• Volume 114, Issue 4

      August 2002,   pages  231-460

    • Foreword

      P Banerjee

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    • Organometallic chemistry of chiral diphosphazane ligands: Synthesis and structural characterisation

      Kannan Raghuraman Swadhin K Mandal T S Venkatakrishnan Setharampattu S Krishnamurthy Munirathinam Nethaji

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      The diphosphazane ligands of the type, (C20H12O2)PN(R)P(E)Y2 (R = CHMe2 or (S)-*CHMePh; E = lone pair or S; Y2 = O2C20H12 or Y = OC6H5 or OC6H4Me-4 or OC6H4OMe-4 or OC6H4But-4 or C6H5) bearing axially chiral 1,1'-binaphthyl-2,2′-dioxy moiety have been synthesised. The structure and absolute configuration of a diastereomeric palladium complex, [PdCl2{ηsu2}-((O2C20H12)PN((S)-*CHMePh)PPh2] has been determined by X-ray crystallography. The reactions of [CpRu(PPh3)2Cl] with various symmetrical and unsymmetrical diphosphazanes of the type, X2PN(R)PYY′ (R = CHMe2 or (S)-*CHMePh; X = C6H5 or X2 = O2C20H12; Y=Y′= C6H5 or Y = C6H5, Y′ = OC6H4Me-4 or OC6H3Me2-3,5 or N2C3HMe2-3,5) yield several diastereomeric neutral or cationic half-sandwich ruthenium complexes which contain a stereogenic metal center. In one case, the absolute configuration of a trichiral ruthenium complex, viz. [Cp*Ruη2-Ph2PN((S)-*CHMePh)*PPh (N2C3HMe2-3,5)Cl] is established by X-ray diffraction. The reactions of Ru3(CO)12 with the diphosphazanes (C20H12O2)PN(R)PY2 (R = CHMe2orMe; Y2=O2C20H12or Y= OC6H5 or OC6H4Me-4 or OC6H4OMe-4 or OC6H4But-4 or C6H5) yield the triruthenium clusters [Ru3(CO)10{η-(O2C20H12)PN(R)PY2}], in which the diphosphazane ligand bridges two metal centres. Palladium allyl chemistry of some of these chiral ligands has been investigated. The structures of isomeric η3-allyl palladium complexes, [Pd(η3-l,3-R′2-C3H3){η2-(rac)-(02C20H12)PN(CHMe2)PY2}](PF6) (R′ = Me or Ph; Y = C6H5 or OC6H5) have been elucidated by high field two-dimensional NMR spectroscopic and X-ray crystallographic studies.

    • Bending crystals. Solid state photomechanical properties of transition metal complexes containing semiquinonate ligands

      Cortlandt G Pierpont

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      The properties of transition metal complexes containing catecholate and radical semiquinonate ligands have often been found to be unusual and unexpected. Crystals of Rh(CO)2(3,6-DBSQ), containing the 3,6-di-tert-butyl-1,2-semiquinonate ligand, form as long thin needles that are observed to bend reversibly upon irradiation with NIR light. Crystallographic characterization reveals a stacked solid state lattice with planar molecules aligned with metal atoms atop one another. Electronic spectra recorded in the solid state and in solution show an intense band at 1600 nm that maps the energy dependence of crystal bend angle. The transition is a property of the stacked assembly, rather than of an individual complex molecule, and appears associated with an MLCT process that transfers charge from an antibonding band formed by interacting Rhdz2 orbitals to the vacant quinone π* orbital. Related observations have been made on the [Co(μ-pyz)(3,6-DBSQ)(3,6-DBCat)]npolymer. Photomechanical properties appear associated with electronic transitions that lead to a physical change in axial length of a linear polymer, coupled with a soft solid state lattice that permits axial contraction/expansion without crystal fracture.

