Structural variation from linear,layer to 3D framework: Syntheses,structures and luminescence

Self‐assembly of Zn (II) or Cd (II) nitrates, flexible bis (pyridyl)‐diamine, as well as arenesulfonic acids, leads to the formation of ten coordination polymers, namely, [Zn(L1)(H₂O)₃]·2(p‐TS)·2H₂O ( 1 ), [Zn(L1)(H₂O)₂]·2(p‐TS)·2H₂O ( 2 ), [Zn(L1)₂(p‐TS)₂] ( 3 ), [Zn(H₂L1)(H₂O)₄]·2(1,5‐NDS)·2H₂O ( 4 ), [Zn(H₂L2)(H₂O)₄]·2(1,5‐NDS)·4MeOH ( 5 ), [Cd(L1)(p‐TS)(NO₃)]·H₂O ( 6 ), [Cd(L1)(1,5 ‐NDS)_0.5(H₂O)]·0.5(1,5‐NDS)·H₂O ( 7 ), [Cd(L2)(H₂O)₂]·(p‐TS)·(NO₃)·3H₂O ( 8 ), [Cd(L2)(1,5‐NDS)] ( 9 ) and [Cd(L2)(1,5‐NDS)]·MeOH ( 10 ) (L1 = N,N′‐bis (pyridin‐4‐ylmethyl) ethane‐1,2‐diamine, L2 = N,N′‐bis (pyridin‐3‐ylmethy l)ethane‐1,2‐diamine, p‐HTS = p‐toluenesulfonic acid, 1,5‐H₂NDS = 1,5‐naphthalene disulfonic acid), which have been characterized by elemental analysis, IR, TG, PL, powder and single‐crystal X‐ray diffraction. Complexes 1 , 4 , 5 and 6 present linear or zigzag chain structures accomplished by the interconnection of adjacent M (II) cations through L1 ligands or protonated H₂L1²⁺/H₂L2²⁺ cations, while complexes 2 , 3 and 8 show similar (4,4) layer motifs constructed from the connection of M (II) cations through L1 and L2. The same coordination modes of L1 and L2 in complexes 7 and 9 join adjacent Cd (II) cations to form double chain structures, which are further connected by bis‐monodentate 1,5‐NDS^2? dianions into different (6,3) and (4,4) layer motifs. The L2 molecules in complex 10 join adjacent Cd (II) cations together with 1,5‐NDS^2? dianions to form 3D network with hxl topology. Therefore, the diverse coordination modes of the bis (pyridyl) ligand with chelating spacer and the feature of different arenesulfonate anions can effectively influence the architectures of these complexes. Luminescent investigation reveals that the emission maximum of these complexes varies from 374 to 448 nm in the solid state at room temperature, in which complexes 4 , 5 , 7 , 9 and 10 show average luminescence lifetimes from 7.20 to 14.82 ns. Moreover, photocatalytic properties of complexes 7–10 towards Methylene blue under Xe lamp irradiation are also discussed.     

Synthesis Characterization,X‐ray Structures,and Solution Studies of Dinuclear Zinc(II) Complexes of Acyclic Schiff Base Ligands

Dizinc(II) complexes of two acyclic Schiff‐base ligands L1 ^– and L2 ^– were synthesized by Schiff base condensation of 2‐[3‐(2‐formylphenoxy)‐2‐hydroxypropoxy]benzaldehyde ( PL ) with 1,2‐diaminopropane and 1,2‐diaminoethane, respectively, in the presence of zinc(II) salts. The isolation of a selection of 2:1 (metal:ligand) complexes of zinc(II) was carried out and conductance measurements, IR, UV/Vis absorption, and fluorescence emission spectroscopy, as well as X‐ray diffraction were employed to probe the nature of the respective complexes in both solid and solution states. The molecular structure of [Zn₂ L1 (NO₃)₃] ( 1 ) complex consists of two six‐coordinate atoms, which are bridged by the deprotonated hydroxy group and one 1,3‐bridging nitrate anion. The structure of [Zn₂ L2 (NO₃)(H₂O)₂](NO₃)₂ · CH₃OH ( 3 ) consists of a dizinc cation and two nitrate anions as counterions. In compound 3 , each zinc atom is bound to water instead of a terminal nitrate anion in a distorted octahedral arrangement. The intermetallic separation distance of Zn ··· Zn in 3 (3.376 Å) is slightly smaller than 1 (3.403 Å) and is similar to that found in zinc phosphotriesterase (3.5 Å). The π–π interactions between the benzene rings of adjacent molecules in 3 are stronger than in 1 .     

