Bidentate Coordination Mode Research Articles

Synthesis, crystal structure, characterization and corrosion inhibition studies of a strontium coordination polymer with tartaric acid

The reaction of anhydrous strontium chloride with the proton transfer compound 1-H-Imidazolium Hydrogen- meso-tartrate in water resulted in the formation of polymeric tartrate complex of strontium which is characterised by SXRD, IR, UV-Visible and TG/DTG analyses. The single crystal X-ray diffraction analysis reveals that each strontium atom is eight coordinate with distorted dodecahedral arrangement. The two metal fragments are linked through central four-membered Sr2O2 ring and there is no imidazole moiety in the complex. The compound displays a rare crystallographic feature where a shared hydrogen atom is located between two carboxylic groups. This unusual arrangement of hydrogen atom with an occupancy factor 0.5, located in between two carboxylate groups balances the total charge of the structure. FT- IR study reveals the bidentate coordination mode of the ligand. The thermal behaviour of the compound was studied using TG/DTG analysis. Corrosion inhibition property of the title compound on mild steel in 1.0M HCl has been investigated using weight loss method. The formation of protective film on the mild steel surface is confirmed by Scanning Electron Microscopy images. The inhibition efficiency increases with increase in concentration of inhibitor.

Iron Complexes of 4,5-Bis(diorganophosphinomethyl)acridine Ligands.

The search for an iron analog of the established ruthenium-based catalysts containing methylene-extended 4,5-bis(diorganophosphinomethyl)acridine ligands, [FeHCl(CO)(LR)], resulted in the discovery of a bidentate coordination mode of these usually tridentate pincer ligands toward iron. The acridines nitrogen atom does not coordinate to iron, leading to the formation of iron diphos-type complexes with unusually large cis bite angles of up to 124° as well as trans bite angles around 155°. The iron-containing complexes [FeCl2(κ2-LR)] (R = iPr, Ph), [FeX2(κ2-LCy)] (X = Cl, Br) and [Fe(CO)3(κ2-LR)] (R = iPr, Cy) have been isolated in crystalline form and characterized by spectroscopic methods and mass spectrometry. Their structures were verified unambiguously through X-ray diffraction. The stability of the iron(II) complexes decreased in the order Cy > Ph > iPr and Cl > Br > I, although all iron(II) complexes were found to be relatively stable enough for short-term handling in air in the solid state. Notably, no iron(0) complex of the phenyl derivative could be isolated. The iron(0) complex [Fe(CO)3(κ2-LCy)] was found to be significantly more stable toward hydrolysis and oxygen compared to [Fe(CO)3(κ2-LiPr)] and can be stored in air for months without significant decomposition in the solid state, while [Fe(CO)3(κ2-LiPr)] decomposes in air within seconds. The decomposition products [FeI2(κ2-O2LCy)], [{Fe(CO)3(κ2-HLR)}2] (R = iPr, Cy) and [FeCl2(CO)2(κ1-LCy)(κ1-OLCy)] were identified and characterized crystallographically. The iron(0) complex [Fe(CO)3(κ2-LCy)] is oxidized by [Fe(Cp)2](BPh4) to give the paramagnetic, low-spin iron(I) cation [Fe(CO)3(κ2-LCy)]+. The electron paramagnetic resonance spectrum of the highly sensitive cation as well as density functional theory calculations suggest a partial delocalization of the unpaired electron over the three carbonyl ligands and the acridines aromatic ring system. The catalytic activity and photophysical properties of the complexes have been preliminarily investigated.

