridin-2-yl)ethylidene)ethanamine (L1), (R)-1-phenyl-N-(1-(pyridin-2-yl)ethylidene)ethanamine (L2), (S)-1-phenyl-N-((pyridin-2-yl)methylene)ethanamine (L3), (R)-1-phenyl-N-((pyridin-2-yl)methylene)ethanamine (L4), (S)-N-(2-(diphenylphosphino)benzylidene)-1-phenylethanamine (L5), and (R)-N-(2-(diphenylphosphino)benzylidene)-1-phenylethanamine (L6) with [Pd(COD)Cl2] afforded the respective palladium complexes [Pd(L1)Cl2] (1), [Pd(L2)Cl2] (2), [Pd(L3)Cl2] (3), [Pd(L4)Cl2] (4), [Pd(L5)Cl2] (5) and [Pd(L6)Cl2] (6) in high yields. Solid-state structures of the complexes established N^N and N^P bidentate coordination mode of the ligands to give distorted square planar geometries. Complexes 1–6 displayed moderate catalytic activities in the methoxycarbonylation of styrene, to give predominantly branched esters of up to 95%. NMR spectroscopy studies pointed to possible decomposition of the active species, via ligand dissociation.

Alkali Metal Salts of 10,12-Pentacosadiynoic Acid and Their Dosimetry Applications.

Wide-dose-range 2D radiochromic films for radiotherapy, such as GAFchromic EBT, are based on the lithium salt of 10,12-pentacosadiynoic acid (Li-PCDA) as the photosensitive component. We show that there are two solid forms of Li-PCDA—a monohydrated form A and an anhydrous form B. The form used in commercial GAFchromic films is form A due to its short needle-shaped crystals, which provide favorable coating properties. Form B provides an enhanced photoresponse compared to that of form A, but adopts a long needle crystal morphology, which is difficult to process. The two forms were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, CP-MAS 13C solid-state NMR spectroscopy, and thermogravimetric analysis. In sum, these data suggest a chelating bridging bidentate coordination mode for the lithium ions. The sodium salt of PCDA (Na-PCDA) is also reported, which is an ionic cocrystal with a formula of Na+PCDA–·3PCDA. The PCDA and PCDA– ligands display monodentate and bridging bidentate coordination to the sodium ion in contrast to the coordination sphere of the Li-PCDA forms. In contrast to its lithium analogues, Na-PCDA is photostable.

Noncovalent-bonded 3D Cd(II) and Zn(II) supramolecular metal-organic frameworks from 3,3′,5,5′-tetramethyl-4,4′-bipyrazole and carboxylates

The present study pertains to the syntheses and characterizations of four mixed-ligand complexes of Cd(H2Bpz)(L1)2(H2O) (1) (L1 = 2-methyl-2-phenoxypropanoic acid), Zn(H2Bpz)(L2)2 (2) (L2 = m-nitrobenzoate), Cd(H2Bpz)2(L3)2 (3) (L3 = 3,4-(methylenedioxy)benzoate) and [Cd2(H2Bpz)3(L4)2]2·2(THF)0.5·4MeOH·4H2O (4) (L4 = o-phthalate). The resulting complexes were formulated via EA, IR and SCXRD, and the TGA. X-ray studies revealed that these complexes have mononuclear to dinuclear structures with distorted octahedral geometry at Cd2+ and square pyramidal geometry for Zn2+, and metal ions show N2O3, N2O4, N3O3 and N4O2 bonding cores. H2Bpz in all compounds is coordinated only in bismonodentate fashion with its neutral N. The CO2 - in 1 and 4 exhibited bisunidentate and monodentate coordination units, the CO2 - in 2 has both chelating bidentate and monodentate coordination mode, and the CO2 - in 3 is only monodentate. The CH3 of H2Bpz in all compounds except 1 participated in noncovalent bonds. Complexes 1-4 have many intra- and intermolecular weak interactions (including classical H-bonds, O···O, C-H···O, CH2···O, CH3···O, C-H···π, CH2···π, CH3-π, OH-π and π-π interactions) in their crystals, which lead to the total 3D supramolecular structures. The thermal stabilities for 1-4 show that the complexes are good candidates for hybrid inorganic-organic materials with good thermal stability.

Syntheses, crystal structures, antioxidant, in silico DNA and SARS-CoV-2 interaction studies of triorganotin(IV) carboxylates

Triorganotin(IV) carboxylate complexes R3SnL, where R = C4H9 (1), CH3 (2) and L = 2-chlorophenyl ethanoate, were synthesized and characterized by elemental analysis, FT-IR, NMR (1H, 13C, 119Sn) and X-ray single crystal analysis. The solid state analyses confirmed a bridging bidentate coordination mode for the carboxylate ligand rendering the tin ion a penta-coordinated center in the synthesized complexes. NMR spectra revealed a change in the coordination number (5→4) for tin when in the solution. The structural geometry and the electronic properties of complexes were calculated by using the density functional theory (DFT) method at B3LYP level 6–31G(d, p) and Lanl2DZ basis sets. A fairly good agreement was found between the observed and theoretical bond length and bond angle values for the complex (1) and (2). The in vitro antioxidant potential of the complexes was investigated by DPPH, ferrous ion chelation, ferric ion reducing, total antioxidant and hydroxyl free radical scavenging assays. The nature of the tin bonded R groups has apparently a significant impact on the antioxidant activity of the complexes. Molecular docking studies suggest intercalation as possible mode of complex-DNA interactions. Docking studies also confirm that interactions of the two complexes with some active site residues of SARS-CoV-2 nucleocapsid protein and angiotensin-converting enzyme 2 (ACE2) are probable.