Enhanced antifungal activities of four Zn(II) complexes based on uniconazole

Four Zn(II) complexes, [Zn L ₂(SO₄)]_n ( 1 ), [Zn L ₄(H₂O)₂]?2(NO₃)?4EtOH ( 2 ), [Zn L ₂Cl₂]? L ( 3 ), and [Zn L ₂Br₂]? L ( 4 ) ( L  = uniconazole), were synthesized using a hydrothermal method and characterized by elemental analysis, FT‐IR spectroscopy, and single‐crystal XRD. Complex 1 formed a one‐dimensional polymer chain. However, complexes 2 ‐ 4 were obtained as zero‐dimensional mononuclear coordination compounds. The antifungal activities of these complexes were then evaluated against four selected fungi using the mycelial growth rate method. The resulting data indicate that all complexes show better antifungal activities than their ligands and mixtures. In addition, the interactions between the metal salts of complexes 1 ‐ 4 and uniconazole seem to be synergistic. Furthermore, the polymer chain structure of complex 1 significantly enhanced the bioactivity, especially against Botryosphaeria ribis ( I ). Density functional theory (DFT) calculations were carried out to help explain the enhanced bioactivity after the formation of Zn(II) complexes. The resulting data show that the HOMO–LUMO energy gaps of complexes 1 ‐ 4 (0.0578, 0.0946, 0.1053, and 0.1245 eV) are smaller than that of the free ligand (0.1247 eV) and correlate with the antifungal activity of the zinc complexes.     

Tweaking the affinity of aryl‐substituted diazosalicylato‐ and pyridine ligands towards Zn (II) and its neighbors in the periodic system of the elements,Cu (II) and Cd (II), and their antimicrobial activity

A series of six new Zn (II) compounds, viz., [Zn(HL^ASA)₂(Py)₂] ( 1 ), [Zn(HL^MASA)₂(Py)₂] ( 2 ), [Zn(HL^MASA)₂(4‐MePy)₂] ( 3 ), [Zn(HL^CASA)₂(4‐MePy)₂] ( 4 ), [Zn(HL^BASA)₂(Py)₂] ( 5 ), [Zn(HL^BASA)₂(4‐MePy)₂] ( 6 ) and representative Cu (II) and Cd (II) complexes, viz., [Cu(HL^ASA)₂(Py)₂(H₂O)] ( 7 ) and [Cd(HL^BASA)₂(Py)₃] ( 8 ) [(HL^XASA)^? = para‐substituted 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoate with X = H (ASA), Me (MASA), Cl (CASA) or Br (BASA); Py = pyridine; 4‐MePy = 4‐methylpyridine] have been synthesized and characterized by spectroscopic techniques and single‐crystal X‐ray diffraction analysis. The structural characterization of the compounds revealed distorted tetrahedral ( 1 – 6 ), square‐pyramidal ( 7 ) and pentagonal‐bipyramidal ( 8 ) coordination geometries around the metal atom, in which the aryl‐substituted diazosalicylate ligands are coordinated only through the oxygen atoms of carboxylate groups, either in an anisobidentate or isobidentate mode; meanwhile, the 2‐hydroxy groups of the monoanionic ligand (HL^XASA)^? are involved only in intramolecular O‐H···O hydrogen bonds with the carboxylate function. In the crystal structures of 1 – 8 , the complex molecules are assembled by π‐stacking interactions giving mostly infinite 1D strands. The intermolecular binding in the solid state structures is accomplished by diverse additional non‐covalent contacts including C‐H···O, C‐H···N, C‐H···π, C‐H···Br, O···Br, Br···π and van der Waals contacts. Although the primary and secondary ligands in the Zn (II) complex series 1 – 6 carry different substituents at the periphery (X = H, Me, Cl, Br for (HL^XASA)^? and R = H, Me for 4‐Py‐R), five of the crystal structures were isostructural. Additionally, the antimicrobial activity of the pro‐ligands H₂L^XASA and their Zn (II), Cu (II) and Cd (II) compounds were studied in a comparative manner, showing high sensitivity (IZD ≥ 20) against Bacillus subtilis.     

