Metal‐Ion Sensing Europium(III) Complexes with Bidentate Phosphine Oxide Ligands Containing a 2,2′‐Bipyridine Framework

Novel Eu^III complexes with bidentate phosphine oxide ligands containing a bipyridine framework, i.e., [3,3′‐bis(diphenylphosphoryl)‐2,2′‐bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)₃(BIPYPO)]) and [3,3′‐bis(diphenylphosphoryl)‐6,6′‐dimethyl‐2,2′‐bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)₃(Me‐BIPYPO)]), were synthesized for lanthanide‐based sensor materials having high emission quantum yields and effective chemosensing properties. The emission quantum yields of [Eu(hfa)₃(BIPYPO)] and [Eu(hfa)₃(Me‐BIPYPO)] were 71 and 73%, respectively. Metal‐ion sensing properties of the Eu^III complexes were also studied by measuring the emission spectra of Eu^III complexes in the presence of Zn^II or Cu^II ions. The metal‐ion sensing and the photophysical properties of luminescent Eu^III complexes with a bidentate phosphine oxide containing 2,2′‐bipyridine framework are demonstrated for the first time.     

New bioactive Pt(II) binary and ternary metal complexes with guaifenesin drug: Synthesis,geometrical structure,and spectroscopic and thermal characterization

Three new binary and ternary metal complexes of Pt(II) with guaifenesin (GFS) drug have been prepared by chelation to guaifenesin ligand (as primary ligand) and glycine amino acid (HGly) and 1,10‐phenanthroline (1,10‐Phen) (as secondary ligands). Characterization was conducted based on elemental analysis, molar conductance, infrared (IR) spectroscopy, thermogravimetric analysis and X‐ray diffraction. The complexes were found to have the formulae [Pt(GFS)₂]⋅3H₂O ( 1 ), [Pt(GFS)₂(Gly)]Cl⋅H₂O ( 2 ) and [Pt(GFS)₂(Phen)]Cl₂ ( 3 ). Magnetic and spectroscopic data revealed complexes 1 – 3 to have octahedral geometry. IR spectra suggested that GFS ligand coordinated in mononegative tridentate mode (OOO) for 1 but in neutral bidentate mode (OO) for 2 and 3 . In addition, HGly behaves as mononegative bidentate coordinated to Pt(II) metal via deprotonated carboxylate O and amino group. IR data also evidenced the bidentate nature of 1,10‐Phen ligand. The molecular and electronic structure of Pt(II) complex 1 was optimized theoretically and the quantum chemical parameters were calculated. Complexes 1 – 3 were screened for their antibacterial activity on Gram‐positive bacteria (Bacillus subtilis and Staphylococcus aureus ) and Gram‐negative bacteria (Escherichia coli and Neisseria gonorrhoeae ) and for their in vitro antifungal activity against Candida albicans . The three Pt(II) complexes showed remarkable biological and cytotoxic activity. The chelates were also screened for their in vitro anticancer activity against the MFC7 breast cell line. Complex 3 showed the highest activity with a low IC₅₀ value of 3.38 μg ml⁻¹.     

Synthesis and Spectroscopic Characterization of Some Ferrocenyl Schiff Bases Containing Pyridine Moiety and Their Complexation with Cobalt,Nickel, Copper and Zinc

Three novel ferrocenyl Schiff base ligands containing pyridine moiety have been formed by 1:2 molar condensation of 1,1′‐diacetylferrocene with 2‐aminopyridine, 2‐amino‐5‐picoline or 2‐amino‐5‐chloropyridine, respectively. The ligands are 1,1′‐bis[1‐(pyridyl‐2‐imino)‐ethyl]ferrocene (L1); 1,1′‐bis[1‐(5‐methyl‐pyridyl‐2‐imino)ethyl]ferrocene (L2) and 1,1′‐bis[1‐(5‐chloropyridyl‐2‐imino)ethyl]ferrocene (L3). These ligands form 1:1 complexes with Co(II), Cu(II), Ni(II) and Zn(II) ions. The prepared ligands and their complexes have been characterized by IR, ¹H NMR, ¹³C NMR, UV/Vis spectra as well as elemental analysis. The spectral data of the ligands and their complexes are discussed in connection with the structural changes due to complexation.     