    • Thiosemicarbazone complexes of the platinum metals. A story of variable coordination modes

      Indrani Pal Falguni Basuli Samaresh Bhattacharya

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      Salicylaldehyde thiosemicarbazone (H2saltsc) reacts with [M(PPh3)3X2] (M = Ru, Os; X = Cl, Br) to afford complexes of type [M(PPh3)2(Hsaltsc)2], in which the salicylaldehyde thiosemicarbazone ligand is coordinated to the metal as a bidentate N,S-donor forming a four-membered chelate ring. Reaction of benzaldehyde thiosemicarbazones (Hbztsc-R) with [M(PPh3)3X2] also affords complexes of similar type, viz. [M(PPh3)2(bztsc-R)2], in which the benzaldehyde thiosemicarbazones have also been found to coordinate the metal as a bidentate N,S-donor forming a four-membered chelate ring as before. Reaction of the Hbztsc-R ligands has also been carried out with [M(bpy)2X2] (M = Ru, Os; X = Cl, Br), which has afforded complexes of type [M(bpy)2(bztsc-R)]+, which have been isolated as perchlorate salts. Coordination mode of bztsc-R has been found to be the same as before. Structure of the Hbztsc-OMe ligand has been determined and some molecular modelling studies have been carried out determine the reason for the observed mode of coordination. Reaction of acetone thiosemicarbazone (Hactsc) has then been carried out with [M(bpy)2X2] to afford the [M(bpy)2(actsc)]ClO4 complexes, in which the actsc ligand coordinates the metal as a bidentate N,S-donorformingafive-membered chelate ring. Reaction of H2saltsc has been carried out with [Ru(bpy)2Cl2] to prepare the [Ru(bpy)2(Hsaltsc)]ClO4 complex, which has then been reacted with one equivalent of nickel perchlorate to afford an octanuclear complex of type [Ru(bpy)2(saltsc-H)4Ni4](ClO4)4.

    • Ruthenium, osmium and rhodium complexes of polypyridyl ligands: Metal-promoted activities, stereochemical aspects and electrochemical properties

      Parimal Paul

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      This article presents a brief overview of the reactions of2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in presence of rhodium(III), ruthenium(II) and osmium(II) under various experimental conditions. Under certain experimental conditions tptz exhibits metal-assisted hydrolysis/hydroxylation at the triazine ring. However, synthetic methods have also been developed to prepare complexes with intact tptz. Molecular structures of some of the complexes, especially stereoisomers of the hydroxylated products, are established by single crystal X-ray studies. A critical analysis of all data suggests that the electron-withdrawing effect of the metal ion (L→Mσ donation) is the predominant factor, rather than angular strain, that is responsible for metal-promoted reactivities. Electrochemical properties of all of these complexes have been investigated, Rh(III) complexes are excellent catalysts for electrocatalytic reduction of CO2, and dinuclear Ru(II) and Os(II) complexes exhibit strong electronic communication between the metal centres.

    • Transition metal catalysed Grignard-like allylic activation across tetragonal tin(II) oxide

      Pradipta Sinha Moloy Banerjee Abhijit Kundu Sujit Roy

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      The reaction of allyl halide and a carbonyl compound under the aegis of tetragonal tin(II) oxide and catalyticd8,d10 metal complexes provides the corresponding homoallylic alcohol, via a novel allyl tin intermediate.

    • Chemistry of dihydrogen complexes containing only phosphorus co-ligands

      Balajir Jagirdar Nisha Mathew

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      A series of new dicationic dihydrogen complexes of ruthenium of the typecis-[(dppm)2Ru(η2-H2)(L)][BF4]2 (dppm = Ph2PCH2PPh2; L = phosphite) have been prepared by protonating the precursor hydride complexescis-[(dppm)2Ru(H)(L)][BF4] using HBF4•Et2O. The precursor hydride complexes have been obtained fromtrans-[(dppm)2Ru(H)(L)][BF4] (L = phosphite) via a rare acid-catalysed isomerization reaction in six coordinate species. Thetrans-[(dppm)2Ru(H)(L)][BF4] complexes (L = phosphine) upon protonation gave the isomerized derivatives, however, further addition of acid resulted in a five-coordinate species, [(dppm)2RuCl]+ presumably via an intermediate phosphine dihydrogen complex. The electronic as well as the steric properties of the co-ligands seem to strongly influence the structure-reactivity behaviour of this series of complexes.

