Macrocyclic cobalt(III) complexes as precursors for metal-polythiophene hybrid materials

A thiophene-functionalised macrocyclic ligand trans-6,13-dimethyl-6-((thiophen-3-ylmethyl)amino)-1,4,8,11-tetraazacyclotetradecane-13-amine (L¹) has been prepared and complexed with Co^III. The ligand L¹ binds as a pentadentate in the crystallographically characterised complexes [CoL¹(OAc)](ClO₄)₂ and [CoL¹Cl]Cl₂. Electro-copolymerisation of [CoL¹Cl]Cl₂ with 3,4-ethylenedioxythiophene (EDOT) in a 1:2 ratio on a preformed poly-3,4-ethylenedioxythiophene (PEDOT) film resulted in metal–polymer hybrid films of high quality, consistency and uniformity in appearance. The copolymerised films were characterised by XPS indicating a 1:11 ratio of incorporation of complex to EDOT. Electrochemistry of the Co-PEDOT film (cast on an indium-doped tin oxide working electrode) in water revealed a Co^III/II redox couple at a potential ca. −600 mV (vs Ag/AgCl) which is similar to that seen in solution for the monomeric aqua complex [CoL¹(OH₂)]³⁺.     

Synthesis and characterization of copper(II) and cobalt(II) complexes with two new potentially hexadentate Schiff base ligands. X-ray crystal structure determination of one copper(II) complex

Two new potentially hexadentate N₂O₄ Schiff base ligands 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy) phenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L¹] and 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy)-5-tert-butylphenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L²] were prepared from the reaction of 3,5-di-tert-butyl-2-hydroxy benzaldehyde with 1,2-bis(2′-aminophenoxy)benzene or 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene, respectively. From the direct reaction of ligands [H₂L¹] and [H₂L²] with copper(II) and cobalt(II) salts in methanolic solution and in the presence of N(Et)₃ the neutral [CuL¹], [CuL²], [CoL¹] and [CoL²] complexes were prepared. All complexes were characterized by IR spectra, elemental analysis, magnetic susceptibility, mass spectra, molar conductance (Λ_m), UV-Vis spectra and in the case of [CuL²] with X-ray diffraction. X-ray crystal structure of [CuL²] showed that the complex contains copper(II) in a distorted square planar environment of N₂O₂ donors. Three CH/π interactions were observed in the molecular structure of latter complex.     

Synthesis and variable coordination modes of a bis-thiophene-appended macrocycle in complex with cobalt(III)

The bis-thiophene appended cyclam derivative L³ (trans-6,13-dimethyl-6,13-bis(thiophene-3′-ylmethylamino)-1,4,8,11-tetraazacyclotetradecane) has been synthesised, characterised and complexed with Co^III. The crystal structure of the diprotonated ligand as its cyanoborohydride salt [H₂L³][NCBH₃]₂ is reported. Variable coordination modes to Co^III have been identified that find the ligand binding either as a tetradentate (cyclam-like) macrocycle in the structurally characterised complexes trans-[CoL³Cl₂]Cl and trans-[CoL³(NCBH₃)(OH)]Cl or as a hexadentate in [CoL³]Cl₃ where both functionalised exocyclic amines coordinate in trans coordination sites. In this case, we have found that the structure of the hexadentate coordinated complex [CoL³]³⁺ is significantly tetragonally elongated due to steric effects of the thiophene rings and this also leads to a very large 500 mV anodic shift in the Co^III/II redox potential relative to the unsubstituted hexaamine complex of Co^III.     

Heterovalent trinuclear Co(III)-Co(II)-Co(III) complexes with N-(2-Carboxyethyl)salicylaldimines

The heterovalent trinuclear cobalt complexes [Co₂^IIIL₄ ⁱ · Co^II(H₂O)₄] · nXmY (L ⁱ are deprotonated Schiff bases derived from substituted salicylaldehydes and β-alanine; i = 1–3) were obtained and characterized. An X-ray diffraction study of the trinuclear cobalt complex with N-(2-carboxyethyl)salicylaldimine showed that the central Co(II) ion and the terminal Co(III) ions are linked by bridging carboxylate groups. Either terminal Co(III) atom is coordinated to two ligand molecules. They form an octahedral environment consisting of two azomethine N atoms, two phenolate O atoms, and two O atoms of two carboxylate groups. The central Co(II) atom is coordinated to four water molecules and to two O atoms of two bridging carboxylate ligands involved in the coordination sphere of the terminal Co(III) atoms.     