Reactivity of tert‐butylperoxyl radical with manganese(III), cobalt(II), and nickel(II) salicylidene Schiff base chelates

Salicylidene Schiff base chelates (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminomanganese(III) chloride, (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminocobalt(II), N,N′‐bis(salicylidene)‐ethylenediaminocobalt(II), N,N′‐bis(salicylidene)ethylenediaminonickel(II), and N,N′‐bis(salicylidene)ethylenediaminoaquacobalt(II), as well as (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)1,2‐cyclohexanediamine, were kinetically examined as antioxidants in the scavenging of tert‐butylperoxyl radical (tert‐butylOO^?). Absolute rate constants and corresponding Arrhenius parameters were determined for reactions of tert‐butylOO^? with these chelates in the temperature range ?52.5 to ?11°C. High reactivity of tert‐butylOO^? with Mn(III) and Co(II) salicylidene Schiff base chelates was established using a kinetic electron paramagnetic resonance method. These salicylidene Schiff base chelates react in a 1:1 stoichiometric fashion with tert‐butylOO^? without free radical formation. Ultraviolet–visible spectrophotometry and differential pulse voltammetry established that the rapid removal rate of tert‐butylOO^? by these chelates is the result of Mn(III) oxidation to Mn(IV) and Co(II) oxidation to Co(III) by tert‐butylOO^?. It is concluded that removal of alkylperoxyl radical by Mn(III) and Co(II) salicylidene Schiff base chelates may partially account for their biological activities. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 431–439, 2007     

Structural,spectroscopic, molecular docking,thermal and DFT studies on metal complexes of bidentate orthoquinone ligand

4‐Triphenylmethyl‐1,2‐benzoquinone (TPMBQ) reacted with some metal ions and the structure of the new compounds had been identified. The metal to ligand ratio was 1:2 which was revealed by elemental analysis. The complexes were found to have octahedral geometry and their thermal stability was studied using thermogravimetric analysis technique. The molar conductance measurements revealed the electrolytic nature of the synthesized chelates. The IR spectra concluded the bidentate nature of the TPMBQ ligand while the ¹H NMR revealed the presence of water molecules. The XRD spectra of Mn (II) and Fe (III) complexes concluded their crystalline structure while Co (II) and Cu (II) chelates refer to amorphous structures. The geometries of the TPMBQ ligand were optimized using Gaussian 09 W; density functional theory B3LYP method. (DFT)/basis set 6–311++G (d, p). HOMO and LUMO energy values for chelates, chemical hardness and electro‐negativity had been calculated. The ligand and its metal complexes had been examined against different kinds of bacteria such as Proteus vulgaris, Escherichia coli, Staphylococcus aurous and Bacillus subtitles to examine their antimicrobial activity. Molecular docking using Auto Dock tools were utilized.     

The Role of an Alkyl–Phenyl Spacer on the Reactivity of Novel Platinum(II) Complexes with Thiourea Nucleophiles

The presented work, submitted as a paper, deals with the substitution reactions of mononuclear and dinuclear platinum(II) complexes of di‐2‐pyridylaminodiaquaplatinum(II), ( Pt1 ); di‐2‐pyridylaminomethylbenzenediaquaplatinum(II), ( Pt2 ); 1,2‐bis(di‐2‐pyridylaminomethyl)benzenetetraquaplatinum(II), ( Pt3 ); 1,3‐bis(di‐2‐pyridylamino‐methyl)benzenetetraquaplatinum(II), ( Pt4 ); and 1,4‐bis(di‐2‐pyridylaminomethyl)‐benzenetetraquaplatinum(II), ( Pt5 ). These reactions were carried out on aqua complexes by three nucleophiles, viz., thiourea, N ,N ′‐dimethylthiourea, and N ,N ,N ′N ′‐tetramethylthiourea under pseudo–first‐order conditions as a function of nucleophile concentration and temperature by stopped‐flow and UV–visible spectrophotometric techniques. In addition, some DFT calculation was performed. The activation parameters support an associative substitution mechanism.     