Crystal growth, characterization and sensing studies of a new metal-organic framework of Sr(II) with phenylmalonic acid

A new metal-organic framework of Sr(II) with phenylmalonic acid, {[Sr(PMA)(H2O)].H2O}n (SPMA) has been prepared by gel diffusion technique. SXRD data show that the crystal belongs to the orthorhombic space group Pbca. In the crystal structure, the phenylmalonate ligand adopts monodentate, bis-monodentate and bidentate coordination modes with the Sr(II) ions. The Sr-phenylmalonate units extend three dimensionally forming a network structure. Intermolecular hydrogen bonding further stabilizes the crystal system. The compound exhibits strong luminescence emission at 290 nm upon excitation at 240 nm. Sensing property of the title compound towards Fe3+ ion is also investigated.

Diastereoselective Synthesis of Sulfoxide-Functionalized N-Heterocyclic Carbene Ruthenium Complexes: An Experimental and Computational Study.

The synthesis of sulfoxide-functionalized NHC ligand precursors were carried out by direct and mild oxidation from corresponding thioether precursors with high selectivity. Using these salts, a series of cationic [Ru(II)(η6-p-cymene)(NHC-SO)Cl]+ complexes were obtained in excellent yields by the classical Ag2O transmetallation route. NMR analyses suggested a chelate structure for the metal complexes, and X-ray diffractometry studies of complexes 4 b, 4 c, 4dBArF and 4 e unambiguously confirmed the preference for the bidentate (κ2-C,S) coordination mode of the NHC-SO ligands. Interestingly, only one diastereomer, in the form of an enantiomeric pair, was observed both in 1H NMR and in the solid state for the complexes. DFT calculations showed a possible intrinsic energy difference between the two pairs of diastereomer. The calculated energy barriers suggested that inversion of the sulfoxide is only plausible from the higher energy diastereomer together with bulky substituents. Inverting the configuration at the Ru center instead shows a lower and accessible activation barrier to provide the most stable diastereomer through thermodynamic control, consistent with the observation of a single species by 1H NMR as a pair of enantiomers. All these complexes catalyse the β-alkylation of secondary alcohols. Complex 4dPF6 bearing an NHC-functionalised S-Ad group has been further studied with different primary and secondary alcohols as substrates, showing high reactivity and high to moderate β-ol-selectivities.

Coumarin-modified ruthenium complexes: Synthesis, characterization, and antiproliferative activity against human cancer cells.

Among ruthenium complexes studied as anticancer metallodrugs, NKP-1339, NAMI-A, RM175, and RAPTA-C have already entered clinical trials due to their potent antitumor activity demonstrated in preclinical studies and reduced toxicity in comparison with platinum drugs. Considering the advantages of ruthenium-based anticancer drugs and the cytostatic activity of organometallic complexes with triazole- and coumarin-derived ligands, we set out to synthesize Ru(II) complexes of coumarin-1,2,3,-triazole hybrids (L) with the general formula [Ru(L)(p-cymene)(Cl)]ClO4. The molecular structure of the complex [Ru(2a)(p-cymene)(Cl)]ClO4 (2aRu) was determined by single-crystal X-ray diffraction, which confirmed the coordination of the ligand to the central ruthenium(II) cation by bidentate mode of coordination. Coordination with Ru(II) resulted in the enhancement of cytostatic activity in HepG2 hepatocellular carcinoma cells and PANC-1 pancreatic cancer cells. Coumarin derivative 2a positively regulated the expression and activity of c-Myc and NPM1 in RKO colon carcinoma cells, while the Ru(II) half-sandwich complex 2cRu induced downregulation of AKT and ERK signaling in PANC-1 cells concomitant with reduced intracellular levels of reactive oxygen species. Altogether, our findings indicated that coumarin-modified half-sandwich Ru(II) complexes held potential as anticancer agents against gastrointestinal malignancies.

Design, Synthesis, and Anti-Cancer Evaluation of Novel Water-Soluble Copper(I) Complexes Bearing Terpyridine and PTA Ligands.