Structure and magnetic properties of Cu(II) bischelate with spin-labeled aminoenal

The molecular and crystal structure of Cu(II) bischelate with the deprotonated stable nitroxide radical 4,4,5,5-tetramethyl-2-(2-oxo-1-(4,4,5,5-tetramethylimidazolidine-2-ylidene)ethyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxylom (HL) are studied. It is revealed that the complex packing is formed of separate CuL₂ molecules. Oxygen atoms in >N∸O groups do not participate in Cu²⁺ ion coordination, and so only weak exchange interactions are observed between paramagnetic centers in CuL₂.     

Synthesis,Structures and Magnetic Properties of Two Binuclear Cobalt(II) Complexes Bridged by Bis(p‐nitrophenyl) Phosphate or Diphenylphosphinate Ion

Two new binuclear cobalt(II) complexes, [Co₂ L¹ (μ₂‐DPP)]²⁺ ( 1 ) (H L¹ = N, N, N′, N′‐ tetrakis (2‐benzimidazolylmethyl)‐2‐hydroxyl ‐1,3‐diaminopropane; DPP = diphenylphosphinate) and [Co₂ L² (μ₂‐BNPP)₂]⁺ ( 2 ) (H L² = 2,6‐bis‐[N,N‐di(2‐ pyridylmethyl)aminomethyl]‐4‐methylphenol, BNPP = bis(4‐nitrophenyl)phosphate) have been synthesized and their crystal structures and magnetic properties are shown. In 1 , each Co^II atom has a distorted trigonal bipyramidal coordination sphere with a N₃O₂ donor set and the central two Co^II atoms are bridged by one alkoxo‐O atom and one μ₂‐DPP ion with the Co1‐Co2 separation of 3.542Å. In 2 , each Co^II atom has a pseudo octahedral environment with a N₃O₃ donor set and the central two Co^II atoms are bridged by a phenolic oxygen atom of L² and two μ₂‐BNPP ions with the Co1‐Co2 separation of 3.667Å. Susceptibility data of 1 and 2 indicate intramolecular antiferromagnetic coupling of the high‐spin Co^II atoms.     

Syntheses and crystal structures of two novel Cu(II) and Co(II) complexes with 3-methyl-4-(p-bromophenyl)-5-(2-pyridyl)-1,2,4-triazole

A new ligand, 3-methyl-4-(p-bromophenyl)-5-(2-pyridyl)-1,2,4-triazole (L) and its complexes, trans-[CuL₂(ClO₄)₂] (1) and cis-[CoL₂(H₂O)₂](ClO₄)₂·H₂O·CH₃OH (2), have been synthesized and characterized by UV, IR, electrospray ionization mass spectrum, elemental analyses, and single-crystal X-ray diffraction methods. In the structure, two L ligands are stabilized by intermolecular π···π interactions between the triazole rings. In the complexes, each L ligand adopts a chelating bidentate mode through N atom of pyridyl group and one N atom of the triazole. Both complexes have a similar distorted octahedral [MN₄O₂] core (M = Cu²⁺ and Co²⁺) with two ClO₄ ⁻ ions in the trans position in 1 but two H₂O molecules in the cis arrangement in 2.     

Coordination compounds of some 3d metals with 3-methyl-1-phenyl-4-formylpyrazol-5-one

CuL₂ · 1.5H₂O and ML₂ · 2H₂O · 2EtOH (M = Co²⁺, Ni²⁺, Mn²⁺) coordination compounds were synthesized via the exchange reaction between the sodium salt of 3-methyl-1-phenyl-4-formylpyrazol-5-one (HL) and metal chlorides.The synthesized compounds were studied by thermogravimetry, magnetochemistry, and electron and IR spectroscopy. The complexes CuL₂ · 2Py and CoL₂ · 2Py · MeOH were obtained via recrystallization from a methanol-pyridine mixture, and their structures were studied by X-ray diffraction. Pyrazolone was found to be coordinated in the deprotonated enol form and to form six-membered chelate rings with a metal. The coordination polyhedron of a metal cation was found to be a square bipyramid (Cu²⁺) or an axially elongated octahedron (Co²⁺) with its vertices occupied by the oxygen atoms of 3-methyl-1-phenyl-4-formylpyrazol-5-one and the nitrogen atoms of pyridine.     