Molecular structure,molecular docking,thermal, spectroscopic and biological activity studies of bis‐Schiff base ligand and its metal complexes

Coordination compounds of Fe(III), Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II) ions were synthesized from the ligand [4,4′‐((((ethane‐1,2‐diylbis(oxy))bis(2,1‐phenylene))bis(methanylylidene))bis(azanylylidene))diphenol]ethane (H₂L) derived from the condensation of bisaldehyde and 4‐aminophenol. Microanalysis, magnetic susceptibility, infrared, ¹H NMR and mass spectroscopies, molar conductance, X ray powder diffraction and thermal analysis were used to confirm the structure of the synthesized chelates. According to the data obtained, the composition of the 1:1 metal ion–bis‐Schiff base ligand was found to be [M(H₂L)(H₂O)₂]Cl_n (M = Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II), n = 2; Fe(III), n = 3). Magnetic susceptibility measurements and reflectance spectra suggested an octahedral geometry for the complexes. Central metals ions and bis‐Schiff base coordinated together via O2 and N2 donor sites which as evident from infrared spectra. The Gaussian09 program was applied to optimize the structural formula for the investigated Schiff base ligand. The energy gaps and other important theoretical parameters were calculated applying the DFT/B3LYP method. Molecular docking using AutoDock tools was utilized to explain the experimental behaviour of the Schiff base ligand towards proteins of Bacillus subtilis (5 h67), Escherichia coli (3 t88), Proteus vulgaris (5i39) and Staphylococcus aureus (3ty7) microorganisms through theoretical calculations. The docked protein receptors were investigated and the energies of hydrogen bonding were calculated. These complexes were then subjected to in vitro antibacterial studies against several organisms, both Gram negative (P. vulgaris and E. coli) and Gram positive (S. pyogones and B. subtilis). The ligand and metal complexes exhibited good microbial activity against the Gram‐positive and Gram‐negative bacteria.     

Coordination modes of multidentate azodye ligand derived from 4,4′‐methylenedianiline towards some transition metal ions: Synthesis,spectral characterization,thermal investigation and biological activity

Nine new azodye metal complexes of Mn(II), Co(II), Ni(II), Cu(II), Cr(III), Fe(III), Ru(III), Hf(IV) and Zr(IV) ions have been prepared via the reaction of 5,5′‐((1E,1′E)‐(methylenebis(1,4‐phenylene))bis(diazene‐2,1‐diyl))bis(6‐hydroxy‐2‐thioxo‐2,3‐dihydropyrimidin‐4(5H)‐one) (H₄L) with the corresponding metal salts affording sandwich (1 L:1 M), mononuclear (2 L:1 M), binuclear (1 L,2 M) and tetranuclear (1 L,4 M) complexes. Elemental analyses, spectral methods, magnetic moment measurements and thermal studies were utilized to confirm the mode of bonding and geometrical structure for the ligand and its metal complexes. Infrared spectral data show that the H₄L ligand chelates with some metal ions in keto–enol–thione or keto–thione manner. It behaves in a neutral/dibasic tetradentate fashion in sandwich and binuclear complexes. Also, it acts as a neutral bidentate moiety in the Cr(III) complex. The spectra reveal that azo group participates in chelation in all complexes. Octahedral geometry was suggested for all chelates but the Cu(II) complex with square planar geometry. The thermal stability and decomposition of the compounds were studied, the data showing that the thermal decomposition ended with metal or metal oxide mixed with carbon as final product. The electron spin resonance spectrum of the Cu(II) complex demonstrates that the free electron is located in the ( ) orbital. Measurements of biological activity against human cell lines Hep‐G₂ and MCF‐7 reveal that the Cu(II) complex has a higher cytotoxicity in comparison to the free ligand and other metal complexes, with IC₅₀ values of 6.10 and 5.2 μg ml^?1, respectively, while the ligand has anti‐tumour activity relative to some of the investigated metal complexes.     

