Binuclear Structure Research Articles

Exploring Anticancer Activities and Structure-Activity Relationships of Binuclear Oxidovanadium(IV) Complexes.

Dimeric mixed-ligand oxidovanadium complexes [V2O2(1,3-pdta)(bpy)2]·9H2O (1) and [V2O2(1,3-pdta)(phen)2]·6H2O (2) feature a symmetric binuclear structure bridged by 1,3-pdta, which is different from our previous reported asymmetric binuclear complex [V2O2(edta)(phen)2]·11H2O (3).In this study, a wide range of analytical techniques were carried out to fully characterize the complexes 1 and 2 and further investigate their structural stabilities. Density functional theory calculations of 1 and 2 also suggest that they might have good reactivity with biomolecules as anticancer agents. To assess and screen the antitumor activities of compounds 1-3 together with their four corresponding monomeric complexes [VO(ida)(phen)], [VO(ida)(bpy)], [VO(OH)(phen)2]Cl, and [VO(Hedta)]-, we have performed in vitro experiments with hepatocellular carcinoma HepG2 and SMMC-7721 cell lines by MTT analyses. Complex 2 was found to have the highest inhibitory potency against the growth of HepG2 and SMMC-7721 cells (IC50 = 2.07 ± 0.72 μM for HepG2; 13.00 ± 3.06 μM for SMMC-7721) compared to other compounds. The structure-activity relationship studies showed that the antitumor effect of compound 2 is higher than that of other compounds. After studying the monomeric compounds of 1-3, their effects were also ranked. Moreover, complex 2 displayed stronger binding affinity toward calf thymus DNA (Kb = 5.71 × 104 M-1) and cleavage activities than the other complexes (Kb = 1.34 × 104 M-1 for 1 and 5.22 × 104 M-1 for 3, respectively). We further extended the cellular mechanisms of drug action and found that 2 could block DNA synthesis and cell division of HepG2 and 7721 cells and further induce apoptosis by flow cytometry assays. In short, these results indicate that binuclear oxidovanadium compounds could have potential as simple, effective, and safe antitumor agents.

Thermodynamic Study of Oxidovanadium(IV) with Kojic Acid Derivatives: A Multi-Technique Approach.

The good chelating properties of hydroxypyrone (HPO) derivatives towards oxidovanadium(IV) cation, VIVO2+, constitute the precondition for the development of new insulin-mimetic and anticancer compounds. In the present work, we examined the VIVO2+ complex formation equilibria of two kojic acid (KA) derivatives, L4 and L9, structurally constituted by two kojic acid units linked in position 6 through methylene diamine and diethyl-ethylenediamine, respectively. These chemical systems have been characterized in solution by the combined use of various complementary techniques, as UV-vis spectrophotometry, potentiometry, NMR and EPR spectroscopy, ESI-MS spectrometry, and DFT calculations. The thermodynamic approach allowed proposing a chemical coordination model and the calculation of the complex formation constants. Both ligands L4 and L9 form 1:1 binuclear complexes at acidic and physiological pHs, with various protonation degrees in which two KA units coordinate each VIVO2+ ion. The joined use of different techniques allowed reaching a coherent vision of the complexation models of the two ligands toward oxidovanadium(IV) ion in aqueous solution. The high stability of the formed species and the binuclear structure may favor their biological action, and represent a good starting point toward the design of new pharmacologically active vanadium species.

Novel Oxidovanadium Complexes with Redox-Active R-Mian and R-Bian Ligands: Synthesis, Structure, Redox and Catalytic Properties.

