Inverse surface melting in confined clusters: Ar-13 in zeolite L

Monte Carlo and molecular dynamics simulations on an Ar-13 cluster in zeolite L have been carried out at a series of temperatures to understand the rigid-nonrigid transition corresponding to the solid-liquid transition exhibited by the free Ar-13 cluster. The icosahedral geometry of the free cluster is no longer preferred when the cluster is confined in the zeolite. The root-mean-squared pair distance fluctuation, delta, exhibits a sharp, well-defined rigid-nonrigid transition at 17 K as compared to 27 K for the free cluster. Multiple peaks in the distribution of short-time averages of the guest-host interaction energy indicate coexistence of two phases.; It is shown that this transition is associated with the inner atoms becoming mobile at 17 K even while the outer layer atoms, which are in close proximity to the zeolitic wall, continue to be comparatively immobile. This may be contrasted with the melting of large free clusters of 40 or more atoms which exhibit surface melting. Guest-host interactions seem to play a predominant role in determining the properties of confined clusters. We demonstrate that the volume of the cluster increases rather sharply at 17 and 27 K respectively for the confined and the free cluster. Power spectra suggest that the motion of the inner atoms is generally parallel to the atoms which form the cage wall.

K-Ar ages of biotite and muscovite from Pangong metamorphic complex, Shyok suture zone, India: Implications for the youngest post-collision metamorphic event in Ladakh Himalaya

The garnet-kyanite-staurolite and garnet-biotite-staurolite gneisses were collected from a locality within Lukung area that belongs to the Pangong metamorphic complex in Shyok valley, Ladakh Himalaya. The kyanite-free samples have garnet and staurolite in equilibrium, where garnets show euhedral texture and have flat compositional profile. On the other hand, the kyanite-bearing sample shows equilibrium assemblage of garnet-kyanite-staurolite along with muscovite and biotite. In this case, garnet has an inclusion rich core with a distinct grain boundary, which was later overgrown by inclusion free euhedral garnet. Garnet cores are rich in Mn and Ca, while the rims are poor in Mn and rich in Fe and Mg, suggesting two distinct generations of growth. However, the compositional profiles and textural signature of garnets suggests the same stage of P -T evolution for the formation of the inclusion free euhedral garnets in the kyanite-free gneisses and the inclusion free euhedral garnet rims in the kyanite-bearing gneiss. Muscovites from the four samples have consistent K-Ar ages, suggesting the cooling age (∼ 10 Ma) of the gneisses. These ages make a constraint on the timing of the youngest post-collision metamorphic event that may be closely related to an activation of the Karakoram fault in Pangong metamorphic complex.

Nucleophilic attacks of 1,2-diaminoethane on MeCN ligands: synthesis, x-ray structure, and spectral and electrochemical properties of [Ru(.mu.-O)(.mu.-O2CAr)2[NH2CH2CH2NHC(Me)NH]2(PPh3)2](ClO4)2(Ar = C6H4-p-X; X = H, Me, OMe, Cl)

The diruthenium(III) complex [Ru2O(O2CAr)2(MeCN)4(PPh3)2](ClO4)2 (1), on reaction with 1,2-diaminoethane (en) in MeOH at 25-degrees-C, undergoes nucleophilic attacks at the carbon of two facial MeCN ligands to form [(Ru2O)-O-III(O2CAr)2-{NH2CH2CH2NHC(Me)NH}2(PPh3)2](ClO4)2 (2) (Ar = C6H4-p-X, X = H, Me, OMe, Cl) containing two seven-membered amino-amidine chelating ligands. The molecular structure of 2 with Ar = C6H4-p-OMe was determined by X-ray crystallography. Crystal data are as follows: triclinic, P1BAR, a = 13.942 (5) angstrom, b = 14.528 (2) angstrom, c = 21.758 (6) angstrom, alpha = 109.50 (2)-degrees, beta = 92.52 (3)-degrees, gamma = 112.61 (2)-degrees, V = 3759 (2) angstrom 3, and Z = 2. The complex has an {Ru2(mu-O)(mu-O2CAr2)2(2+)} core. The Ru-Ru and average Ru-O(oxo) distances and the Ru-O-Ru angle are 3.280 (2) angstrom, 1.887 [8] angstrom, and 120.7 (4)-degrees, respectively. The amino group of the chelating ligand is trans to the mu-oxo ligand. The nucleophilic attacks take place on the MeCN ligands cis to the mu-oxo ligand. The visible spectra of 2 in CHCl3 display an absorption band at 565 nm. The H-1 NMR spectra of 2 in CDCl3 are indicative of the formation of an amino-amidine ligand. Complex 2 exhibits metal-centered quasireversible one-electron oxidation and reduction processes in the potential ranges +0.9 to +1.0 V and -0.3 to -0.5 V (vs SCE), respectively, involving the Ru(III)2/Ru(III)Ru(IV) and Ru(III)2/Ru(II)Ru(III) redox couples in CH2Cl2 containing 0.1 M TBAP. The mechanistic aspects of the nucleophilic reaction are discussed.

