Photoluminescence, photoredox properties and crystal structures of rhenium(v)-benzylidyne complex with phosphine ligands.

Several rhenium(v)-benzylidyne complexes [Re(CR)(pdpp)2Cl]+[R=C6H2Me3-2,4,6,pdpp= o-phenylenebis(diphenylphosphine)], [Re(CR)L2(CO)(H2O)Cl]+ [L=PPh3, P(C6H4OMe-p)3 or PMe2Ph] and trans-[Re(CR)(dppe)(CO)2Cl]+ [dppe= 1,2-bis(diphenylphosphino)ethane] have been prepared. The structures of trans-Re(CR)(pdpp)2Cl]ClO4.CHCl3.0.25MeOH and [Re(CR)(PPh3)2 (CO)(H2O)Cl]ClO4. 1.5MeOH have been determined by X-ray analyses. The Re≡C distances are 1.802(5) and 1.784(8) Å respectively. In acetonitrile and dichloromethane the complexes show intense absorption bands at 318-330 nm and weak ones at 405-450 nm, the latter being tentatively assigned to dxy → dn* (dxz,dyz) transitions. Photoexcitation in the solution, solid or glassy state gives intense orange to red emissions, and the emitting states are tentatively assigned to 3[(dxy)1](dπ*)1]. The variation in non-radiative decay rate constants for the emissions of the rhenium(v)-benzylidyne complexes are consistent with a predication from the energy-gap law. The excited states are better oxidants and reductants than the grounds states. The values of E°(Rev*-ReIV ) and E° (ReVI-ReV*) in acetonitrile have been determined using spectroscopic and electrochemical data as well as by Stern-Volmer  quenching experiments

Algebraic Aspects of Abelian Sandpile Models

The abelian sandpile models feature a finite abelian group G generated by the operators corresponding to particle addition at various sites. We study the canonical decomposition of G as a product of cyclic groups G = Z_{d_1} X Z_{d_2} X Z_{d_3}...X Z_{d_g}, where g is the least number of generators of G, and d_i is a multiple of d_{i+1}. The structure of G is determined in terms of toppling matrix. We construct scalar functions, linear in height variables of the pile, that are invariant toppling at any site. These invariants provide convenient coordinates to label the recurrent configurations of the sandpile. For an L X L square lattice, we show that g = L. In this case, we observe that the system has nontrivial symmetries coming from the action of the cyclotomic Galois group of the (2L+2)th roots of unity which operates on the set of eigenvalues of the toppling matrix. These eigenvalues are algebraic integers, whose product is the order |G|. With the help of this Galois group, we obtain an explicit factorizaration of |G|. We also use it to define other simpler, though under-complete, sets of toppling invariants.Comment: 39 pages, TIFR/TH/94-3

On the Performance of Slider Bearing under Fluctuating Speed using a Non-Newtonian Visco-Elastic Fluid as Lubricant

In the present paper effect of fluctuations on the performance of a slider bearing has been considered using a non-Newtonian viscoelastic fluid as lubricant. It has been obtained that load-carrying capacity of the hearing always exceeds its value in steady case except for a brief initial period. The effect of visco-elasticity has been found to be advantageous for the increase of load-carrying capacity

On the Performance of Slider Bearing under Fluctuating Speed using a Non-Newtonian Visco-Elastic Fluid as Lubricant

In the present paper effect of fluctuations on the performance of a slider bearing has been considered using a non-Newtonian viscoelastic fluid as lubricant. It has been obtained that load-carrying capacity of the hearing always exceeds its value in steady case except for a brief initial period. The effect of visco-elasticity has been found to be advantageous for the increase of load-carrying capacity

The quality of care in provision of female sterilization and IUD services: an assessment study in Bihar

"With funding from the Packard Foundation, the International Center for Research on Women (ICRW) conducted a study in Bihar, where contraceptive use is low and women’s unmet fertility needs are high. We specifically assessed the quality of care related to the provision of IUD insertion and sterilization in an effort to better understand the nature of quality of care provided and identify the areas of care that require more attention.

Photochemical and electrochemical properties of tetranuclear Ru (II) complexes

The luminescent and redox active multinuclear Ru (II) Complex containing both electron poor (2,3-bis (2-pyridyl) pyrazine, 2,3-dpp) and electron rich (3,5-bis (pyridyn-2yl)-1,2,4-¬triazole, Hppt) polypyridine bridging ligands has been synthesized. The novel complex is [ (phen)2 Ru (µ-bpt)Ru{(µ-2,3-dpp) Ru(Phen)2}2]7+ (1:Phen-=1,10-Phenanthroline) Its absorption spectrum, luminescence properties, and redox behavior have been studied and compared with the properties of parent complexes [Ru {(µ-2,3-dpp) Ru (Phen)2}3]8+ (2) and [(Phen)2 Ru (µ-bpt) Ru (Phen)2]3+ (3). The absorption spectrum of 1 is dominated by ligand centered bands in the U.V. region and by metal to ligand CT bands in the visible region. Excited states and oxidation and reduction processes are localized in specific sites of the multicomponent structure. However, perturbations of each component on the redox and excited state properties, as well as electronic interactions between the chromospheres can be observed. Intercomponent energy transfer from the upper lying (µ-bpt) (Phen) Ru ï§Phen CT ¬excited state of the Ru (Phen)2 (µ-bpt)+ component to the lower lying (Phen)2 RUï§ µ 2,3-dpp CT excited - state of the Ru (Phen)2 (µ-2,3-dpp)2+ subunit(s) is efficient in fluid solution at room . And the process is not observed in a rigid matrix at 77 K. A two step energy transfer mechanism is proposed to explain the photophysical properties of the new complex

Electron transfer quenching studies of luminescent complex’s of Ru (iii) with mixed ligands

In the present paper the reaction of Ru (III) perchlorates with some polytertiary phosphines and arsines has been investigated. The study of quenching of excited states of Ru (LL’-)33+  complexes and subsequent reaction occuring with potential reductant - amines, aromatic ether, nitro compounds, p-hydroquinone and water have been observed. Both laser flash and convensional spectroscopic techniques have been used to monitor the quencher products. The photo reduction of complex (I) with triethylamine can be shown to consists of two component, a primary photoprocess and a subsequent dark reaction while for complex (II) only the first process is observed. The reduced complex Ru (LL’)+23 produced in the reaction are relatively stable and dry deacrated solution but can be observed rapidly with both oxygen and water. The reaction of reduced (I) with water is a relatively produce Ru (LL’) +3H+2 which yields hydrogen and to starting. Complex (I) with colloidal platinum excited states of (I) are also quenched by aromatic ether and hydroquionones in process giving transients having spectra similar to that the reduced (I). The reaction between excited (I) with water (K = 1x 107M-1 S-1) gives a short lifed transient (ïŠ= 245ns) more lightly an adduct or ligand protonated species more lightly and adduct or ligand protonated species

Marcus inverted region in the photoinduced electron transfer reactions of ruthenium(ii)-polypyridine complexes with phenolate ions.

Ruthenium (II)- polypyridy1 complexes of similar size but with variable reduction potential undergo efficient photoinduced electron- transfer reactions with phenolate ions in aqueous medium. All these reactions are exergonic and are in accordance with the Marcus theory of electron transfer. At high negative G° Marcus inverted region is observed in this bimolecular photoinduced charge separation reaction