A new monoiminoacenaphthenone 3,5-(CF3)2C6H3-mian (complex 2) was synthesized and further exploited, along with the already known monoiminoacenaphthenone dpp-mian, to obtain oxidovanadium(IV) complexes [VOCl2(dpp-mian)(CH3CN)] (3) and [VOCl(3,5-(CF3)2C6H3-bian)(H2O)][VOCl3(3,5-(CF3)2C6H3-bian)]·2.85DME (4) from [VOCl2(CH3CN)2(H2O)] (1) or [VCl3(THF)3]. The structure of all compounds was determined using X-ray structural analysis. The vanadium atom in these structures has an octahedral coordination environment. Complex 4 has an unexpected structure. Firstly, it contains 3,5-(CF3)2C6H3-bian instead of 3,5-(CF3)2C6H3-mian. Secondly, it has a binuclear structure, in contrast to 3, in which two oxovanadium parts are linked to each other through V=O···V interaction. This interaction is non-covalent in origin, according to DFT calculations. In structures 2 and 3, non-covalent π-π staking interactions between acenaphthene moieties of the neighboring molecules (distances are 3.36–3.40 Å) with an estimated energy of 3 kcal/mol were also found. The redox properties of the obtained compounds were studied using cyclic voltammetry in solution. In all cases, the reduction processes initiated by the redox-active nature of the mian or bian ligand were identified. The paramagnetic nature of complexes 3 and 4 has been proven by EPR spectroscopy. Complexes 3 and 4 exhibited high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The yields of products of cyclohexane oxidation were 43% (complex 3) and 27% (complex 4). Based on the data regarding the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play the most crucial role in the reaction. The initial products in the reactions with alkanes are alkyl hydroperoxides, which are easily reduced to their corresponding alcohols by the action of triphenylphosphine (PPh3). According to the DFT calculations, the difference in the catalytic activity of 3 and 4 is most likely associated with a different mechanism for the generation of ●OH radicals. For complex 4 with electron-withdrawing CF3 substituents at the diimine ligand, an alternative mechanism, different from Fenton’s and involving a redox-active ligand, is assumed.

Synthesis, structural characterizations and spectroscopic properties of binuclear CoIII complex and its Schiff ligand as a chemosensor for fuorescent recognition of ZnII

Binuclear CoIII complex [Co2(L)3(DMF)3] containing a Schiff ligand H2L was synthesized and analyzed by elemental analysis, single crystal X-ray crystallography, FT-IR, UV–Vis absorption spectroscopy, Hirshfeld surface analysis and DFT calculation. The CoIII complex was a 3:2 ((L)2− : CoIII) binuclear structure. The spatial configuration of central CoIII ions was six-coordinated slightly twisted octahedron. The 3D supramolecular network structure was linked by intermolecular hydrogen bonds, CH···π and π···π stacking interactions. The Schiff ligand H2L exhibits weak luminescence, but this weak fluorescence is turned on after coordination with the ZnII ion. Furthermore, H2L could as an “OFF-ON” chemosensor for fluorescent recognition of ZnII.

Pyrazolate-based porphyrinic metal-organic frameworks as catechol oxidase mimic enzyme for fluorescent and colorimetric dual-mode detection of dopamine with high sensitivity and specificity

• A dual-signal readout sensor with good sensitivity and selectivity has been developed for dopamine detection. • The study of catechol oxidase mimicking MOF nanozymes has the potential to expand the range of biomimetic MOFs. • The type of modular used in the synthesis process of MOFs can influence the activity of the final enzyme. Enzyme-simulating nanomaterials, with obvious advantages of high activity, stability and cost-effectiveness, can surrogate the complex natural enzymes and catalyze enzyme-like reactions in various harsh applications. Herein, a novel fluorescent and colorimetric dual-readout sensing platform toward dopamine detection based on pyrazolate-based porphyrinic metal-organic frameworks (MOFs) by coordination regulation strategy to improve the performance of catechol oxidase mimic enzyme activity was constructed. Specifically, BA (benzoic acid) or PA (4-Formyl-1( H )-pyrazole) was introduced as auxiliary ligands to regulate the growth mode of pyrazolate-based porphyrinic MOF materials. H 4 TPP (5,10,15,20-Tetra(1 H -pyrazol-4-yl) porphyrin) and auxiliary ligands coordinated with Cu(II), exposing Cu sites with insufficient coordination and enhancing the interaction with oxygen-active species. Benefiting from the binuclear copper center structure and the preferential adsorption of reactants in the self-reinforced interface, a highly sensitive and selective detection method for dopamine based on Cu-TPP(PA) MOF material was proposed under the intervention of H 2 O 2 . The feasibility of Cu-TPP(PA) MOF in detecting dopamine in human serum samples and as a paper-based analytical device was investigated. This achievement will expand the applications of MOFs in analytical chemistry and open up a new avenue for the design of highly active and stable nano-enzymes.

