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Chapter II Experimental Chapter II Experimental 2.1 Chemicals and Reagents 2.1.1 Solvents The solvents used in the present investigation are dichloromethane, chloroform, petroleum ether, methanol, ethanol, diethyl ether, acetone and acetonitrile were obtained from sd-fine and were purified and dried by conventional methods [1]. 2.1.2 Other reagents ¾ Methyl anthranilate, benzaldehyde, p-anisaldehyde, p-nitrobenzaldehyde, nBu4NClO4 from Alfa Aesar. ¾ Diethylether, benzoyl chloride, perchloric acid, hydrazine hydrate from Sd-fine. ¾ Triphenylphosphine, cis-1,2-bis (diphenylphosphino)ethane from Aldrich. ¾ CuCl2.2H2O, Cu(NO3)2.2.5H2O, CuCO3, Cu2O, NaHCO3, Na2SO3, HBF4 from E-Merck, India 2.2 Synthesis 2.2.1. Metal salts 2.2.1.1 Synthesis of copper(I) chloride The copper(I) chloride was prepared according to literature procedure [2]. To the stirred solution of 10 g of copper(II) chloride [CuCl2.2H2O] in 10 ml water, a solution of 7.6 g anhydrous sodium sulphite (Na2SO3) in 50 ml water was added slowly at room temperature. The dark brown coloured copper(II) chloride solution was stirred till the colour disappears and white solid of copper(I) chloride. After complete addition of sodium sulphite and stirring, CuCl settles readily with greenish supernatant liquid. The precipitate along with supernatant liquid are then poured in to about a liter of water containing 1 g of Na2SO3 and 2 ml Conc. HCl. The mixture was stirred well and allowed to stand until all the CuCl has settled. The precipitate of CuCl is filtered on suction and quickly washed with dilute sulphurous acid. The CuCl was 43 Chapter II Experimental washed 4-5 times with 20 to 25 ml of glacial acetic acid, again with absolute alcohol and six times with 15 ml anhydrous ether. After last washing ether is removed and white solid transferred to dry watch glass and placed in oven for 20-25 minute. 2.2.1.2. [Cu(MeCN)4]NO3 The Cu(CH3CN)4NO3 was prepared according to literature procedure [3]. To a solution of Cu(NO3).2.5H2O (0.03 g) in minimum distilled water, equal volume of acetonitrile and few Cu strips were added. The whole solution was stirred at room temperature until it turns colourless. The solid product obtained was filtered and dried under vacuum. 2.2.1.3. Synthesis of [Cu(MeCN)4]ClO4 The copper(I) salt Cu(MeCN)4]ClO4 was prepared according to the literature procedure [4]. Step I: 1g of CuCO3 was taken in 100 ml beaker and HClO4 was added until effervescences ceases. It was diluted with distilled water and concentrated up to 1/6 of the volume. Keeping to overnight, the crystals of Cu(ClO4)2 were formed. [Precaution- Cu(ClO4)2 is explosive in nature so it should not be too concentrate]. Step II: 20 ml distilled acetonitrile was taken with metallic Cu pieces, 1 spatula of blue crystals Cu(ClO4)2 was added and the solution was refluxed till the blue colour disappear. On cooling, white crystals of copper acetonitrile perchlorate comes out. Metallic Cu reduces Cu(II) to Cu(I). The product was stored in acetonitrile as it is very hygroscopic in nature. 2.2.1.4. Synthesis of [Cu(MeCN)4]BF4 The [Cu(MeCN)4]BF4 was prepared according to literature procedure with slight modification [5]. 1.43 g of Cu2O was added to little acetonitrile, the solution was stirred till the Cu2O dissolved completely. To the dissolved solution, 0.627 g of HBF4 44 Chapter II Experimental was added and the solution was further stirred for 2 hrs, a white crystals of [Cu(MeCN)4]BF4 appears. The residue was filtered, washed with absolute alcohol and with 15 ml anhydrous ether. After washing white solid transferred to dry watch glass and placed in oven for 20-25 minute. The product was kept in acetonitrile as it is very hygroscopic in nature. 