Microwave Spectroscopic and Atoms in Molecules Theoretical Investigations on the ArPropargyl Alcohol Complex: ArHO, Ar, and ArC Interactions

The structure of the Arpropargyl alcohol (ArPA) complex is determined from the rotational spectra of the parent complex and its two deuterated isotopologues, namely ArPA-D(OD) and ArPA-D(CD). The spectra confirm a geometry in which PA exists in the gauche form with Ar located in between OH and CCH groups. All a, b and c types of transitions show small splitting due to some large-amplitude motion dominated by COH torsion, as in the monomer. Splittings in a- and b-type transitions are of the order of a few kilohertz, whereas splitting in the c-type transitions is relatively larger (0.92.6 MHz) and decreases in the order ArPA>ArPA-D(CD)>ArPA-D(OD). The assignments are well supported by ab initio calculations. Atoms in molecules (AIM) and electrostatic potential calculations are used to explore the nature of the interactions in this complex. AIM calculations not only reveal the expected OHAr and Ar interactions in the Argauche-PA complex, but also novel CAr (of CH2OH group) and OHAr interactions in the Artrans-PA complex. Similar interactions are also present in the Armethanol complex.

Insertion Reactions of Six-Membered Cyclopalladated N,N `,N `'-Triarylguanidine, Pd{kappa(2)(C,N)-C6H3Me-3(NHC(NHAr)(=NAr))-2)(mu-Br)](2) (Ar=2-MeC6H4) with PhCC C-C(O)OR (R = Me and Et): A Gateway to Second Orthopalladation through Novel Rearrangements

The reaction of Pd{kappa(2)(C,N)-C6H3Me-3-(NHC(NHAr)(=NAr))-2}(mu-Br)](2) (Ar = 2-MeC6H4; 1) with 4 equiv of PhC C-C(O)OMe in CH2Cl2 afforded Pd{kappa(2)(C,N)-C(Ph)=C(C(O)OMe)C(Ph)=C(C(O)-OMe)C6H3Me-3(N=C(NH Ar)(2))-2}Br] (Ar = 2-MeC6H4; 2) in 70% yield, and the aforementioned reaction carried out with 10 equiv of PhC C-C(O)OR (R = Me, and Et) afforded an admixture of two regioisomers of Pd{kappa(3)(N,C,O)-O=C(OR)-C5Ph3(C(O)OR)C(C(O)OR)C6H3Me-3(N=C(NHAr)( 2))- 2}Br] (Ar = 2-MeC6H4; R = Me (3a/3b), Et (4a/4b)) in 80 and 87% yields, respectively. In one attempt, the minor regioisomer, 4b, was isolated from the mixture in 6% yield by fractional crystallization. Palladacycles 3a/3b and 4a/4b, upon stirring in CH2Cl2/MeCN (1/1, v/v) mixture at ambient condition for S days, afforded Pd{eta(3)-allyl,(KN)-N-1)-C-5(C(O)OR)(2)Ph3C-(C(O)OR)C6H3Me-3(N=C(NH Ar)(2))(-2)}Br] (Ar = 2-MeC6H4; R = Me (5a/5b), Et (6a/6b)) in 94 and 93% yields, respectively. Palladacycles 3a/3b and 4a/4b, upon reaction with AgOTf in CH2CH2/Me2C(O) (1/1, v/v) mixture at ambient temperature for 15 min, afforded Pd{kappa(3)(N,C,O)-O=C(OR)C5Ph3(C(O)OR)C(C(O)OR)C6H3Me-3(N=C(NHAr)(2 ))-2}(OTf)] (Ar = 2-MeC6H4; R = Me (7a/7b), Et (8a/8b)) in 79 and 77% yields, respectively. Palladacycles 7a/7b and 8a/ 8b, upon reflux in PhC1 separately for 6 h, or palladacycles 5a/5b and 6a/6b, upon treatment with AgOTf in CH2Cl2/Me2C(O) (7/3, v/v) mixture for 15 min, afforded Pd{(eta(2)-Ph)C5Ph2(C(O)OR)kappa(2)(C,N)-C(C(O)OR)C6H3Me-3(N=C(NHAr) (2))-2}(OTf)] (Ar = 2-MeC6H4; R = Me (9a/9h), Et (10a/10b)) in >= 87% yields. Palladacycles 9a/9b, upon stirring in MeCN in the presence of excess NaOAc followed by crystallization of the reaction mixture in the same solvent, afforded Pd{kappa(3)(N,C,C)-(C6H4)C5Ph2(C(O)OMe)(2)C(C(O)OMe)(2)C6H3Me-3(N=C( NHAr)(2))-2}(NCMe)] (Ar = 2-MeC6H4; 11a/11b) in 82% yield. The new palladacycles were characterized by analytical, IR, and NMR (H-1 and C-13) spectroscopic techniques, and the molecular structures of 2, 3a, 4a, 4b, 5a, 6a, 7a, 9a, 10a, and 11a-d(3) were determined by single crystal X-ray diffraction. The frameworks in the aforementioned palladacycles, except that present in 2, are unprecedented. Plausible pathways for the formation of new palladacycles and the influence of the guanidine unit in 1, substituents in alkynes, reaction conditions, and electrophilicity of the bromide and the triflate upon the frameworks of the insertion products have been discussed.

Performance study of a cesium iodide photocathode-based UV photon detector in Ar/CH4 mixture

The detection efficiency of a gaseous photomultiplier depends on the photocathode quantum efficiency and the extraction efficiency of photoelectrons into the gas. In this paper we have studied the performance of an UV photon detector with P10 gas in which the extraction efficiency can reach values near to those in vacuum operated devices. Simulations have been done to compare the percentage of photoelectrons backscattered in P10 gas as well as in the widely used neon-based gas mixture. The performance study has been carried out using a single stage thick gas electron multiplier (THGEM). The electron pulses and electron spectrum are recorded under various operating conditions. Secondary effects prevailing in UV photon detectors like photon feedback are discussed and its effect on the electron spectrum under different operating conditions is analyzed. (C) 2014 Chinese Laser Press