    • Innocent or guilty? Redox activity in and magnetic and optical behaviour of dinuclear molydenum complexes

      Jon A McCleverty Michael D Ward

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      The phenomenon of ‘non-innocence’, first articulated by Jørgensen in 1966, is briefly reviewed. Spectroelectrochemical studies of a range of dinuclear complexes of the type [Mo(NO)Tp*Cl2(bridge)] (bridge = dipyridyls) and [Mo(O)Tp*Cl2(bridge)] (bridge = diphenolates) which are redox active, show that oxidised or reduced forms of these species exhibit ‘non-innocence’. The spectral behaviour is associated with metal-to-ligand or ligand-to-metal charge transfer phenomena, probably the first time that monodentate bridging ligands have been implicated in ‘non-innocent’ behaviour. These bridging ligands also determine the nature and extent of magnetic interaction between the unpaired spins in [Mo(NO)Tp*Cl2(bridge)] and [Mo(O)Tp*Cl2(bridge)], the dominant mechanism of spin-exchange relying on the extent of {ie291-01}-delocalisation within the bridging ligands. The unusual optical behaviour of these dinuclear complexes when oxidised (oxomolybdenum diphenolates) or reduced (nitrosyl molybdenum dipyridyls) has led to the exploration of electrochromism as a means to develop variable optical attenuators operating in the near-infrared region.

    • Inverted porphyrins and expanded porphyrins: An overview

      S K Pushpan S Venkatraman V G Anand J Sankar H Rath T K Chandrashekar

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      Porphyrins and metallopophyrins have attracted the attention of chemists for the past 100 years or more owing to their widespread involvement in biology. More recently, synthetic porphyrins and porphyrin-like macrocycles have attracted the attention of researchers due to their diverse applications as sensitizers for photodynamic therapy, MRI contrasting agents, and complexing agents for larger metal ions and also for their anion binding abilities. The number of π-electrons in the porphyrin ring can be increased either by increasing the numberof conjugated double bonds between the pyrrole rings or by increasing the number of heterocyclic rings. Thus, 22π sapphyrins, 26π rubyrins, 30π heptaphyrins, 34π octaphyrins and higher cyclic polypyrrole analogues containing 40π, 48π, 64π, 80π and 96π systems have recently been reported in the literature. These macrocycles show rich structural diversity where normal and different kinds of inverted structures have been identified. In this review, an attempt has been made to collect the literature of the inverted porphyrins and expanded porphyrins reported until December 2001. Since themeso aryl expanded porphyrins have tendency to form both inverted and non-inverted structures more emphasis has been given tomeso aryl expanded porphyrins.

    • Design and synthesis of multidentate ligands via metal promoted C-N bond formation processes and their coordination chemistry

      Kunal K Kamar Amrita Saha Sreebrata Goswami

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      This presentation reports some novel examples of organic ring amination reactions via metal mediation. The organic transformations are highly regioselective and can be controlled by the proper selection of the mediator complex. The two isomeric organic ligands viz. HL1 and HL2 were isolated in their pure states by the removal of the metal ions. These were fully characterized. The ligand HL1 has lowpKa, 8.5. Upon deprotonation, it behaves as a potentialbis chelating N,N,N-donors. The coordination chemistry of the HL1 ligand involving some 3d-metal ions is described. Two unusual low-spin complexes of manganese(II) and iron(III) are reported. The ferric complex displayed a rhombic EPR while, the corresponding manganese compound showed a complex pattern due to hyperfine coupling. All the complexes displayed large number of redox responses. A brief mention about the future projection of this work is noted.

    • Is copper(I) really soft? Probing the hardness of Cu(I) with pyridinecarboxaldehyde ligands

      D Saravanabharathi M Nethaji A G Samuelson

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      Cu(I) complexes of formula Cu(PPh3)2LClO4 [L = 2 or 3 pyridine carboxaldehyde] are synthesised and characterised to explore the coordination of an aldehyde, a hard and neutral oxygen donor to a soft Cu(I) centre. The structural and spectroscopic results illustrate that only in 2-pyridinecarboxaldehyde, the ‘C=O’ group coordinates to soft Cu(I) centres due to a favourable chelate effect, while in 3-pyridinecarboxaldehyde, it remains uncoordinated. Upon chelation via N and O donors, 2-pyridinecarboxaldehyde resembles bipyridine or phenanthroline in terms of its bite angle and spectroscopic features. Such chelation can be easily challenged with coordinating anions like bromide, or more basic pyridines. A drastic change in the MLCT absorption signals the decomplexation of the ‘C=O’ group. The observed results point out that the Cu(I) centre can readily exchange the hard ‘O’ donor for softer ligands.

