Studies on Transition Metal Chelates of some Tridentate Aroylhydrazones

The ability of aroylhydrazones to bind with transition metals is a developing area of research interest and the coordinating properties of hydrazones can be tuned by the appropriate choice of parent aldehyde or ketone and the hydrazide. So in the present work we selected four different aroylhydrazones as principal ligands. Introduction of heterocyclic bases like 1,10-phenanthroline, 2,2′-bipyridine, 3-picoline and pyridine leads to the syntheses of mixed ligand metal chelates which can cause different bonding modes, spectral properties and geometries in coordination compounds. The importance of aroylhydrazones and their complexes in various fields and their interesting coordinating properties stimulate our interest in the investigation of transition metal chelates with four different aroylhydrazones. The aroylhydrazones selected are 4-benzyloxy-2-hydroxybenzaldehyde-4-nitrobenzoylhydrazone dimethylformamide monosolvate, 5-bromo-2-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone dihydrate methanol monosolvate, 4-diethylamino-2- hydroxybenzaldehyde nicotinoylhydrazone monohydrate and 2-benzoylpyridine- 4-nitrobenzoylhydrazone. The selection of 4-benzyloxy-2-hydroxybenzaldehyde- 4-nitrobenzoylhydrazone was based on the idea of developing ligands having D-π-A general structure, so that the proligand and metal complexes exhibit NLO activity. Hence it is interesting to explore the coordinating capabilities of the synthesized hydrazones and to study the NLO activity of hydrazones and some of the metal complexes.

Selective Methyl Tert-Butyl Ether Synthesis over Metal Exchanged Pillared Clays

Iron and mixed iron aluminium pillared montmorillonites prepared by partial hydrolysis method was subjected to room temperature exchange with transition metals of the first series. The materials exhibit good structural as well as thermal stability. Exchanged metals were found to be present inside the porous network, in the environs of the pillars. Mixed pillaring resulted in the intercalation of Al 13 like polymers in which Al is partially substituted by Fe. The acidic structure was followed by temperature programmed desorption of ammonia and cumene cracking test reaction. Weak and medium sites overshadow the strong sites in all systems. However, exchange with metals increases the number of strong sites. The prepared materials are efficient catalysts for gas phase MTBE synthesis. The catalytic activity can be well correlated with the total amount of weak and medium acid sites.

Surface properties and catalytic activity of phosphate modified zirconia

Preparation and physico-chemical characterization or phosphate modified zirconia systems and their application to Friedel-Crafts benzylation and benzoylation of toluene have been reported. The influence of transition metals on the surface properties and catalytic activity has also been discussed.

Characterisation of the acid-base properties of pillared montmorillonites

Iron and mixed iron aluminium pillared montrnorillonites prepared by partial hydrolysis method were subjected to room temperature exchange with transition metals of the first series. The resulting materials were characterised by different spectroscopic techniques and surface area measurements. About 1-3% transition metals were incorporated into the porous network. The structural stability of the porous network was not affected by exchange. XRD and AI NMR spectroscopy evidenced the presence of iron substituted Al13 like polymers in FeAl pillared systems. Acidity and basicity benefited much as a result of metal exchange. Acidity and basicity were quantified by model reactions, viz., cumene cracking and cyclohexanol decomposition respectively. The presence of basic sites in otherwise acidic pillared clays, though diminutive in amount can be of much importance in acid base catalysed reactions.

Organic Synthesis Mediated by Heterogeneous Catalysts

Catalysis is a technologically important field which determines the quality of life in future. Catalyst research in pharmaceutical industry,fine chemical synthesis and emission control demands supported catalysts in bulk quantities.In the present work it was observed that clay supported catalysts mentioned in various chapters could also be used for the synthesis of similar molecules. The K10Ti catalyst can be used for the synthesis similar substituted imidazole derivatives under solvent free conditions and synthetically important Mannich bases of substrates containing various substitutes.Al-pillared saponite can be used for acetalation of other polyhydroxy compounds like glycerol,mannitol etc.Cu-Pd KSF catalyst has found application in C-C bond forming reactions which can be applied to other reactions and similar methods can be adopted for the synthesis of other catalyst by changing the transition metals. Montmorillonite K10 catalysed synthesis of triarylpyridines can be extended to the synthesis tetrasubstuted pyroles.K10Ti can also be utilized for the synthesis of similar heterocycles.