Cyclometalated Ruthenium Complexes of 1,2,3-Triazole-containing Ligands: Synthesis, Structural Studies, and Electronic Properties

Six bis‐tridentate and two tris‐bidentate cyclometalated ruthenium complexes with a 1,2,3‐triazole‐containing ligand have been prepared and characterized. Single‐crystal X‐ray analyses of complexes [(MeOptpy)Ru(Budtab)](PF₆) and [(Mebip)Ru(Budtab)](PF₆) are presented, where MeOptpy is 4′‐p‐methoxyphenyl‐2,2′:6′,2′′‐terpyridine, Budtab is the 2‐deprotonated form of 1,3‐di(N‐n‐butyl‐1,2,3‐triazol‐4‐yl)benzene, and Mebip is bis(N‐methyl‐benzimidazolyl)pyridine. The electronic properties of these complexes are probed by spectroscopic and electrochemical analyses. Time‐dependent density functional theory calculations have been performed to assist the assignment of the absorption spectra.     

Platinum and Palladium Complexes Bearing New (1R,2R)‐(–)‐1,2‐Diaminocyclohexane (DACH)‐Based Nitrogen Ligands: Evaluation of the Complexes Against L1210 Leukemia

The reaction of (1R,2R)‐(–)‐1,2‐diaminocyclohexane ( 1 ) [DACH] with the aldehyde (1R)‐(–)‐myrtenal ( 2 ) in MeOH afforded the bidentate diimine ligand, (1R,2R)‐(–)‐N¹,N²‐bis{(1R)‐(–)myrtenylidene}‐1,2‐diaminocyclohexane ( 3 ) in a high yield. Reduction of 3 using LiAlH₄ led to the formation of the desired ligand ( 4 ) (1R,2R)‐(–)‐N¹,N²‐bis{(1R)‐(–)myrtenyl}‐1,2‐diaminocyclohexane. Treatment of compound 4 with K₂PtCl₄ or K₂PdCl₄ yielded the corresponding platinum(II) and palladium(II) complexes, Pt‐5 and Pd‐6 , respectively. The reaction of compound 3 with K₂PtCl₄ gave the diimine complex Pt‐7 . The cytotoxic activity of the complexes Pt‐5 , Pd‐6 and Pt‐7 was tested and compared to the approved drugs, cisplatin ( Cis ‐Pt ) and oxaliplatin ( Ox‐Pt ). The complexes ( Pt‐5 , Pd‐6 and Pt‐7 ) inhibit L1210 cell line proliferation with an IC₅₀ of 0.6, 4.2, and 0.7 μL, respectively as evidenced by measuring thymidine incorporation.     

Platinum(II) Mixed Ligand Complexes with Thiourea Derivatives,Dimethyl Sulphoxide and Chloride: Syntheses,Molecular Structures,and ESCA Data