This study presents a simple and energy-efficient self-assembly LAG synthetic method for novel water-soluble copper(I) complexes [Cu(terpy)(PTA)][PF6] (1) and [Cu(terpy)(PTA)2][PF6] (2). They were characterized by FT-IR, 1H, and 31P{1H} NMR spectroscopy, elemental analysis, and single-crystal/powder X-ray diffraction (for 2). The X-ray analysis of compound 2 indicates a bidentate coordination mode of terpyridine to the metal center. Variable-temperature NMR tests indicate dynamic properties for terpyridine in the case of both compounds, as well as for the PTA ligands in the case of 2. Additionally, compounds 1 and 2 exhibit interesting cytotoxic activity, which was tested on normal human dermal fibroblasts (NHDFs), human lung carcinoma (A549), human breast adenocarcinoma (MCF-7), and human cervix carcinoma (HeLa) established cell lines. In comparison to the other tested compounds, complexes 1 and 2 seem to have significantly lower IC50 values against cancer cells (A549, HeLa, MCF-7), indicating their potential as prospective anticancer agents. Moreover, both compounds show no significant toxicity towards normal skin cells (NHDFs), suggesting a certain selectivity in their action on cancer cells. Cisplatin as a reference compound also exhibited considerable cytotoxicity against cancer cells but with a low level of selectivity, which could lead to unwanted effects on normal cells. Remarkably, compounds 1 and 2 exhibit up to 30 times the cytotoxic activity of cisplatin, with a six-fold lower toxicity to normal cells. They also interact strongly with human serum albumin, suggesting potential therapeutic applications. Overall, these compounds hold significant promise as potential chemotherapeutic agents.

Ab initio molecular dynamics of solvation effects and reactivity at the interface between water and ascorbic acid covered anatase TiO2 (101).

In this work, we present a detailed study of the interaction between ascorbic acid (L-asc) and anatase TiO2 (101) surface both in gas phase and in contact with water by using density functional theory and ab initio molecular dynamics simulations. In gas phase, L-asc strongly binds the TiO2 (101) surface as a dianion (L-asc2- ), adopting a bridging bidentate coordination mode (BB), with the two acid protons transferred to two surface 2-fold bridging oxygens (O2c). AIMD simulations show that the interaction between the organic ligand and the anatase surface is stable and comparable to the vacuum one despite the possible solvent effects and/or possible structural distortions of the ligand. In addition, during the AIMD simulations hydroxylation phenomena occur forming transient H3 O+ ions at the solid-liquid interface. For the first time, our results provide insight into the role of the ascorbic acid on the electronic properties of the TiO2 (101), the influence of the water environment on the ligand-surface interaction and the nature of the solid-liquid interface.

Nine Cd2+ complexes containing 3,5-dimethylpyrazole and carboxylic acids: Synthesis, spectroscopic and crystallographic characterization

