Peroxo Complexes of Molybdenum(VI) Containing Mannich Base Ligands

The molybdenum(VI)-peroxo complexes containing Mannich base ligands having a formula as [MoO(O2)2(L-L)] [where L-L＝morpholinobenzyl benzamide (MBB), piperidinobenzyl benzamide (PBB), morpholinobenzyl urea (MBU), piperidinobenzyl urea (PBU), morpholinobenzyl thiourea (MBTU), piperdinobenzyl thiourea (PBTU)] have been synthesized and characterized by physico-chemical, electrochemical techniques and TGA/DTA studies. The complexes have been prepared by stirring ammonium molybdate and excess of 30% aqueous-H2O2 and then treatment with ethanolic solution of the ligand. Studies revealed that these complexes were non-electrolytes and diamagnetic in nature. The ligands are bound to metal in a bidentate mode through carbonyl oxygen/thiocarbonyl sulphur and the ring nitrogen. The cyclic voltammograms of the complexes show two quasi-reversible steps involving complexes. The complexes have also been tested for antibacterial activity against Salmonella and Kleibsella. The antibacterial study of the ligands and complexes indicate that the complexes exhibit higher activity than the free ligands.     

Peroxo complexes of uranium(VI) containing nitrogen and oxygen donor ligands

The uranium(VI) peroxo complexes containing Mannich base ligands having composition [UO(O₂)L-L(NO₃)₂] {where L-L = morpholinobenzyl acetamide (MBA), piperidinobenzyl acetamide (PBA), morpholinobenzyl benzamide (MBB), piperidinobenzyl benzamide (PBB), morpholinomethyl benzamide (MMB), piperidinomethyl benzamide (PMB), morpholinobenzyl formamide (MBF)}, piperidinobenzyl formamide (PBF) are reported. In a typical reaction UO₂(NO₃)₂ · 6H₂O (1 mmol, 0.502 g) was dissolved in methanol. An equimolar (1 mmol) methanolic solution (30 mL) of the ligand (Mannich bases) was added to a solution of uranyl nitrate followed by addition of potassium hydroxide (KOH) (2 mmol, 0.1122 g). The solution was refluxed for 15 min and then 10 mL of 30% hydrogen peroxide (H₂O₂) was added dropwise and was refluxed for an additional 1 h. The synthesized complexes have been characterized by various physico-chemical techniques, viz. elemental analysis, molar conductivity, magnetic susceptibility measurements, infra red, electronic, mass spectral and TGA/DTA studies. These studies revealed that the synthesized complexes are non-electrolytic and diamagnetic in nature. The ligands are bound to metal in a bidentate mode through carbonyl oxygen and the ring nitrogen. Thermal analysis result provides conclusive evidence for the absence of water molecule in the complexes. Mass spectra confirm the molecular mass of the complexes. Antibacterial activity of complexes revealed enhanced activity of complexes as compared to corresponding free ligands. Molecular modeling suggests pentagonal bipyramidal structure for complexes.     

Synthesis and characterization of oxodiperoxo complexes of tungsten(VI) with some Mannich base ligands

Six oxodiperoxotungsten(VI) complexes, [WO(O₂)₂L–L] (where L–L?=?morpholinobenzyl benzamide (MBB), piperidinobenzyl benzamide (PBB), piperidinobenzyl urea (PBU), morpholinobenzyl urea (MBU), piperidinobenzyl thiourea (PBTU) and morpholinobenzyl thiourea (MBTU)) have been prepared by stirring WO₃?·?H₂O with excess 30% aqueous (w/v) H₂O₂ and then treating with an ethanolic solution of the Mannich base ligand (L–L). These have been characterized by elemental analysis, conductance and magnetic susceptibility measurements, IR spectra, electronic spectra, ¹H NMR, TGA/DTA and cyclic voltammetric studies. These complexes are non-electrolytes and diamagnetic in nature. The ligands are bound to metal in a bidentate mode through carbonyl oxygen/thiocarbonyl sulphur and the ring nitrogen. The complexes also inhibit the growth of pathogen “Fusarium Spp.” up to 60%. The cyclic voltammograms of the complexes indicate quasi-reversible redox steps involving complexes.     