Reactions of Cu(II) and Co(II) acetates, acetylacetonates, and valinates with α,α-Dipyrrolylemethen

The reactions of Co(II) and Cu(II) acetates, valinates, and acetylacetonates with 3,3′,5,5′-tetramethyl-4,4′-dibutyldipyrrolylmethen (HL) in DMF at 298.15 K are studied by spectrophotometric method. The compositions and thermodynamic constants of formation of the Cu(II) and Co(II) complexes are determined using the methods of molar ratios and continuous changes. With an excess in Cu(II) acetate or acetylacetonate, the formation of mixed-ligand complexes CuL(OAc) and CuL(Acac), respectively, was observed, whereas CuL₂ complex was detected in the case of HL excess. At either ratio of the reagent concentrations, reactions of Co(II) acetate and acetylacetonate with HL always afforded CoL₂ complex, while in the case of Cu(II) and Co(II) valinates, only one amino acid ligand was replaced to give ML(Val) complexes (HVal is valine). The chelating capability of the ligand HL toward the Cu²⁺ ion was found to be higher than that toward the Co²⁺ ion.     

Synthesis and characterization of Co(II), Ni(II), Zn(II) and Cu(II) complexes with a new tetraazamacrocyclic Schiff base ligand containing a piperazine moiety: X-ray crystal structure determination of the Co(II) complex

Two macrocyclic Schiff base ligands, L¹ [1+1] and L² [2+2], have been obtained in a one-pot cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,3-diaminopropane. Unfortunately, because of the low solubility of both ligands, their separation was unsuccessful. In the direct reaction of these mixed ligands (L¹ and L²) and the appropriate metal ions only [CoL¹(NO₃)]ClO₄, [NiL¹](ClO₄)₂, [CuL¹](ClO₄)₂ and [ZnL¹(NO₃)]ClO₄ complexes have been isolated. All the complexes were characterized by elemental analyses, IR, FAB-MS, conductivity measurements and in the case of the [ZnL¹(NO₃)]ClO₄ complex with NMR spectroscopy.     

Studies in the flexibility of macrocyclic ligands. Crystal and molecular structure of 2,13-dimethy1-3,6,9,12,18-pentaazabicyclo (12.3.1) octadeca-(18),14,16-triene-dichloroion (III) hexafluorophosphate

The crystal structure of the title compound [FeL²Cl₂] [PF₆] is reported. Crystals are monoclinic with a = 11.747(9), b = 16.051(11), c = 11.964(10)Å, β = 98.1(1)°, Z = 4, Spacegroup P2₁/n. 1173 independent reflections above background have been refined to R 0.09. The coordination geometry around the Fe(III) ion is pentagonal bipyramidal with the two chlorine atoms in axial positions [Fe-Cl 2.348(7), 2.354(7)Å]. The five donor nitrogen atoms of the macrocycle form a pentagonal girdle with lengths in the range 2.20(2)–2.25(2)Å. The macrocycle conformation is compared to that found in [CuL²]²⁺ and [CoL²Cl]²⁺ where the 5N donor set provides respectively trigonal bipyramidal and square pyramidal environments and also to that found in the comparable 7-coordinate [FeL¹(NCS)₂]⁺ where L¹ is the related pentaene.     

Metallkomplexe mit N2O2S2‐Koordinationssphäre. Synthese und Charakterisierung der Cobalt(II)‐, Nickel(II)‐ und Kupfer(II)‐Komplexe eines 15‐ und eines 16‐gliedrigen N,N′‐bis(2‐hydroxyethyl)‐funktionalisierten makrocyclischen Liganden