Studies on Catalysis by Titania

Scientists throughout the world are in search of a better methodology to reduce the use of environmentally hazardous chemicals common in industries .A significant contribution in this field is given by different redox catalysts in oxidation reactions. The oxidation of organic substrates represents one of the most important industrial chemical reactions, explaining the significant efforts invested in the research and development of new heterogeneous catalysts with increased activities and selectivities in these type reactions[l-4|. Hence liquid phase reactions like epoxidation of cylcohexene and hydroxylation of phenol were carried out with a new outlook in the challenge using CeO2/TiO;; and CuO/TiO2 catalysts denoted as TiO2-Ce as TiO2-Cu respectively in this work. Also different wt% of metals incorporated titania catalysts like 3, 6, 9 wt% CeO2/TiO; and CuO/TiO;were subjected to the present study .The interaction between metal oxides and the oxide supports have attracted much attention because of the wide applications of supported metal oxide systems[7,8]. It is well known that supported oxides of transition metals are widely used as catalysts for various reactions. Titania as well its metal modified catalysts systems afford high activity and selectivity in the liquid phase epoxidation of cyclohexene[9]. Cyclohexene epoxide is obtained as the major product during the reaction with small amounts of allylic substitution products.This chapter gives an idea about the liquid phase oxidation reactions like epoxidation of cylcohexene and hydroxylation of phenol in which many industrially important products are formed. Here discusses about the redox properties of the ceria and copper incorporated titania catalysts.The epoxidation of cyclohcxene is carried out efficiently over the prepared systems with the selective formation of cyclohexane epoxide. This reaction hints that it might be possible to create cleaner nylon chemistry. The total acidity of the prepared systems plays an important role in determining the catalytic activity in the dehydrogenation of cyclohexane and cyclohexene. The total acidity of the prepared systems plays an important role in determining the catalytic activity in the dehydrogenation of cyclohexane and cyclohexene.

Structural studies on some metal complexes of embelin

This thesis deals with the studies on the synthesis and characterisation of the complexes of embelin with manganese (II), cobalt(II), nickel (II), copper (II), zinc (II), cadmium (II), chromium (III), iron (III) lanthanum(III), praseodymium (III) neodymium (III) Samarium (III), gadolinium (III) dysprosium (III), yttrium (III) thorium (IV) and uranium (VI). Elemental analysis as well as spectral, thermal and magnetic data were used to ascertain the composition of the complexes and to establish the structures of the metal complexes. Wherever possible, the electronic spectra and magnetic data were used to predict the stereochemistry of the complexes.The thesis is divided into four chapters.

Catalysis by Modified Pillared Clays and Porous Clay Heterostructures

In this venture three distinct class of catalysts such as, pillared clays and transition metal loaded pillared clays , porous clay heterostructures and their transition metal loaded analogues and DTP supported on porous clay heterostructures etc. were prepared and characterized by various physico chemical methods. The catalytic activities of prepared catalysts were comparatively evaluated for the industrially important alkylation, acetalization and oxidation reactions.The general conclusions drawn from the present investigation are  Zirconium, iron - aluminium pillared clays were synthesized by ion exchange method and zirconium-silicon porous heterostructures were Summary and conclusions 259 prepared by intergallery template method. Transition metals were loaded in PILCs and PCHs by wet impregnation method.  Textural and acidic properties of the clays were modified by pillaring and post pillaring modifications.  The shift in 2θ value to lower range and increase in d (001) spacing indicate the success of pillaring process.  Surface area, pore volume, average pore size etc. increased dramatically as a result of pillaring process.  Porous clay heterostructures have higher surface area, pore volume, average pore diameter and narrow pore size distribution than that of pillared clays.  The IR spectrum of PILCs and PCHs are in accordance with literature without much variation compared to parent montmorillonite which indicate that basic clay structure is retained even after modification.  The silicon NMR of PCHs materials have intense peaks corresponding to Q4 environment which indicate that mesoporous silica is incorporated between clay layers.  Thermo gravimetric analysis showed that thermal stability is improved after the pillaring process. PCH materials have higher thermal stability than PILCs.  In metal loaded pillared clays, up to 5% metal species were uniformly dispersed (with the exception of Ni) as evident from XRD and TPR analysis. Chapter 9 260  Impregnation of transition metals in PILCs and PCHs enhanced acidity of catalysts as evident from TPD of ammonia and cumene cracking reactions.  For porous clay heterostructures the acidic sites have major contribution from weak and medium acid sites which can be related to the Bronsted sites as evident from TPD of ammonia.  Pillared clays got more Lewis acidity than PCHs as inferred from α- methyl styrene selectivity in cumene cracking reaction.  SEM images show that layer structure is preserved even after modification. Worm hole like morphology is observed in TEM image of PCHs materials  In ZrSiPCHS, Zr exists as Zr 4+ and is incorporated to silica pillars in the intergallary of clay layers as evident from XPS analysis.  In copper loaded zirconium pillared clays, copper exists as isolated species with +2 oxidation state at lower loading. At higher loading, Cu exists as clusters as evident from reduction peak at higher temperatures in TPR.  In vanadium incorporated PILCs and PCHs, vanadium exist as isolated V5+ in tetrahedral coordination which is confirmed from TPR and UVVis DRS analysis.  In cobalt loaded PCHs, cobalt exists as CoO with 2+ oxidation state as confirmed from XPS.  Cerium incorporated iron aluminium pillared clay was found to be the best catalyst for the hydroxylation of phenol in aqueous media due to the additional surface area provided by ceria mesopores and its redox properties. Summary and conclusions 261  Cobalt loaded zirconium porous clay heterostructures were found to be promising catalyst for the tertiary butylation of phenol due to higher surface area and acidic properties.  Copper loaded pillared clays were found to be good catalyst for the direct hydroxylation of benzene to phenol.  Vanadium loaded PCHs catalysts were found to be efficient catalysts for oxidation of benzyl alcohol.  DTP was firmly fixed on the mesoporous channels of PCHs by Direct method and functionalization method.  DTP supported PCHs catalyst were found to be good catalyst for acetalization of cyclohexanone with more than 90% conversion.

