Syntheses,Structures, and Electronic Properties of Mono- and Bimetallic Thiolato Complexes Containing Unusual Coordination Modes of Thiolato Ligands

Synthesis, bonding and chemistry of mono- and bimetallic complexes supported by chelating thiolato ligands have been established. Treatment of [Cp*VCl₂]₃ ( 1 ) with [LiBH₄ ⋅ THF] followed by the addition of ethane-1,2-dithiol led to the formation of an EPR active bimetallic vanadium thiolato complex [(Cp*V){μ-(SCH₂CH₂S)-κ²S,S′)₂{V(SCH₂CH₂S-SH)}] ( 2 ). In complex 2 , two ethane-1,2-dithiolato ligands are symmetrically coordinated to two vanadium atoms through μ-S atoms. Interestingly, when similar reactions were carried out with heavier group 5 metal precursors, such as [Cp*NbCl₄] ( 3 a ), it afforded monometallic thiolato complex [Cp*Nb(SCH₂CH₂S)(SCH₂CH₂S−CH₂S)] ( 4 a ). On the other hand, the Ta-analogue [Cp*TaCl₄] ( 3 b ) yielded thiolato species [Cp*Ta(SCH₂CH₂S)(SCH₂CH₂S−CH₂S)] ( 4 b ) and [Cp*Ta(SCH₂CH₂S) (SCH₂CH₂S−S)] ( 5 ). In complexes 4 a and 4 b , one ethane-1,2-dithiolato and one trithiolato ligand are coordinated to Nb and Ta centers, respectively. Whereas, in complex 5 , one ethane-1,2-dithiolato and one 2-disulfanylethanethiolato is coordinated to the Ta center. Moreover, the photolytic reaction of 5 with [Mo(CO)₅ ⋅ THF] yielded heterobimetallic thiolato complex [(Cp*Ta){μ-(SCH₂CH₂S)-κ²S,S′}{μ-(SCH₂CH₂S−CH₂(CH₃)S)κ²S′′ : κ¹S-′′′′ : κ¹S′′′′′}{Mo(CO)₃}] ( 6 ). All the complexes have been characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction studies. Further, computational analyses were performed to provide an insight into the bonding of these complexes.     

Kinetics of aquation and base hydrolysis ofcis-(carboxylato) (ethylamine)bis(ethylenediamine)cobalt(III) ions

Summary The aquation ofcis-[Co(en)₂(NH₂Et)O₂CR]²⁺ [R=H or Me] is strongly acid-catalysed and the rate and activation parameters for this process are reported. No significant rate difference is observed in the spontaneous aquation path for the complexes. The acetato complex undergoes acid catalysed aquation at a rate comparable to the of the corresponding formato complex, in contrast with the relative basicities of the coordinated formate and acetate. This result is interpreted in terms of relative solvation effects of the initial and transition states of both complexes.The base hydrolysis of both complexes obeys overall second order kinetics in the 0.05[OH^–]_T 0.35 mol dm^–3 range (I=0.5 mol dm^–3). The formato complex reacts five times faster than its acetato analogue under comparable conditions, which is fully consistent with the dissociative mode of activation of the amido conjugate base involving Co–O bond heterolysis. A substantially large positive value for the activation entropy supports SN₁CB mechanism for base hydrolysis.     

Medium effect on the reactions of complexes: kinetics and mechanism of the base hydrolysis of cis-[(salicylato)(amine)bis(ethylenediamine)cobalt(III)] compounds in methanol-water

Summary The kinetics of base hydrolysis of cis-[(salicylato)(RNH₂) (en)₂CO^III]²⁺ (R = H, Me or Et) have been studied in MeOH-H₂O medium at 35.0°C, I = 0.1 (ClO ₄ ^– ) and 0.01 [OH^-]_Tmol dm^-3 0.10. The phenoxide species [(RNH₂)(en)₂CoO₂C₆H₄O]⁺, underwent both OH^--independent (SNICB) and OH^--catalysed (SN₁CB) hydrolysis with K _obs=k ₁+k ₂[OH^–]. Both k ₁ and k ₂ are appreciably enhanced by the medium for MeNH₂ and EtNH₂ complexes. In contrast, for the NH₃ complex, k ₁ decreases with increasing MeOH content and k ₂ was non-existent beyond 60% (v/v) MeOH. These rate variations illustrate the importance of the solute-solvent interaction, presumably partly of hydrophobic origin, and solvent structure in existing stabilizing/destabilizing effects on the initial and transition states.     