Metal Complexes with N₂O₂S₂ Donor Set. Synthesis and Characterization of the Cobalt(II), Nickel(II), and Copper(II) Complexes of a 15‐ and a 16‐Membered Bis(2‐hydroxyethyl) Pendant Macrocyclic Ligand The macrocyclic ligands 6, 10‐bis(2‐hydroxyethyl)‐7, 8, 9, 11, 17, 18‐hexahydro‐dibenzo‐[e, n][1, 4, 8, 12]‐dithiadiaza‐cyclopentadecine ( 1 ) (L¹) and 5, 13‐bis(2‐hydroxyethyl)‐7, 8, 9, 10, 16, 17, 18, 19, 20‐nonahydro‐dibenzo‐[g, o][1, 9, 5, 13]‐dithiadiaza‐cyclohexadecine (L⁴) have been prepared. They form the stable complexes [CoL¹(‐H)CoL¹](ClO₄)₃ ( 2 ), [NiL¹](ClO₄)₂·MeOH ( 3 ), Λ‐[CuL¹](ClO₄)₂·MeOH ( 4a ) and rac‐[CuL¹](ClO₄)₂·MeOH ( 4b ), [NiL⁴](ClO₄)₂ ( 5 ), and [CuL⁴](ClO₄)₂ ( 6 ). The compounds 1 to 6 have been characterized by standard methods and single‐crystal X‐ray diffraction. In the complexes 2 to 6 the metal atoms are octahedrally coordinated by the N₂O₂S₂ donor set of the ligands. L¹ and L⁴ are folded herein along the N···M···S‐ and the N···M···N′‐axes, respectively. This results at the metal atom in a all‐cis‐configuration for the complexes of L¹ and a trans‐N₂‐cis‐O₂‐cis‐S₂‐configuration for the complexes of L⁴. The cobalt(II) complex 2 is a dimer, bridged by a rather short hydrogen bridge of 2.402(12)Å length. The copper(II) complexes of L¹ and L⁴ differ with respect to the Jahn‐Teller‐distortion.     

Synthesis,characterization, and electrochemical study of two new macroacyclic Schiff bases and their copper(II) and zinc(II) complexes

Two new potentially octadentate N₂O₆ Schiff-base ligands 2-((E)-(2-(2-(2-((E)-2-hydroxy-3-methoxybenzylideneamino)phenoxy)phenoxy)phenylimino)methyl)-6-methoxyphenol H₂L¹ and 2-((E)-(2-(2-(2-((E)-2-hydroxy-3-methoxybenzylideneamino)phenoxy)-4-tert-butylphenoxy)phenylimino)methyl)-6-methoxyphenol H₂L² were prepared from the reaction of O-Vaniline with 1,2-bis(2′-aminophenoxy)benzene or 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene, respectively. Reactions of H₂L¹ and H₂L² with copper(II) and zinc(II) salts in methanol in the presence of N(Et)₃ gave neutral [CuL¹]?·?0.5CH₂Cl₂, [CuL²], [ZnL¹]?·?0.5CH₂Cl₂, and [ZnL²] complexes. The complexes were characterized by IR spectra, elemental analysis, magnetic susceptibility, ESI–MS spectra, molar conductance (Λ_m), UV-Vis spectra and, in the case of [ZnL¹]?·?0.5CH₂Cl₂ and [ZnL²], with ¹H- and ¹³C-NMR. The crystal structure of [ZnL¹]?·?0.5CH₂Cl₂ has also been determined showing the metal ion in a highly distorted trigonal bipyramidal geometry. The electrochemical behavior of H₂L² and its Cu(II) complex, [CuL²], was studied and the formation constant of [CuL²] was evaluated using cyclic voltammetry. The logarithm value of formation constant of [CuL²] is 21.9.     

Fe(II) complex with chiral pyrazolylquinoline L and Fe(II), Co(II), and Cu(II) complexes with achiral pyrazolylquinoline L1: Synthesis and properties. The crystal structures of [ML1Cl2] (M = Fe, Co, and Cu)

The complexes FeLCl₂ (I), [FeL¹Cl₂] (II), [CoL¹Cl₂] (III), and [CuL¹Cl₂] (IV) (where L and L¹ are chiral and achiral pyrazolylquinolines, respectively) were obtained. Complexes II–IV were structurally characterized by single-crystal X-ray diffraction analysis. Crystals of complexes II and III are triclinic (space group P $ \bar 1 The complexes FeLCl₂ (I), [FeL¹Cl₂] (II), [CoL¹Cl₂] (III), and [CuL¹Cl₂] (IV) (where L and L¹ are chiral and achiral pyrazolylquinolines, respectively) were obtained. Complexes II–IV were structurally characterized by single-crystal X-ray diffraction analysis. Crystals of complexes II and III are triclinic (space group P ) and crystals of complex IV are monoclinic (space group P2₁/n). Structures II–IV are built from discrete mononuclear acentric molecules. In these complexes, the M²⁺ ion (M = Fe, Co, and Cu) coordinates two N atoms of the bidentate chelating ligand L¹ and two Cl atoms. The coordination cores MCl₂N₂ are distorted tetrahedra. For complexes I and II, μ_eff = 5.05 and 5.07 μ_B, respectively, correspond to the high-spin configuration d ⁶. For complex III, μ_eff = 4.51 μ_B (high-spin configuration d ⁷) and for complex IV, μ_eff = 1.80 μ_B (configuration d ⁹). Original Russian Text ? Z.A. Savel’eva, L.A. Glinskaya, R.F. Klevtsova, S.A. Popov, A.V. Tkachev, N.V. Semikolenova, V.A. Zakharov, S.V. Larionov, 2008, published in Koordinatsionnaya Khimiya, 2008, Vol. 34, No. 4, pp. 285–292.     

