Cu(II) and Ni(II) complexes of n (2 hydroxybenzyl) amino acid ligands synthesis, structures, properties and catecholase activity 2

Chapter Dinuclear Copper(II) Complexes as Functional Models for the Catechol Oxidase 47 Chapter 2-1. Prelude to Parts A and B Next to iron, copper is the most important bioessential element and its biological relevance is recognized to the highest degree in the last decades due to the rapid development of bioinorganic chemistry which offers a successful interaction between model complexes and metalloenzyme chemistry. Transport, activation and metabolism of dioxygen are very important processes in living systems. Metalloenzymes containing one or more copper centers are responsible for these functions. Many copper containing metalloenzymes such as hemocyanin (dioxygen carrier), tyrosinase (hydroxylation of monophenols and melanin pigment formation), catechol oxidase (oxidation of catechols), dopamine β-hydroxylase (production of catecholamine for nerve and metabolic function), superoxide dismutase (disposal of potentially damaging radicals formed during normal metabolism), plastocyanin of plant chloroplasts (electron transport for photosynthesis), celuroplasmin (potential extra cellular free radical scavenger) and other enzymes such as tryptophan oxygenase, ascorbate oxidase have been discovered.1-4 Proteins containing dinuclear copper centers play paramount roles in biology, including dioxygen transport or activation, electron transfer, reduction of nitrogen oxides and hydrolytic chemistry.5 Copper proteins are classified as Type 1, Type and Type 3. Among them many copper enzymes have oxidase or oxygenase activities. Type copper proteins are characterized by an antiferromagnetically coupled dicopper core with three histidine ligands on each copper ion and µ-hydroxo bridging in the met Cu(II)-Cu(II) form which results in the EPR silent active site. Among the well-known representatives of Type copper proteins, catechol oxidase with active dicopper(II) sites is a ubiquitous enzyme in living systems for catalyzing the oxidation 48 Chapter of a wide range of ortho-diphenols (catechols) to ortho-diquinones (Figure 2-1). The subsequent auto polymerization of the highly active quinones into polyphenolic catechol melanins is considered to be responsible for the defense mechanism observed in plants against pathogens or pests.6 While tyrosinase catalyzes the hydroxylation of tyrosine to dopa (cresolase activity) and the oxidation of dopa to dopaquinone (catecholase activity) with electron transfer to dioxygen, catechol oxidase exclusively catalyzes the oxidation of catechols to quinones without acting on tyrosine. This reaction is of great importance in medical diagnosis for the determination of the hormonally active catecholamines adrenaline, noradrenaline and dopa.8 Oxidation of mono- and diphenol-containing neurotransmitters such as dopamine, epinephrine, norepinephrine and serotonin have been found associated with the Fe(II) and Cu(II) centered redox chemistry related to Alzheimer’s disease.8b-d Figure 2-1. Catecholase reaction in natural systems. In fact, the two copper atoms of dicopper(II) bio-active centers present in different metalloenzymes are found to act cooperatively within the proximity of ~3.5 Ǻ with each Cu(II) centre coordinated by three histidine donors.5 As confirmed by the recent X-ray crystal structure analysis, catechol oxidase in the met oxidized form contains the dicopper active centers with a Cu···Cu distance of 2.9 Å.9 49 Chapter The crystal structure of catechol oxidase reported recently by Krebs and co-workers shown in Figure 2-2 reveals new insight into the functional properties of the Type III copper