Metal Hydrazine Cinnamates. Synthesis and Characterization

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Chapter 2.3. Physico-chemical techniques:

The instrumental techniques used in the present study are, Infrared spectroscopy (IR), Thermo Gravimetry-Differential Thermal Analysis/Differential Scanning Calorimetry (TG-DTA/TG-DSC), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDX).
2.3.1 Infrared spectral analysis:

The infrared spectrum of a molecule is considered to be its unique and characteristic physical property. The basic interpretation of an IR spectrum leads to the characterization and identification of the sample. The IR 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. Bonds with different bond lengths, strength, bending and torsional characteristics absorb different wavelengths of IR radiation, and the absorption maxima maybe characteristics of the types of linkages present; the absorption generally occurs in the 4000-400 cm-1 region of the spectrum.
Infrared radiation is capable of affecting both rotational and vibrational energy levels in the molecules [212, 213]. Some molecular vibrations are characteristic of the entire molecule, whereas others are associated with certain functional groups. IR spectra of solids are usually complex with a considerable number of peaks, each corresponding to a particular vibrational transition. Since a complete assignment of all the peaks to the specific vibrational modes is possible, straight forward identification of specific functional groups, covalently bonded linkage such as hydroxyl groups, trapped water, oxyanions, carbonates, nitrates, sulphates etc., and the modes of binding of the ligand to the metal ion can be made. As such, infrared spectroscopy has become an important technique in the elucidation of the structure of organic compounds and metal complexes. Plots of IR spectra show the frequency or wave number of incident radiation on the x-axis and percentage of transmittance on the y-axis. The wave number unit is used more often since it is directly proportional to the energy of vibration and such modern IR instruments are linear in cm-1 scale.
In the present study, the IR spectra of all the complexes were recorded by the KBr disc techniques using Perkin Elmer 597/1650 spectrophotometer.
2.3.2. Thermogravimetric analysis (TGA):

The thermal analysis is a technique in which the physical and chemical transitions of a substance are recorded as a function of temperature. In thermogravimetric analysis (TGA), the mass of the sample is recorded continuously as a function of temperature. TGA curves are specific for a given compound or system due to the unique sequence of physiochemical reactions that occur at definite temperatures and at rates controlled by the molecular structure. Changes in the mass of the sample take place as a result of the rupture and formation of various chemical bonds at higher temperatures, which leads to the evolution of volatile products or formation of reaction products.
In present study, the simultaneous TG-DTA experiments were carried out in Shimadzu DT40, Stanton 781 and STA 1500 thermal analyzers. Thermal analyses were carried out in air at the heating rate of 10°C per minute using 5-10 mg of the samples. Platinum cups were used as sample holders and alumina as reference. The temperature range was ambient to 700°C.
TG-DSC was performed using the Universal V4.5A TA Instrument in a temperature range of 50-700 °C with a heating rate of 20 °C/min.
2.3.3. Scanning Electron Microscopy (SEM) - Energy Dispersive X-ray analysis (EDX):

SEM is another powerful technique used to study the morphology (surface structures) of nanoparticles. SEM is able to provide 3-dimensional images of the objects, since it does not record the electrons passing thorough the specimen; on the other hand, it records the secondary electrons that are released from the sample as a result of interaction with falling electron beam. In SEM, high-energy electrons impinging on a solid sample experience elastic scattering by atomic nuclei and inelastic scattering by sample electrons. Inelastic scattering results in the transferring of energy from the high-energy electrons to the sample electrons. Thus, sample electrons can be excited to high-energy states. Some of the excited electrons travelling to the sample surface can be emitted out of the sample as secondary or Auger electrons. By collecting these low energy electrons, high-resolution surface images can be obtained to give morphological information about the sample.
Energy dispersive X-ray analysis is a chemical microanalysis technique used for elemental composition analysis. This technique is used in conjunction with scanning electron microscopy (SEM). The EDX technique detects X-rays emitted from the sample during bombardment by an electron beam to characterize the elemental composition. When the sample is bombarded by the SEM's electron beam, electrons are ejected from the atoms comprising the sample's surface. The resulting electron vacancies are filled by electrons from a higher state, and an X-ray is emitted to balance the energy difference between the two electronic states. The X-ray energy is characteristic of the element from which it was emitted. The spectrum of X-ray energy versus counts is evaluated to determine the elemental composition of the samples.
In the present study, SEM and EDX of the samples were performed with a HITACHI Model S-3000H.