The platinum(II) mixed ligand complexes [PtCl(L^1‐6)(dmso)] with six differently substituted thiourea derivatives HL, R₂NC(S)NHC(O)R′ (R = Et, R′ = p‐O₂N‐Ph: HL¹; R = Ph, R′ = p‐O₂N‐Ph: HL²; R = R′ = Ph: HL³; R = Et, R′ = o‐Cl‐Ph: HL⁴; R₂N = EtOC(O)N(CH₂CH₂)₂N, R′ = Ph: HL⁵) and Et₂NC(S)N=CNH‐1‐Naph (HL⁶), as well as the bis(benzoylthioureato‐κO, κS)‐platinum(II) complexes [Pt(L^{1, 2})₂] have been synthesized and characterized by elemental analysis, IR, FAB(+)‐MS, ¹H‐NMR, ¹³C‐NMR, as well as X‐ray structure analysis ([PtCl(L¹)(dmso)] and [PtCl(L^{3, 4})(dmso)]) and ESCA ([PtCl(L^{1, 2})(dmso)] and [Pt(L^{1, 2})₂]). The mixed ligand complexes [PtCl(L)(dmso)] have a nearly square‐planar coordination at the platinum atoms. After deprotonation, the thiourea derivatives coordinate bidentately via O and S, DMSO bonds monodentately to the Pt^II atom via S atom in a cis arrangement with respect to the thiocarbonyl sulphur atom. The Pt—S‐bonds to the DMSO are significant shorter than those to the thiocarbonyl‐S atom. In comparison with the unsubstituted case, electron withdrawing substituents at the phenyl group of the benzoyl moiety of the thioureate (p‐NO₂, o‐Cl) cause a significant elongation of the Pt—S(dmso)‐bond trans arranged to the benzoyl‐O—Pt‐bond. The ESCA data confirm the found coordination and bonding conditions. The Pt 4f_7/2 electron binding energies of the complexes [PtCl(L^{1, 2})(dmso)] are higher than those of the bis(benzoylthioureato)‐complexes [Pt(L^{1, 2})₂]. This may indicate a withdrawal of electron density from platinum(II) caused by the DMSO ligands.     

Metallomacrocycles with a Difference: Macrocyclic Complexes with Exocyclic Ruthenium(II)‐Containing Domains

The templated synthesis of organic macrocycles containing rings of up to 96 atoms and three 2,2′‐bipyridine (bpy) units is described. Starting with the bpy‐centred ligands 5,5′‐bis[3‐(1,4‐dioxahept‐6‐enylphenyl)]‐2,2′‐bipyridine and 5,5′‐bis[3‐(1,4,7‐trioxadec‐9‐enylphenyl)]‐2,2′‐bipyridine, we have applied Grubbs’ methodology to couple the terminal alkene units of the coordinated ligands in [FeL₃]²⁺ complexes. Hydrogenation and demetallation of the iron(II)‐containing macrocyclic complexes results in the isolation of large organic macrocycles. The latter bind {Ru(bpy)₂} units to give macrocyclic complexes with exocyclic ruthenium(II)‐containing domains. The complex [Ru(bpy)₂(L)]²⁺ (isolated as the hexafluorophosphate salt), in which L=5,5′‐bis[3‐(1,4,7,10‐tetraoxatridec‐12‐enylphenyl)]‐2,2′‐bipyridine, undergoes intramolecular ring‐closing metathesis to yield a macrocycle which retains the exocyclic {Ru(bpy)₂} unit. The poly(ethyleneoxy) domains in the latter macrocycle readily scavenge sodium ions, as proven by single‐crystal X‐ray diffraction and atomic absorption spectroscopy data for the bulk sample. In addition to the new compounds, a series of model complexes have been fully characterized, and representative single‐crystal X‐ray structural data are presented for iron(II) and ruthenium(II) acyclic and macrocyclic species.     

Synthesis,characterization and in vitro biological activity of new zinc(II) complexes of the nonsteroidal anti‐inflammatory drug sulindac and nitrogen‐donor ligands