protein which includes the closely related and well known tyrosinase as well as hemocyanin.9a These proteins have a dinuclear copper center and have similar spectroscopic behavior and functional relationships. Figure 2-2. Overall structure of catechol oxidase from sweet potato (ipomoea batatas). Copper atoms are shown in orange, α helices in blue, β sheets in green.9a One of the interesting structural aspects encountered in the active site of catechol oxidase from sweet potatoes (Ipomoea batatas) and in the active sites of some hemocyanins is an unusual thioether bond between a carbon atom of one of the histidine ligands and the sulfur atom of a nearby cysteine residue from the protein backbone. A cysteinyl-histidinyl bond has also been reported for other Type copper proteins such as tyrosinase from Neurospora crassa,10a and hemocyanin from Helix pomatia10b and Octopus dofleini.10c A thioether bond between cysteine and tyrosine is also present in the mononuclear copper enzyme galactose oxidase.10d Biomimetic models mimicking this unique feature were reported by Belle and Reedjik10e and Wieghart and co-workers.10f In an attempt to further mimic this quite unusual 50 Chapter structural feature, recently, Krebs et al. demonstrated that adjacent thioether group enhanced the activity of dicopper(II) complexes by weakening the exogenous acetate bridging.11h Figure 2-3. Oxy and met forms during the activity of tyrosinase and/or catechol oxides. Based on the spectroscopic and biochemical evidences as well as the recent X-ray crystallographic structural findings of catechol oxidase,9 a plausible mechanism has been proposed for catecholase activity of tyrosinase and /or catechol oxidase.9a, 12 The catalytic cycle begins with the oxy and met states. A diphenol substrate binds to the met state, followed by the oxidation of the substrate to the first quinone and the formation of the reduced state of the enzyme. Binding of the dioxygen leads to the oxy state which is subsequently attacked by the second diphenol molecule. Oxidation to the second quinone forms the met state again and closes the catalytic cycle. Thus, in short, the catecholase activity of tyrosinase and catechol oxidase is carried out by the oxy form (Cu(II)-O22--Cu(II)) and by the met form (Cu(II)-Cu(II)) of the enzymes through a two electron-transfer reaction as shown in Figure 2-3. Coordination sphere of the dinuclear copper center in the met state is shown in Figure2-4.9a 51 Chapter Figure 2-4. Coordination sphere of the dinuclear copper center in the met state.9a In order to gain deeper insight into the copper-mediated substrate oxidations and to understand the influence of various parameters that determine bimetallic reactivity both in natural metalloenzymes and in synthetic analogues, studies of the well defined and appropriate dicopper(II) complexes are obviously essential. For this reason, quite a number of mono- and dinuclear copper(II) complexes have been investigated as biomimetic catalysts for catechol oxidation.11-14 Krebs and Reim demonstrated that that complexes with strained structures show catalytic activity, whereas complexes present in relaxed and energetically favored conformations are essentially inactive towards catechol oxidation.11j Krebs et al. have shown the dicopper(II) complex [Cu2bbpen](ClO4)2.3MeOH as a structural and functional model for catechol oxidase.14a In all the modeling studies,1114 a common and convenient model substrate, 3,5-DTBC, has been employed as a model substrate (Figure 2-5) since its low redox potential makes it easy to oxidize,15 and the bulky substituents prevent further side reactions such as ring opening. 