Tailored Ion Imprinted Polymer Materials for the Preconcentrative Separation of Noble Metals

Tailored ion imprinted polymer materials for the preconcentrative separation of noble metals. This study deals with the synthesis, separation,characterization and analytical application of the noble metals especially palladium and platinum. Platinum group metals(PGM) are currently receiving world wide attention. This group include Palladium(Pt),rhodium(Rh), ruthenium(Ru), iridium(Ir) and osmium(Os).PGM are used as catalysts for a wide variety of hydrogenation, oxidation, isomerization,cyclization,dehydrogenation and dehalogenation reactions.The corrosion resistance of PGM enables them to use in jewellery,electrical and glass industries,extrusion of synthetic fibres,manufacture of laboratory utensils,dental and medical devices. This study clearly establishes selective recovery of platinum from other noble and transition elements.

Studies on Some Simple and Zeolite-Y Encapsulated 3d-Transition Metal Complexes of Schiff Bases Derived From 2-Aminobenzothiazole

In this regard Schiff base complexes have attracted wide attention. Furthermore, such complexes are found to play important role in analytical chemistry, organic synthesis, metallurgy, refining of metals, electroplating and photography. Many Schiff base complexes are reported in literature. Their properties depend on the nature of the metal ion as well as on the nature of the ligand. By altering the ligands it is possible to obtain desired electronic environment around the metal ion. Thus there is a continuing interest in the synthesis of simple and zeolite encapsulated Schiff base complexes of metal ions. Zeolites have a number of striking structural similarities to the protein portion of natural enzymes. Zeolite based catalysts are known for their remarkable ability of mimicking the chemistry of biological systems. In view of the importance of catalysts in all the areas of modern chemical industries, an effort has been made to synthesize some simple Schiff base complexes, heterogenize them by encapsulating within the supercages of zeoliteY cavities and to study their applications. The thesis deals with studies on the synthesis and characterization of some simple and zeoliteY encapsulated Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes and on the catalytic activity of these complexes on some oxidation reactions. Simple complexes were prepared from the Schiff base ligands SBT derived from 2-aminobenzothiazole and salicylaldehyde and the ligand VBT derived from 2-aminobenzothiazole and vanillin (4-hydroxy-3- methoxybenzaldehyde). ZeoliteY encapsulated Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes of Schiff base ligands SBT and VBT and also of 2-aminobenzothiazole were synthesized. All the prepared complexes were characterized using the physico-chemical techniques such as chemical analysis (employing AAS and CHN analyses), magnetic moment studies, conductance measurements and electronic and FTIR spectra. EPR spectra of the Cu(II) complexes were also carried out to know the probable structures and nature of Cu(II) complexes. Thermogravimetric analyses were carried out to obtain the information regarding the thermal stability of various complexes. The successful encapsulations of the complexes within the cavities of zeoliteY were ascertained by XRD, surface area and pore volume analysis. Assignments of geometries of simple and zeoliteY encapsulated complexes are given in all the cases. Both simple and zeoliteY encapsulated complexes were screened for catalytic activity towards oxidation reactions such as decomposition of hydrogen peroxide, oxidation of benzaldehyde, benzyl alcohol, 1-propanol, 2-propanol and cyclohexanol.