Effect of plasticizer on microstructure and electrical properties of a sodium ion conducting composite polymer electrolyte

A plasticized composite polymer electrolyte (PCPE) based on Poly (ethylene oxide) + NaI with Na₂SiO₃ as the ceramics filler and Poly (ethylene glycol) as the plasticizer has been prepared by solution cast technique. Effect of plasticization on microstrucutre and electrical properties of the materials has been investigated. The changes in the structural and microstructural properties of the material have been investigated by XRD and SEM studies. The electrical conductivity estimated using a. c. impedance spectroscopy was found to be dependent on plasticizer concentration. An enhancement in the ionic conductivity value by three times has been recorded on addition of plasticizer when compared with that of unplasticized composite polymer electrolyte. The temperature dependence of conductivity of the polymer films is found to obey the Arrhenius behavior below and above the melting temperature of PEO. The electrical transport has been found to be a thermally activated process with ions being the predominant charge carrier.     

Preparation and characterization of manganese ferrite-based magnetic liposomes for hyperthermia treatment of cancer

Comparative evaluation of two different methods of magnetic liposomes preparation, namely thin film hydration (TFH) and double emulsion (DE) with different molar ratios of egg-phosphatidyl choline (egg-PC) and cholesterol using lauric acid coated manganese ferrite-based aqueous magnetic fluid, is reported. TFH was found to be a better method of encapsulation and TFH 2:1 (egg-PC: cholesterol) magnetic liposomes showed the highest encapsulation efficiency and comparable heating ability to that of magnetic fluids. Stealth TFH 2:1 magnetic liposomes containing DSPE-PEG₂₀₀₀ were three-fold more cytocompatible as compared to the magnetic fluid. Stealth TFH 2:1 manganese ferrite-based magnetic liposomes might be useful for hyperthermia treatment of cancer.     

LRS Bianchi Type-I Universe in Barber’s Second Self Creation Theory

We consider Barber’s second self creation theory with perfect fluid source for an LRS Bianchi type-I metric by using deceleration parameter to be time dependent where the metric potentials are taken as function of x and t. The present models are free from singularity and the results are consistent within the observational limit. Some physical properties of the models are also discussed.     

Magnetic and spectroscopic characteristics of ZnMnO system

We report on the observation of room-temperature ferromagnetism in epitaxial (Zn,Mn)O films grown by a pulsed-laser deposition technique using high-density targets. The X-ray, microscopic, spectroscopic and magnetic properties of target material containing 6 at.% of Mn and films were compared. The target shows the presence of large clusters exhibiting paramagnetic behavior. However, ferromagnetic properties were observed in (Zn,Mn)O films grown at a substrate temperature of 500 °C and with an oxygen partial pressure of 1 mTorr. Although, crystalline quality of the film improves with increasing substrate temperature, the ferromagnetism becomes weaker.     

Massive String Cosmology in Bianchi Type ⅢSpace-Time with Electromagnetic Field

Exact solution of Einstein＇s field equations is obtained for massive string cosmological model of Bianchi III space-time using the technique given by Letelier （1983） in presence of perfect fluid and electromagnetic field. To get the deterministic solution of the field equations the expansion 0 in the model is considered as proportional to the eigen value σ2^2of the shear tensor σi^j and also the fluid obeys the barotropic equation of state. It is observed that in early stage of the evolution of the universe string dominates over the particle whereas the universe is dominated by massive string at the late time. It is also observed that the string phase of the universe disappears in our model because particle density becomes negative. Some physical and geometric properties of the model are also discussed.