52 Chapter Figure 2-5. Biomimetic oxidation of 3,5-DTBC catalyzed by dicopper(II) complex. Figure 2-6. Formation of 3,5-DTBQ band from the oxidation of 3,5-DTBC catalyzed by [Cu2bbpen2](ClO4)2·3MeOH. The inset shows the course of the absorption maximum at 405 nm with time for 10 and 100 equivalents of 3,5-DTBC.14a Further, the oxidation product, 3,5-DTBQ is sufficiently stable and displays a strong absorption at ca. λmax = 390 nm the growth of which can be monitored by UV-Vis spectroscopy as shown in Figure 2-6.14a For a dicopper(II) complex to act as an efficient catalyst towards the oxidation of 3,5-DTBC, a steric match between substrate and complex is believed to be the determining factor: two metal centers have to be located in the proximity of Å to facilitate proper binding of the two hydroxyl oxygen atoms of catechol prior to the electron transfer.16 (Figure 2-7). This view is supported by the observation that 53 Chapter dinuclear copper complexes are generally more active towards the oxidation of catechol than the corresponding mononuclear complexes.16 Further, Nishida et al. have shown that square-planar mononuclear copper(II) complexes are less active than non-planar mononuclear copper(II) complexes.17 Figure 2-7. Proposed steric match and binding of substrate with complex. With dinuclear copper(II) complexes, only a few structurally characterized complex/substrate adducts are reported. The first, described by Karlin et al.18 was prepared by the oxidative addition reaction from a phenoxo-bridged dicopper(II) complex and tetrachloro-o-benzoquinone (tcbq) which displayed a bridging tetrachlorocatechol (tcc) between the two copper(II) ions with a Cu···Cu distance of 3.248 Å. Recently, crystal structures of the different adducts of complex/substrate exemplifying various coordination modes of catecholate have been reported as shown in Figure 2-8.19 Figure 2-8. TCBQ complexes, [HL3Cu2(TCC)(H2O)2]2.ClO4 (left) and [HL4Cu2(TCC)(H2O)]2.ClO4 (right) as models for substrate binding.19b 54 Chapter Comparing the activity of a series of dicopper(II) complexes containing various endogenous and exogenous bridging moieties, Mukherjee and Mukherjee reported that nature of the bridging group has profound effects on the ability of the complexes to perform the oxidation.20 It has been assumed that for the square pyramidal dicopper(II) complex to act as an active catalyst, the dissociation of bridging group/axial donor must occur so that a vacant coordination site will be readily available for the binding of substrate in a bridging mode. As the binding strength of exogenous bridge decreases, the ability of the complex to bind to the substrate increases and the oxidation becomes more efficient. The compounds [Cu2(L5O)2(OClO3)2] (L5-OH = 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol) (Figure 2-9 (left)) was found inactive, probably the bridging structure changes due to reaction with catechol.20 Figure 2-9. Dicopper(II) complexes studied by Mukherjee et al. (left)20a and Jager et al. (right).11f The complex, {1,2-O-isopropylidene-6-N-(3-acetyl-2-oxobut-3-enyl)amino-6- deoxy-glucofuranoso}copper(II) (Figure 2-9 (right) reported by Jager et al. has been found to be highly active among the model complexes. 