    • Organotellurium ligands — designing and complexation reactions

      Ajai K Singh

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      A variety of tellurium ligands has been designed and studied for their complexation reactions in the last decade. Of these hybrid telluroethers, halotellurium ligands and polytellurides are the most notable ones. RTe-andpolytelluride ions have also been used to design clusters. Ligation of ditelluroethers and several hybrid telluroethers is extensively studied in our laboratories. The ditelluroether ligand RTeCH2TeR (where R = 4-MeOC6H4) (1), similar to dppm [1,2-bis(diphenylphosphino)methane], has been synthesized in good yield (∼80%) by reacting CHCl3 with RTe- (generatedin situ by borohydride reduction of R2Te2). Iodine reacts with1 to give tetra-iodo derivative, which has intermolecular Te.I interactions resulting in a macro structure containing rectangular Te-I.Te bridges.1 readily forms four membered rings with Pd(II) and Ru(II). On the formation of this chelate ring, the signal in125Te NMR spectra shifts significantly upfield (50-60 ppm). The bridging mode of1 has been shown in [Ru(p-cymene)Cl2]](μ-l)[Ru(p-cymene)Cl2]. The hybrid telluroether ligands explored are of the types (Tex, Sy ), (Tex, Ny) and ( Tex,Oy ). The tellurium donor site has strongtrans influence, which is manifested more strongly in square planar complexes of palladium(II). The morpholine N-donor site has been found to have weaker donor characteristics in (Tex, Ny) ligands than pyridine and alkylamine donor sites of analogous ligands. The singlet oxygen readily oxidises the coordinated Te. This oxidation follows first order kinetics. The complexation reaction of RuCl3].xH2O with N-[2-(4-methoxyphenyltelluro)ethyl]phthalimide (2) results in a novel (Te, N, O)-heterocycle, Te-chloro,Te-anisyl-1a-aza-4-oxa-3-tellura-1H, 2H, 4aH-9 fluorenone. The (Te, O) ligands can be used as hemilabile ligands, the oxygen atom temporarily protects the vacant coordination site before the arrival of the substrate. The chelate shifts observed in125Te NMR spectra of metal complexes of Te-ligands have a close parallel to those of31P NMR. For the formation of five-membered rings, the value is positive and of the order of 130 ppm whereas for six-membered rings it is negative and ∼30 ppm only.

    • Chemistry of selected cyclic P(III) compounds possessing a P-Cl bond

      K C Kumaraswamy Sudha Kumaraswamy Praveen Kommana N Satish Kumar K Senthil Kumar

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      The compounds [CH2(6-t-Bu-4-Me-C6H2O)2]PCl (1), (OCH2CMe2CH2O)-PCl (2), and [ClPN(t-Bu)]2 (3) have been utilized as precursors in the synthesis of (i) new pentacoordinate phosphorus compounds [e.g. CH2(6-t-Bu-4-Me-C6H2O)2 P(NRR′)(O2C6C14), CH2(6-t-Bu-4-Me-C6H2O)2PX[OC(O-i-Pr)N=N(C(O)O-i-Pr)],(ii) cyclic phosphates and their complexes [e.g. imidazolium+CH2(6-t-Bu-4-Me-C6H2O)2PO2-.MeOH], (iii) new cycloaddition products [e.g. CH2(6-t-Bu-4-Me-C6H2O)2PC(CO2Me)C(CO2Me)C(O)N, (iv) macrocyclic compounds [e.g. [(t-BuN)P]2[-OCH2CMe2CH2O-]h2] and (v) phosphonates [e.g. (OCH2CMe2CH2O)P (O)CH2C(CN)=CHC5H4FeC5H5]. The synthetic and structural aspects of these new products are discussed.