Mononuclear metal (II) complexes of a Bis(organoamido)phosphate ligand with antimicrobial activities against Escherichia coli

A new tripodal ligand [PO(NH²MePy)₃] ( L ) (²MePy = 2‐(4‐methyl pyridyl)) have been synthesized by treating phosphorous oxychloride with 2‐Amino‐4‐methylpyridine in toluene under refluxing condition. The ligand was appeared as a white solid and characterized by several standard analytical and spectroscopic techniques such as FT‐IR, NMR (¹H, ¹³C{¹H} and ³¹P{¹H}) and ESI‐MS spectroscopy. The ligand ( L ) undergone metal‐assisted hydrolysis of one P–N bond when treated it with hydrated metal nitrates, M(NO₃)₂·xH₂O (M = Zn, Cu, Co and Ni) under hydrothermal reaction condition in DMF‐H₂O (1:1). This results in the formation of four mononuclear complexes [{PO₂(NH²MePy)₂}₂M] [M = Zn ( 1 ), Cu ( 2 ), Co ( 3 ), Ni ( 4 )], where ligand ( L ) hydrolyses to a anionic bis(organoamido)phosphate, [PO₂(NH²MePy)₂]⁻. All complexes were completely characterized by various analytical techniques and their solid state molecular structures were established by single crystal X‐ray diffraction. All complexes are isostructural with a metal (II) ion situating at the centre of a distorted octahedron. Two tridentate [PO₂(NH²MePy)₂]⁻ ligands are coordinated to metal(II) ion through N‐ and O‐donor atoms, thus neutralizing the charge of the complex. Optical properties of all complexes in solid state have been studied. Moreover, antimicrobial activities of complexes 1 – 4 have been explored. To the best of our knowledge, this is the first report of such compounds investigated for their antimicrobial activities.     

Green Synthesis of new Trizole Based Heterocyclic Amino Acids Ligands and their Transition Metal Complexes. Characterization,Kinetics, Antimicrobial and Docking Studies

Two novel amino acids imine ligands (H₂L₁ and H₂L₂) have been synthesized using green condensation reaction from 2‐[3‐Amino‐5‐(2‐hydroxy‐phenyl)‐5‐methyl‐1,5‐dihydro‐[1, 2, 4]triazol‐4‐yl]‐3‐(1H‐indol‐3‐yl)‐propionic acid with benzaldehyde/p‐flouro benzaldehyde (1:1 molar ratio) in the presence of lemon juice as a natural acidic catalyst in aqueous medium. Their transition metal complexes have been prepared in a molar ratio (1:1). Characterization of the ligands and complexes using elemental analysis, spectroscopic studies, ¹HNMR, ¹³CNMR, and thermal analysis has been reported. E*, ΔH*, ΔS* and ΔG* thermodynamic parameters, were calculated to throw more light on the nature of changes accompanying the thermal decomposition process of these complexes. The molar conductance measurement of metal complexes showed nonelectrolyte behavior. The metal complexes of the two ligands have tetrahedral geometry with a general molecular structure [M(H₂L)X_n], where [(M = Mn (II), Co (II), Cu (II) and Zn (II), X = Cl, n = 2]; M = VO (II), X = SO₄, n = 1] for H₂L₁. [M = Co (II), Cu (II), Zn (II)] for H₂L₂. Antibacterial activity of the complexes against (Bacillis subtilis, Micrococcus luteus, Escherichia coli), also antifungal activity against (Aspergillus niger, Candida Glabarta, Saccharomyces cerevisiae) have been screened. The results showed that all complexes have antimicrobial activity higher than free ligands. Molecular docking studies results showed that, all the synthesized compounds having minimum binding energy and have good affinity toward the active pocket, thus, they may be considered as good inhibitor of targeting PDB code: 1SC7 (Human DNA Topo‐isomerase I).     

Similarities and differences of thermal behaviour of 2-hydroxymethylbenzimidazole complexes with Zn(II) and Cd(II) ions