2.2.2. Synthesis 2-aminobenzoylhydrazide 2-aminobenzoylhydrazide was synthesized by adopting and modifying the reported method in literature [6, 7] as shown in Scheme 2.1. Hydrazine hydrate (0.625 g, 12.5 mmol) in ethanol was added drop wise to the stirred solution of methyl anthranilate (1.29 g, 10 mmol) in ethanol and stirred for 1.5 h at 500C. The mixture was then refluxed for 4 h on water bath. The compound separated on standing over night was filtered and washed with distilled water. The pure 2-aminobenzoylhydrazide was obtained by recrystallization from hot ethanol (Yield. 77%, M.P. Thert. 119 °C, Obs. 121 °C). O O OCH3 NH2 NH2NH2 .H2 O Reflux 4 hrs N H NH2 NH2 Scheme 2.1: Synthesis of 2-aminobenzoylhydrazide 2.2.3. Synthesis of Schiff base ligands: 2.2.3.1. Synthesis of 2(4-substituted-phenyl)-3(4-substituted-benzylamino)-1,2dihydro-quinazolin-4(3H)-one (L1-3) 2-phenyl-3-(benzylamino)1,2-dihydroquinazolin-4-(3H)-one (L1), 2-(4'-methoxyphenyl)-3-(4''-methoxybenzylamino)-1,2-dihydroquinazolin-4-(3H)-one (L2) and 2(4'-nitrophenyl)-3(4''-nitrobenzylamino)-1,2-dihydroquinazolin-4-(3H)-one (L3) were prepared by adopting and modifying the method described in literature [8,9] as shown in Scheme 2.2. 45 Chapter II Experimental To a solution of aromatic aldehydes (2 mmol, 0.212 g, benzaldehyde; 0.272 g, panisaldehyde and 0.302 g, p-nitrobenzaldehyde) was added in an ethanolic solution of 2-aminobenzoylhydrazide (1 mmol, 0.151 g) and the mixture was refluxed for 2h. The separated solid was collected by filtration, washed with cold ethanol and dried in vacuo to give the yellow product. This was then characterized by infrared, 1H NMR and mass spectral studies. (Yield: 86%). R O O N H NH2 NH2 O H + ethanol 2 R Reflux, 4 hrs N N N H R R = H, OCH 3 , NO 2 Scheme 2.2: Synthesis of 2-(4-substituted-phenyl)-3(4-substituted-benzylamino)-1,2- dihydro-quinazolin-4(3H)-one L1: Yield 78%; elemental analysis (C, H, N wt %) Anal. Cal. For C21H15N3O: C, 77.52; H, 4.65; N, 12.91; Found: C, 77.36; H, 4.48; N, 12.72; IR (KBr) (cm-1): 3276, υ(NH); 1665, υ(C=O); 1625, υ(C=N); UV-Vis. (CH2Cl2) λmax (nm): 272, 288; 1H NMR (CDCl3) (400 MHz): 9.19 (s, HC=N), 6.70-7.30 (m, Ar-H), 7.97 (m, N-H). L2: Yield 81 %; elemental analysis (C, H, N wt %) Anal. Cal. For C23H21N3O3: C, 71.30; H, 5.46; N, 10.85; Found: C, 71.12; H, 5.32; N, 10.70; IR (KBr) (cm-1): 3280, υ(NH); 1667, υ(C=O); 1622, υ(C=N); UV-Vis (CH2Cl2) λmax (nm): 275, 285; 1H NMR (CDCl3) (400 MHz): 9.29 (s, HC=N), 6.78-7.42 (m, Ar-H), 7.98 (m, N-H), δ 3.45 (s, OCH3). L3: Yield 83 %; elemental analysis (C, H, N wt %) Anal. Cal. For C21H15N5O5: C, 60.43; H, 3.62; N, 16.78; Found: C, 71.12; H, 5.32; N, 10.70; IR (KBr) (cm-1): 3285, υ(NH); 1668 υ(C=O); 1624, υ(C=N); 1565, 1345, υ(NO2); UV-Vis (CH2Cl2) λmax (nm): 278, 285; 1H NMR (CDCl3)(400 MHz): 9.32 (s, HC=N), 6.80-7.45 (m, Ar-H), 7.96 (m, N-H). 46 Chapter II Experimental 2.3 Analysis of the complexes 2.3.1 Estimation of Carbon, Hydrogen and Nitrogen The carbon, hydrogen, nitrogen and sulphur content provide correct picture about the molecular formula as well as the purity of the compounds. Carbon, hydrogen, nitrogen and sulphur content of the complexes were estimated on a Thermo Finnegan FLASH EA-112 CHNS analyzer at IISc, Bangalore. 2.4. Physico-chemical methods: 2.4.1. IR spectroscopy: The vibrational spectrum of a molecule is considered to be a unique physical property and is characteristic of the molecule. As such, the infrared spectrum can be used as a fingerprint for identification by the comparison of the spectrum from an ‘‘unknown’’ with previously recorded reference spectra. The qualitative aspects of infrared spectroscopy are one of the most powerful attributes of this diverse and versatile analytical technique. Over the years, much work has been published in terms of the fundamental absorption frequencies (also known as group frequencies) which are the key to unlocking the structure spectral relationships of the associated molecular