Bijay Sarkar

Reversible phase transitions within self-assembled fibrillar networks of (R)-18-(n-alkylamino)octadecan-7-ols in their carbon tetrachloride gels.

The CCl(4) gel phases of a series of low-molecular-mass organogelators, (R)-18-(n-alkylamino)octadecan-7-ols (HSN-n, where n = 0-5, 18 is the alkyl chain length), appear to be unprecedented in that the fibrillar networks of some of the homologues undergo thermally reversible, gel-to-gel phase transitions, and some of those transitions are evident as opaque-transparent changes in the appearance of the samples. The gels have been examined at different concentrations and temperatures by a wide variety of spectroscopic, diffraction, thermal, and rheological techniques. Analyses of those data and data from the neat gelators have led to an understanding of the source of the gel-to-gel transitions. IR and SANS data implicate the expulsion (on heating the lower-temperature gel) or the inclusion (on cooling the higher-temperature gel) of molecules of CCl(4) that are interspersed between fibers in bundles. However, the root cause of the transitions is a consequence of changes in the molecular packing of the HSN-n within the fibers. This study offers opportunities to design new gelators that are capable of behaving in multiple fashions without entering the sol/solution phase, and it identifies a heretofore unknown transformation of organogels.

Stable Silver(I) Hydride Complexes Supported by Diselenophosphate Ligands

The first stable structure of silver(I) cluster cations [Ag(8)(mu(4)-H){Se(2)P(OR)(2)}(6)](+) [R = (i)Pr, 1; Et, 2] containing Ag(I)-hydride bridges (Ag-mu-H-Ag) in T symmetry was reported. The clusters having an interstitial hydride were composed of an octanuclear silver core in tetracapped tetrahedral geometry, which was inscribed within a Se(12) icosahedron represented by six dialkyl diselenophosphate ligands in a tetrametallic-tetraconnective (mu(2), mu(2)) bonding mode. The presence of hydride was unequivocally corroborated by both (1)H and (109)Ag NMR spectroscopies of which a nonet in the (1)H NMR spectrum for the hydride resonance coupled with a doublet peak observed in the (109)Ag NMR spectrum clearly suggests that eight silver nuclei are equivalent in the NMR time scale and a fast exchange of the positions between the vertex and capping silver atoms in solution must occur. The hypothesis was also supported by a density functional theory (DFT) investigation on a simplified model [Ag(8)(H)(Se(2)PH(2))(6)](+), which confirmed that the Ag(8)H cubic core of T(h) symmetry may not be formed as it is energetically highly unfavorable (0.67 eV less stable than the T structure).

Electrical and optical properties of a single Sb2Se3 nanorod

In this paper we present the methods to chemically synthesize the Sb2Se3 nanorods and study the electrical and optical properties of a single Sb2Se3 nanorod with an average size of 70 nm in diameter and a length of about 1 μm to 2 μm. The techniques we devised can immobilize and allocate a single nano-object on an electron beam (E-beam) patterned smart substrate. It can also overcome the limitation of the spatial resolution of conventional optical techniques (∼ 1 mm) to obtain optical spectroscopy in an individual nano-object less than 100 nm in size. We also demonstrate the techniques in using E-beam defined metallic coordination markers as electrodes to measure the conductance of a single Sb2Se3 nanorod.

The chemistry of phosphorodiselenoates: structure, catalysis and formation of Se-esters

Though metal complexes of dialkyl diselenophosphate ligands [Se2P(OR)2]− (dsep) have been reported in several occasions, the solid-state structure of isolated dsep ligands is still unknown. Herein the ammonium salt of the dsep ligand, NH4Se2P(OiPr)2, is structurally characterized and N–H⋯Se type of H-bonding interactions are revealed. In addition, the NH4Se2P(OR)2 ligands serve as an ammonia source in the Fe powder catalyzed condensation of acetone with ammonia to form 2,2,6,6-tetramethyl-4-oxopiperidinium salts of the dsep ligand, [{H2N(CH2)2(CMe2)2CO}{Se2P(OR)2}] (1a = iPr, 1b = Et) of which 1b is structurally characterized. Novel syntheses of Se-esters of O,O′-dialkylphosporodiselenoic acid, 2, 3, 4, 5, 6, 7, directly from the ammonium salts have been achieved. The reactions, where one of the Se atoms of the dsep unit acts as the nucleophilic center, include Michael addition, epoxide ring opening addition, acylation and α-alkynation.