For a comparison of structural data and thermal behaviour of Zn(II) and Cd(II) complexes with biologically important ligand, 2-hydroxymethylbenzimidazole (L) the complex of the formula [ZnL₃](NO₃)₂L_0.67L′_0.33 was prepared and characterized by elemental analysis, infrared (IR) spectra, single-crystal X-ray diffraction and thermal analysis (where L′ = 2-carbaldehydebenzimidazole). IR and X-ray studies have confirmed a bidentate fashion of coordination of the 2-hydroxymethylbenzimidazole to Zn(II) ion (through the nitrogen atom of heteroaromatic ring and oxygen atom of hydroxymethyl group). The zinc ion is hexacoordinated and the shape of polyhedron can be described as pseudo-octahedron (N₃O₃ chromophore type). The decomposition process of studied Zn(II) and Cd(II) benzimidazole complexes in the air atmosphere proceeds in three or four main stages and traces structures of complexes. On the basis of the first DTG_max of the decompositions the thermal stability of the complexes follows the order: [CdL₃](NO₃)₂LEtOH_0.25 < [CdL₂(NO₃)₂] < [ZnL₃](NO₃)₂L_0.67L′_0.33. As the final solid products of thermal decomposition suitable metal oxides are formed.     

Synthesis,Structures and Various Biological Applications of New Zn(II) Complexes Having Different Coordination Modes Controlled by the Drug Furosemide in Presence of Bioactive Nitrogen Based Ligands

Novel Zn(II) complexes with the general formula: [Zn(furo)₂(L)_n], n = 1 or 2, (furo = furosemide = (4‐chloro‐2‐(furan‐2‐ylmethylamino)‐5‐sulfamoylbenzoic acid) were prepared. The complexes [Zn(furo)₂(MeOH)₂] ( 1 ; MeOH = methanol), [Zn(furo)₂(2‐ampy)₂] ( 2 ; 2‐ampy = 2‐aminopyridine), [Zn(furo)₂(2‐ammepy)₂] ( 3 ; 2‐ammepy = 2‐aminomethylpyridine), [Zn(furo)₂(H₂O)(2,2‐bipy)] ( 4 ; 2,2′‐bipy = 2,2′‐bipyridine), [Zn(furo)₂(H₂O)(4,4′‐bipy)] ( 5 ; 4,4′‐bipy = 4,4′‐bipyridine), [Zn(furo)₂(1,10‐phen)] ( 6 ; 1,10‐phen = 1,10‐phenanthroline), [Zn(furo)₂(2,9‐dmp)] ( 7 ; 2,9‐dmp = 2,9‐dimethyl‐1,10‐phenanthroline), and [Zn (furo)₂(quin)₂] ( 8 ; quin = quinoline) were synthesized and characterized using different techniques such as IR, UV–Vis, ¹H NMR, ¹³C NMR, LC/MS and others. The crystal structure of complex ( 4 ) was determined using single‐crystal X‐ray diffraction. The anti‐bacterial activity of complexes ( 1 – 8 ) was tested using agar diffusion method against three gram‐positive (Staphylococcus aureus, Bacillus subtilis and Staphylococcus epidermidis) and three gram‐negative bacteria (Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa). The obtained results showed different Inhibition Zone Diameters (IZD) with various anti‐bacterial activities against the selected gram‐positive and gram‐negative bacteria. In addition, the rate of bis‐(4‐nitrophenyl) phosphate hydrolysis was measured at different temperatures, different pH values and different concentrations. The rates for the eight complexes were in the following order: complex 4 > 2 > 5 > 8  >  7  >  6  >  3  >  1 .     

Preparation of a novel Mixed-Ligand divalent metal complexes from solvent free Synthesized Schiff base derived from 2,6-Diaminopyridine with cinnamaldehyde and 2,2′‐Bipyridine: Characterization and antibacterial activities

The solvent-free conditions were employed to synthesise symmetrical Schiff base ligand from 2,6-diaminopyridine with cinnamaldehyde in (1 min) with a fair yield utilizing formic acid as a catalyst. Through coordination chemistry, new heteroleptic complexes of Cu(II), Co(II), Ni(II), Pt(II), Pd(II) and Zn(II) were achieved from Schiff base as a primary chelator (L¹) and 2,2′‐bipyridine (2,2′-bipy) as a secondary chelator (L²). The prepared compounds have been characterized by elemental analysis, molar conductivity, magnetic susceptibility, FTIR, ¹H NMR, UV–visible, mass spectrometry, and thermal gravimetric analysis, and screened in vitro for their potential as antibacterial activity by the agar well diffusion method. The metal complexes were formulated as [M (L¹) (L²) (X)] Y⋅nH₂O, L¹ = Schiff base, L² = 2,2′-bipy, (M = Cu(II), Co(II), Zn(II), Y = 2NO₃, n = 1), (M = Ni(II), X = 2H₂O, Y = 2NO_3, n = 0) and (M = Pd(II) Pt(II), Y = 2Cl, n = 0). Both L¹ and L² act as a neutral bidentate ligand and coordinates via nitrogen atoms of imine and 2,2′-bipy to metal ions. The metal complexes were found to be electrolytic, with square-planar heteroleptic Cu(II), Co(II), Pt(II), and Pd(II) chelates and octahedral Ni(II) complex. As well as tetrahedral geometry, has been proposed for the complex of Zn(II). Furthermore, the biological activity study revealed that some metal chelates have excellent activity than Schiff base when tested against Gram-negative and Gram-positive strains of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Finally, it was found that the Zn(II) and Pd(II) complexes were more effective against both types of bacteria tested than the imine and other metal complexes.     