Dinuclear peroxo complexes of molybdenum(VI) containing Mannich base ligands

Dinuclear molybdenum(VI) peroxo complexes containing Mannich base ligands having formulae [Mo₂O₄(O₂)₂L-L(H₂O)₂] · H₂O [where L-L = N-[1-morpholinobenzyl] acetamide (MBA), N-[1-piperidinobenzyl] acetamide (PBA), N-[1-morpholino(-4-nitrobenzyl)] benzamide (MPNBB), N-[1-piperidino(-3-nitrobenzyl)] benzamide (PMNBB), N-[1-morpholino(-2-nitrobenzyl)] acetamide (MONBA), and N-[1-morpholino(-3-nitrobenzyl)] acetamide (MMNBA)] have been synthesized by stirring ammonium heptamolybdate with excess 30% aqueous hydrogen peroxide followed by treatment with ethanolic solution of corresponding ligands. The complexes have been characterized by elemental analysis, molar conductance, magnetic measurements, infrared (IR), electronic, TGA/DTA, mass spectral, and ¹H NMR studies. The complexes are non-electrolytes and diamagnetic. The IR spectral studies suggest that the ligands are bidentate to metal through carbonyl oxygen and ring nitrogen. Thermal analyses provide conclusive evidence for the presence of coordinated, as well as lattice water in the complexes. Dinuclear complexes preserve the individuality of the molybdenum oxo peroxo core. The complexes exhibit higher antibacterial activity against bacterium Ralastonia solanacearum (Pseudomonas solanacearum) than the free ligands.     

Synthesis and characterization of peroxo complexes of uranium(VI) with some Mannich base ligands

Abstract  

Uranium(VI) peroxo complexes of composition [UO(O₂)L–L(NO₃)₂], where L–L are the Mannich base ligands morpholinobenzyl urea, piperidinobenzyl urea, morpholinobenzyl thiourea, piperidinobenzyl thiourea, morpholinomethyl thiourea, piperidinomethyl thiourea, or morpholinomethyl urea, are reported. The synthesized complexes were characterized by use of a variety of physicochemical techniques, viz. elemental analysis, molar conductivity, magnetic susceptibility measurements, IR, electronic, mass, ¹H NMR, and ¹³C NMR spectroscopy, and TGA/DTA studies. These studies revealed that the complexes are both non-electrolytic and diamagnetic in nature. The ligands are bound to the metal in a bidentate mode through carbonyl oxygen or thiocarbonyl sulfur and the ring nitrogen. Mass spectra confirm the molecular mass of the complexes. The antifungal activity of the complexes is greater than that of the corresponding free ligands.     

Reactivity of metal-bound peroxides; alkali triperoxovanadate(V) trihydrates,A[V(O2)3]·3H2O (A = Na or K), as oxidants resembling alkali—H2O2 reagent for some organic substrates

The efficacy of the triperoxovanadium(V) complexes, A[V(O₂)₃]·3H₂O (A = Na or K), as potential oxidants with respect to certain organic substrates has been investigated. Aqueous solutions of the complexes are basic (pH ca. 11) in nature. The complexes efficiently oxidise an α,β-unsaturated ketone to the corresponding epoxide and benzonitrile to benzamide. Such reactions are usually accomplished using alkaline-H₂O₂ reagent. The complexes are also capable of bringing about Bayer-Villiger-type oxidation and oxidise benzil to benzoic acid. The peroxo-depleted vanadium product, isolated after the oxidations, has been identified as a diperoxovanadate(V) complex, [VO(O₂)₂(H₂O)]⁻.     

Acetate and acetamide complexes of [Ni(Me4[12]aneN4)]PF6: a tale of two ligands

Although there are many examples of acetate complexes, acetamide complexes are virtually unknown. A side‐by‐side comparison in (acetato‐κ²O,O′)(1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane‐κ⁴N)nickel(II) hexafluoridophosphate, [Ni(C₂H₃O₂)(C₁₂H₂₈N₄)]PF₆, (1), and (acetamidato‐κ²O,O′)(1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane‐κ⁴N)nickel(II) hexafluoridophosphate, [Ni(C₂H₄NO)(C₁₂H₂₈N₄)]PF₆, (2), shows the steric equivalence between these two ligands, suggesting that acetamide could be considered as a viable acetate replacement for electronic tuning.     