The non-templating synthesis of macro-cyclic Schiff base ligands containing pyrrole and homopiperazine and their binuclear nickel(II), cobalt(II) and mononuclear platinum(II) complexes: X-ray single crystal and anticancer studies

A new dialdehyde N, N'-bis(5-formylpyrrol-2-ylmethyl) homopiperazine (A) was synthesized by the Mannich reaction of pyrrole 2-carbaldehyde, formaldehyde and homopiperazine in the presence of hydrochloric acid. From the direct reaction of A with 1,3-diaminopropane or 1,4- diaminobutane two new macrocyclic Schiff base ligands were obtained, L1 and L2, respectively. The reaction of these ligands with Ni(II), Co(II) and Pt(II) metal ions results in formation of the relevant macrocyclic Schiff base complexes. Compounds were characterized by FT-IR, elemental analysis, mass spectrometry, UV-Vis and, in the case of the ligands, by 1H and 13C-NMR. The crystal structure of the complex [Ni2L2(CH3O)]ClO4 (4) showed a binuclear macro-cyclic structure, with each Ni coordinated by three nitrogen atoms from the ligand and by a methoxide bridging the two metal centers. The cytotoxic activities of these compounds indicated that the ligands, and some of the complexes, have high anti-proliferative effect towards A549 and HeLa cells, but not HT29 cells. Pt complex with L1 and L2 displayed stronger anti-proliferative activity toward HeLa (IC50 = 11 µM for both of them and A549 IC50 = 7 µM and 8 µM, respectively) relative to L1 and L2. In addition, the cytotoxic effects of the compounds were assayed in rat fibroblast cells as a model of the normal cell, however none of them showed any significant cytotoxic effects. Thereby upholding the potential of these compounds for further development as chemotherapeutic agents.

Copper(I) Complexes Containing PCP Ligand Catalyzed Hydrogenation of Carbon Dioxide to Formate under Ambient Conditions.

The five new copper(I) complexes [Cu2(μ-Cl)2(κ1-PCPt-Bu)] (1), [Cu2(μ-Br)2(κ1-PCPt-Bu)] (2), [Cu2(μ-I)2(κ1-PCPt-Bu)] (3), [Cu2(μ-CN)2(κ1-PCPt-Bu)] (4), and [Cu4(μ3-SCN)4(κ1-PCPt-Bu)2]·CH2Cl2 (5) bearing a 1,3-bis[(di-tert-butylphosphino)methyl]benzene ligand were synthesized and characterized spectroscopically, and the molecular structures of 1, 3, and 5 were determined by single-crystal X-ray diffraction techniques. Structural studies for 1 and 3 revealed their binuclear structures with Cu···Cu separations of 2.609(3) and 2.6359(19) Å, respectively. However, 5 has a tetranuclear cubane structure with an 18-electron configuration at each copper without any metal-metal bonds. The two copper centers in 1 and 3 are bonded to one bridging PCPt-Bu ligand in a κ1-manner and two bridging (pseudo)halido ligands in a μ2-bonding mode to generate a nonplanar Cu2(μ-X)2 framework. The four copper centers in 5 are at the vertices of a tetrahedron. Each copper center has pseudo-tetrahedral coordination provided by two bridging PCPt-Bu ligands in a κ1-manner and the four bridging thiocyanate groups in a μ3-manner. These complexes were used as catalysts for the hydrogenation of CO2 to formate in the presence of DBU as a base to produce valuable energy-rich chemicals, and therefore it is a promising, safe, and simple strategy to conduct reactions under ambient pressure at room temperature. Among all of the five copper(I) complex based catalysts, 3 displayed the best catalytic performance with turnover number (TON) values of 38-8700 in 12-48 h of reaction at 25-80 °C. The outstanding catalytic performance of [Cu2(μ-I)2(κ1-PCPt-Bu)] (3) makes it a potential candidate for realizing the large-scale production of formate by CO2 hydrogenation.