Nine mixed-ligand Cd2+ complexes of [Cd(Hdmpz)2(bcaa)2] (1) (Hbcaa = 3-(benzylcarbamoyl)-acrylic acid), Cd4(Hdmpz)4(tcba)8(2) (Htcba = 2,4,6-trichlorobenzoic acid), [Cd(Hdmpz)(napa)2] (3) (Hnapa = 1-naphthoic acid), [Cd(Hdmpz)2(cnba2] (4) (Hcnba = 2-chloro-4-nitrobenzoic acid), Cd(Hdmpz)2(hmba)2 · H2O (5) (Hhmba = 4-hydroxy-3-methoxybenzoic acid), [Cd(Hdmpz)2(msal)2] (6) (Hmsal = 3-methylsalicylic acid), [Cd(Hdmpz)2(dbta)(H2O)] · 2H2O (7) (H2dbta = dibenzoyltartaric acid), [Cd(Hdmpz)4(tpda)] (8) (H2tpda = 2,5-thiophenedicarboxylic acid) and [Cd3(Hdmpz)6(btca)2(H2O)4] · 2H2O (9) (H3btca = 1,2,4-benzenetricarboxylic acid) were synthesized and formulated by EA, IR spectra + SCXRD, their TGA were also conducted.The SCXRD reports indicated that the complexes exhibit mononuclear to tetranuclear structures with octahedral geometry at the Cd2+. The Hdmpzs in all examples are coordinated only through the monodentate fashion with its neutral N. The carboxylate at 8 displays only as unidentate coordination, while the ones in 1, 4 and 5–7 take the chelating bidentate coordination mode. The CO2− at 2–3 adopts both the chelating bridging tridentate and bismonodentate coordination fashion. 9 contains both unidentate and bidentate chelating coordinate CO2−. There all existed the NH···O H-bond from the NH of the Hdmpz. 6 has the intramolecular OH···O H-bond from the ortho phenol and the CO2−, resulting the S11(6) pattern. 5, 7 and 9 have the intermolecular OH···O H-bond. 2, and 4–6 bear only the intermolecular NH···O H-bond; 3, and 8–9 have only the intramolecular NH···O H-bond. Compounds 1 and 7 bear both the intra- and intermolecular NH···O H-bonds.There featured intricate intra- and intermolecular classical H-bonds (NH···O/OH···O) together with CH-π/CH2-π/CH3-π, CH3-CH/CH3-CH3, CH3-C, CH-O/CH3-O, CH-Cl/CH3-Cl, Cl-O, Cl-π, O-π, OC plus OO associates which are illuminated by the X-ray crystallographic technique, tethering the discrete units into high-dimensional ordered supramolecular systems.

Designing and Exploration of the Biological Potentials of Novel Centrosymmetric Heteroleptic Copper(II) Carboxylates.

Copper(II) complexes with a general formula [Cu2(3,4-F2C6H3CH2COO)4(L)2], where L = 2-methylpyridine (1) and 3-methylpyridine (2), are reported here. The FTIR spectra of the complexes confirmed the bridging bidentate coordination mode of the carboxylate ligand. The low (475 and 449 cm-1) and strong (727 & 725 cm-1) intensity bands in the FTIR spectra, due to Cu-N stretches and pyridyl ring vibrations, confirmed coordination of the 2-/3-methyl pyridine co-ligands in complexes 1 and 2, respectively. A binuclear paddlewheel structural arrangement with a square pyramidal geometry was confirmed for copper atoms in the complexes via single-crystal X-ray analysis. The DPPH, •OH radical, and α-amylase enzyme inhibition assays showed higher activities for the complexes than for the free ligand acid. The binding constant (Kb = 1.32 × 105 for 1 and 5.33 × 105 for 2) calculated via UV-VIS absorption measurements and docking scores (-6.59 for 1 and -7.43 for 2) calculated via molecular docking showed higher SS-DNA binding potential for 2 compared to 1. Viscosity measurement also reflected higher DNA binding ability for 2 than 1. Both complexes 1 and 2 (docking scores of -7.43 and -6.95, respectively) were found to be more active inhibitors than the free ligand acid (docking score of -5.5159) against the target α-amylase protein. This in silico study has shown that the herein reported compounds follow the rules of drug-likeness and exhibit good potential for bioavailability.

Benzothiadiazolyl‐pyridine and ‐2,2′‐bipyridine Ligands for Luminescent and Magnetic Complexes