11f These investigations also confirmed that the copper(II) complexes are reduced to copper(I) complexes during 55 Chapter catalysis and electron transfer from catechol to the copper(II) complex begins after the formation of a copper-catechol intermediate which could be prevented by the competitive formation of copper-quinone complex.16 Reactivity of the dicopper(II) complexes towards catechols have established both geometry around the copper(II) ions and Cu···Cu distance as two key factors in determining the catalytic ability of the complexes.11f, 20-21 The short Cu···Cu distance allows the bridging catechol coordination compatible with the distance between the two o-diphenol oxygen atoms.11f, 20-21 Jager and Klemm 11f proposed a mechanism which was adapted from Karlin22 and Casella23 as shown in Figure 2-10. In this mechanism, dinuclear copper(I) species with the o-quinone, µ-peroxo moieties with copper(II) are the key intermediates. Figure 2-10. Mechanism of 3,5-DTBC oxidation catalyzed by dicopper(II) complexes.11f 56 Chapter (Part C) angles are given in Table 2-37. The two copper atoms in Cu2O2 ring are separated by a Cu···Cu distance of 3.0076(6) Å. The structure of IIC-2 consists of [Cu2(Scp11)2] units similar to IIC-1 as shown in Figure 2-52 which indicates that the two water molecules are indeed bonded to Cu(II) but in anti fashion. Figure 2-52. Perspective view of dicopper(II) unit in IIC-2. Table 2-37. Selected bond lengths and bond angles in IIC-2 Cu(1)-O(1)a 1.948(1) Cu(1)-O(2) 1.953(1) Cu(1)-N(1) 1.965(2) Cu(1)-O(1) 1.970(1) Cu(1)-O(4) 2.336(2) O(1)-Cu(1)a 1.948(1) Cu(1)-Cu(1)a 3.0076(6) O(1)a-Cu(1)-O(2) 102.5(7) O(1)a-Cu(1)-N(1) 170.9(8) O(1)a-Cu(1)-O(1) 79.73(7) O(1)a-Cu(1)-Cu(1)a a O(1) -Cu(1)-O(4) 88.1(8) N(1)-Cu(1)-Cu(1)a 132.5(6) O(2)-Cu(1)-Cu(1) C(1)-O(1)-Cu(1)a a 40.13(4) 141.2(5) 130.6(1) Cu(1)a-O(1)-Cu(1) 100.3(7) Symmetry transformations used to generate equivalent atoms: a = -x+1,-y+1,-z+1 159 Chapter (Part C) In the crystal lattice IIC-2 forms an interesting one-dimensional hydrogen bonded polymer as shown in Figure 2-53. In the crystal structure of IIC-2 the close Cu(I) O(3) interactions (2.808(2) Å) are sustained by strong O-H···O and weak NH···O hydrogen bonds. Hydrogen bond parameters are given in Table 2-38. Figure 2-53. A portion of 1D Hydrogen-bonded polymeric structure in IIC-2. Table 2-38. Hydrogen bond parameters in IIC-2 D-H d(D-H) d(H A) ∠DHA d(D A) A symmetry O4-H4A 0.70(4) 2.12(4) 170(4) 2.811(4) O5 2-x,1-y,1-z O4-H4B 0.69(3) 2.13(3) 174(4) 2.818(3) O3 -1+x, y, z N1-H1 0.89(2) 2.56(3) 133(2) 3.237(3) O2 2-x,1-y,1-z 2-C-4. Physicochemical studies 2-C-4-1. Thermogravimetric studies The TG traces of IIC-2 reveal that the weight loss occurs in two steps in the temperature range, 76-151 ºC. The total weight loss observed (20.9%) agrees with the calculated value (20.4%) for the loss of two acetone and two water molecules. The anhydrous IIC-2 absorbs moisture instantly in air, which is confirmed by running TG 160 Chapter (Part C) of the anhydrous sample after cooling to room temperature. It shows the weight loss of 5.2% (calculated, 5.7%) in the temperature range, 60-110 ºC and this behavior is similar to that of IIA-1. Hence it is concluded that IIC-2 can be converted to IIA-1 by heating and cooling cycles. It is obvious that the driving force for the removal of aqua ligands below 120 ºC in IIA-1 is due to the formation of new bonds between Cu(II) and carboxylate oxygen atom. It appears that repulsive interactions exist in the solidstate after the formation of new Cu-O bonds, which is likely to contribute to the observed behavior.15 However, the solvent medium provided opportunity to reorient these dimeric building blocks to form IIC-2. Further, the diffusion (precipitating) liquid plays a major role in controlling the ratio of IIC-1 and IIC-2. 2-C-4-2. X-ray Powder Diffraction Studies As shown by thermogravimetric studies, the anhydrous IIC-2 has been found to absorb moisture instantly in air and shows the similar thermal dehydration behavior as IIA-1 when TG was recorded after heating and cooling cycle. Figure 2-54. X-ray powder pattern of IIC-2. 