The Au26 cluster is one of the widely studied gold clusters in the size range of n = 21-30. It has been proposed in a more recent combined experimental and theoretical study that the neutral Au26 cluster is fluxional. The fluxionality of a cluster is relevant to its catalytic applications. In this context, to explore the extent of fluxionality, Born Oppenheimer Molecular Dynamical (BOMD) simulations are carried out on experimentally and theoretically proposed fluxional Au26 conformations (three compact or core-shell structures and a high symmetry cage structure). The simulations reveal that the high energy golden tube outperforms the ground state structure (compact C2v conformation) as well as the other two low-symmetry compact conformations in terms of thermal stability. The enhancement in the thermal stability is explained on the basis of structural integrity imposed by the open skeleton of shortest bond distances within Au26-Tube. In addition to this, the homogeneous distribution of charges and the strong s-d hybridization exhibited by FMOs are seen to play a pivotal role in increasing the stability of Au26-Tube. The present investigation also reveals that the characteristic fluxionality proposed to exist in the Au26 system is noted only above 400 K and it is missing at room temperature. The simulations also bring forth the question of how relevant a ground state conformation is at working temperatures.

Finite-temperature behaviour of a hollow golden cage (HGC) plays a crucialrole in its potential applications as a catalyst, drug delivery agent, contrasting agent and so on. This physico-chemical property of HGCs is not well understood so far. In that context, Born-Oppenheimer molecular dynamics (BOMD) simulations are performed on a well-known 'free-standing' HGC. The cluster considered in this study is the ground state Au 18 cluster (a cage with a diameter of about >5.5Å).The results thus obtained are compared with the BOMD simulation results reported earlier on Au 32 icosahedron cage, a conformation with a diameter of nearly. The sphericity of both the clusters is studied using a shape deformation parameter as a function of time and temperature. These results are supplemented by radial distribution function at various temperatures. The observations and analysis of results indicate that, both the clusters retain an HGC conformation from 300 to 400 K, admitting structural fluxionality by the Au 18 cluster. Remarkably, the Au 18 cluster is able to maintain its hollowness and sphericity up to a high temperature of 1000 K. Underlying structural and electronic properties influencing the individualistic behaviour of cages are highlighted. Composition of the frontier molecular orbitals and the charge distribution play a crucial role in the finite-temperature behaviour of the Au cages. The conclusions are supplemented by supporting calculations on another degenerate ground state Au 18 hollow cage and a well-known pyramidal Au 18 cage at 300 and 400 K.

1D phosphorene nanoribbon edges activating water molecules under sunlight.

Luminescent phosphorene quantum dots (PQDs) have emerged as fascinating nanomaterials for potential applications in optoelectronics, catalysis, and sensing. Herein, we investigate the structural distortion of black phosphorus (BP) under an applied electric field to yield blue luminescent PQDs [average diameter 8 ± 1.5 nm (N = 60)]. The electrosynthesized PQDs exhibit photoluminescence emission independent of excitation wavelength with 84% quantum efficiency. Structural distortion that occurred during the transformation of BP to PQDs is confirmed by results obtained during transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Further, using first-principles-based density functional theory, calculations on oxygenated and nonoxygenated PQDs augment the experimental observations that an optimum oxygen content maintains the structural integrity of PQDs, above which the structural robustness of PQDs is drastically diminished.

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The reaction of isatin with benzamidine hydrochloride in methanol yields the title compound, benzamidium (2-acetamidobenzoyl)formate (C7H 9-N~.CmHsNO4). In the benzamidinium cation the configuration about the exocyclic C atoms is planar, resulting in electron delocalization in the C--N bonds. The C--O bond distances in the carboxylate © 1994 International Union of Crystallography Printed in Great Britain -all rights reservedThe IR spectrum (KBr pellet) of the compound showed the following absorptions: 3400-3240 (broad, NH, NH2), 1700 (CO), 1450 (C--N), 1320 (C~N) cm-1. The following IH NMR parameters confirm the structure of the compound: & 2.18 (s, 3H, CH3) , 3.48 (broad, 4H, NH2), 9H, Ar), 11.88 (s, 1H, NH). The mass spectrum showed the molecular ion peak at m/z 327 (M÷).The title compound (I) is composed of two parts: the benzamidinium cation and the (2-acetamidobenzoyl)formate anion. The formation of this salt appears to occur through a ring-opening reaction in which a C--N bond of isatin is cleaved, followed by the addition of a water molecules resulting in the formation of (II) (an intermediate under these conditions), then a simple acid-base reaction of (II) with benzamidine rather than a Schiff base condensation.[~, OK_~ OH-p COCH 3" 00Acta Crystallographica Section C ISSN 0108-2701 ©1994 K. C. JOSHI, R. BOHRA, R. JAIN AND S. ARORA 1793The benzamidinium cation has the expected structure. The rr electrons are delocalized over the C(7), N(1) and N(2) atoms, which is evident from the average C--N distance of 1.309 (7)A, indicating considerable double-bond character. The sums of the bond angles about C(7), N(1) and N(2) are 359.9(14), 360.6(10) and 360(13) °, respectively. These data indicate the essentially planar hybridization about these atoms. The distance between C(1) and C(7) [1.479 (7) A,] represents a normal C~p2--Csp2 single bond.The average value of the C(15)--0(2) and C(15)--0(4) bond distances in the anion is 1.238 (6)A, indicating that the negative charge is delocalized over these atoms. The N(3)--H3n bond length is 1.13 (8) A indicating normal single-bond character. The dihedral angle between the plane defined by C(14), O(1), C(15) and C(13) and that defined by C(8), C(9), C(10), C(I1) and C(12) is 7.33_ 1.19 °, which is a measure of the non-coplanarity of the phenyl ring of the indole and the carbonyl groups. The dihedral angle between the plane defined by C(7), N(1), N(2) and H lna and H lnb and that defined by C(1), C(2), C(3), C(4), C(5) and C (6) ExperimentalA mixture of N-acetyl isatin (0.01 mol), benzamidine hydrochloride (0.01 tool) and K2CO3 (1 g) was refluxed in methanol (50 ml) for 3 h. A white product was obtained on cooling, which was then recrystallized from methanol (yield 2.25 g, 69%); m.p. 469 K. Analysis: calculated for N(1)--C (7) 1.289 (7) O(4)---42 (15) 1.222 (6) N(2)---C (7) 1.329 (7) N(3)---C(12) 1.379 (7)1.380 (7) C (9) (7) 121.4 (5) N(3)--C(12)--<2(13) 117.6 (5) C(6)--C(1)--C (7) 119.5 (5) The data were corrected for Lorentz and polarization effects. There...

Surface functionalization through adsorption of ligands or non-metal atoms is considered to be an interesting and viable approach for tuning the physicochemical properties of gold clusters. Highly stable and magic...