Metal carboxylate compounds with nitrogen‐ and/or oxygen‐donor ligands with various carboxylate coordination modes, monodentate, bidentate and bridging bidentate, have been shown to be important from biological and chemical aspects. Five zinc ion binary compounds, diaqua‐bis‐(2‐((E )‐5‐fluoro‐2‐methyl‐1‐(4‐(methylsulfinyl)benzylidene)‐1H –inden‐3‐yl)acetato)zinc(II) ( 1 ), aqua‐bis‐(2‐((E )‐5‐fluoro‐2‐methyl‐1‐(4‐(methylsulfinyl)benzylidene)‐1H –inden‐3‐yl)acetato)pyridin‐2‐aminezinc(II) ( 2 ), (2‐((E )‐5‐fluoro‐2‐methyl‐1‐(4‐(methylsulfinyl)benzylidene)‐1H –inden‐3‐yl)acetato) pyridin‐2‐ylmethanaminezinc(II) (2‐((E )‐5‐fluoro‐2‐methyl‐1‐(4‐(methylsulfinyl)benzylidene)‐1H –inden‐3‐yl)acetate) ( 3 ), bis‐(2‐((E )‐5‐fluoro‐2‐methyl‐1‐(4‐(methylsulfinyl)benzylidene)‐1H –inden‐3‐yl)acetato)‐1,10‐phenanthrolinezinc(II) ( 4 ) and bis‐(2‐((E )‐5‐fluoro‐2‐methyl‐1‐(4‐(methylsulfinyl)benzylidene)‐1H –inden‐3‐yl)acetato)‐1,10‐phenanthrolinezinc(II) ( 5 ), have been prepared and fully characterized. In addition, the complexes were evaluated for their antibacterial activity using the in vitro agar diffusion method against two Gram‐positive (Staphylococcus epidermidis , Staphylococcus aureus ) and two Gram‐negative (Bordetella , Escherichia coli ) bacteria and yeast species (Saccharomyces and Candida ). Complex 5 showed reasonable activity against yeast. All compounds showed greater antibacterial activity against Gram‐positive than Gram‐negative bacteria. Results indicated that the efficiency of complex 5 in preventing the formation of β‐hematin was 67.6%. The efficiency of chloroquine as a standard drug was reported as 93%. Furthermore, the phosphatase activity of the Zn(II) complexes was studied and results indicated an effect of the zinc complexes on phosphatase activity.     

Two bicyclic dinuclear complexes generated from 3,3′‐[1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoic acid (L) and dimethylformamide (DMF): [Cu(L)(DMF)]2 and [Zn(L)(DMF)]2

A new 1,3,4‐thiadiazole bridging ligand, namely 3,3′‐[1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoic acid (L), has been used to create the novel isomorphous complexes bis{μ‐3,3′‐[1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoato}bis[(N,N‐dimethylformamide)copper(II)], [Cu₂(C₁₈H₁₂N₂O₄S₃)₂(C₃H₇NO)₂], (I), and bis{μ‐3,3′‐[1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoato}bis[(N,N‐dimethylformamide)zinc(II)], [Zn₂(C₁₈H₁₂N₂O₄S₃)₂(C₃H₇NO)₂], (II). Both exist as centrosymmetric bicyclic dimers constructed through the syn–syn bidentate bridging mode of the carboxylate groups. The two rings share a metal–metal bond and each of the metal atoms possesses a square‐pyramidal geometry capped by the dimethylformamide molecule. The 1,3,4‐thiadiazole rings play a critical role in the formation of a π–π stacking system that expands the dimensionality of the structure from zero to one. The thermogravimetric analysis of (I) indicates decomposition of the coordinated ligands on heating. Compared with the fluorescence of L in the solid state, the fluorescence intensity of (II) is relatively enhanced with a slight redshift, while that of (I) is quenched.     

Polymer complexes. LXXVII. Synthesis,characterization, spectroscopic studies and immune response in cattle of quinoline polymer complexes

A series of novel polymeric metal complexes of Co(II), Ni(II), Cu(II), Zn(II) and Cr(III) with 5,5′‐{(1E,1E′)‐1,4‐phenylenebis(diazene‐2,1‐diyl)}bis(quinolin‐8‐ol) (H₂L) ligand were synthesized and characterized using elemental analyses, ¹H NMR, mass, infrared, UV–visible and electron spin resonance (ESR) spectroscopies, magnetic moment and conductivity measurements as well as thermal analyses. The spectral and analytical data revealed the ligand adopted a neutral bidentate fashion when binding to metal ions via the nitrogen of azomethine of pyridine ring and the deprotonated hydroxyl group. Electronic and magnetic susceptibility measurements of the polymer complexes indicated octahedral geometry for all polymer complexes. The ESR spectral data provided information about the structures on the basis of Hamiltonian parameters and the degree of covalency. Molecular docking was used to predict the binding between the H₂L and the receptor of breast cancer (3hb5). The immune response of the synthesized polymer complexes with bovine respiratory syncytial (BRS) vaccine in cattle was studied using serum neutralizations test (SNT). It was found that the isolated polymer complexes with BRS vaccine caused a significant increase in the antibody titre against BRS virus in SNT compared to BRS vaccine alone.     