Synthesis,characterization, and X-ray crystal structures of metal complexes with new Schiff-base ligands and their antibacterial activities

Two new potentially hexadentate Schiff bases, [H₂L¹] and [H₂L²], were prepared by condensation of 2-(3-(2-aminophenoxy)naphthalen-2-yloxy)benzenamine with 3,5-di-tert-butyl-2-hydroxy benzaldehyde and o-vanillin, respectively. Reaction of these ligands with cobalt(II) chloride, copper(II) perchlorate, and zinc(II) nitrate gave complexes ML. The ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution state investigations show that the complexes are neutral. Molecular structures of [CuL¹], [CoL¹]?·?C₇H₈, and [ZnL²]?·?CH₃CN, which have been determined by single-crystal X-ray diffraction, indicate that [CuL¹] and [ZnL²]?·?CH₃CN display distorted square planar and distorted trigonal-bipyramidal geometry, respectively; the geometry around cobalt in [CoL¹]?·?C₇H₈ is almost exactly between trigonal bipyramidal and square pyramidal. The synthesized ligands and their complexes were screened for their antibacterial activities against eight bacterial strains and the ligands and complexes have antibacterial effects. The most effective ones are [CuL²] against Proteus vulgaris, Serratia marcescens, Staphylococcus subtilis, [H²L¹] against S. subtilis, and [H₂L²] against S. subtilis.     

Synthesis,complex formation kinetics and thermodynamic study of some acyclic polyamine and N2O2 ligands with copper(II)

The polydentate ligands, 3-(2-aminocyclohexylamino)-2-(2-aminocyclohexyl aminomethyl) propionic acid (L¹ ), 4,7,10-triazatridecanedinitrile trihydrochloride (L² ), and 2,2′-(ethane-1,2-diyl) bis(methylazanediyl) diethanol (L³ ) were prepared and their structures investigated by FT-IR, NMR, and MS. The kinetics of complex formation between Cu(II) and L¹, L², and L³ were investigated in acidic aqueous solutions using the stopped-flow method. The stability constants of the complexes were determined by spectrophotometric titration (T?=?293?K, μ?=?0.1?mol?L^?1 NaClO₄), using a diode array UV-Vis spectrophotometer equipped with peristaltic pump and pH meter. The stability constants for the complexes were CuL^1?>?CuL^2?>?CuL³. Activation enthalpies (ΔH#) of these complexes were 55?kJ?mol^?1 for CuL¹, 61?kJ?mol^?1 for CuL², and 36?kJ?mol^?1 for CuL³, respectively.     

Complexes of Cu(II) and Pd(II) with 2-R-1,3,11,11<Emphasis Type="Italic">c</Emphasis>-tetraazacyclopenta[<Emphasis Type="Italic">c</Emphasis>]phenanthrenes

Paramagnetic complexes CuL¹SO₄·0.5H₂O, CuL²SO₄·2H₂O and diamagnetic Pd(HL²)Cl₃ (L¹ = 2-methyl-1,3,11,11c-tetraazacyclopenta[c]phenanthrene complex (L² = 2-phenyl-1,3,11,11c-tetraazacyclopenta-[c]phenanthrene) were synthesized. The most probable structure of the complexes was suggested on the basis of the IR and ESR spectra. Coordination units of paramagnetic complexes contain N atoms of the bidentate cycle-forming ligands, L¹ and L² molecules. The square PdCl₃N unit of the diamagnetic complex includes the N atom of the triazole fragment of the monodentate ligand, (HL²)⁺ cation.     