vibrations. Applying this knowledge at the practical routine level tends to be a mixture of art and science. In the most basic terms, the infrared spectrum is formed as a consequence of the absorption of electromagnetic radiation at frequencies that correlate to the vibration of specific sets of chemical bonds from within a molecule. First, it is important to reflect on the distribution of energy possessed by a molecule at any given moment, defined as the sum of the contributing energy terms (Equation 1): E total = E electronic + E vibrational + E rotational + E translational 47 (1) Chapter II Experimental The translational energy relates to the displacement of molecules in space as a function of the normal thermal motions of matter. Rotational energy, which gives rise to its own form of spectroscopy, is observed as the tumbling motion of a molecule, which is the result of the absorption of energy within the microwave region. The vibrational energy component is a higher energy term and corresponds to the absorption of energy by a molecule as the component atoms vibrate about the mean center of their chemical bonds. The electronic component is linked to the energy transitions of electrons as they are distributed throughout the molecule, either localized within specific bonds, or delocalized over structures, such as an aromatic ring. In order to observe such electronic transitions, it is necessary to apply energy in the form of visible and ultraviolet radiation (Equation 2): E = hυ Frequency/ energy (2) The fundamental requirement for infrared activity, leading to absorption of infrared radiation, is that there must be a net change in dipole moment during the vibration for the molecule or the functional group under study. The IR spectroscopy provides information on whether ligand molecules have coordinated to transition metal cations; if different patterns appear in the free or in the chelated state, or if characteristic bands exhibit defined shift upon chelation. FTIR spectroscopy in the framework region (4000-400 cm-1) provides additional information about the structural details of the support [10, 11]. Infrared spectra of the ligands as well as their metal complexes were recorded on Perkin Elmer FTIR-100 spectrometer as KBr pellets in the 4000-400 cm-1 spectral range. 2.4.2. UV-visible spectroscopy: The UV-Vis Spectroscopy is known to be very sensitive and useful technique for the identification of the electronic state of the metal atom as well as ligand geometry 48 Chapter II Experimental in complexes. It gives information about the d-orbital splitting through the d-d transitions and the ligand-metal interaction through the ligand to metal charge-transfer transitions. The electronic spectra of the ligands and their metal complexes were recorded on a Shimadzu UV-3600 UV-visible NIR spectrophotometer in the range 200 to 1100 nm. Quartz cell with 10 mm size was used. The radiant energy sources are the deuterium lamp for the ultraviolet region and a tungsten lamp for the visible region. A cell containing the pure solvent was used as reference. All the measurements were made at room temperature. 2.4.3. 1H NMR spectroscopy: Nuclear magnetic resonance is powerful tool for investing nuclear structure. Nuclear magnetic resonance is technique that enables us to shape and structure of molecules. In particular it reveals the different chemical environment of the various forms of hydrogen present in molecule, from which we are dealing. It is method of both qualitative and quantitative analysis. 