Chapter 4 - ... Chapter 4 Reactivity of M(acac) 2 (M = Cu, Ni, Co, Mn) towards iminodiacetic acid in...

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Transcript of Chapter 4 - ... Chapter 4 Reactivity of M(acac) 2 (M = Cu, Ni, Co, Mn) towards iminodiacetic acid in...

  • 83

    Chapter 4

    Reactivity of M(acac)2 (M = Cu, Ni, Co, Mn) towards

    iminodiacetic acid in presence of α-diimine:

    Synthesis, X-ray crystallography, spectroscopic

    characterization and biological studies

  • 84

    INTRODUCTION

    Functionalized dicarboxylic acids and their metal complexes have potential

    uses for developing novel pharmaceutical agents [1]. The coordination chemistry of

    iminodiacetic acid (H2imda) has been a subject of continuous investigations due to its

    tridentate chelating behaviour towards metal ions resulting in complexes which show

    structural diversities [2]. In aqueous biological pH range (pH = 6–7), the carboxylic

    acid protons of H2imda dissociate to give iminodiacetate (imda 2–

    ) dianion which is

    quite reactive to transition metal ions forming metal iminodiacetate complexes [3].

    Reactions of metal iminodiacetate with an α-diimine viz. 1,10-phenanthroline (phen)

    or 2,2'-bipyridine (bipy) produce mixed-ligand complexes, some of which have been

    successfully exploited as model compounds to explain binding modes and structural

    features in several metalloenzymes [4]. Several mixed-ligand complexes have been

    found to exhibit superoxide dismutase (SOD) activity [5,6] which is related to the

    flexibility of the geometric transformations around the metal centres [7]. Moreover,

    some of these complexes play a decisive role not only in activation of enzymes but

    also in the storage and transport of active substances through biological membranes

    [8]. Transition metal ternary complexes have received particular focus and have been

    employed in mapping protein surfaces [9], as probes for biological redox centers [10]

    and in protein capture for purifications [11].

    The study of the structure of model ternary complexes provides information

    about how biological systems achieve their specificity and stability, as well as

    strategies to improve these features for biotechnological applications. Ternary

    complexes of oxygen donor ligands and heteroaromatic N-bases have been of special

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    interest as they can display exceptionally high stability [12]. X-ray structural data of

    the ternary complexes [2,3] with iminodiacetate (imda 2–

    ) or its substituted analogues

    as primary ligand and N-donors as secondary ligand have revealed the influence of the

    secondary (auxiliary) ligand on the conformations of the primary iminodiacetate

    ligands. Studies of such complexes have also explained the observed changes in the

    protein conformations at the metal-protein centers in the absence as well as in the

    presence of appropriate substrates [13]. The structure of the ternary complexes bearing

    the composition M/H2imda/N-heterocycle in the mole ratio 1/1/2 display a

    hexacoordinate elongated octahedral (4+1+1) geometry where imda is in a fac-

    tridentate conformation [14]. Complexes having the composition M/H2imda/N-

    heterocycle in 1/1/1 mole ratio, invariably adopt a five coordinate square pyramidal

    (4+1) coordination geometry.

    Prompted by the biological activities exhibited by the transition metal ternary

    complexes and also the possible structural diversities, it was contemplated to carry out

    the syntheses of mixed-ligand metal iminodiacetate complexes, which were

    characterized by spectral and X-ray crystallographic technique.

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    EXPERIMENTAL

    Materials

    The reagents metal salts (Merck), 2, 2’-bipyridine (Merck) and iminodiacetic

    acid (Aldrich) used were of synthetic grades. Ultrapure water was used for all

    experiments. The commercially available solvents were distilled and then used for

    synthesis.

    Instrumentation

    Melting points were determined by open capillary method and are uncorrected.

    The IR spectra as KBr pellets were recorded on a Shimadzu FT-IR 157

    spectrophotometer. 1 H and

    13 C NMR spectra were recorded on a Varian Mercury Plus

    300 spectrometer using TMS as an internal standard. The X-band EPR spectra were

    taken at room temperature as well as liquid nitrogen temperature on a Varian E-112

    spectrometer operating at 9.1 GHz. FAB-Mass spectra on Jeol SX-102/DA-6000 mass

    spectrometer using argon (6 kV, 10 mA) as the FAB gas. The accelerating voltage was

    10 kV and m-nitrobenzyl alcohol (NBA) was used as matrix.

    X-ray crystallographic data collection

    Single-crystal X-ray diffraction of complex (1) and (2) was performed on a

    BRUKER SMART 1000 CCD diffractometer equipped with a graphite crystal

    monochromator situated in the incident beam for data collection. The structure of the

    complex (1) and (2) was solved by direct methods and refined against F 2

    using the

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    SHELXL-97 software [15]. The X-ray data of the complex was recorded at IIT,

    Kanpur.