AbstractTwo new luminescent ligands, 4‐(2‐pyridine)‐7‐methyl‐2,1,3‐benzothiadiazole (L1) and 4‐(2,2‐bipyridine)‐7‐methyl‐2,1,3‐benzothiadiazole (L2), based on 2,1,3‐benzothiadiazole and pyridine or bipyridine were obtained by Suzuki coupling reactions. DFT and TD‐DFT type calculations have been performed on L1 and L2 in order to assign their experimental UV‐visible and emission bands. Reaction of L1 and L2 with metal(II) chlorides (M=Zn, Mn, Cu) provided the neutral complexes of formulas [ZnL1Cl2] (1), [Zn(L1)2Cl2] (2), [ZnL2Cl2] (3), [MnL2Cl2] ⋅ 0,5CH2Cl2 (4) and [CuL2Cl2] ⋅ H2O (5) which have been structurally characterized. The Zn(II) ions in 1 and 2 are four‐coordinate in somewhat distorted tetrahedral N2Cl2 surroundings with L1 adopting bidentate (1) and monodentate (2) coordination modes. Complexes 3–5 are isostructural and their metal atoms are five‐coordinate in distorted square pyramidal environments with three nitrogen atoms from the tridentate L2 ligand and a chlorine building the basal plane and another chlorine atom occupying the apical position. The three Zn(II) complexes are strongly luminescent in solution and the solid state, while the cryomagnetic study of the paramagnetic compounds 4 and 5 in the temperature range 2.9–300 K shows a Curie‐Weiss behaviour typical of small antiferromagnetic interactions which are mediated by weak intermolecular contacts.

QM/MM and MM MD Simulations on Enzymatic Degradation of the Nerve Agent VR by Phosphotriesterase.

V-type nerve agents are hardly degraded by phosphotriesterase (PTE). Interestingly, the PTE variant of BHR-73MNW can effectively improve the hydrolytic efficiency of VR, especially for its Sp-enantiomer. Here, the whole enzymatic degradation of both Sp and Rp enantiomers of VR by the wild-type PTE and its variant BHR-73MNW was investigated by quantum mechanics/molecular mechanics (QM/MM) calculations and MM molecular dynamics simulations. Present results indicate that the degradation of VR can be initiated by the nucleophilic attack of the bridging OH- and the zinc-bound water molecule. The QM/MM-predicted energy barriers for the hydrolytic process of Sp-VR are 19.8 kcal mol-1 by the variant with water as a nucleophile and 22.0 kcal mol-1 by the wild-type PTE with OH- as a nucleophile, and corresponding degraded products are bound to the dinuclear metal site in monodentate and bidentate coordination modes, respectively. The variant effectively increases the volume of the large pocket, allowing more water molecules to enter the active pocket and resulting in the improvement of the degradation efficiency of Sp-VR. The hydrolysis of Rp-VR is triggered only by the hydroxide with an energy span of 20.6 kcal mol-1 for the wild-type PTE and 20.7 kcal mol-1 for the variant BHR-73-MNW PTE. Such mechanistic insights into the stereoselective degradation of VR by PTE and the role of water may inspire further studies to improve the catalytic efficiency of PTE toward the detoxification of nerve agents.

Unraveling the Ag+ ion coordination and solvation thermodynamics in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

The solvation of the Ag+ ion in the 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) ionic liquid (IL) has been studied by means of experimental and theoretical methods with the aim of elucidating the cation coordination structure and thermodynamic properties. Car-Parrinello molecular dynamics (CPMD) simulations showed that the Ag+ ion is coordinated by an average number of four [BF4]− anions in a pseudo-tetrahedral geometry. A high configurational disorder of the first solvation sphere is found, where the anions can be found both in mono- and bidentate coordination mode around the Ag+ ion. Also, a solvational equilibrium is observed as due to [BF4]− anion dissociation along the trajectory. The analysis of X-ray absorption spectroscopy data confirmed the picture provided by the CPMD simulation. Classical molecular dynamics simulations were carried out to obtain the single-ion solvation thermodynamic parameters. The negative water → IL free energy of transfer suggests that the Ag+ ion is more favorably solvated in the [C4mim][BF4] IL than in water. This behavior is due to a balance between the enthalpic and entropic contributions, which allows to find a rationale to the strong solvation capabilities of BF4-based ILs towards Ag+.