1 H NMR spectra were recorded on a Bruker ACF 300 MHz spectrometer using [TMS(CH3)4Si] as the internal reference. Chemical shifts were measured on the δ (ppm) scale and are reported in ppm. 2.4.4. Cyclic voltammetry Cyclic voltammetry is a technique used to investigate the electrochemical behavior of the complexes. Cyclic voltammetry consists of cyclic potential of an electrode immersed in an unstirred solution across two limits, and measuring the resultant current. The cyclic voltammogram is obtained by measuring the current at the working electrode during the scan. When the applied potential is sufficiently strong to reduce the complex a cathodic current is produced and the process occurring as [Complex] + e- [Complex]49 Chapter II Experimental The cathodic current continues to increase until the concentration of complex at the electrode surface is substantially diminished; causing the current to peak at Ec. The current then decays as the solution surrounding the electrode is depleted of [complex] when the electrode becomes a sufficiently strong oxidant, the [complex]which has been accumulating can be oxidized causing an anodic current, peak at Ea. [Complex]+ + [Complex] e- The forwarded scan produces a new oxidation state; the reverse scan gives information on the stability of the new complex. Cyclic voltammetry can be used to investigate the electronic communication between metal centers in a complex. If two or more metal centers can interact via intervalence charge transfer (IVCT) then they will have different redox potentials, as the oxidation of one center will make it more difficult to oxidize another centre; this may result in different waves in the voltammogram. Fig. 2.3: Schematic diagram of cyclic voltammetry experiment Cyclic voltammetry measurements of the ligands and their complexes were performed with Electrochemical Quartz Crystal Microbalance CHI-400. A three 50 Chapter II Experimental electrode configuration, consisting of Pt disk working electrode, Pt wire counter electrode and Ag/AgCl reference electrode containing aqueous 3M KCl were used. All potentials were converted to SCE scale. All measurements were carried out in CH2Cl2 solution at room temperature using tetrabutylammonium perchlorate (TBAP) as supporting electrolyte with scan rate 50 mVs-1. 2.4.5. X-ray diffraction study: The most powerful tool for the characterization of coordination solids is the single crystal X-ray crystallography. This technique provides us with an accurate account of the structure and properties of materials in crystalline state. Additional advanced analytical and graphical tools associated with this process allows for an in-depth study of the chemistry of materials and provides us with the means to effectively communicate these results to others. In the following paragraphs, we will present a brief introduction to crystallography and X-ray diffraction as well as some key concepts and terms that are used throughout this dissertation. The term crystallography, itself, is the study of the structure and properties of the crystalline state. The notion of what a crystal really is might be based solely on visual observations, describing crystals as having flat surfaces with sharp edges such as seen with the precious gems or the all too common quartz crystals. This definition breaks down when we consider all the crystalline solids, including polycrystalline solids with crystals so small that the material more resembles an amorphous powder, than that of a crystalline solid. A more precise definition is that a crystal consists of atoms that are arranged in a three-dimensional periodically repeating pattern. These patterns of atoms, as they combine to form molecules, which in turn form patterns of molecules, are defined by sectioning off the smallest unit of the solid that repeats over and over again in regular intervals. Each of 51 Chapter II Experimental these points, called the lattice points, have identical positions within the net with each point having exactly the same surroundings. Other lattice points in this design can easily be selected and would be just as valid of choice. Of course, our crystalline solids reside in a three-dimensional net. We