Ethylene homopolymerizaton and copolymerizaton by vanadium(III) complexes containing tridentate or tetradentate iminopyrrolyl ligands

Iminopyrrolyl vanadium(III) complexes 2a–b bearing tridentate ligands [C₄H₃NCH?NC₆H₄L]VCl₂(THF) [L = 2‐P(C₆H₅)₂ ( 2a ), 2‐SMe ( 2b )] and complexes 2c–d with tetradentate ligands [(C₄H₃NCH?N)₂R]VCl(THF) [R = 1,2‐C₆H₄ ( 2c ), 1,2‐C₂H₄ ( 2d )] have been synthesized in high yields. With diethylaluminium chloride as a cocatalyst, complexes 2a–d were investigated as efficient catalysts for ethylene polymerization under various reaction conditions, and exhibited high catalytic activity and remarkable thermal stability. With these complexes, high molecular weight polymers with unimodal molecular weight distributions were obtained, indicating that the polymerization reaction took place in a single‐site nature. Ethylene/1‐hexene copolymerizations were also investigated in the presence of Et₂AlCl. Both increasing ligand denticity and introducing softer atom into the sidearm of the ligands significantly influenced catalytic activity, comonomer incorporation, and the molecular weights of the resultant polymers, suggesting that both the steric and the electronic effects of the ligands played an important role in adjusting chain propagation and transfer rate. The chain transfer mechanisms involved in the copolymerization process were investigated by carefully analyzing the microstructure of the copolymers. The signals of vinyl, disubstituted and tri‐substituted vinylene double bond end groups were detected in the copolymer obtained by 2a /Et₂AlCl system but not in those by 2b–c /Et₂AlCl systems, indicating that bulky electron‐donating group, ? P(C₆H₅)₂, may lead to those unusual transfer reactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Spectroscopic and Crystal Structure of Europium(III) Picrate Complexes with Novel BINOL Derivatives

Two novel ligands N‐Benzyl‐2‐{2′‐[(benzyl‐phenyl‐carbamoyl)‐methoxy]‐[1,1′]binaphthalenyl‐2‐yloxy}‐N‐phenyl‐acetamide (L1) and N‐Methyl‐2‐{2′‐[(methyl‐phenyl‐carbamoyl)‐methoxy]‐[1,1′]binaphthalenyl‐2‐yloxy}‐N‐phenyl‐acetamide (L2), and their europium(III) complexes with picrate, [Eu(pic)₃(L1)] and [Eu(pic)₃(L2)], were synthesized and characterized by elemental analysis, IR, UV‐Vis and fluorescence spectroscopy. The crystal structure of [Eu(pic)₃(L1)]·2CHCl₃ was determined by single crystal X‐ray diffraction. The europium atom is coordinated by nine oxygen atoms of four from the L1 and five from two bidentate and one unidentate picrates. The fluorescent intensity of [Eu(pic)₃(L2)] is about 2.6 times that of [Eu(pic)₃(L1)] in solid states. But in CHCl₃ solution, the fluorescent intensity of [Eu(pic)₃(L1)] is stronger slightly than [Eu(pic)₃(L2)].     

Synthesis,spectral characterization,C?C coupling,oxidation reactions and antibacterial activities of new ruthenium(III) Schiff base complexes

A new series of hexa‐coordinated stable Ru(III) Schiff base complexes of the type [RuX(EPh₃)(L)] (where X = Cl/Br; E = P/As; L = tetradentate N₂O₂ donor Schiff ligands) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurement, FT‐IR, UV–vis, ¹³C{¹H}‐NMR, ESR spectra, electrochemical and powder X‐ray diffraction pattern studies. The selective oxidation of alcohols to their corresponding carbonyl compounds occurred in the presence of N‐methylmorpholin‐N‐oxide (NMO), H₂O₂ and O₂ atmosphere at ambient temperature as co‐oxidants and C? C coupling reactions. Further, these new Schiff base ligands and their Ru(III) complexes were also screened for their antibacterial activity against K. pneumoniae, Shigella sp., M. luteus, E. coli and S. typhi. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparative Study of three Mononuclear Vanadium‐Aromatic 1, 2‐Diol Complexes: Structure,Characterization and Anti‐Proliferating Effects Against Cancer Cells