Structure of the Cu(II) chloride complex with 4-amino-l,2,4-triazole Cu(C2H4N4)Cl2

The coordination compounds of copper(II) chloride and bromide with 1,2,4-triazole (L¹) and 4-amino1,2,4-triazole (L²), CuL¹Hal₂ and CuL²Hal₂, possess interesting magnetic properties [1, 2]. For example, at very low temperatures CuL¹Cl₂ and CuL¹Br₂ are ferromagnets [2](T _c ≈ 3.3 and 6.5 K, respectively). To explain the magnetic behavior of copper(II) halide complexes with the above nitrogen heterocycles it is generally assumed that the complexes are polynuclear chain compounds in which the copper atoms are bridged by two halogen ions and bridging bidentate heterocycle molecules (coordination of N1 and N2 atoms). This hypothesis is made on the basis of the X-ray diffraction analysis of CuL¹Cl₂ [3]. It is interesting to perform an X-ray diffraction study of CuL²Cl₂ and CuL2Br2; this is important for obtaining reliable magnetostructural correlations for this group of compounds. In this study, we investigated single crystals of the complexes; this demanded choosing special conditions of synthesis, which differ from the conditions suggested for the synthesis of polycrystals in [1]. In this communication we report on the results of synthesis and X-ray diffraction analysis of the single crystals of the coordination compound CuL²Cl₂. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 1, pp. 207–212, January–February, 1997.     

A hexanuclear discrete assembly and a two dimensional coordination polymer constructed from heterotrinuclear [(CuL)2Zn]2+ nodes and dicyanamide spacer (H2L = salen type Schiff base ligands)

Two new Cu(II)–Zn(II) complexes as a discrete hexanuclear cluster [{(CuL¹)₂Zn}₂(μ_1,5-N(CN)₂)₂](ClO₄)₂ (1) and a two dimensional (2D) coordination polymer [(CuL²)₂Zn(μ_1,5-N(CN)₂)₂]_n (2) have been isolated by mixing two similar tetradentate Schiff bases H₂L¹ (N,N′-bis(ɑ-ethylsalicylidene)-1,3-propanediamine) and H₂L² (N,N′-bis(salicylidene)-1,3-pentanediamine) separately with Cu(ClO₄)₂·6H₂O, Zn(ClO₄)₂·6H₂O and NaN(CN)₂ ?at same reaction condition. The heterometallic complexes have been structurally characterized by single crystal X-ray analyses showing that both are formed by angular trinuclear nodes and μ_1,5-dicyanamide spacers. The trinuclear nodes ([(CuL¹)₂Zn]²⁺ in 1 and [(CuL²)₂Zn]²⁺ in 2 are produced in situ from their corresponding reactants. The two Schiff base ligands coordinating the Cu(II) ions through the N₂O₂ donor set are additionally bonded to a Zn(II) ion with the four phenoxido oxygen atoms that act as bridging atoms. The zinc ion completes its coordination geometry with two terminal nitrogen atoms of two different dicyanamide spacers. The orientation of spacers from zinc ion are convergent in 1 whereas divergent in 2. Thus, two [(CuL¹)₂Zn]²⁺ nodes are interconnected by double μ_1,5-dicyanamide bridges via Zn(II) centres to form discrete hexanuclear assembly of complex 1. On the other hand, [(CuL²)₂Zn]²⁺ nodes in 2 are joined by μ_l,5-dicyanamide that bridge Zn(II) to Cu(II) centres of symmetry related units in order to construct a 2D coordination polymer. Consequently, the final coordination environment around Zn(II) is octahedral in both complexes whereas that around Cu(II) are square planar and square pyramidal in 1 and 2 respectively.     

Cobalt(II) Schiff Base Complexes Bearing Aza Crown Ether Pendants as Synthetic Hydrolase Catalyzing PNPP Hydrolysis

Two Co^II complexes with aza crown ether substituted salicylaldimine Schiff base, CoL¹ ₂ and CoL² ₂, have been synthesized and employed as models to mimic hydrolase in catalytic hydrolysis of a carboxylic ester. The specific change of u.v.–vis. absorption spectra of the hydrolytic reactive systems has been observed, which indicates that key intermediates are formed by PNPP and Co^II complexes. The kinetics and the mechanism of PNPP hydrolysis have been investigated. The kinetic mathematical model for PNPP cleavage catalyzed by the Co^II complexes has been proposed. The results show that, compared with the crown-free analogous CoL³ ₂, the bis(aza crown ether)s Co^II complexes CoL¹ ₂ and CoL² ₂ exhibit high activity in the PNPP catalytic hydrolysis; the rate of the PNPP hydrolysis catalyzed by the complexes increases with the increase of pH of the buffer solution; the pseudo-first-order rate constants (k _ob) of PNPP hydrolysis catalyzed by the complexes is 1000 times more than that of spontaneous hydrolysis of PNPP.