Anindya Sundar Das

Synthesis, structure and electrochemical properties of a group of ruthenium(III) complexes of N-(aryl)picolinamide

Reaction of N-(aryl)picolinamide (HL–R; R = OCH3, CH3, H, Cl and NO2) with ruthenium trichloride or [Ru(DMSO)4Cl2] in refluxing 2-methoxyethanol in the presence of a base (NEt3) affords tris complexes of the type [Ru(L–R)3]. The structure of the [Ru(L–OCH3)3] complex has been determined by X-ray crystallography. In these complexes the amide ligands are coordinated to the metal center as monoanionic bidentate N,N-donors. All the [Ru(L–R)3] complexes are one-electron paramagnetic and show rhombic ESR spectra at 77 K. They also show intense LMCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a ruthenium(III)/ruthenium(IV) oxidation within the range of 0.89 to 1.21 V vs. SCE and a ruthenium(III)/ruthenium(II) reduction within the range of −0.22 to −0.41 V vs. SCE. Representative one-electron oxidized and reduced complexes, viz. [RuIV(L–H)3]+ and [RuII(L–H)3]−, respectively, have also been generated in solution and characterized spectroscopically as well as electrochemically.

Chemistry of osmium in N2P2Br2 coordination sphere: Synthesis, structure and reactivities

Abstract A family of three mixed-ligand osmium complexes of type [Os(PPh3)2(N-N)Br2], where N-N=2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (Me2bpy) and 1,10-phenanthroline (phen), have been synthesized and characterized. The complexes are diamagnetic (low-spin d6, S=0) and in dichloromethane solution they show intense MLCT transitions in the visible region. The two bromide ligands have been replaced from the coordination sphere of [Os(PPh3)2(phen)Br2] under mild conditions by a series of anionic ligands L (where L=quinolin-8-olate (q), picolinate (pic), oxalate (Hox) and 1-nitroso-2-naphtholate (nn)) to afford complexes of type [Os(PPh3)2(phen)(L)]+, which have been isolated and characterized as the perchlorate salt. The structure of the [Os(PPh3)2(phen)(pic)]ClO4 complex has been determined by X-ray crystallography. The PPh3 ligands occupy trans positions and the picolinate anion is coordinated to osmium as a bidentate N,O-donor forming a five-membered chelate ring. The [Os(PPh3)2(phen)(L)]+ complexes are diamagnetic and show multiple MLCT transitions in the visible region. The [Os(PPh3)2(N-N)Br2] complexes show an osmium(II)–osmium(III) oxidation (−0.02 to 0.12 V vs. SCE) followed by an osmium(III)–osmium(IV) oxidation (1.31 to 1.43 V vs. SCE). The [Os(PPh3)2(phen)(L)]+ complexes display the osmium (II)–osmium (III) oxidation (0.26 to 0.84 V vs. SCE) and one reduction of phen (−1.50 to −1.79 V vs. SCE). The osmium (III)–osmium (IV) oxidation has been observed only for the L=q and L=Hox complexes at 1.38 V vs. SCE and 1.42 V vs. SCE respectively. The osmium(III) species, viz. [OsIII(PPh3)2(N-N)Br2]+ and [OsIII(PPh3)2(phen)(L)]2+, have been generated both chemically and electrochemically and characterized in solution by electronic spectroscopy and cyclic voltammetry.

Chemistry of 2-(phenylazo)pyridine complexes of osmium: synthesis, characterization and reactivities

Abstract Reaction of 2-(phenylazo)pyridine (pap) with [Os(PPh3)3Br2] afforded a mixed ligand complex of the type [Os(PPh3)2(pap)Br2]. The structure of this complex was determined by X-ray crystallography. The PPh3 ligands are trans and the bromides are in cis positions. The pap ligand is coordinated to osmium as a bidentate N,N-donor forming a five-membered chelate ring. The complex is diamagnetic (low-spin d6, S=0) and in dichloromethane solution shows intense MLCT transitions in the visible region. The two bromides were replaced from the coordination sphere of [Os(PPh3)2(pap)Br2] under mild conditions by a series of anionic ligands L (where L=quinolin-8-olate (q), picolinate (pic), oxalate (Hox), 1-nitroso-2-naphtholate (nn) and acetyl acetonate (acac)) to afford complexes of the type [Os(PPh3)2(pap)(L)]+, which were isolated and characterized as the perchlorate salt. The structure of the [Os(PPh3)2(pap)(acac)]ClO4 complex was determined by X-ray crystallography. The PPh3 ligands occupy trans positions and the acetylacetonate anion is coordinated to osmium as a bidentate O,O-donor forming a six-membered chelate ring. The [Os(PPh3)2(pap)(L)]+ complexes are diamagnetic and show multiple MLCT transitions in the visible region. [Os(PPh3)2(pap)Br2] shows an osmium(II)–osmium(III) oxidation at 0.49 V versus SCE. The same oxidation is displayed by the [Os(PPh3)2(pap)(L)]+ complexes within 0.69 to 0.96 V versus SCE. Two successive one-electron reductions of the coordinated pap ligand are also observed in all the complexes below −0.90 V versus SCE.

