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V Chandrasekhar

Publications and source records attributed to V Chandrasekhar.

At least 19 recordsLinked to original sources
PubMed2005

Thermal conductance of Andreev interferometers.

We calculate the thermal conductance G(T) of diffusive Andreev interferometers, which are hybrid loops with one superconducting arm and one normal-metal arm. The presence of the superconductor suppresses G(T); however, unlike a conventional superconductor, G(T)/G(T)(N) does not vanish as the temperature T-->0, but saturates at a finite value that depends on the resistance of the normal-superconducting interfaces, and their distance from the path of the temperature gradient. The reduction of G(T) is determined primarily by the suppression of the density of states in the proximity-coupled normal metal along the path of the temperature gradient. G(T) is also a strongly nonlinear function of the thermal current, as found in recent experiments.

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PubMed2001

Tethered pyrazolyl phosphinate: pyrazolyl-N- and phosphoryl-O-metal coordination in Ph(2)P(O)[OCH(2)CH(2)(3,5-Me(2)Pz)].

Phosphorus pyrazolides, P(O)(3,5-Me(2)Pz)(3) or RP(E)(3,5-Me(2)Pz)(2) [E = S or O, R = Me or Ph], are hydrolytically sensitive particularly upon interaction with transition metal ions. In this paper, we report a new tethered pyrazolyl phosphinate, Ph(2)P(O)[OCH(2)CH(2)(3,5-Me(2)Pz)] DPEP (1), where the pyrazolyl group is separated from the phosphorus by means of an ethyleneoxy spacer. 1 has two potential coordination sites in the form of a phosphoryl oxygen atom and a pyrazolyl nitrogen atom. 1 forms hydrolytically stable complexes, (DPEP-CoCl(2))(n)(2), (DPEP)(2)-CuCl(2) (3), (DPEP-ZnCl(2))(n )(4), and (DPEP)(2)-PdCl(2) (5). The cobalt(II) and the zinc(II) complexes 2 and 4 show a zigzag polymeric structure in the solid state with a tetrahedral coordination geometry around the metal ion; the ligand DPEP coordinates through its phosphoryl oxygen and the pyrazolyl nitrogen to two neighboring metal ions and functions as a bridging ligand to form the polymeric structure. In contrast to 2 and 4, the copper(II) and the palladium(II) complexes 3 and 5 show a square-planar geometry around the metal ion. Exclusive coordination through the pyrazolyl nitrogens of the ligand 1 is observed. An extensive supramolecular sheetlike two-dimensional polymeric network is observed in the solid-state structures of 3 and 5 as a result of two weak interactions: (a) an intermolecular C-H- - -O interaction involving the phosphoryl oxygen and an aromatic C-H and (b) a pi-pi face-to-face stacking interaction between the phenyl groups of two adjacent molecules.

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PubMed2000

Formation of a tetranuclear copper (II) cluster assembled by metal-assisted hydrolysis and desulfurization of bis(3,5-dimethylpyrazolyl)methylphosphine sulfide, MeP(S)(3,5-Me2Pz)2.

The reaction of methylphosphine sulfide, MeP(S)(3,5-Me2Pz)2, 1, with anhydrous CuCl2 affords a tetranuclear copper cluster[Cu2Cl2(3,5-Me2Pz)3(MePO3)]2, 2, and a dinuclear compound Cu2Cl4(3,5-Me2Pz)4, 3. This reaction involves a metal-assisted desulfurization along with concomitant hydrolysis of P-N bonds. The X-ray structures of 1-3 have been determined, and the crystal parameters for these are the following. 1: space group = C2/c, a = 15.2552(1) A, b = 8.7364(2) A, c = 21.4490(3) A, beta = 93.349(1) degrees, V = 2853.74(8) A3, and Z = 8. 2: space group = P2(1)/n, a = 12.5964(4) A, b = 15.7773(4) A, c = 13.9781(4) A, beta = 116.6280(10) degrees, V = 2483.32(12) A3, and Z = 2. 3: space group = P2(1)/c, a = 8.7137(8) A, b = 13.5493(14) A, c = 11.8847(12) A, beta = 106.179(2) degrees, V = 1347.6(2) A3, and Z = 2. The structure of 2 shows that it comprises two dinuclear copper cores bridged together by two tripodal methylphosphinate, MePO3, ligands. 2 is weakly antiferromagnetically coupled, as revealed by variable temperature magnetic susceptibility measurements.

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PubMed2000

A Dodecanuclear Copper(II) Cage Containing Phosphonate and Pyrazole Ligands This work was supported by a grant from the Department of Science and Technology (DST), New Delhi (V.C.). V.C. is also grateful to the Homi Bhabha Fellowship Council for a fellowship. We thank the DST for funding the National Facility for X-ray Crystallography at the Indian Institute of Technology, Kanpur. We thank Prof. Dr. P. K. Bharadwaj for his help in the data collection and X-ray analysis, and Prof. Dr. A. R. Chakravorthy, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, India for the magnetic measurements on 1.

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Journal Article↗
PubMed2000

Metal alkoxides as versatile precursors for group 4 phosphonates: synthesis and X-ray structure of a novel organosoluble zirconium phosphonate.

Reactions of Ph2P(O)(OH) and t-BuP(O)(OSiMe3)(OH) with Ti(O-i-Pr)4 in equimolar ratios gave titanium phosphonates of the type [(O-i-Pr)3Ti(mu-O)2PR1R2]2 (1, R1 = R2 = Ph; 2, R1 = t-Bu, R2 = OSiMe3) as colorless crystalline solids in moderate yields. Reactions of Ph2P(O)(OH) and the isopropoxides of zirconium and hafnium resulted in products of the composition [(O-i-Pr)3M(mu-O-i-Pr)2(mu-OPOPh2)M(O-i-Pr)2]Ph2P(O)(OH) (M = Zr (3), Hf (4)) in high yields. The compounds were characterized by 1H, 31P, and 29Si NMR, infrared (IR), and mass spectroscopic (MS) techniques. The molecular structures of 2 and 3 were confirmed by X-ray crystallography.

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PubMed1988

Cicatrical gastric stenosis caused by corrosive ingestion.

Sixteen patients with gastric cicatrization due to ingestion of corrosive agents were treated over a 7 year period at Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER) Hospital, Pondicherry. Fifteen patients developed gastric outlet obstruction due to ingestion of corrosives, while another had midgastric stenosis due to formalin intake. An associated oesophageal stricture was present in 62.5% of the cases. Partial gastrectomy was found to be the most satisfactory procedure and carried out in 60% of the cases. Pyloroplasty done in one patient was found inadequate within 1 year of surgery. Gastrojejunostomy carried out in two patients was associated with prolonged hospitalization due to malfunction of the anastomotic site.

Acids↗