161 Chapter (Part C) Figure 2-55. X-ray powder patterns of IIA-1 (bottom) and IIC-2 after heating and cooling cycle (top). X-ray powder diffraction studies and, the powder patterns of IIC-2 (Figure 2-54) after first heating and cooling cycle and IIA-1 (Figure 2-55) further corroborate the observed thermal behavior. A comparison of the XRD powder patterns has provided evidence that the crystal structure of IIC-2 after desolvation and exposure in air converts to the micro tubular IIA-1. Figure 2-56 shows the SEM image of the micro tubular morphology observed in the bulk IIA-1. Figure 2-56. SEM image showing microcrystalline IIA-1. 162 Chapter (Part C) 2-C-5. Summary By changing the combination of solvents for the recrystallization of IIA-1 two different compounds IIC-1 and IIC-2 were obtained. Recrystallization of IIA-1 in DMF/MeCN solvent mixture furnished dark green cubic single crystals of IIC-1 (Cubic space group, Ia-3d, No. 230). The three-dimensional network structure has hexagonal diamondoid architecture (if the net is defined by considering four fused dinuclear units as a single node) with star-like channels along the body diagonal of the unit cell and partially occupied guest water molecules, leaving about 27% empty space in the crystal lattice. Figure 2-57. Single-pot crystallization of IIA-1 furnishing IIC-1 and IIC-2.15b Compound IIA-1 on crystallization from DMF/acetone solvent mixture afforded single crystals of IIC-2 which has one-dimensional hydrogen-bonded polymeric 163 Chapter (Part C) structure in the solid-state (triclinic space group Pī, No. 2). When the precipitating solvent is evaporated from the solution, IIC-1 and IIC-2 slowly converted to microsize tubular crystals of IIA-1. It is interesting to note that simple one-pot crystallization produced crystals (Figure 2-57) that belong to two extreme ends of the International Tables for Crystallography (No.2 and No.230).21 Compared to our previously reported cubic diamondoid14 3D network structures, the hexagonal diamondoid 3D network topology observed in IIC-1 exemplifies the fact that by replacing the substituent on the side arm of the amino acid part, the conformational changes can be induced in the flexible backbone of the reduced Schiff base ligands and thus it is often possible to generate different but closely related structures.14, 15 2-C-6. Experimental H2Scp11 ligand has been prepared according to the procedure described in Part-A. 2-C-6-1. Synthesis of complexes [Cu2(Scp11)2(H2O)2], IIA-1 IIA-1 was prepared according the procedure described in Part-A. [Cu2(Scp11)2].1.5H2O, IIC-1 and [Cu2(Scp11)2(H2O)2]·2Me2CO, IIC-2 A clear dark green saturated solution of IIA-1 in DMF (2.5 mL) was allowed to mix with clear acetone (6 mL) in a test tube through slow diffusion of the later. After three to four days, dark green cubic crystals of IIC-1 and light bluish green rod like single crystals of IIC-2 suitable for X-ray diffraction were obtained in nearly equal 164 Chapter (Part C) amounts. These crystals were separated by hand picking while observing under microscope and characterized. When the acetonitrile was used as a diffusing solvent the dark green cubic single crystals of IIC-1 were obtained. Characterization of [Cu2(Scp11)2].1.5H2O, IIC-1 Anal. Calcd.for C26H32N2O7Cu2: C, 50.3; H, 5.4; N, 4.5. H2O, 4.4. Found: C, 50.0; H, 5.4; N, 4.0; H2O, 4.6 (from TGA). The water content in the crystal structure may be underestimated. IR (KBr, cm-1): υ(OH) 3398; υ(NH) 2934; υas(COO-) 1617, υs(COO-) 1376, υ(phenolic C-O) 1266. UV-Vis (DMF): λmax/nm (ε/dm3 mol-1 cm-1) 368 (750), 654 (150). Characterization of [Cu2(Scp11)2(H2O)2]·2Me2CO, IIC-2 Elemental analysis of the compound IIC-2 was obtained after running TG to show that it absorbed back two water molecules. Anal. Calcd. for (C26H34N2O8Cu2) desolvated IIC-2: C, 49.6; H, 5.4; N, 4.5. Found: C, 49.8; H, 5.1; N, 4.7. IR (KBr, cm1 ): υ(OH) 3429, υ(NH) 2954, υas(CO2-) 1618, υs(CO2-) 1376, υ(Phenolic C-O) 1266. UV-Vis (DMF): λmax/nm (ε/dm3 mol-1 cm-1) 365 (880), 665 (250). TGA: 20.9% [calculated for two H2O and two acetone molecules: 20.4%]. 