    • Novel vanadium phosphate phases as catalysts for selective oxidation

      Arunabha Datta Monika Agarwal Soumen Dasgupta

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      In our effort to induce novel modifications in the structure of some important vanadium phosphate phases used as selective oxidation catalysts, it has been observed that metal ions such as Zn2+, Ni2+, Pd2+can be incorporated into the vanadyl hydrogen phosphate VOHPO40.5H2O phase in very different ways depending upon the medium of preparation. It has been found that the metal ions are either substituted into the lattice with retention of structure of the parent compound or intercalated between the layers of a new mixed-valent phase. These new metal-incorporated phases are catalytically active and the palladium incorporated compound in particular displays shape selective catalysis for different oxidation and reduction reactions. In another approach, the preparation of VOHPO40.5H2O) has been modified to give a novel crystalline phase containing mixed-valentvanadium and having NH3 species bound to the lattice. This phase could be a potential catalyst for ammoxidation reactions. In addition, novel mesostructured vanadium phosphate phases have been prepared using a long-chain amine as the templating agent involving a ligand templating mechanism of formation.

    • Copper complexes as chemical nucleases

      Akhil R Chakravarty Pattubala A N Anreddy Bidyut K Santra Anitha M Thomas

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      Redox active mononuclear and binuclear copper(II) complexes have been prepared and structurally characterized. The complexes have planar N-donor heterocyclic bases like 1,10-phenanthroline (phen), dipyridoquinoxaline (dpq) and dipyridophenazine (dppz) ligands that are suitable for intercalation to B-DNA. Complexes studied for nuclease activity have the formulations [Cu(dpq)2(H2O)] (ClO4)2.H2O (1), [CuL(H2O)2(μ-ox)](ClO4)2 (L = bpy,2; phen,3; dpq,4; and dppz,5) and [Cu(L)(salgly)] (L = bpy,6; phen,7; dpq,8; and dppz,9), where salgly is a tridentate Schiff base obtained from the condensation of glycine and salicylaldehyde. The dpq complexes are efficient DNA binding and cleavage active species. The dppz complexes show good binding ability but poor nuclease activity. The cleavage activity of thebis-dpq complex is significantly higher than thebis-phen complex of copper(II). The nuclease activity is found to be dependent on the intercalating nature of the complex and on the redox potential of the copper(II)/copper(I) couple. The ancillary ligand plays a significant role in binding and cleavage activity.

    • New mixed ligand complexes of ruthenium(II) that incorporate a modified phenanthroline ligand: Synthesis, spectral characterization and DNA binding

      S Murali C V Sastri Bhaskar G Maiya

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      The hexafluorophosphate and chloride salts of two ruthenium(II) complexes, viz. [Ru(phen)(ptzo)2]2 and [Ru(ptzo)3]2+, where ptzo = 1,10-phenanthrolino[5,6-e]1,2,4-triazine-3-one (ptzo) — a new modified phenanthroline (phen) ligand, have been synthesised. These complexes have been characterised by infrared, UV-Vis, steady-state emission and1H NMR spectroscopic methods. Results of absorption and fluorescence titration as well as thermal denaturation studies reveal that both thebis- and tris-complexes of ptzo show moderately strong affinity for binding with calf thymus (CT) DNA with the binding constants being close to 105M-1 in each case. An intercalative mode of DNA binding has been suggested for both the complexes. Emission studies carried out in non-aqueous solvents and in aqueous media without DNA reveal that both [Ru(phen)(ptzo)2]2+ and [Ru(ptzo)3]2+ are weakly luminescent under these solution conditions. Successive addition of CT DNA to buffered aqueous solutions containing [Ru(phen)(ptzo)2]2+results in an enhancement of the emission. These results have been discussed in the light of the dependence of the structure-specific deactivation processes of the MLCT state of the metallo-intercalator with the characteristic features of its DNA interaction. In doing so, attempts have been made to compare and contrast its properties with those of the analogous phenanthroline-based complexes including the ones reported by us previously.

    • Copper(II) complexes with aroylhydrazones

      Samudranil Pal

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      The coordination chemistry of copper(II) with tridentate aroylhydrazones is briefly discussed in this article. Two types of aroylhydrazones derived from aroylhydrazines and ortho-hydroxy aldehydes or 2-pyridine-carboxaldehyde have been used. The characterization of the complexes has been performed with the help of various physico-chemical techniques. Solid state structural patterns have been established by X-ray crystallography. In the solid state, structural varieties of these complexes are seen to range from monomeric, dimeric, polymeric and one-dimensional self-assembly via hydrogen bonds and π-π interactions. EPR spectroscopy and variable temperature magnetic susceptibility measurements have been used to reveal the nature of the coordination geometry and magnetic characteristics of these complexes.