Synthesis, structures and selective luminescence sensing of cobalt(II) and copper(II) coordination architectures with 5,5'-(diazene-1,2-diyl)diisophthalic acid and 1,10-phenanthroline

Co(II) and Cu(II) complexes, [Co2(H2L)2(phen)2(H2O)4](H2O)2 (1) and [Cu2(L)0.5(phen)2Cl2]n (2) [H4L = 5,5'-(diazene-1,2-diyl)diisophthalic acid, phen = 1,10-phenanthroline], have been solvothermally synthesized by a mixed-ligand strategy and structurally characterized by elemental analyses, IR spectra and X-ray diffraction (XRD) analyses. Single crystal XRD analyses indicate that 1 and 2 exhibit a binuclear structure and a 1D chain structure, respectively. The results reveal that the coordination configuration of M(II) has a pivotal part in formation of final structures. Moreover, they can conditionally detect Fe3+ through luminescence quenching. In addition, 1 can also detect Cr2O7 2− ions in the absence of S2− and H2P2O7 2− ions.

An oxalate-bridged oxidovanadium(IV) binuclear complex that improves the in vitro cell uptake of a fluorescent glucose analog

The centrosymmetric oxidovanadium(IV) complex (Et3NH)2[{VO(OH2)(ox)}2(μ–ox)] (I), where ox2− = oxalate, was synthesized and characterized by X-ray diffraction (single-crystal and powder, PXRD), thermogravimetric (TGA), magnetic susceptibility (at room temperature) and spectroscopic analyses (infrared, Raman and electron paramagnetic resonance, EPR, spectroscopies). In the solid state, each vanadium center is coordinated by the oxygen atoms of a bis-bidentate oxalate bridging ligand, a terminal oxalate, an oxo group and one water molecule. The electronic structure of the binuclear complex was investigated by density functional theory (DFT) calculations, both in vacuum and in a simulated aqueous environment, employing the ωB97XD functional and the def2TZVP basis set. The cytotoxicity of I was evaluated in vitro in the human hepatocellular carcinoma cell line HepG2, giving an IC50 value of 15.67 µmol L−1 after incubation for 24 h. The EPR analysis of I in aqueous solution suggested the maintenance of the binuclear structure, while in the hyperglycemic medium DMEM the complex suffers dissociation to give a mononuclear oxidovanadium(IV) species. HepG2 cell treatment with 0.10 and 0.50 µmol L−1 of I in DMEM increased 2-NBDG (2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-d-glucose) uptake significantly (up to 91% as compared to HepG2 in hyperglycemic condition, 59%). These results indicate a promising activity of I to be investigated further in additional antidiabetic studies.

Phosphasalalen Rare-Earth Complexes for the Polymerization of rac-Lactide and rac-β-Butyrolactone.

A series of new phosphasalalen pro-ligands, analogues of salalen but with an iminophosphorane replacing the imine functionality, and their corresponding rare-earth alkoxide and siloxide complexes were synthesized. The multinuclear NMR spectra and X-ray diffraction analyses revealed that, for the tert-butoxide and ethoxide complexes, the resulting phosphasalalen rare-earth product was composed of a mononuclear alkoxide and a binuclear complex containing bridged alkoxo and hydroxo groups, while an analogous binuclear complex was isolated as the sole product for the siloxide complex. All the complexes could catalyze the heteroselective ring-opening polymerization (ROP) of rac-lactide (Pr up to 0.77) with high catalytic activities and a controlled polydispersity. Remarkably, the yttrium and lutetium phosphasalalen complexes could also efficiently catalyze the ROP of rac-β-butyrolactone to produce syndiotactic polymers (Pr up to 0.73) while their salalen analogues were inert, revealing the special effects of the iminophosphorane moiety. Detailed end-group analyses and kinetic investigations suggested that the alkoxo-hydroxo-bridged complexes maintained their binuclear structures in the polymerization.