Structural and Optical Properties of V2O5-MoO3-ZnO Glass-Nanocomposite System

ABSTRACT The present work points to highlight the physical, structural and the optical properties of some semiconducting V2O5-MoO3-ZnO glass-nanocomposites using density, molar volume, X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and UV-VIS absorption spectra. We have observed that addition of V2O5 increases (or decreases) the density (or molar volume) of the glassy system due to structural changes. Distribution of Zn3V2MoO11, Zn2.5VMoO8 and Zn2V2O7 nanoparticles has been confirmed from FESEM and XRD studies. It has been observed from FTIR spectra that the network structure depends upon isolated strongly deformed M oO4 polyhedra and VO4 metavanadate chains. Vibrations of MoO6 octahedra, Zn2V2O6, Zn2V2O7, Zn3V2MoO11 and VO2 are observed from the Raman spectroscopic studies. The fundamental UV-VIS absorption spectra have been analyzed, which indicates indirect transitions. GRAPHICAL ABSTRACT

V 2 O 5 -MoO 3 -ZnO thick film resistors as highly selective trace level ethanol gas sensors

The Glass nanocomposite materials in the form of fine granular powders were synthesized by conventional melt quenching technique. Thick films of the synthesized powders were fabricated by screen printing technique, followed by firing at 100oC, for 2 hours. Upon exposure to 50 ppm ethanol gas, due to oxidation or reduction reaction at the surface of the as prepared nanocomposite materials with the target gas, exchange of electrons take place thereby affecting the sensors resistance greatly leading to drastic change in conductance. The glass nanocomposite of composition xV2O5-(1−x) (0.05MoO3-0.95ZnO) where x = 0.95 (sample-C) was observed to most sensitive to ethanol at room temperature. The surface misfits, operating temperature, gas concentrations, etc. affect the microstructure and gas sensing performance of the sensing element. The quick response and fast recovery are the main features of this sensor. The microstructure of the as prepared glass nanocomposites was analyzed to study the gas response and selectivity of the sensor in the presence of ethanol and some other gases also.

Vibration Control of Rotor Shaft Systems Using Electromagnetic Actuator

Applicability of electro-magnetic actuator for active vibration control of long rotors, commonly found in power-plant turbines is addressed in this work through simulations. Appreciable vibration reduction with the Proportional-Derivative (PD) control law applied on the difference between nominal and instantaneous air-gap between rotor surface and actuator poles is reported in literature. This paper investigates and finds that the Proportional and high frequency band limited Derivative control action (abbreviated as PDhfbl) is much more efficient than the former in terms of unbalanced response reduction and increment of Stability Limit Speeds (SLS) of long rotor-shaft systems. This paper also establishes a philosophical link between the PDhfbl control action and a multi-element mechanical suspension model, or viscoelastic suspension model, reported to reduce response and increase stability limit speed of rotors in literature. Examples of simulations are presented in support of the conclusions.

Stability Study for Vibration Control of an Active Magnetic Bearing Supported Rotor Mounted on a Moving Base

Active Magnetic Bearings (AMBs) suspend rotor systems and also facilitate active rotor vibration control through feedback control law for appropriate contactless electromagnetic force. However for rotors on moving bases e.g. ships, airplanes, the equations of rotor motion become parametrically excited and so a feedback control methodology, e.g. with Proportional Derivative (PD) control law needs assessment of stability. It is observed that the equations of motion of a rigid rotor with respect to base, translating and pitching in one plane, under the action of linearized electromagnetic forces from AMBs at ends, take the form of forced damped Mathieu equations. This paper first attempts the stability analysis to tune controller parameters and then uses the Active Disturbance Rejection Control (ADRC) with Extended State Observers (ESO) to reject disturbances. Simulated results show considerable rotor vibration suppression and thus prove AMBs as effective suspensions for vibration control of rotor-shaft systems on moving platforms.