Structurally rigid bis(pyrazolyl)pyridine Zn(II) and Cu(II) complexes: Structures and kinetic studies in ring‐opening polymerization of ε‐caprolactone

Four bis(pyrazolyl)pyridine Zn(II) and Cu(II) carboxylate complexes have been structurally elucidated and used as initiators in the ring‐opening polymerization (ROP) of ε‐carprolactone (ε‐CL). Reactions of bis(3,5‐dimethyl‐pyrazol‐1‐yl)pyridine ( L1 ) with the appropriate Zn(II) and Cu(II) carboxylates afforded the corresponding complexes; [Zn(L1)(C₆H₅COO)₂] ( 1 ), [Zn(L1)(2‐Cl‐C₆H₄COO)₂] ( 2 ), [Zn(L1)(OAc)₂] ( 3 ) and [Cu(L1)(OAc)₂] ( 4 ) in moderate to good yields. Molecular structures of compounds 1 , 2 , 3 confirmed the presence of one tridentate bound ligand L1 in the metal coordination sphere and two carboxylate anions to give five coordination number around Zn(II) and Cu(II) atoms. Complexes 1 , 2 , 3 , 4 initiated the ROP of ε‐CL at 110 °C to give polymers of moderate molecular weights. Kinetic analyses of the ROP reactions indicate pseudo ‐first‐order dependency on ε‐CL monomer and initiator. ¹H NMR and mass spectral data established a coordination insertion mechanistic pathway and behaviour of 1 , 2 , 3 , 4 as initiators in the ROP of ε‐CL. Copyright © 2016 John Wiley & Sons, Ltd.     

Structure and cytotoxicity of zinc (II) and cobalt (II) complexes based on 1,3,5‐tris(1‐imidazolyl) benzene

Three novel complexes, [Zn (tib)₂·(H₂O)₂]·(NO₃)₂ ( 1 ), [Co (tib)₂]·2NO₃ ( 2 ) and [Co₂(tib)₂(btc)]·H₂O ( 3 ) [H₄btc = 1,2,4,5‐benzenetetracarboxylic acid; H₂tib = 1,3,5‐tris(1‐imidazolyl)benzene], were synthesized and characterized by single‐crystal X‐ray, IR and elemental analysis. The interaction of these complexes with FS‐DNA (fish sperm DNA) was monitored, and binding constants were determined using UV/Vis, which revealed that they have the ability to bind to FS‐DNA. DNA‐binding constants (K) for the three complexes were 2.2 × 10⁴ m ^?1, 0.7 × 10⁴ m ^?1 and 0.09 × 10⁴ m ^?1, respectively. The interaction capacity of the complexes with FS‐DNA has been investigated by fluorescence spectroscopy. Stern–Volmer quenching plot values for complexes 1 , 2 and 3 were 0.3784, 0.1028 and 0.076, respectively. The viscosity measurement suggested that complexes 1 , 2 and 3 interact with DNA in an intercalation mode. In addition, anti‐cancer activities of these complexes investigated through MTT assays in vitro indicated that the complexes showed good cytotoxic activity against cancer cell lines. Cytotoxic activity of test complexes against two different cancer cell lines (HeLa and KB cells) showed significant cancer cell inhibition rates. Flow cytometry experiments and morphological apoptosis studies showed that the complexes induced apoptosis of HeLa tumor cell lines. Finally, a further molecular docking technique was employed to confirm the binding of the complexes toward the molecular target DNA.     