Three mononuclear vanadium complexes containing aromatic 1, 2‐diols (catechol and naphthalene‐2, 3‐diol) ligands,[V^IVO(cat)₂][1, 3‐HPDA]₂ · CH₃OH ( 1 ), [V^IVO(N‐2, 3‐D)₂][1, 3‐H₂PDA] ( 2 ), and [V^VO₂(N‐2, 3‐D)(1, 3‐HPDA)] · 1, 3‐PDA ( 3 ) (cat = catechol, N‐2, 3‐D = naphthalene‐2, 3‐diol, 1, 3‐PDA = 1, 3‐propanediamine) were synthesized and characterized by X‐ray diffraction, IR and UV/Vis spectroscopy, and cyclovoltammetry. X‐ray analysis reveals that the spatial frameworks of complexes 1 – 3 are all constructed by hydrogen bonds donated by [1, 3‐H_nPDA]ⁿ⁺ (n = 1, 2) cation, forming distinct chain structures. Complexes 1 and 2 are both in the non‐chiral form of VO(L)₂, but 2 crystallizes in the chiral space group (P6₅22), due to the symmetry element of spiral axis, whereas complex 3 contains both enantiomers of chiral VO₂(L₁)(L₂) units, but crystallizes in the non‐chiral space group (P$\bar{1}$ ). The electrochemical behavior of the three complexes is studied in comparison with that of the free ligands. Complex 1 shows a pair of potentials assigned to the redox behavior of vanadium, while complexes 2 and 3 exhibit no such redox potentials. Pharmaceutical screening of complexes 1 – 3 were carried out against three representative cancer cell lines: A‐549 (lung cancer), Bel‐7402 (liver cancer) and HCT (colonic cancer) by MTT [3‐(4, 5‐dimethylthiazoyl‐2‐yl)‐2, 5‐diphenyltetrazolium bromide] assay. The results show that the vanadium‐catechol complex 1 exhibits more obvious anti‐proliferating effects against the three cell‐lines, whereas the two vanadium‐N‐2, 3‐D complexes 2 and 3 basically display no such effects.     

Synthesis, Spectroscopic and Electrochemical Investigations of Two vic-Dioximes and Their Mononuclear Ni（Ⅱ）, Cu（Ⅱ） and Co（Ⅱ） Metal Complexes Containing Morpholine Group

Two vic-dioxime ligands （LxH2） containing morpholine group have been synthesized from 4-[2-（dimethylaminoethyl）] morpholine with anti-phenylchloroglyoxime or anti-monochloroglyoxime in absolute THF at -15 ℃. Reaction of two vic-dioxime ligands with MCl2·nH2O （M： Ni, Cu or Co and n=2 or 6） salts in 1 ： 2 molar ratio afforded metal complexes of type [M（LxH）2] or [M（LxH）2·2H2O]. All of metal complexes are non-electrolytes as shown by their molar conductivities （Am） in DMF （dimethyl formamide） at 10^-3 mol·L^-1. Structures of the ligands and metal complexes have been solved by elemental analyses, FT-IR, UV-Vis, ^1H NMR and ^13C NMR, magnetic susceptibility measurements, molar conductivity measurements. Furthermore, redox properties of the metal complexes were investigated by cyclic voltammetry.     

Oxovanadium(IV) and ruthenium(II) carbonyl complexes of ONS‐donor ligands derived from dehydroacetic acid and dithiocarbazate: Synthesis,characterization, antioxidant activity,DNA binding and in vitro cytotoxicity

A series of new complexes of oxovanadium(IV) [VO(L)(B)] and ruthenium(II) [Ru(CO)(PPh₃)₂(L)] ( 1.1- 1.3,  2.1–2.3 ) (H₂L = dehydroacetic acid Schiff base of S‐methyldithiocarbazate, H₂smdha ( 1 ) or S‐benzyldithiocarbazate, H₂sbdha ( 2 ); B = 2,2′‐bipyridine (bpy) or 1,10‐phenanthroline (phen)) have been synthesized. The structure of these complexes was authenticated using elemental analyses and spectroscopic techniques, and their magnetic properties and electrochemical behaviour were studied. The molecular structures of oxovanadium(IV) complexes [VO(smdha)(bpy)]?CH₂Cl₂ ( 1.1 ) and [VO(sbdha)(phen)]?2H₂O ( 2.2 ) were confirmed using single‐crystal X‐ray crystallography. Analytical data showed that the ligands 1 and 2 are chelated to the metal centres in a bi‐negative tridentate fashion through azomethine N, thiol S and deprotonated hydroxyl group. The antioxidant activity of the synthesized compounds was tested against 2,2‐diphenyl‐1‐picrylhydrazyl) radical, which showed that the complexes demonstrate a better scavenging activity than their corresponding ligands. The cupric ion reducing antioxidant capacity method was also employed and the total equivalent antioxidant capacity values were found to be higher for the oxovandium(IV) complexes. DNA binding affinity of the compounds was determined using UV–visible and fluorescence spectra, revealing an intercalation binding mode. Higher cytotoxicity for the complexes compared to their ligands was found against human liver hepatocellular carcinoma (HepG2) and breast adenocarcinoma (MCF7) cell lines using MTT assay.     