Synthesis, Crystal Structure, and Luminescent Sensing Properties of a Supramolecular 3D Zinc(II) Metal–Organic Framework with Terephthalate and Bis(imidazol-1-yl)methane Linkers

Supramolecular 3D Zn(II) coordination polymer {[Zn(bim)(bdc)]⋅0.8DMF⋅0.4EtOH⋅0.1H2O }n (Zn-MOF), constructed from Zn2+ ions, bis(imidazol-1-yl)methane (bim) and terephthalate (bdc2−) anions, was synthesized and structurally characterized. Zn-MOF crystallizes in the tetragonal crystal system, space group P42/n. Each Zn(II) ion coordinates two neutral bim molecules in a bridging bidentate coordination mode via nitrogen atoms at position 3 of the imidazole rings and two bdc2− anions, with monodentate coordination of the carboxylate group for one of them and bidentate coordination for another. Zn(II) cations are in a distorted square pyramidal ZnN2O3 coordination environment. Metal cations are alternately linked by the bim and bdc2− ligands, forming a two-dimensional layered structure along the crystallographic plane ab. As a result of layer interpenetration, a supramolecular 3D network is formed. Zn-MOF demonstrated blue (aquamarine) emission with a maximum at 430 nm upon excitation at 325 nm. The luminescence lifetime of 6 ns is characteristic for ligand-centered fluorescence. The luminescent sensing properties of Zn-MOF in ethanol suspension toward inorganic cations and anions were evaluated and an emission quenching response was observed for Fe3+ and chromate/dichromate ions. Photoinduced electron transfer from Zn-MOF to Fe3+ was elucidated as a possible quenching mechanism on the basis of DFT calculations.

Deciphering the specific interaction of humic acid with divalent cations at the nanoscale

Humic acid (HA), a representative class of natural organic matter (NOM), can interact with a variety of divalent cations to form the metal-HA complexes, which is of vital significance in both the natural and engineered environments. To decipher the specific HA-divalent cation interaction mechanism, the intermolecular forces and adhesion energies between two HA surfaces in aqueous environment with varying divalent cations were directly quantified at the nanoscale using atomic force microscope (AFM). In the presence of Ca2+, the considerably increased HA aggregation and HA-Ca(II)-HA adhesion were detected with elevated Ca2+ concentration mainly due to the enhanced bridging effect, while the excessive amounts of Ca2+ could significantly suppress the aggregation and adhesion behavior. The adhesion energy was also found to be dependent on other aqueous conditions (e.g., pH, cation type), with the highest adhesion energy measured for Cu2+ (∼1.642 mJ m−2), approximately 2 ∼ 3-fold higher than the case of Zn2+ (∼0.950 mJ m−2), Ca2+ (∼0.829 mJ m−2) and Mg2+ (∼0.583 mJ m−2). Such robust adhesion for Cu2+ could stem from the synergistic bonding of Cu2+ with both the oxygen and amine sites of HA, which was evidently different from the single metal–oxygen bonding for Zn2+, Ca2+ and Mg2+ shown by X-ray photoelectron spectroscopy (XPS). Based on density functional theory (DFT) simulation, HA molecules could bridge with all these four types of divalent cations mainly by the deprotonated catechol and phthalic acid (PA) structures in the bidentate coordination mode, while the deprotonated aniline could only bond with Cu2+, ultimately leading to the highest Cu(II)-HA binding energy among the studied divalent cations. This work provides insights into the quantitative understanding of HA-divalent cation interaction mechanisms, shedding light on developing effective strategies to modulate the aggregation, transport and fate of NOM in aqueous environments as well as engineering applications.

Chromium-Based Complexes Bearing Aminophosphine and Phosphine-Imine-Pyrryl Ligands for Selective Ethylene Tri/Tetramerization.