X‐ray crystal of diprotonated tetra‐(2‐pyridyl)pyrazine (H2TPPZ), aqua Fe3+‐phen crystal and new lanthanide complexes of TPPZ and their biochemical studies

New complexes derived from M³⁺ salts with polyazine as monometallic such as [Fe (TPPZ)Cl₃].½H₂O (1) , [Cr (TPPZ)₂Cl₂]Cl.2EtOH (2) , [La (TPPZ)(NO₃)₂(H₂O)₂]NO₃.H₂O (3) in addition to [Fe (Phen)₃]3Cl.7H₂O (4) were isolated. Three bimetallic, [H₂TPPZ][(AuCl₄)₂]. H₂O (5) , [Ce₂(TPPZ)EtOH (NO₃)₃]3NO₃ (6) and [Nd₂TPPZCl₂(H₂O)₄]4Cl.CHCl₃. 4H₂O (7) and mixed ligand complexes, [Fe (TPPZ)(Phen)₂]Cl₃ (8) , [Fe (TPPZ) (Phen)₂][TPPZCl₃] (9) , [La₂(TPPZ)(Phen)₂(EtOH)₂]6Cl.CHCl₃.EtOH.H₂O (10) and [Nd₂(TPPZ)(Phen)Cl₄]2Cl.3H₂O (11) were synthesized and characterized. Crystal data of (4) is tetragonal, I4₁/a, a = b 35.951 (3) Å, c = 11.9055 (8) Å, α = 80.201 (2)° β = 78.846 (2)°, γ = 89.687 (2)° V = 741.06 (5)ų, Z = 1 while triclinic, P1, a = 7.3913 (3) Å, b = 9.7344 (4) Å, c = 10.6577 (4) Å, α = β = γ = 90°, V = 741.06 (5)ų and Z = 170 for (5) . Analyses, spectral and cyclic voltammetry studies indicate the bonding and the redox properties. Anticancer studies promised to be effective in lanthanides and some complexes were screened against antibacterial or antifungal.     

Syntheses and Structural Characterization of 1D Chain and 1D Ladder Coordination Polymers Assembled from Exo‐bidentate Imidazolyl Ligands

Five novel coordination polymers, [(Cu(L¹)₂OH) · Cl · 3H₂O] ( 1 ) [L¹ = bis(N‐imidazolyl)methane], [Cd(L¹)₂(NCS)₂] ( 2 ), [Zn(L¹)₂(NCS)₂] ( 3 ), [Cu(L¹)₂(NO₃)₂] ( 4 ), and [Cu(L²)_1.5(NCS)₂] ( 5 ) [L² = 1,4‐bis(N‐imidazolyl)butane] were obtained from self‐assembly of the corresponding metal salts with flexible ligands and their structures were fully characterized by X‐ray diffraction (XRD) analysis, Fourier Transform Infrared (FT‐IR) spectroscopy, elemental analysis and thermogravimetric (TGA) measurements. X‐ray diffraction analyses revealed that complexes 1 , 2 , 3 , and 4 exhibit 1D double‐stranded chain structures, which result from doubly bridged [CuOH], [M(NCS)₂] (M = Cd, Zn), and [Cu(NO₃)₂] units, respectively. The polymeric copper complex 5 displays 1D ladder structure., These complexes, with the exception of complex 1 , are stable up to 300 °C.     

Neutral and cationic half‐sandwich arene d6 metal complexes containing pyridyl and pyrimidyl thiourea ligands with interesting bonding modes: Synthesis,structural and anti‐cancer studies

The reaction of [(p‐cymene)RuCl₂]₂ and [Cp*MCl₂]₂ (M = Rh/Ir) with benzoyl (2‐pyrimidyl) thiourea (L1) and benzoyl (4‐picolyl) thiourea (L2) led to the formation of cationic complexes bearing formula [(arene) M (L1)к² _(N,S) Cl]⁺ and [(arene) M (L2)к²_(N,S)Cl]⁺ [(arene) = p‐cymene, M = Ru, ( 1 , 4 ); Cp*, M = Rh ( 2 , 5 ) and Ir ( 3 , 6 )]. Precursor compounds reacted with benzoyl (6‐picolyl) thiourea (L3) affording neutral complexes having formula [(arene) M (L3)к¹_(S)Cl₂] [arene = p‐cymene, M = Ru, ( 7 ); Cp*, M = Rh ( 8 ), Ir ( 9 )]. X‐ray studies revealed that the methyl substituent attached to the pyridine ring in ligands L2 and L3 affects its coordination mode. When methyl group is at the para position of the pyridine ring (L2), the ligand coordinated metal in a bidentate chelating N, S‐ mode whereas methyl group at ortho position (L3), it coordinated in a monodentate mode. Further the anti‐cancer studies of the thiourea derivatives and its complexes carried out against HCT‐116, HT‐29 (human colorectal cancer), Mia‐PaCa‐2 (human pancreatic cancer) and ARPE‐19 (non‐cancer retinal epithelium) cell lines showed that the thiourea ligands are inactive but upon complexation, the metal compounds displayed potent and selective activity against cancer cells in vitro. Iridium complexes were found to be more potent as compared to ruthenium and rhodium complexes.     