In Situ Ligand Formation in the Synthetic Processes from Mononuclear Dy(III) Compounds to Binuclear Dy(III) Compounds: Synthesis, Structure, Magnetic Behavior, and Theoretical Analysis.

Guided by the self-assembled process and mechanism, the strategy of in situ Schiff base reaction would be capable of bringing a feasible method to construct and synthesize lanthanide compounds with distinct structures and magnetic properties. A mononuclear Dy(III) compound was synthesized through a multidentate Schiff base ligand and a chelating β-diketonate ligand, which was named as [Dy(L)(bppd)]·CH3OH [1; H2L = N,N'-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and bppd = 3-bis(pyridin-2-yl)propane-1,3-dione]. Furthermore, a new binuclear Dy(III) compound, [Dy2(H2Lox)(bppd)3]·8CH3OH [2; H4Lox = N,N'-bis[2-hydroxy-5-methyl-3-(hydroxyiminomethyl)benzyl]-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine], was obtained via an in situ synthetic process. Under similar synthetic conditions, [Dy(L)(ctbd)] [3; ctbd = 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione] and [Dy2(H2Lox)(ctbd)3]·CH3OH·C4H10O (4) were synthesized by modifying the β-diketonate ligand and in situ Schiff base reaction. Compound 3 is a mononuclear configuration, while compound 4 exhibits a binuclear Dy(III) unit. Therein, formylbenzyl groups of H2L in 1 and 3 were changed to (hydroxyiminomethyl)benzyl groups in 2 and 4, respectively. In isomorphous 2 and 4, two Dy(III) centers are connected through two phenol O- atoms of the H2Lox2- ligand to form a binuclear structure. Eight-coordinated Dy(III) ions with different distortions can be observed in 1-4. The crystals of 1 and 3 suffered dissolution/precipitation to obtain 2 and 4, respectively. The relationship between the structure and magnetism in compounds 1-4 was discussed through the combination of structural, experimental, and theoretical investigations. Especially, the rates of quantum tunneling of magnetization of 1-4 were theoretically predicted and are consistent with the experimental results. For 2 and 4, the theoretically calculated dipolar parameters Jdip are consistent with the experimental observation of weak ferromagnetic coupling.

A new Bi(III)-based coordination complex: Treatment and nursing application values on pediatric pneumonia

In the current work, through applying the mixed-ligand generation method, [Bi4Cl8(PDC)2 (2,2′-bpy)4]·2MeCN (1), a fresh bismuth (III)-organic compound synthesized with the solvothermal reactions between 2,2′-bipyridine (2,2′-bpy); 2,6-pyridinedicarboxylic acid (H2PDC); and bismuth chloride. The structural characterization results show that complex 1 features a binuclear discrete structure which is further extended into a 1D chain–like supramolecular network via π–π interactions. Furthermore, the compound’s treatment and nursing application values on pediatric pneumonia was explored and the novel compound’s corresponding mechanism was also investigated. First of all, in our research, the enzyme-linked immunosorbent assay (ELISA) detection kit was employed for the determination of the inflammatory cytokines content released into alveolar lavage fluid. Subsequently, the adenosine 5‘-monophosphate (AMP)–activated protein kinase (AMPK) signaling pathway activation in alveolar epithelial cells was explored exploiting the real-time reverse transcription–polymerase chain reaction (RT-PCR). Molecular docking demonstrated that although multiple pyridine rings are presented in the Bi complex, however, only the carboxylate groups have been observed to interact with the active residues.