2-C-6-2. X-ray crystallography The details of the crystal data and structure refinement parameters of IIC-1 and IIC-2 are given below in Table 2-39. 165 Chapter (Part C) Table 2-39. Crystallographic data and structure refinement details Complex IIC-1 IIC-2 Formula C26H32Cu2N2O7 C32H46Cu2N2O10 f.w 611.62 745.79 T/K 223(2) 223(2) λ/Å 0.71073 0.71073 Crystal system Cubic Triclinic Space group Ia-3d (No. 230) Pī (No. 2) a/Å 33.5375(3) 7.5399(6) b/Å 33.5375(3) 10.3300(8) c/Å 33.5375(3) 11.3540(9) α/o 90 81.523(2) β/o 90 73.016(2) γ/o 90 78.365(2) V/Å 37721.8(6) 824.7(1) Z 48 d(cald)/g.cm-3 1.292 1.502 μ/mm-1 1.393 1.349 Reflns. Col. 66509 6784 Ind. Reflns. 2781 4514 Rint 0.0610 0.0183 GooF 1.046 1.022 Final R[I>2σ], 0.0417 0.0434 0.147 0.0866 R1a wR2b a R1 = Σ||Fo| - |Fc||/Σ|Fo|. b wR2 = [Σw(Fo2 - Fc2)2/Σw(Fo2)2]1/2 166 Chapter (Part C) 2-C-7. References 1. a) Kesanli, B.; Lin, W. Coord. Chem. Rev. 2003, 246, 305; b) MacGillivray, L. R.; Subramanian, S.; Zaworotko, M. J. J. Chem. Soc., Chem. Commun. 1994, 1325; c) Zaworotko, M. J. Chem. Soc. Rev. 1994, 283. 2. a) Schmuck, C. Angew. Chem. Int. Ed. 2003, 42, 2448; b) Gardner, G. B.; Venkataraman, D.; Moore, J. 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Chem. 2001, 40, 7003. 17. Wells. A. F. Further Studies of Three-dimensional Nets, ACA Monograph: Washington, DC, 1979, Vol. 8, p 10. 18. O’Keeffe, M.; Hyde, B. G. Crystal Structures 1. Patterns and Symmetry, Mineralogical Society of America: Washington, DC, 1996, p 320. 19. Abourahma, H.; Moulton, B.; Kravtsoy, V.; Zaworotko, M. J. J. Am. Chem. Soc. 2002, 124, 9990. 20. Spek, A. L. Acta. Crystallogr. 1990, A46, C34. 21. Steed, J. W. CrystEngComm. 2003, 5, 169. 169 Chapter Part D Experimental Section 170 Chapter (Part D) 2D-1. General All reagents were commercially available and were used as received otherwise stated. Reagents used for the physical measurements were of spectroscopic grade. Yields are reported with respect to the metal salts. 2D-2. NMR spectroscopy The NMR spectra of the compounds were recorded on a Bruker ACF300FT-NMR machine at 25 °C for 1H and 13 C spectra in appropriate deuterated solvents such as D2O, DMSO, etc. 2D-3. Infrared spectroscopy The IR spectra (KBr pellet) were recorded using FTS165 Bio-Rad FTIR spectrophotometer. IR spectra of both ligands and complexes were recorded in the range of 400 – 4000 cm-1. 2D-4. Electronic spectroscopy The electronic transmittance spectra were recorded on a Shimadzu UV-2501 PC UV-vis spectrophotometer in the wavelength range of 300 – 800 nm using Nujol mulls and in MeOH or DMSO solutions. 2D-5. Optical Rotation Optical rotations were measured on the specified solutions in a 0.1 dm cell at 27°C using a Perkin-Elmer model 341 polarimeter. The concentration of the solutions was 5.5 mg/mL both for the ligands (as sodium salt in MeOH) and complexes (in DMSO). 171 Chapter (Part D) The optical rotation of the ligands was recorded at the wavelength of 365 nm where as for the complexes the measurements were conducted at D wavelength of the D line (578 nm) of Sodium. 2D-6. Magnetic susceptibility measurements Room-temperature magnetic susceptibility measurements were carried out on a Johnson-Matthey Magnetic Susceptibility balance with Hg[Co(SCN)4] as standard. Variable temperature magnetic studies were made using a Quantum Design MPMSXL5 SQUID magnetometer operating in an applied field of 5kOe. Corrections for diamagnetism were made using Pascal’s constants. VT magnetic susceptibility measurements were carried out by Prof. Song Gao at Peking University P. R. China. 