Experimental and theoretical studies of Mn(II) and Co(II) metal complexes of a tridentate Schiff's base ligand and their biological activities

We have used the condensation method to synthesize 2-acetyl-5-methylsemicarbazone ligand. Manganese(II) and Cobalt(II) complexes having formula [ML₂]X₂ were synthesized where M = Mn(II) and Co(II), L = ligand, X = Cl⁻, CH₃COO⁻, NO₃⁻, ½SO₄²⁻. The characterization data suggests the octahedral geometry for all the synthesized complexes. Tridentate nature of the 2-acetyl-5-methylsemicarbazone ligand was revealed by IR studies. Molar conductance analysis suggested the electrolytic nature of the complexes. The theoretical study includes geometrical optimization, HOMO-LUMO energy gap, energetic parameters and dipole moment. These results also confirmed the tridentate nature of the ligand and the octahedral geometry of complexes. The molecular electrostatic potential (MEP) study suggested the reactive sites for an electrophilic or nucleophilic attack in the ligand. We tested the synthesized compounds for their antifungal and antibacterial action via well diffusion method and found that parent ligand after the coordination with the metal ion showed more effective inhibition against bacteria and fungi.     

Luminescent mononuclear and dinuclear cycloplatinated (II) complexes comprising azide and phosphine ancillary ligands

A new series of cycloplatinated (II) complexes with general formulas of [Pt (bhq)(N₃)(P)] [bhq = deprotonated 7,8‐benzo[h]quinoline, P = triphenyl phosphine (PPh₃) and methyldiphenyl phosphine], [Pt (bhq)(P^P)]N₃ [P^P = 1,1‐bis (diphenylphosphino)methane (dppm) and 1,2‐bis (diphenylphosphino)ethane] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂] [P^P = dppm and 1,2‐bis (diphenylphosphino)acetylene] is reported in this investigation. A combination of azide (N₃^?) and phosphine (monodentate and bidentate) was used as ancillary ligands to study their influences on the chromophoric cyclometalated ligand. All complexes were characterized by nuclear magnetic resonance spectroscopy. To confirm the presence of the N₃^? ligand directly connected to the platinum center, complex [Pt (bhq)(N₃)(PPh₃)] was further characterized by single‐crystal X‐ray crystallography. The photophysical properties of the new products were studied by UV–Vis spectroscopy in CH₂Cl₂ and photoluminescence spectroscopy in solid state (298 or 77 K) and in solution (77 K). Using density functional theory calculations, it was proved that, in addition to intraligand charge‐transfer (ILCT) and metal‐to‐ligand charge‐transfer (MLCT) transitions, the L′LCT (L′ = N₃, L = C^N) electronic transition has a remarkable contribution in low energy bands of the absorption spectra (for complexes [Pt (bhq)(N₃)(P)] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂]). It is indicative of the determining role of the N₃^? ligand in electronic transitions of these complexes, specifically in the low energy region. In this regard, the photoluminescence studies indicated that the emissions in such complexes originate from a mixed ³ILCT/³MLCT (intramolecular) and also from aggregations (intermolecular).     

Synthesis and structural studies of new Mannich base ligands and their metal complexes

The new Mannich bases bis(1,4-diphenylthiosemicarbazide methyl) phosphinic acid H₃L¹ and bis(1,4-diphenylsemicarbazide methyl) phosphinic acid H₃L² were synthesised from the condensation of phosphinic acid, formaldehyde with 1,4-diphenyl thiosemicarbazide and 1,4-diphenylsemicarbazide, respectively. Monomeric complexes of these ligands, of general formulae K₂[Cr^III(L ⁿ )Cl₂], K₃[Mn^II(L ⁿ )Cl₂] and K[M(L ⁿ )] (M = Co(II), Ni(II), Cu(II), Zn(II) or Hg(II); n = 1, 2), are reported. The mode of bonding and overall geometry of the complexes were determined through physico-chemical and spectroscopic methods. These studies revealed octahedral geometries for the Cr(III), Mn(II) complexes, square planar for Co(II), Ni(II) and Cu(II) complexes and tetrahedral for the Zn(II) and Hg(II) complexes.     