Mixed Ligand Complexes of Oxovanadium (IV) Oxalate

The oxovanadium(IV) complexes VOC₂O₄ · 2DMF, VOC₂O₄ · 2 formamide, VOC₂O₄ · 2 ethylene urea, VOC₂O₄ · 2 urea and VOC₂O₄ · en have been prepared and characterized. The oxalato group functions as a bidentate ligand in all these complexes. Except ethylene diamine the remaining ligands – DMF. formamide, ethylene urea and urea – act as monodentate ligand coordinating through their carbonyl oxygen. Ethylene diamine is bound to the metal through nitrogen. In all the complexes vanadium is five coordinated in distorted tetragonal-pyramidal structures.     

Hydrothermal Synthesis,Crystal Structures,and Catalytic Properties of Three Coordination Polymers Containing ­Flexible Bis(benzimidazole) and Dicarboxylate Ligands

Three metal‐organic coordination polymers, namely {[Cd(L1)(1,2‐chdc)] · 2H₂O}_n ( 1 ), {[Ni(L2)(1,2‐chdc)] · H₂O}_n ( 2 ), and [Cd(L2)(npht)]_n ( 3 ) [L1 = 1,2‐bis(2‐methylbenzimidazol‐1‐ylmethyl)benzene, L2 = 1,2‐bis(5,6‐dimethylbenzimidazol‐1‐ylmethyl)benzene, 1,2‐H₂chdc = 1,2‐cyclohexanedicarboxylic acid, H₂npht = 3‐nitrophthalic acid] were synthesized under hydrothermal conditions and structurally characterized by single‐crystal X‐ray diffraction methods, IR spectroscopy, TGA, and elemental analysis. In compound 1 , two 1,2‐chdc^2– ligands connect two neighboring Cd atoms to form a dinuclear [Cd₂(1,2‐chdc)₂] subunit, which is further linked by L1 ligands to construct a 1D ladder‐like chain. Compound 2 exhibits a 2D (4,4) coordination network with {4⁴.6²} topology, whilst compound 3 shows a 1D helical chain structure. The fluorescence, UV/Vis diffuse reflection spectra, and catalytic properties of complexes 1 – 3 for the degradation of the congo red azo dye in a Fenton‐like process are investigated.     

Substituent and Temperature Effect on the Assemblies of Three Lead(II) Coordination Polymers based on Asymmetrical Biphenyl Tritopic Ligands

Three Pb‐based metal‐organic frameworks, [Pb₆(L1)₄] · H₂O ( 1 ), [Pb₂(L2)₂(H₂O)] · H₂O ( 2 ), and [Pb(L2)(H₂O)] · H₂O ( 3 ) were constructed based on two asymmetrical tritopic ligands, 3‐(2′,5′‐dicarboxylphenyl)benzoic acid (H₃L1) and 3‐(2′,5′‐dicarboxylphenyl)pyridine acid (H₂L2), under hydrothermal conditions. The substituents on the two ligands and the induced temperature had effects on the resulting structures. All of the complexes were structurally characterized by X‐ray diffraction analyses and further identified by infrared spectra, elemental analyses, powder X‐ray diffraction, and thermogravimetric analyses. Complexes 1 and 3 are 3D frameworks, which construct from 1D inorganic Pb–O–Pb rod‐shaped secondary building units (SBUs) and H₃L1/H₂L2 ligands as pillars. Complex 2 is a 3D framework based on discrete tetranuclear Pb₄(COO)₈ clusters SBUs and H₂L2 ligands. The effects of both the substituent groups on the aromatic rings and the reaction temperature are discussed in details. The fluorescence properties and thermal stabilities of complexes 1 – 3 were also measured.     

Supramolecular Stuctures from Mononuclear,Binuclear and 2D Net of Copper(II) Complexes with 6‐Hydroxypicolinic Acid

