Some new coordination polymers have been synthesized by combining adipyl bis-biuret and azelyl bis-biuret with metals of first transition series viz Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). They were characterized by elemental analysis, infrared and reflectance spectral and magnetic studies. A detailed thermal study was carried out and thermal stability compared. The results obtained have been discussed.
Cobalt(II) complexes of tetradentate Schiff bases of the type CoL [H2L=C20H16N2O2 (H2dsp), C21H18N2O2 (H2dst), C20H15N3O4 (H2ndsp) and C16H16N2O2 (H2salen)] have been synthesized and characterized by UV-visible, IR, and magnetic studies. Various thermodynamic parameters have been calculated for the decomposition step using TG/DTA. C20H14N2O2Co complex has the minimum and C16H14N2O2Co complex has the maximum activation energy.
The thermal decomposition using TG, DTG and DTA, of seven complexes of the types Bu2SnL(I) and Bu2SnL(II) (where H2L(I)=Schiff base derived from acetylacetone and glycine [H2L-1(I)] or L-leucine [H2L-4(I)] or methionine [H2L-5(I)] or phenylglycine [H2L-6(I)]; H2L(II)=Schiff base derived from o-hydroxynaphthaldehyde and β-alanine [H2L-2(II)] or DL-valine [H2L-3(II)] or L-leucine [H2L-4(II)] is shown to fall into one of two categories, viz, (1) Bu2SnL(I) complexes that decompose without melting to give SnO as the final tin containing product, (2) Bu2SnL(II) complexes that melt and then decompose to give SnO. Mathematical analysis of TG data using Coats-Redfern equation,
Horowitz-Metzger equation, and Fuoss method shows that the first order kinetics is applicable in all the complexes except
Bu2SnL-2(II). Kinetic parameters such as the energy and entropy of activation and pre-exponential factor are reported.
A number of ionic chelate complexes of maltol(A) and hafnium(IV) the type[(η5−C5H5)2HfL]+[MCl3]− (B) [HL=maltol; M=Zn(II), Cd(II), Hg(II), Cu(II)]have been synthesized and characterized by spectral studies (IR, UV, 1H NMR and 13C NMR). The stoichiometry of the complexes has been confirmed by conductance measurements. Thermogravimetric (TG) and differential
thermal analytical (DTA) studies have been carried out for these complexes and from TG curves, the order, apparent activation
energy and apparent activation entropy of the thermal decomposition reactions have been elucidated .The order in each case
has been determined to be one and the degree of spontaneity and lability have been inferred from the apparent activation energy
and entropy, respectively. Thermal parameters have been correlated with some structural aspects of the complexes concerned.
From differential thermal analysis curves, the heat of reaction has been calculated.
Summary Cobalt(II), nickel(II) and copper(II) complexes of some aroylhydrazone Schiff’s bases derived from isoniazide (hydrazide of isonicotinic acid) with p-hydroxybenzaldehyde; 2,4-dihydroxybenzaldehyde or 2-hydroxy-1-naphthaldehyde are prepared and characterized. The study reveals that the ligands coordinate in the keto form. That transformed to the enol through the loss of HCl upon heating the solid complexes. The copper(II) complexes are thermochromic in the solid-state while the cobalt(II) complex, 3 of 2,4-dihydroxybenzaldehyde moiety is solvatochromic in hot DMF. The chromisms obtained were discussed in terms of change in the ligand field strength and/or coordination geometry.
The nitrate complexes of copper, nickel and zinc with diethylenetriamine (dien) i.e. [Cu(dien)2](NO3)2, [Ni(dien)2](NO3)22H2O and [Zn(dien)2](NO3)2 have been prepared and characterised. Thermal studies were undertaken using TG-DTG, DSC, ignition delay (tid) and ignition temperature (IT) measurements. Impact sensitivity was measured using drop mass technique. The kinetic parameters for both non-isothermal
and isothermal decomposition of the complexes were evaluated by employing Coats-Redfern (C-R) method and Avrami-Erofeev (A-E)
equations (n=2 and 3), respectively. The kinetic analysis, using isothermal TG data, was also made on the basis of model free isoconversional
method and plausible mechanistic pathways for their decomposition are proposed. Rapid process was assessed by ignition delay
measurements. All these complexes were found to be insensitive towards impact of 2 kg mass hammer up to the height limit (110
cm) of the instrument used. The heat of reaction (?H) for each stage of decomposition was determined using DSC.
Thermal studies have been carried out on trans-[Co(NH3)4Cl2]X · YH2O complexes (whereX=IO3, BrO3, NO3, or NO2 andY=0, 1, or 2) in an effort to find cases of trans to cis isomerization as occurs for the iodate. No evidence of isomerization was found for any of the other compounds. The complexes decompose in a series of steps and these reactions have been identified and kinetic parameters determined.
Ionic chelate complexes of kojic acid(I) and hafnium(IV) of the type [(η5-C5H5)2HfL]+[MCl3]– (II)[HL=kojic acid; M=Zn(II), Cd(II), Hg(II), Cu(II)] have been synthesised and characterised by spectral studies (IR, UV, 1H NMR and 13CNMR). Thermogravimetric (TG) and differential thermal analytical (DTA) studies have been carried out for these complexes
and from the TG curves, the order and apparent activation energy for the thermal decomposition reactions have been elucidated.
The various thermal studies have been correlated with some structural aspects of the complexes concerned. From DTA curves,
the heat of reaction has been calculated.
A free-base tetraphenyl porphyrin (TPP) and its corresponding metalloporphyrins (MTPP) where M = Co, Fe and Sn were synthesized
and characterized by UV–visible spectroscopy, FTIR and 1Hnmr spectroscopy. Thermal studies of these porphyrins were carried out in synthetic air from room temperature to 800 °C using
thermal analyser. The residues of MTPP after thermal treatment were qualitatively analysed, which showed the presence of corresponding
metal oxides. Further, the above MTPP were subjected to thermogravimetry–evolved gas and mass spectrometry (TG–EGA–MS) analysis
for the detailed information about evolved gases at their corresponding decomposition temperatures. This information may be
used to predict the probable mechanism for ring opening of the macromolecular porphyrins.
Eight N-substituted maleic acid monoamide derivatives were studied by DSC, TG (DTG) and IR techniques. The thermal studies revealed that the compounds containing a free carboxyl group start to decompose before melting, and the decomposition continues in the melt phase as the temperature is elevated. This was explained by the presence of dimers involving strong intermolecular hydrogen-bonds. This assumption concerning the structure was supported by the results of the IR spectroscopic studies.