Metal‐Sensitive Hydrothermal Synthesis and Structural Characterization of a Mixed‐Metal and Porous Coordination Polymer Containing 2,3‐Pyridinedicarboxylate

The hydrothermal reaction of 2,3‐pyridinedicarboxylic acid (2,3‐H₂pda) with a mixture of Cd(NO₃)₂ and Ni(NO₃)₂ afforded a coordination polymer, [CdNi(2,3‐pda)₂(H₂O)₃]_∞ ( 1 ); in contrast, that with a mixture of Cd(NO₃)₂ and Zn(NO₃)₂ surprisingly produced a discrete molecule, trans‐[Cd(3‐pa)₂(H₂O)₄] ( 2 ) (3‐pa^? = 3‐pyridinecarboxylate). Since a direct reaction between a single metal salt, Cd(NO₃)₂ or Zn(NO₃)₂, and 3‐pyridinecarboxylic acid (3‐Hpa) under similar hydrothermal conditions yielded different coordination polymers containing 3‐pa^?, it appears that the apparently thermal decarboxylation from ligated 2,3‐pda^2? to 3‐pa^? occurs after complexation of both metal cations, Cd(II) and Zn(II). A new coordination mode, formed for 2,3‐pda^2? in structure 1 , appears to help formation of microporous channels by piling up the observed 2D hydrogen‐bonded heteropolynuclear layers. Each channel apparently consists of two interpenetrating 6³ Cd(II) and Ni(II) nets.     

Spectral and electrochemical studies of ruthenium(II) complexes with N-methyl-4-nitrobenzaldehyde and N-methyl-4-nitrobenzophenone thiosemicarbazone: Potential anti-trypanosomal agents

N⁴-Methyl-4-nitrobenzaldehyde thiosemicarbazone (H4NO₂Fo4M), N⁴-methyl-4-nitrobenzophenone thiosemicarbazone (H4NO₂Bz4M) and their ruthenium(II) complexes [Ru(4NO₂Fo4M)₂(PPh₃)₂] (1), [Ru(4NO₂Bz4M)₂(PPh₃)₂] (2), [Ru(4NO₂Fo4M)₂(dppb)] (3) and [Ru(4NO₂Bz4M)₂(dppb)] (4) (dppb = 1,4-bis(diphenylphospine)butane) were obtained and characterized. The crystal structure of H4NO₂Fo4M has been determined. Electrochemical studies have shown that the nitro anion radical, one of the proposed intermediates in the mechanism of action of nitro-containing anti-trypanosomal drugs, is formed at approximately −1.00 V in the free thiosemicarbazones as well as in their corresponding ruthenium(II) complexes, suggesting their potential to act as antitrypanosomal drugs. The natural fluorescence of H4NO₂Fo4M, H4NO₂Bz4M and complexes (1)–(4) provides a way to identify and to monitor their concentration in biological systems.     

Synthesis and characterization of stable thiazolylazo anion radical complexes of ruthenium(II)

Two stable thiazolylazo anion radical complexes of ruthenium(II), [Ru(L1^•−)(Cl)(CO)(PPh₃)₂] (1) and [Ru(L2^•−)(Cl)(CO)(PPh₃)₂] (2) (where L1 = 2′-Thiazolylazo-2-imidazole and L2 = 4-(2′-Thiazolylazo)-1-n-hexadecyloxy-naphthalene), have been synthesized and characterized by spectroscopic and electrochemical techniques. The radical nature of the complexes has been confirmed from their room temperature magnetic moments and X-band ESR spectra. The radical complexes display a moderately intense (ε ~ 10⁴ M⁻¹ cm⁻¹) and relatively broad band in 430–460 nm region. In the microcrystalline state, complexes (1) and (2) display strong ESR signals at g = 1.951 and g = 1.988, respectively. In CH₂Cl₂ solution, complexes (1) and (2) show a quasireversible one-electron response near −0.64 and −0.59 V, respectively, versus Ag/AgCl due to the radical redox couple [Ru^II(L)(Cl)(CO)(PPh₃)₂]/[Ru^II (L^•−)(Cl)(CO)(PPh₃)₂].