First examples of transition metal complexes with HpicOH [Cu(picOH)₂(H₂O)₂] ( 1 ), [Cu(picO)(2,2′‐bpy)]·2H₂O ( 2 ), [Cu(picO)(4,4′‐bpy)_0.5(H₂O)]_n ( 3 ), and [Cu(picO)(bpe)_0.5(H₂O)]_n ( 4 ) (HpicOH = 6‐hydroxy‐picolinic acid; 2,2′‐bpy = 2,2′‐bipyridine; 4,4′‐bpy = 4,4′‐bipyridine; bpe = 1,2‐bis(4‐pyridyl)ethane) have been synthesized and characterized by single‐crystal X‐ray diffraction. The results show that HpicOH ligand can be in the enol or ketonic form, and adopts different coordination modes under different pH value of the reaction mixture. In complex 1 , HpicOH ligand is in the enol form and adopts a bidentate mode. While in complexes 2 – 4 , as the pH rises, HpicOH ligand becomes in the ketonic form and adopts a tridentate mode. The coordination modes in complexes 1 – 4 have not been reported before. Because of the introduction of the terminal ligands 2,2′‐bpy, complex 2 is of binuclear species; whereas in complexes 3 and 4 , picO ligands together with bridging ligands 4,4′‐bpy and bpe connect Cu^II ions to form 2D nets with (12³)₂(12)₃ topology.     

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).     

Copper(II) bromide,nitrate and perchlorate complexes with sterically demanding N‐(6‐methylpyridin‐2‐yl)acetamide ligands

Functionalized acid amides are widely used in biology, medicine, environmental chemistry and many other areas. Among them, pyridine‐substituted amides, in particular N‐(pyridin‐2‐yl)acetamide and its derivatives, play an important role due to their excellent chelating properties. The donor properties of these ligands can be effectively modified by introducing electron‐donating substituents (e.g. alkyl groups) into the heterocycle. On the other hand, substituents in the α‐position of the pyridine ring can create steric hindrance, which significantly influences the coordination number and geometry. To achieve a better understanding of these effects, copper(II) complexes with sterically demanding N‐(6‐methylpyridin‐2‐yl)acetamide ligands (L ) and monoanions of different size, shape and coordination ability have been chosen as model compounds. The crystal structures of three new compounds, bromidobis[N‐(6‐methylpyridin‐2‐yl‐κN )acetamide‐κO ]copper(II) bromide, [CuBr(C₈H₁₀N₂O)]Br, (I), aquabis[N‐(6‐methylpyridin‐2‐yl‐κN )acetamide‐κO ]copper(II) dinitrate, [Cu(C₈H₁₀N₂O)(H₂O)](NO₃)₂, (II), and aquabis[N‐(6‐methylpyridin‐2‐yl‐κN )acetamide‐κO ]copper(II) bis(perchlorate), [Cu(C₈H₁₀N₂O)(H₂O)](ClO₄)₂, (III), have been determined by single‐crystal X‐ray diffraction analysis. It has been shown that the presence of the 6‐methyl group results in either a distorted square‐pyramidal or a distorted trigonal–bipyramidal coordination geometry around the Cu^II centres instead of the typical octahedral geometry observed when the methyl substituent is absent or occupies any other position on the pyridine ring. Moreover, due to the steric hindrance provided by the L ligands, only the bromide ligand, the smallest of the series, enters into the first coordination sphere of the Cu^II ion in (I). In (II) and (III), the vacant coordination site of the Cu^II ion is occupied by a water molecule, while the nitrate and perchlorate anions are not involved in coordination to the metal centre. The structures of (I)–(III) are characterized by the presence of one‐dimensional infinite chains formed by hydrogen bonds of the types N—H…Br [in (I)], N—H…O and O—H…O [in (II) and (III)] between the amide groups of the L ligands, the coordinated water molecules and the uncoordinated anions. The hydrogen‐bonded chains are further interconnected through π–π stacking interactions between the pyridine rings of the L ligands, with approximate interplanar separations of 3.5–3.6 Å.     

Two Pairs of Homochiral Coordination Polymers with Helices Based on Semi‐rigid Lactic Acid Ligands

Utilizing semirigid lactic acid derivatives (R)‐H₂CBA and (S)‐H₂CBA as chiral ligands, two pair of homochiral coordination polymers formulated as [Zn((R)‐CBA)(1,4‐DIB)] · H₂O ( 1 ‐ D ), [Zn((S)‐CBA)(1,4‐DIB)] · H₂O ( 1 ‐ L ), [Co((R)‐CBA)(1,4‐DIB)] · H₂O ( 2 ‐ D ) and [Co((S)‐CBA)(1,4‐DIB)] · H₂O ( 2 ‐ L ) were prepared under solvothermal reaction condition. Single X‐ray diffraction study reveals that all the complexes are comprised of three kinds of helical chains, which are constructed by corresponding metal ions, CBA^2– ligands, and/or 1,4‐DIB ligands. Moreover, some physical characteristics, such as PXRD, thermal stabilities, solid‐state circular dichroism (CD), luminescent and magnetic properties are also investigated.