2D-7. ESI-MS spectra ESI mass spectra were recorded on Finnigan MAT LCQ Mass Spectrometer using syringe-pump method. The solvents employed were MeOH, DMSO which were of reagent grade. 2D-8. Elemental analysis The elemental analyses were performed in the microanalytical laboratory, Chemistry Department, National University of Singapore. 172 Chapter (Part D) 2D-9. Thermogravimetry Water present in the compounds was determined using a SDT 2960 TGA Thermal Analyzer with a heating rate of °C or 10 °C min-1 from room temperature to 600 °C. The sample size maintained was 7-10 mg per each run. 2D-10. X-ray powder diffraction The X-ray powder diffraction of the samples were recorded using a D5005 Bruker AXS diffractometer with Cu-Kα radiation (λ = 1.5410) at room temperature (25 °C) using a sample size of 70-110 mg. 2D-11. Scanning Electron Microscopy The SEM images were obtained using a Jeol JSM 220A scanning electron microscope using an accelerating voltage of 20 eV. The samples were smeared over a double sided adhesive tape placed over a copper stub. 2D-12. Single crystal X-ray crystallography The diffraction experiments were carried out on a Bruker AXS SMART CCD diffractometer with MoKα ((λ = 0.71073 Å) sealed tube. The program SMART1 was used for collecting frames of data, indexing reflection and determination of lattice parameters, SAINT1 for integration of the intensity of reflections and scaling, SADABS2 for absorption correction and SHELXTL3 for space group and structure determination, least-squares refinements on F2. The space groups were determined from the systematic absences and their correctness was confirmed by successful solution and refinement of structures. All the non-hydrogen atoms were refined anisotropically. All the C-H hydrogen atoms were placed in calculated positions. All 173 Chapter (Part D) the hydrogen atom positions of imine/amine groups, methanol and water molecules were located and their positional parameters were refined in the least-squares cycles. 2D-13. References (1) SMART & SAINT Software Reference manuals, Version 5.0, Bruker AXS Inc. Madison, WI, 1998. (2) Sheldrick, G. M., SADABS software for empirical absorption correction, University of Gottingen, Germany, 1996. (3) SHELXTL Reverence Manual, Version 5.1, Bruker AXS Inc. Madison, WI, 1998. 174 [...]... hydrogen bonds generate 3D hydrogen bonded network connectivity in IIA-4 Hydrogen bond distances and angles are shown in Table 2- 8 A portion of the hydrogen bonding connectivity in IIA-4 has been shown in Figure 2- 21 and Figure 22 2 71 Chapter 2 (Part-A) Figure 2- 21 Packing diagram of IIA-4 Figure 2- 22 A segment of H-bonded 3D network in IIA-4 72 Chapter 2 (Part-A) Table 2- 8 Hydrogen bond distances (Å) and. .. methanol as in IIA-1a and by both aqua ligand and DMF solvent as in IIA-2a giving the Cu-O bond distances in the range 2. 21 3 (2) -2. 660(3) Å The common 1-aminocyclopentanecarboxylate side arm of the ligands in IIA-1a, IIA-2a, IIA-3a and IIA-4 resulted in the formation of five membered rings where as the bridging phenolate oxygen generated four membered Cu2O2 rings 63 Chapter 2 (Part-A) The crystal packing... along a axis displays intermolecular hydrogen bonding between amine hydrogen and lattice methanolic oxygen (N- H···O(5)) and also between methanolic hydrogen and carboxylate oxygen atoms (O(4)-H(4)···O(3) and O(5)H(5)···O (2) ) Carboxylate oxygen atoms of the neighboring molecules involved in weak interactions with each Cu(II) ion in syn-anti fashion giving the Cu···O distance of 2. 