Synthesis,coordination behavior,and investigations of pharmacological effects of some transition metal complexes with isoniazid Schiff bases

Two isoniazid Schiff bases, N-isonicotinamido-2-furanketimine (INH-F¹) and N-isonicotinamido-5-methyl-2-furanketimine (INH-F²), possessing potential N and O coordination sites have been prepared by the reaction of isoniazid with 2-acetylfuran and 2-acetyl-5-methylfuran, respectively. Complexes of Pd(II) and Pt(II) have been prepared and characterized by elemental analyses, melting point determinations and electronic, infrared, ¹H NMR, ¹³C NMR spectral studies, and X-ray powder diffraction studies. In all the complexes, the monobasic bidentate nature of the ligand is evident. Antibacterial and antifungal studies of these compounds against various pathogenic bacterial and fungal strains have been carried out. Both the ligands and their metal chelates were active against all the microbial strains investigated. However, the chelates were found to be more active than the ligands. The antimycobacterial activity of the ligands and their metal complexes has been evaluated against Mycobacterium smegmatis, which showed clear enhancement in this activity upon metal complexation with Schiff bases.     

New organic–inorganic frameworks incorporating iso‐ and heteropolymolybdate units and a 3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1H‐pyrazole‐2,2′‐diium multiple hydrogen‐bond donor

Poly[bis(3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1H‐pyrazole‐2,2′‐diium) γ‐octamolybdate(VI) dihydrate], {(C₁₀H₁₆N₄)₂[Mo₈O₂₆]·2H₂O}_n, (I), and bis(3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1H‐pyrazole‐2,2′‐diium) α‐dodecamolybdo(VI)silicate tetrahydrate, (C₁₀H₁₆N₄)₂[SiMo₁₂O₄₀]·4H₂O, (II), display intense hydrogen bonding between the cationic pyrazolium species and the metal oxide anions. In (I), the asymmetric unit contains half a centrosymmetric γ‐type [Mo₈O₂₆]⁴⁻ anion, which produces a one‐dimensional polymeric chain by corner‐sharing, one cation and one water molecule. Three‐centre bonding with 3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1H‐pyrazole‐2,2′‐diium, denoted [H₂Me₄bpz]²⁺ [N...O = 2.770 (4)–3.146 (4) Å], generates two‐dimensional layers that are further linked by hydrogen bonds involving water molecules [O...O = 2.902 (4) and 3.010 (4) Å]. In (II), each of the four independent [H₂Me₄bpz]²⁺ cations lies across a twofold axis. They link layers of [SiMo₁₂O₄₀]⁴⁻ anions into a three‐dimensional framework, and the preferred sites for pyrazolium/anion hydrogen bonding are the terminal oxide atoms [N...O = 2.866 (6)–2.999 (6) Å], while anion/aqua interactions occur preferentially viaμ₂‐O sites [O...O = 2.910 (6)–3.151 (6) Å].     