Synthesis and Characterisation of New Transition Metal Complexes of Schiff Bases Derived from 3-hydroxyquinoxaline-2- carboxaldehyde and Application of Some ofthese Complexes as Hydrogenation and Oxidation Catalysts

The thesis deals with studies on the synthesis, characterisation and catalytic applications of some new transition metal complexes of the Schiff bases derived from 3-hydroxyquinoxaline 2-carboxaldehyde.. Schiff bases which are considered as ‘privileged ligands’ have the ability to stabilize different metals in different oxidation states and thus regulate the performance of metals in a large variety of catalytic transformations. The catalytic activity of the Schiff base complexes is highly dependant on the environment about the metal center and their conformational flexibility. Therefore it is to be expected that the introduction of bulky substituents near the coordination sites might lead to low symmetry complexes with enhanced catalytic properties. With this view new transition metal complexes of Schiff bases derived from 3-hydroxyquinoxaline-2-carboxaldehyde have been synthesised. These Schiff bases have more basic donor nitrogen atoms and the presence of the quinoxaline ring may be presumed to build a favourable topography and electronic environment in the immediate coordination sphere of the metal. The aldehyde was condensed with amines 1,8-diaminonaphthalene, 2,3-diaminomaleonitrile, 1,2-diaminocyclohexane, 2-aminophenol and 4-aminoantipyrine to give the respective Schiff bases. The oxovanadium(IV), copper(II) and ruthenium(II)complexes of these Schiff bases were synthesised and characterised. All the oxovanadium(IV) complexes have binuclear structure with a square pyramidal geometry. Ruthenium and copper form mononuclear complexes with the Schiff base derived from 4- aminoantipyrine while binuclear square planar complexes are formed with the other Schiff bases. The catalytic activity of the copper complexes was evaluated in the hydroxylation of phenol with hydrogen peroxide as oxidant. Catechol and hydroquinone are the major products. Catalytic properties of the oxovanadium(IV) complexes were evaluated in the oxidation of cyclohexene with hydrogen peroxide as the oxidant. Here allylic oxidation products rather than epoxides are formed as the major products. The ruthenium(II) complexes are found to be effective catalysts for the hydrogenation of benzene and toluene. The kinetics of hydrogenation was studied and a suitable mechanism has been proposed.

Geochemistry of transition, non-transition and rare-earth elements in the surficial sediments of continental shelf of Kerala and an annex to the Cochin estuarine system

The metals present in the surface sediments have high demand on a global perspective, and the main reservoir of these elements is believed to be the ocean floor. A lot of studies on metals are going on throughout the world for its quantification and exploitation. Even though, some preliminary attempts have been made in selected areas for the quantitative study of metals in the western continental shelf of India, no comprehensive work has been reported so far. The importance of this study also lies on the fact that there has not been a proper evaluation of the impact of the Great Tsunami of 2004 on the coastal areas of the south India. In View of this, an attempt has been made to address the seasonal distribution, behavior and mechanisms which control the deposition of metals in the sediments of the western continental shelf and Cochin Estuary, an annex to this coastal marine region.Surface sediment samples were collected seasonally from two subenvironemnts of southwest coast of India, (continental shelf of Kerala and Cochin estuarine system), to estimate the seasonal distribution and geochemical behavior of non-transition, transition, rare-earth elements, Th and U. Bottom water samples were also taken from each station, and analysed for temperature, salinity and dissolved oxygen, hence the response of redox sensitive elements to oxygen minimum zone can be addressed. In addition, other sedimentary parameters such as sand, silt, clay fractions, CaCO3 and organic carbon content were also estimated to evaluate the control factors on level of metals present in the sediment. The study used different environmental data analysis techniques to evaluate the distribution and behavior of elements during different seasons. This includes environmental parameters such as elemental normalisation, enrichment factor, element excess, cerium and europium anomalies and authigenic uranium.

Transition metal complexes of some N4-phenylsemicarbazones: crystal structures and spectral studies

The unusual coordination modes of semicarbazones when bound to metals, the wide applications and structural diversity of metal complexes of semicarbazones provoked us to synthesize and characterize the tridentate ONO and NNO-donor semicarbazones and their transition metal complexes. This work is focused on the studies on complexes of three N4-phenylsemicarbazones synthesized by changing the carbonyl compounds. This work is concerned with the studies of two new semicarbazones, 2- formylpyridine-N4-phenylsemicarbazone (HL1) and 3-ethoxysalicylaldehyde- N4-phenylsemicarbazone (H2L2) and a reported semicarbazone 2-benzoylpyridine-N4-phenylsemicarbazone (HL3) [29]. The compositions of these semicarbazones were determined by the CHN analyses and IR, UV and NMR spectral studies were used for the characterization of these compounds. The molecular structure of 3-ethoxysalicylaldehyde-N4-phenylsemicarbazone (H2L2) was obtained by single crystal X-ray diffraction studies. Also, we have synthesized Cu(II), Cd(II), Zn(II) and Ni(II) complexes of these three semicarbazones. The complexes were characterized by various spectroscopic techniques, magnetic and conductivity studies. We could isolate single crystals of some complexes of all metals suitable for X-ray diffraction studies. This thesis is divided into six chapters.