The role of the phosphorus lone pair in the low-energy binuclear phospholyl vanadium carbonyl structures: comparison with cyclopentadienyl analogues

The structures and energetics of the binuclear phospholyl vanadium carbonyls (C4H4P)2V2(CO)n (n = 7, 6, 5, 4, 3, 2, 1) have been investigated using density functional theory. The lowest energy heptacarbonyl (C4H4P)2V2(CO)7 structures resemble those of the dimanganese pentacarbonyl (C4H4P)2Mn2(CO)5 with one seven-electron donor bridging η5,η1-C4H4P ring and no direct vanadium–vanadium bond. Similarly, the lowest energy hexacarbonyl (C4H4P)2V2(CO)6 structure resembles that of the dimanganese tetracarbonyl (C4H4P)2Mn2(CO)4 with two seven-electron donor bridging η5,η1-C4H4P rings and no direct vanadium–vanadium bond. The lowest energy pentacarbonyl (C4H4P)2V2(CO)5 structure has terminal η5-C4H4P phospholyl rings and a formal V≡V triple bond of length ~ 2.45 A similar to the experimentally known and structurally characterized cyclopentadienyl analogue (η5-C5H5)2V2(CO)5. Various combinations of V=V double bonds or V≡V triple bonds, four-electron donor bridging carbonyl groups and seven-electron donor bridging η5,η1-C4H4P rings are found in the more highly unsaturated derivatives (C4H4P)2V2(CO)n (n = 4, 3, 2) to give 17- and 18-electron vanadium configurations for triplet- and singlet-state structures, respectively. Formal V≣V quadruple bonds are found only in the highly unsaturated lowest energy singlet (C4H4P)2V2(CO)n (n = 2, 1) structures, which, however, lie at somewhat higher energies than isomeric triplet structures.

Synthesis of an unprecedented H-stitched binuclear crystal structure based on selective fluorescence recognition of Zn2+ in newly synthesized Schiff base ligand with DFT and imaging application in living cells

Single hydrogen atom stitched giant binuclear crystal.

Visible light-assisted photocatalytic degradation of methylene blue in water by highly chemically stable Cd-coordination polymers at room temperature

Mesoporous YAU-10 based on a binuclear 3D structure has been synthesized as a photocatalytic material exhibiting excellent visible light-assisted degradation of methylene blue.

Synthesis, crystal structures, and luminescent properties of Zn(II)/Cd(II) complexes assembled by 4-aminophenylhydroxamic acid

Two coordination complexes, namely [Zn2(4-APha)2(CH3COO)2(H2O)2] (1) and [Cd(4-APha)·(CH3COO)(H2O)0.5]4·6H2O (2) (4-APha = 4-aminophenylhydroxamic acid), are synthesized by the solvothermal method. They are characterized by single crystal X-ray diffraction, IR, TGA, and elemental analysis. Structural analyses reveal that both complexes 1 and 2 belong to the monoclinic system, space group C2/c. The difference is that complex 1 shows a binuclear structure and complex 2 displays a 3D structure. It is noteworthy that complex 1 exhibits an excellent thermal stability and no weight loss below 117 °C. Meanwhile, the luminescent pro­perties of complexes 1 and 2 in the solid state are also investigated at room temperature.

The Uniqueness of Tryptophan in Biology: Properties, Metabolism, Interactions and Localization in Proteins.

Tryptophan (Trp) holds a unique place in biology for a multitude of reasons. It is the largest of all twenty amino acids in the translational toolbox. Its side chain is indole, which is aromatic with a binuclear ring structure, whereas those of Phe, Tyr, and His are single-ring aromatics. In part due to these elaborate structural features, the biosynthetic pathway of Trp is the most complex and the most energy-consuming among all amino acids. Essential in the animal diet, Trp is also the least abundant amino acid in the cell, and one of the rarest in the proteome. In most eukaryotes, Trp is the only amino acid besides Met, which is coded for by a single codon, namely UGG. Due to the large and hydrophobic π-electron surface area, its aromatic side chain interacts with multiple other side chains in the protein, befitting its strategic locations in the protein structure. Finally, several Trp derivatives, namely tryptophylquinone, oxitriptan, serotonin, melatonin, and tryptophol, have specialized functions. Overall, Trp is a scarce and precious amino acid in the cell, such that nature uses it parsimoniously, for multiple but selective functions. Here, the various aspects of the uniqueness of Trp are presented in molecular terms.