    • Intervalence charge transfer transition in mixed valence complexes synthesised from RuIII(edta)- and FeII(CN)5-cores

      H C Bajaj Atindra D Shukla Amitavaitava Das

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      Intervalence charge transfer properties were studied for a set of mixed valence complexes incorporating Ru(III) and Fe(II)-centres linked by various saturated and unsaturated bridging ligands (BL). Studies reveal that degree of ground state electronic interaction and coupling between Ru(III) and Fe(II)-centrescanbe attenuated by changing the nature of the bridging ligand. Further, inclusion of the bridging ligand with interrupted π-electron system in a β-CD cavity initiate an optical electron transfer from Fe(II) to Ru(III) which is otherwise not observed.

    • Bridging function mediated intermetallic coupling in diruthenium-bis(bipyridine) complexes

      Soma Chakraborty Biplab Mondal Biprajit Sarkar Goutam Kumar Lahiri

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      The interactions of potentially dinucleating bridging functionalities (I–VI) with the ruthenium-bis(bypyridine) precursor [RuII(bpy)2(EtOH)2]2+have been explored. The bridging functionsI,II andVI directly result in the expected dinuclear complexes of the type [(bpy)2RuIILnRuII(bpy)2]z+ (1,2,7 and 8) (n = 0,z =4 andn = -2,z = 2). The bridging ligandIII undergoes N-N or N-C bond cleavage reaction on coordination to the RuII(bpy)2 core which eventually yields a mononuclear complex of the type [(bpy)2RuII(L)]+,3, where L =-OC6H3(R)C(R′)=N-H. However, the electrogenerated mononuclear ruthenium(III) congener, 3+in acetonitrile dimerises to [(bpy)2RuIII {-OC6H3(R)C(R′)=N-N=(R′)C(R)C6H3O-}RuIII(bpy)2]4+ (4). In the presence of a slight amount of water content in the acetonitrile solvent the dimeric species (4) reduces back to the starting ruthenium(II) monomer (3). The preformed bridging ligandIV undergoes multiple transformations on coordination to the Ru(bpy)2 core, such as hydrolysis of the imine groups ofIV followed by intermolecular head-to-tail oxidative coupling of the resultant amino phenol moieties, which in turn results in a new class of dimeric complex of the type [(bpy)2RuII-OC6H4-N=C6H3(=NH)O-RuII(bpy)2]2+ (5). In5, the bridging ligand comprises of twoN,O chelating binding sites each formally in the semiquinone level and there is ap-benzoquinonediimine bridge between the metal centres. In complex6, the preformed bridging ligand, 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine, H2L (V) undergoes oxidative dehydrogenation to aromatic tetrazine based bridging unit, 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine, L. The detailed spectroelectrochemical aspects of the complexes have been studied in order to understand the role of the bridging units towards the intermetallic electronic coupling in the dinuclear complexes.

    • Mesoporous titanium phosphates and related molecular sieves: Synthesis, characterization and applications

      Asim Bhaumik

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      Titanium (IV) phosphates TCM-7 and -8 with mesoporous cationic framework topologies using both cationic and anionic surfactants have been synthesized. Experimental data suggest the stabilization of the tetrahedral state of Ti in TCM-7/8 (O-P-O-Ti-O-, at Ti/P = 1:1)vis-à-vis the most stable octahedral state of Ti in the rutile/anatase or pure mesoporous TiO2. Mesoporous TCM-7 and-8 show anion exchange capacity due to the framework phosphonium cation and cation exchange capacity due to defective P-OH groups. Grafting the organic functionality in the surface or bridging the organic moiety in between the inorganic phosphorus precursors can enhance hydrophobicity of these materials similar to that of mesoporous silica materials. The high catalytic activity in the liquid phase partial oxidation of cyclohexene over such organically surface modified mesoporous titanium phosphate using a dilute H2O2 oxidant supports the tetrahedral coordination of Ti in these materials. These materials also show excellent photocatalytic activity in the production of H2 by photo-reduction of water under UV light irradiation.

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