Exploring Excited‐State Tunability in Luminescent Tris‐cyclometalated Platinum(IV) Complexes: Synthesis of Heteroleptic Derivatives and Computational Calculations

The synthesis, structure, electrochemistry, and photophysical properties of a series of heteroleptic tris‐ cyclometalated Pt^IV complexes are reported. The complexes mer‐[Pt(C^N)₂(C′^N′)]OTf, with C^N=C‐deprotonated 2‐(2,4‐difluorophenyl)pyridine (dfppy) or 2‐phenylpyridine (ppy), and C′^N′=C‐deprotonated 2‐(2‐thienyl)pyridine (thpy) or 1‐phenylisoquinoline (piq), were obtained by reacting bis‐ cyclometalated precursors [Pt(C^N)₂Cl₂] with AgOTf (2 equiv) and an excess of the N′^C′H pro‐ligand. The complex mer‐[Pt(dfppy)₂(ppy)]OTf was obtained analogously and photoisomerized to its fac counterpart. The new complexes display long‐lived luminescence at room temperature in the blue to orange color range. The emitting states involve electronic transitions almost exclusively localized on the ligand with the lowest π–π* energy gap and have very little metal character. DFT and time‐dependent DFT (TD‐DFT) calculations on mer‐[Pt(ppy)₂(C′^N′)]⁺ (C′^N′=thpy, piq) and mer/fac‐[Pt(ppy)₃]⁺ support this assignment and provide a basis for the understanding of the luminescence of tris‐cyclometalated Pt^IV complexes. Excited states of LMCT character may become thermally accessible from the emitting state in the mer isomers containing dfppy or ppy as chromophoric ligands, leading to strong nonradiative deactivation. This effect does not operate in the fac isomers or the mer complexes containing thpy or piq, for which nonradiative deactivation originates mainly from vibrational coupling to the ground state.     

New dimeric Schiff base quinoline complexes: Synthesis,spectral characterization,electrochemistry and cytotoxicity

A novel Schiff base ligand (H‐DPPMHQ) derived from 2‐hydrazineylquinoline and 1,3‐diphenyl‐1H‐pyrazole‐5‐carbaldehyde and its dimeric complexes with compositions [Cr(DPPMHQ)Cl]₂?2Cl and [M(DPPMHQ)Cl]₂ (where M = Cu(II), Co(II), Ni(II) and Zn(II)) have been synthesized and characterized using physicochemical methods like elemental analysis, magnetic susceptibility and molar conductivity measurements, multispectral techniques and electrochemical studies. The molar conductance data reveal that all metal chelates are non‐electrolytes, except the Cr(III) complex which shows a Λ_M value of 146.82 Ω^?1 cm² mol^?1, indicating that it is a 1:2 electrolyte. Infrared spectral results show that the metal is organized through four nitrogen atoms (azomethine and deprotonated imine groups, pyrazole and quinoline rings) besides chlorine atoms. The NH proton is also displaced during complexation, as indicated by ¹H NMR spectral data. Based on the electron spin resonance and ligand field parameter data, the bonding parameters of these complexes have been calculated. Using Coats–Redfern and Horowitz–Metzger equations, thermodynamic parameters were determined. The spectral data indicate that the dimeric complexes have octahedral geometry around the central metal ions. The cytotoxic activities of all compounds were evaluated towards human breast cancer (MCF‐7) and lung cancer (A549) cell lines.     

A one‐dimensional zinc(II) coordination polymer incorporating [1,1′‐biphenyl]‐4,4′‐dicarboxylate and N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands

In the title compound, catena‐poly[[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[1,1′‐biphenyl]‐4,4′‐dicarboxylato‐[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]], [Zn₂(C₁₄H₈O₄)Cl₂(C₂₆H₂₂N₄O₂)₃]_n, the Zn^II centre is four‐coordinate and approximately tetrahedral, bonding to one carboxylate O atom from a bidentate bridging dianionic [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand, to two pyridine N atoms from two N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands and to one chloride ligand. The pyridyl ligands exhibit bidentate bridging and monodentate terminal coordination modes. The bidentate bridging pyridyl ligand and the bridging [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand both lie on special positions, with inversion centres at the mid‐points of their central C—C bonds. These bridging groups link the Zn^II centres into a one‐dimensional tape structure that propagates along the crystallographic b direction. The tapes are interlinked into a two‐dimensional layer in the ab plane through N—H...O hydrogen bonds between the monodentate ligands. In addition, the thermal stability and solid‐state photoluminescence properties of the title compound are reported.