Synthesis and spectroscopic properties of two different structural Schiff base Zn(II) complexes constructed with/without auxiliary ligands

The Schiff base binuclear Zn(II) complexes, [Zn2(L)2∙(H2O)2]∙2DMF (1) and its coordination polymer [Zn2(L)2∙(4,4′-bpy)2]n (2) (H2L = 3-[(5-chloro-2-hydroxy-benzylidene)-amino]-4-hydroxy-chromen-2-one, 4,4′-bpy = 4,4′-bipyridine), were synthesized under the same experimental condition without or with the auxiliary ligand 4,4′-bpy, respectively. The structural analysis revealed that complexes 1 and 2 have different crystal structures. The complex 1 was a centrosymmetric binuclear structure. It is noteworthy that the linker 4,4′-bpy was introduced during the synthesis of complex 2, so that two water molecules in complex 1 were replaced by two 4,4′-bpy linkers to form one-dimensional (1D) chain-like coordination polymer. The central Zn(II) ions in complex 1 were penta-coordinated distorted square pyramid geometry with τ = 0.42. However, the Zn(II) ions of complex 2 were hexa-coordinated distorted octahedral geometry. The fluorescence spectrum showed the complex 2 containing 4,4′-bpy was substantially quenching of the fluorescence as compared with the complex 1. In addition, it could be seen from the DFT calculation the energy gaps of the complexes 1 and 2 were both reduced compared to the ligand H2L. However, the LUMO and HOMO orbits of the complex 2 were occupied by the 4,4′-bpy, which is different from complex 1, resulting in 1 and 2 had different spectral properties.

Synthesis and crystal structures of two new lead(II) complexes with the pincer-type ligand 4′-(4-chlorophenyl)-2,2′:6′,2″-terpyridine (Cl-Ph-tpy): subtle interplay of weak intermolecular interactions

Abstract A dinuclear and a tetranuclear complex of lead(II) with the pincer-type ligand 4′-(4-chlorophenyl)-2,2′:6′,2″-terpyridine (Cl-Ph-tpy), [Pb2(Cl-Ph-tpy)2(μ-I)2I2] (1) and [Pb4(Cl-Ph-tpy)4(μ-Br)4(μ-OH2)Br4]·2CH3OH (2), have been synthesized and characterized by elemental analysis, FT-IR and 1H NMR spectroscopy, and by single-crystal X-ray diffraction. In the binuclear structure of 1, the Pb atom has a hemidirected PbN3I3 environment with a Pb(μ-I)2Pb central unit. In the tetranuclear structure of 2, two crystallographically independent Pb(II) centres having hemidirected PbN3Br3 and PbN3OBr2 environments are connected to Pb(μ-Br)Pb(μ-Br)2(μ-OH2)Pb(μ-Br)Pb chains. The supramolecular features in 1 and 2 are supported through weak but directional C–H···Cl, C–H···I and C–H···Br, C–H···O, O–H···Br, and O···Br interactions and aromatic π-π stacking.

Synthesis, Molecular Structure, and Spectral Characteristics of Lead(II) Complexes with 1,5-Dimethyl-4-[2-(3-methyl-5-oxo-1-phenyl-1,5-dihydro-4H-pyrazol-4-ylidene)hydrazinyl]-2-phenyl-1,2-dihydro-3H-pyrazol-3-one

Pb(II) cations form complexes with 1,5-dimethyl-4-[2-(3-methyl-5-oxo-1-phenyl-1,5-dihydro-4H-pyrazol-4-ylidene)hydrazinyl]-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) in an aqueous-ethanolic solution. The C42H41N13O9Pb2 compound has been isolated in the crystalline state and its spectral characteristics have been determined. As per X-ray diffraction analysis data, it is a cocrystallizate of the Pb2L2(OH)2·(H2O)2 binuclear complex and the PbLNO3 dimeric associate. According to the simulation using the Bader method, the lead cations both in the binuclear structure and in the dimeric associate have not interacted.