A series of Cr-based complexes 6-10 bearing aminophosphine (P,N) ligands Ph2P-L-NH2 [L = CH2CH2 (1), L = CH2CH2CH2 (2), and L = C6H4CH2 (3)] and phosphine-imine-pyrryl (P,N,N) ligands 2-(Ph2P-L-N=CH)C4H3NH [L = CH2CH2CH2 (4) and L = C6H4CH2 (5)] were prepared, and their catalytic properties were examined for ethylene tri/tetramerization. X-ray crystallographic analysis of complex 8 indicated the κ2-P,N bidentate coordination mode at the Cr(III) center and the distorted octahedral geometry of monomeric P,N-CrCl3. Upon activation by methylaluminoxane (MAO), complexes 7-8 bearing P,N (PC3N backbone) ligands 2-3 showed good catalytic reactivity for ethylene tri/tetramerization. On the other hand, complex 6 bearing the P,N (PC2N backbone) ligand 1 was found active for non-selective ethylene oligomerization, while complexes 9-10 bearing P,N,N ligands 4-5 only produced polymerization products. In particular, the high catalytic activity of 458.2 kg/(g·Cr·h), excellent selectivity of 90.9% (1-hexene and 1-octene combined), and extremely low PE content of 0.1% were obtained with complex 7 in toluene at 45 °C and 45 bar. These results suggest that rational control of P,N and P,N,N ligand backbones, including a carbon spacer and rigidity of a carbon bridge, can lead to the high-performance catalyst for the ethylene tri/tetramerization process.

Mononuclear Zn(ii) compounds supported by iminophenolate proligands binding in the bidentate (N, O) and tridentate (N, O, S) coordination mode: synthesis, characterization and polymerization studies

We synthesized eight Zn(ii) compounds containing unsymmetrical phenoxy–imine ligands with a thiophen-2-ylmethanimine side arm and used them towards the ROP of rac-LA and ROCOP of epoxides with CO2.

Copper(ii) and silver(i) complexes with dimethyl 6-(pyrazine-2-yl)pyridine-3,4-dicarboxylate (py-2pz): the influence of the metal ion on the antimicrobial potential of the complex.

Dimethyl 6-(pyrazine-2-yl)pyridine-3,4-dicarboxylate (py-2pz) was used as a ligand for the synthesis of new copper(ii) and silver(i) complexes, [CuCl2(py-2pz)]2 (1), [Cu(CF3SO3)(H2O)(py-2pz)2]CF3SO3·2H2O (2), [Ag(py-2pz)2]PF6 (3) and {[Ag(NO3)(py-2pz)]·0.5H2O} n (4). The complexes were characterized by spectroscopic and electrochemical methods, while their structures were determined by single crystal X-ray diffraction analysis. The X-ray analysis revealed the bidentate coordination mode of py-2pz to the corresponding metal ion via its pyridine and pyrazine nitrogen atoms in all complexes, while in polynuclear complex 4, the heterocyclic pyrazine ring of one py-2pz additionally behaves as a bridging ligand between two Ag(i) ions. DFT calculations were performed to elucidate the structures of the investigated complexes in solution. The antimicrobial potential of the complexes 1-4 was evaluated against two bacterial (Pseudomonas aeruginosa and Staphylococcus aureus) and two Candida (C. albicans and C. parapsilosis) species. Silver(i) complexes 3 and 4 have shown good antibacterial and antifungal properties with minimal inhibitory concentration (MIC) values ranging from 4.9 to 39.0 μM (3.9-31.2 μg mL-1). All complexes inhibited the filamentation of C. albicans and hyphae formation, while silver(i) complexes 3 and 4 had also the ability to inhibit the biofilm formation process of this fungus. The binding affinity of the complexes 1-4 with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) was studied by fluorescence emission spectroscopy to clarify the mode of their antimicrobial activity. Catechol oxidase biomimetic catalytic activity of copper(ii) complexes 1 and 2 was additionally investigated by using 3,5-di-tert-butylcatechol (3,5-DTBC) and o-aminophenol (OAP) as substrates.