885 Å Hydrogen bond... phenolate oxygen atoms The ONO donor set arising from amine nitrogen, phenolate oxygen and one of the carboxylate oxygen atoms completes the tridentate coordination of the ligands to the Cu(II) ions (Figure 2- 13) All these complexes contain phenolato bridged dinuclear Cu2O2 cores with Cu···Cu distance of ca 3 Å With respect to the ligands, IIA-1a, IIA-2a, IIA-3a and IIA-4 contain 1-aminocyclopentanecarboxylate... carboxylate oxygen The Cu-O bond distances due to the coordination of each Cu(II) to the bridging phenolate and carboxylate oxygen atoms in the basal plane fall in the range of 1.93 4 (2) -2. 0 02( 3) Å and 1.87 6 (2) -1.9 82( 7) Å respectively while the bond distances due to Cu -N (amine nitrogen) are observed in the range of 1.95 0 (2) -2. 004(8) Å The apical position is occupied by aqua ligands as in IIA-4, by solvent molecules... transformations used to generate equivalent atoms: a = -x+1,-y+1,-z+1; b = -x,-y,z; c = -x+1,-y+1,-z Table 2- 12 Hydrogen bond distances (Å) and angles (º) for IIA-8 d(H··A) ∠DHA D-H d(D-H) N1 -H1 0.81(17) 2. 38(16) 157(19) 3.14(1) O5 N2 -H2 0. 8 (2) O8 N3 -H3 0.85(18) 2. 13(19) 170(15) 2. 9 7 (2) 2. 4 (2) d(D··A) A 164(18) 3.1 8 (2) O 12 O11-H11C 0.9(3) 1.9(3) 16 5 (26 ) 2. 83(3) O 12 O11-H11D 0. 9 (2) 2. 0 (2) 16 4 (27 ) 2. 8 4 (2) O6 O 12- H12C... (O(4)-H(4)···O(3) and O(5)-H(5)···O (2) ) Hydrogen bond parameters are given in Table 2- 10 Table 2- 10 Hydrogen bond distances (Å) and angles (º) for IIA-6a D-H d(D-H) d(H··A) ∠DHA d(D··A) A Symmetry N1 -H1 1.01(3) 1. 92( 3) 16 7 (2) 2. 905(3) O5 O4-H4 0.71(3) 2. 08(3) 171(4) 2. 77 5 (2) O3 x-1, y, z O5-H5 0.75(3) 2. 11(3) 169(3) 2. 851(3) O2 -x +2, -y+1, -z+1 2- A -2- 2-6 [{Cu2(Sch 12) 2 }2 Cu2(Sch 12) 2(H2O )2] .4H2O, IIA-8 For Z = 3 in... molecule of acetonitrile solvent in the asymmetric unit (Figure 2- 16) Figure 2- 16 A perspective view of the unit cell contents of IIA-2a 66 Chapter 2 (Part-A) Table 2- 3 Selected bond distances (Å) and bond angles (º) for IIA-2a Cu(1)-O(4) 1.94 9 (2) Cu(1) -N( 1) 1.9 62( 3) Cu(1)-O (2) 1.964(3) Cu(1)-O(1) 2. 0 02( 3) Cu(1)-O(8) 2. 230(3) Cu(1)-Cu (2) 3.0 428 (6) O(4)-Cu(1) -N( 1 68 .25 (13) O(4)-Cu(1)-O (2) 1 02. 42( 11) N( 1)-Cu(1)-O (2) ... shown in Figure 2- 26 and these (4, 4) nets are well known in coordination polymeric structures .29 Table 2- 11 Selected bond distances (Å) and bond angles (º) for IIA-8 Cu(1)-O (2) 1.910( 12) Cu(1)-O(1) 1.948( 12) Cu(1)-O(1)a 1.973( 12) Cu(1) -N( 1) 1.980(15) Cu(1)-O(6) 2. 355( 12) Cu (2) -O(5) 1. 929 ( 12) b Cu (2) -O(9) 2. 513(13) Cu (2) -O(4) 1.957(11) O(1)-Cu(1)a 1.973( 12) O(4)-Cu (2) b 1.957(11) Cu(3)-O(7)c 1.957( 12) ... Figure 2- 26 Portion of packing diagram of IIA-8 showing the 2D connectivity The hydrogen atoms and lattice water molecules have been omitted for clarity The axial bonding of the carbonyl oxygen atoms O6 and O9 from neighboring dimeric units to Cu1 and Cu2 centres produces a 2D coordination polymeric structure 76 Chapter 2 (Part-A) and the interdimer connectivity leads to the formation of 2D (4, 4) network . Oxidation of mono- and diphenol-containing neurotransmitters such as dopamine, epinephrine, norepinephrine and serotonin have been found associated with the Fe(II) and Cu(II) centered redox. in IIA-2a giving the Cu-O bond distances in the range 2. 21 3 (2) -2. 660(3) Å. The common 1-aminocyclopentanecarboxylate side arm of the ligands in IIA-1a, IIA-2a, IIA-3a and IIA-4 resulted in. base ligands display tridentate coordination mode with binucleating ability through bridging phenolate oxygen atoms. The ONO donor set arising from amine nitrogen, phenolate oxygen and one of