Rollover Cyclometalation as a Valuable Tool for Regioselective C-H Bond Activation and Functionalization.

Rollover cyclometalation constitutes a particular case of cyclometallation reaction. This reaction occurs when a chelated heterocyclic ligand loses its bidentate coordination mode and undergoes an internal rotation, after which a remote C–H bond is regioselectively activated, affording an uncommon cyclometalated complex, called “rollover cyclometalated complex”. The key of the process is the internal rotation of the ligand, which occurs before the C–H bond activation and releases from coordination a donor atom. The new “rollover” ligand has peculiar properties, being a ligand with multiple personalities, no more a spectator in the reactivity of the complex. The main reason of this peculiarity is the presence of an uncoordinated donor atom (the one initially involved in the chelation), able to promote a series of reactions not available for classic cyclometalated complexes. The rollover reaction is highly regioselective, because the activated C–H bond is usually in a symmetric position with respect to the donor atom which detaches from the metal stating the rollover process. Due to this novel behavior, a series of potential applications have appeared in the literature, in fields such as catalysis, organic synthesis, and advanced materials.

Synthesis, crystal structure, theoretical calculation, spectroscopic and antibacterial activity studies of copper(II) complexes bearing bidentate schiff base ligands derived from 4-aminoantipyrine: Influence of substitutions on antibacterial activity

A novel series of Cu(II) complexes, including: [Cu(L1)2]: C1, [Cu(L2)2]: C2, [Cu(L3)2]: C3, [Cu(L4)2]: C4, with four bis-N,O-bidentate Schiff base ligands (HL1: (E)-4-[(2‑hydroxy-3-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one; HL2: (E)-4-[(2‑hydroxy-4-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one; HL3: (E)-4-[(2‑hydroxy-5-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one; HL4: (E)-4-[(2‑hydroxy-6-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one have been synthesized and characterized by elemental analyses, FT-IR, 1H NMR and 13C NMR spectroscopic techniques. Furthermore, the crystal structures of HL4 and C2 were determined by single crystal X-ray analysis. Single crystal X-ray analyses, the structure of C2 confirmed the bidentate coordination mode. The metal center possesses a distorted tetrahedral geometry with bis-N,O donor atoms coordinating from Schiff base ligand. Theoretical calculation of the synthesized compounds were carried out by DFT using B3LYP method with employing the Def2-SVPD (for ligands) and Def2-SV(P) (for complexes) basis sets. Calculated data are in good accordance with the experimental investigations. The in vitro biological activities of the synthesized ligands and their copper(II) complexes were evaluated against Staphylococcus aureus and Escherichia coli. The activity data showed that the metal complexes have a promising biological potential comparable with the parent Schiff base ligands against bacterial species.

Synthesis, structure and photophysical properties of two tetranuclear copper(I) iodide complexes based on acetylpyridine and diphosphine mixed ligands.

Two copper(I) iodide tetramers, namely, [μ2-1,3-bis(diphenylphosphanyl)propane-κ2P:P']di-μ3-iodido-di-μ2-iodido-[1-(pyridin-3-yl)ethan-1-one-κN]tetracopper(I) dichloromethane disolvate, [Cu4I4(C6H7NO)2(C27H26P2)2]·2CH2Cl2 (CuL3), and [μ2-1,3-bis(diphenylphosphanyl)propane-κ2P:P']di-μ3-iodido-di-μ2-iodido-[1-(pyridin-4-yl)ethan-1-one-κN]tetracopper(I), [Cu4I4(C6H7NO)2(C27H26P2)2] (CuL4), have been synthesized from reactions of CuI, 1,3-bis(diphenylphosphanyl)propane (dppp) and 3- or 4-acetylpyridine (3/4-acepy). The complexes were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), powder XRD and photoluminescence spectroscopy. Both complexes possess a stair-step [Cu4I4] cluster structure with a crystallographic inversion centre located in the middle of a Cu2I2 ring (Z' = 1/2). The dppp ligands each adopt a bidentate coordination mode that bridges two CuI centres on one side of the [Cu4I4] cluster and the acepy ligands act as terminal ligands. The solid-state samples of similar complexes show highly efficiency thermally activated delayed fluorescence (TADF) at room temperature. At ambient temperature, both CuL3 and CuL4 exhibit photoluminescence, with a maximum emission in the region 560-580 nm and with short emissive decay times, but only phosphorescence was observed at 77 K. The narrow gaps between the higher lying singlet state and the triplet state, ΔE(S1 - T1), also confirm the presence of TADF. Structure analysis and consideration of photoluminescence indicates that the position of the acetyl group on the heterocyclic ligand has an obvious influence on the structural arrangement, on intermolecular interactions and on the observed photophysical properties.