can adjust our design by simply adding depth to our net, which generates a series of identical parallelepipeds with definite a, b and c sides and corresponding α, β, and γ angles. Each of these individual parallelepipeds, are the defining feature of our crystalline solid and are called the unit cell of the structure. The contents within a unit cell repeat over and over again and, if we know the atomic arrangement inside a unit cell, we then know the atomic arrangement of the entire crystalline solid. Smallest repeating collection of atoms unique for every structure is called the asymmetric unit. Fig. 2.4 The Unit Cell showing the a, b and c sides as well as the corresponding α, β, and γ angles. The asymmetric unit is the most basic form of the crystalline structure as each atom in this unit are related to all the other atoms in the crystal via a variety of symmetry elements of which we will explore in greater detail below. Every unit cell is classified into one of seven crystal systems, each having symmetrical restrictions placed on the lattice vectors, providing each system with distinctive and unique geometric 52 Chapter II Experimental parameters. The triclinic system, for example has no restrictions placed on the unit cell dimensions, while the monoclinic is similar with the exception that α = λ = 90°. As all possible centering occurrences are taken into account, these seven crystal systems develop into fourteen Bravais lattices. These types of centering include body centering (symbol I), C-centered (symbol C), and the centering of all four faces as face-centered (symbol F). A cell lacking any type of centering is designated as a primitive (symbol P) cell. The seven crystal systems and the restrictions placed on the axial systems can be seen in Table 2.1. Table 2.1 The Seven Crystal Systems Crystal system Restriction of the axial system Triclinic a ≠ b ≠ c, α≠β≠λ Monoclinic a ≠ b ≠ c, α = λ = 90°, β > 90° Orthorhombic a ≠ b ≠ c, α = β = λ = 90° Tetragonal a = b ≠ c, α = β = λ = 90° Trigonal a = b = c, α = β = λ ≠ 90° Hexagonal a = b, α = β = 90°, λ = 120° Cubic a = b = c, α = β = λ = 90° A single crystal of complex suitable for X-ray analysis was obtained by slow diffusion of diethyl ether into the dichloromethane solution of complex. The intensity data were collected on a Nonius MACH-3 four-circle diffractometer with graphitemonochromatized MoKα radiation. The structure was solved by direct methods using the SHELXS 93 program and refined by using SHELXL 97 software [12-14]. The non-hydrogen atoms were refined with anisotropic thermal parameters. All of the hydrogen atoms were geometrically fixed and refined using a riding model. 53 Chapter II Experimental References [1] D.D. Perin, W.L.F. Armarego, D.R. Perin, Purification of Laboratory Chemicals, Pergamon Press, Oxford, U.K. (1981). [2] A.I. Vogel, Text book of practical organic chemistry, third Ed., Woolwich Polytechnic, London, (1955) 190. [3] D. Li, Inorg, Chem. Commun. 6 (2003) 469. [4] B.J. Hathaway, D.G. Holah, J.D. Postlethwaite, J. Chem. Soc. Dalton trans, (1961) 3215. [5] G.J. Cubas, Inorg. Synth. 19 (1979) 90. [6] S. Ghosh, A. Malti, N. Pavalram, P. Vedanathan, R. Revathi, Biol. Pharma. Bull. 26 (2003) 557. [7] S. Ghosh, A. Malti, Proc. Ind. Acad. Sci. (Chem. Sci.) 98 (1987) 185. [8] F. Fulop, M. Simeonov, K. Philaja, Tetrahedron, 48 (1992) 187. [9] K.B. Gudasi, S.A. Patil, R, Vadavi, R.V. Shenoy, M. Nethaji, Trans. Met. Chem. 31 (2006) 586. [10] S.K. Ramalingam, S. Soundarajan, J. Inorg. Nucl. Chem. 29 (1967) 1763. [11] A. Earnshaw, Introduction to Magneto Chemistry, Academic Press, New York, (1980) 80. [12] H. Zeinab, E.L. Wahab, Spectrochimica Acta Part A. 67 (2007) 25. [13] G.M. Sheldrick, Acta Crystalogr. A 46 (1990) 467. [14] G.M. Sheldrick, Siemens SHELXTL, version 5.03; Siemens Crystallographic Research Systems, Madison, WI 53719 (1994). 54