Differentiating contribution to desolvation ability from molecular structure and composition for screening highly-effective additives to boost reversibility of zinc metal anode

Optimizing aqueous electrolytes with additives is a practical strategy to postpone dendrite formation on Zn metal anode (ZMA) and therefore boost rechargeability of full zinc metal batteries (ZMBs). However, the fundamental screening principles of additives diverse in molecular structure and composition are still elusive. Herein, thiourea, urea, and allantoin are investigated as additives to regulate ZnSO4 baseline electrolyte. By combining systematical electrochemical measurements with detailed numerical simulation analysis, two fundamental principles for screening the additives with stronger desolvation ability toward hydrated zinc ions have been identified: (i) in molecular composition, carbonyl (urea) is better than thiocarbonyl (thiourea), and (ii) in molecular structure, bidentate coordination mode (allantoin) outperforms monodentate mode (urea). Consequently, an electrostripping/plating lifespan over 600 h in the Zn||Zn symmetric cell cycling under a depth of discharge up to 5.2% is realized with the optimum allantoin-ZnSO4 hybrid electrolyte, significantly boosting the rechargeability (85.7% capacity retention over 2000 cycles) of assembled ZMA||carbon-cloth@MnO2 full ZMBs than that with additive-free ZnSO4 electrolyte (40.5%). This work provides closer insights into the correlation between desirable dendrite-free behavior of ZMA and molecular characteristics of additives, and practical guidance for rational selection of more efficient additives to inhibit hydration of Zn2+ and suppress dendrite grown on ZMA.

Bidentate and tridentate coordination modes of bis(3-methylindolyl)-2-(1-methylimidazolyl)methane in complexes of aluminum and gallium

Bis(3-methylindolyl)-2-(1-methylimidazolyl)methane (1) was synthesized by acid-catalyzed condensation of methyl-2-formylimidazole and two equivalents of 3-methylindole, followed by deprotonation of the imidazole moiety of the protonated compound, [(1-CH3C3H2N2H)HC(3-CH3C8H4NH)2][HSO4] ([1•H][HSO4 ]). Reactions of a trialkylaluminum or tri‑tert-butylgallium with 1 produced complexes (1-CH3C3H2N2)HC(3-CH3C8H4N)(3-CH3C8H4NH)MR2 (M = Al, R = Me (2a), Et (2b), iBu (2c), tBu (2d); M = Ga, R = tBu (3)) in which mono-deprotonated 1 adopts a bidentate coordination mode. Thermolysis of 2a-2d or 3 in refluxing toluene did not result in further alkane elimination. Deprotonation of 1 with two equivalents of nBuLi followed by reaction with an alkylaluminum dichloride yielded monomeric, tripodal complexes (1-CH3C3H2N)HC(3-CH3C8H4N)2MR (M = Al, R = Me (4a), Et (4b), iBu (4c), tBu (4d)) in which bis-deprotonated 1 adopts a tridentate coordination mode. Reaction of 1 with two equivalents of trimethylaluminum or triethylaluminum yields dialuminum complexes (1-CH3C3H2N)HC(3-CH3C8H4N)2Al2R4 (R = Me (5a), Et (5b). In addition to NMR (1H, 13C) spectroscopy, compounds 1, 2d, 3, and 4b were further characterized by X-ray crystallography as CH2Cl2 or toluene solvates.

Complexing properties of 2-pyridylphoshonate and 2-pyridylsulfonate ligands for Zn2+ and Ag+ central atoms

The Zn2+/Ag+-pypo and pysu (pypo = 2-pyridylphosphonate, pysu = 2-pyridylsulfonate) complexes speciation in aqueous solution at I = 0.1 M (KNO3) and 25 °C is described in detail under our experimental synthetic conditions. Protonation and stability constants were determined, and distribution diagrams show protonated and deprotonated complexes formation in the case of Zn2+/Ag+ pypo/pysu binary system, respectively. Moreover, the new complex, {[Zn(H2pypo)2(H2O)2]}n(ClO4)2n·2nH2O, was isolated and its spectral and structural properties were determined. An unusual pypo bidentate coordination mode is described and compared with published ones.