    Synthesis of M(acac)2 (M = Cu, Ni, Co, Mn)

    Synthesis of bis(acetylacetonato) copper(II), [Cu(acac)2]

    To a 25 mL aqueous solution of CuCl2·2H2O (24 mmol, 4 gm) was slowly

    added a solution of 5 mL methanolic solution of with rapid stirring. Now sodium

    acetate (84 mmol, 6.8 gm) in 15 mL distilled water was added to the resulting mixture

    dropwise. The mixture was then heated to about 80 0 C for 15 minutes while the rapid

    stirring was maintained. The reaction mixture was first cooled to room temperature &

    then cooled further in ice bath. The blue grey product was collected by vacuum

    filteration and washed with 100 mL of cold distilled water. The product was dried at

    110 0 C in an oven. The crude product was recystallised from hot methanol.

    [Yield 85%; m.p.284-288 C (dec)] Anal Calc. (%) for Cu(C5H7O2)2: C, 30.96

    ; H, 3.61 , Found (%), C, 30.68; H, 3.60. FT-IR ( as KBr disc, cm -1

    ): ν (CH3), 2922,

    2854 cm -1

    ; ν(C C) + ν (C O), 1576 cm -1

    ; ν(C O) + ν (C C), 1529 cm -1

    ;

    п(CH), 783 cm -1

    ; ν(MO) + ν(C-CH3), 454 cm -1

    ; ν(C C) + ν (C O), 939 cm -1

    ; Pr

    (CH3), 1017 cm -1

    ; δ(CH) + ν(C-CH3), 1190 cm -1

    ; ν(C-CH3) + ν (C C), 1273 cm -1

    ;

    δs(CH3), 1357 cm -1

    ; δd(CH3), 1414 cm -1

    ; п(CH3-C(O)-C), 652 cm -1

    .

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    Synthesis of bis(acetylacetonato) nickel(II), [Ni(acac)2]

    To a solution of NiCl2.6H2O (0.25 mol, 59.4 gm) in 250 mL of water was

    added a solution of acetylacetone (0.5 mol, 50 g) in 100 mL of methanol, while

    stirring. A solution of 0.5 mol of sodium acetate in 150 mL of water was added to the

    resulting mixture. The mixture was heated, cooled to room temperature, and placed in

    the refrigerator for several hours. The green solid was filtered off, washed with water,

    and dried in vacuum desiccator.

    [Yield 80%; m.p. 235 C ] Anal Calc. (%) for Ni(C5H7O2)2: C, 31.3; H, 3.65,

    Found (%), C, 31.28; H, 3.61. FT-IR ( as KBr disc, cm –1

    ): ν (CH), 3081 cm -1

    ; ν

    (CH3), 2994, 2927 cm -1

    ; ν(C C) + ν (C O), 1523 cm -1

    ; ν(C O) + ν (C C), 1529

    cm -1

    ; п(CH), 767 cm -1

    ; ring def.+ ν(MO), 593 cm -1

    ; ν(C C) + ν (C O), 933 cm -1

    ;

    Pr (CH3), 1024 cm -1

    ; δ(CH) + ν(C C), 1463 cm -1

    ; ν(C-CH3) + ν (C C), 1265 cm -1

    ;

    δd(CH3), 1404 cm -1

    ; п(CH3-C(O)-C), 668 cm -1

    .

    Synthesis of diaquobis(acetylacetonato) cobalt(II), [Co(acac)2·2H2O]

    To a solution of 80 mg NaOH in 1 mL water, was slowly add distilled

    acetylacetone (2 mmol, 200 mg), with swirling. The yellow solution is added

    dropwise, with stirring, to a solution of CoCl2·6H2O (1 mmol, 238 mg) in 1.5 mL of

    water. The product was isolated by suction filteration and washed with water until the

    washings are nearly colourless. After drying, the crude product was dissolved in a hot

    mixture of 2 mL ethanol and 1.3 mL chloroform (do not boil the resulting solution).

    The resulting mixture was filtered by vacuum pump and dried in desiccator.

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    [Yield 85%; m.p. 167.5 C (dec)] Anal Calc. (%) for Co(C5H7O2)2·2H2O: C,

    28.64; H, 4.29, Found (%), C, 28.60; H, 3.61. FT-IR ( as KBr disc, cm –1

    ): ν (OH),

    3424 cm –1

    ; ν (CH3), 2994, 2927 cm -1

    ; ν(C C) + ν (C O), 1521 cm -1

    ; ν(C O) + ν

    (C C), 1529 cm -1

    ; п(CH), 770 cm -1

    ; ring def.+ ν(MO), 575 cm -1

    ; ν(C C) + ν (C

    O), 933 cm -1

    ; Pr (CH3), 1020 cm -1

    ; δ(CH) + ν(C –CH3), 1203 cm -1

    ; ν(C-CH3) + ν (C

    C), 1263 cm -1

    ; δd(CH3), 1402 cm -1

    ; п(CH3-C(O)-C), 675 cm -1

    ; ν(MO) + ν (C-CH3),

    424 cm -1

    ; δ(CH) + ν(C C), 1461 cm -1

    .

    Synthesis of bis(acetylacetonato) manganese, [Mn (acac)2]

    To a solution of MnCl2.4H2O (0.25 mol, 49.5 g) in 250 mL of water at room

    temperature is added a solution of