334 research outputs found
The picture superiority effect in recognition memory: A developmental study using the response signal procedure
No full textItems studied as pictures are better remembered than items studied as words even when test items are presented as words. The present study examined the development of this picture superiority effect in recognition memory. Four groups ranging in age from 7 to 20 years participated. They studied words and pictures, with test stimuli always presented as words, and time to respond to test stimuli was manipulated. The picture superiority effect showed a clear developmental trend. In the condition in which participants had ample response time, a significant picture superiority effect appeared in all but the youngest group. With short response time, a significant picture superiority effect appeared only among 11- and 20-year-old groups, while a significant reverse of the picture superiority effect was detected in the youngest group. These results were interpreted as suggesting that different memory processes (familiarity and recollection) contribute differently to the picture superiority effect at different stages of development. © 2009 Elsevier Inc. All rights reserved
The synthesis and x-ray structure analysis of Os6(CO) 17(NC5H5)2: A cluster compound with an unusual mode of metal-CO bonding
No full textReaction of the neutral hexaosmium cluster Os6(CO)18 with excess of pyridine (py) gives the pentanuclear dianion [Os 5(CO)15]2- together with small amounts of a neutral hexanuclear cluster Os6(CO)17(py)2 (1); X-ray analysis shows that (1) exhibits an unusual type of metal-carbonyl linkage
A new type of decaosmium cluster geometry : The synthesis and x-ray structure analysis of Os10(S)2(CO)23
No full textPyrolysis of Os3(CO)12 with elemental sulphur gives a range of clusters including Os3(S)2(CO)9, Os5S(CO)15, Os6(CO)18, Os 7(S)2(CO)20, and Os10(S) 2(CO)23 (1); X-ray analysis shows that (1) has a new type of Os10 metal core geometry
Synthesis of the cluster dianion [Os11C(CO)27]2- by pyrolysis and its reactions with electrophiles; X-ray structure analysis of the mixed-metal derivative [PMePh3][Os11C(CO)27Cu(NCMe)]·CH 2Cl2 and the hydrido derivative [PMePh3][Os11C(CO)27H]
No full textThe new cluster species [Os11C(CO)27]2- (2) has been identified as one of the products resulting from the pyrolysis of [Os3(CO)12]. It reacts with [Cu(NCMe)4] BF4 to yield the monoanion [Os11C(CO)27Cu(NCMe)]- (4) and [Os11C(CO)27Cu(NCMe)2] (5). The reaction of (2) with iodine-iodide produces a series of iodo-clusters [Os11C(CO)27I]- (8) and [Os11C(CO)27I2] (9) which are converted back into (2) by addition of halide ions. The unstable monoanionic species [Os11C(CO)27M(PMe2Ph)]- [M = Au (3) or Cu (7)] are obtained on reaction of (2) with [M(PMe2Ph)]+, and further reaction of (3) yields [Os11C(CO)27Au(PMe2Ph)2] (6). The dianionic cluster (2) reacts with acid to give the monoanion [Os11C(CO)27H]- (10) and [Os11C(CO)27H2] (11). The reaction with Hg(C6Cl5) (O2CCF3) yields initially the unstable monoanion [Os11C(CO)27Hg(C6Cl5)]- (12) which is rapidly converted into the known cluster dianion [Os20Hg(C)2(CO)48]2-. X-Ray analysis of the [PMePh3]+ salts of (4) and (10) reveal identical Os11 core geometries, but in (4) the copper ligand occupies a μ3-bridging position, while the hydride in (10) appears to be located in an interstitial site
The first nona-osmium cluster species; synthesis and x-ray structure analysis of [Os9(CO)21CHC(R)CH]- (R = Me or Et)
No full textWhen Os3(CO)12 is heated under reflux in isobutyl alcohol or 2-methylbutan-1-ol the novel cluster monoanions [Os 9(CO)21CHC(R)CH]- (R = Me or Et respectively) are produced in low yield; X-ray analyses of the [N(Ph3P) 2]+ salts of both monoanions show that they both have the same unusual Os9 core with 2 cluster valence-electrons less than the number predicted by the effective atomic number (E.A.N.) rule
Synthesis, photophysical properties, and nanocrystal formation of a new class of tetra-n-substituted perylenes
No full textA new class of perylene-derived dyes, tetra (carboxamido) perylenes, has been obtained by a generally applicable synthetic method. Derivative A is shown to form nanocrystalline aggregates in DMSO which display significantly modified photophysical behavior with respect to the monomer and were studied by using atomic force microscopy techniques
Improved syntheses of the hexanuclear clusters [Ru6(CO)18]2-, [HRu6(CO)18]- and [H2Ru6(CO)18]. The x-ray analysis of [HRu6(CO)18]-, a polynuclear carbonyl containing an interstitial hydrogen ligand
No full textThe X-ray analyses of two crystalline modifications, (I) and (II), of [N(PPh3)2][HRu6(CO)18] are reported, together with improved synthetic routes to this and the related clusters [Ru6(CO)18]2- and H2Ru6(CO)18. Crystals of (I) are triclinic, space group P1, with a = 18.083(4), b = 19.101(4), c = 19.238(5) Å, α = 117.70(4), β = 78.13(2), γ = 97.05(2)°, and Z = 4. Crystals of (II) are monoclinic, space group P21/n, with a = 33.82(8), b = 52.55(10), c = 9.832(2) Å;, β = 92.66(2)°, and Z = 12. Least-squares refinement using diffractometer data (Mo-Kα) has given an R of 0.068 1 for 9 165 reflections for (I) and an R of 0.23 (Ru only) for 1 485 reflections for (II). The unit cell in (I) contains two independent molecules of [HRu6(CO)18]-, cluster (1) which is ordered and cluster (2) which is disordered between two sites (2A) and (2B) that are related by a non-crystallographic two-fold axis. The combined evidence of the X-ray analyses, 1H n.m.r. studies, i.r. [v(CO)] spectra, and variable-temperature 13C n.m.r. is only consistent with the hydrogen ligand lying inside the Ru6 octahedron
Synthesis and X-ray structure analysis of the neutral nitrosyl hydrido cluster HRu6C(CO)15(NO)
No full textProtonation of the anion [Ru6C(CO)15(NO)]-, formed from the reaction of Ru6C(CO)17 with [N(PPh3)2][NO2], gives the neutral nitrosyl hydrido cluster HRu6C(CO)15(NO); X-ray analysis shows that the overall structure of this compound is very similar to that of the previously reported derivative Ru6C(CO)15(NO)(AuPPh3). © 1983
The synthesis of the first undeca-osmium cluster species, [PPh 3Me]2[Os11C(CO)27], and the x-ray structure analysis of its [Cu(NCMe)]+ derivative [PPh 3Me][Os11C(CO)27Cu(NCMe)]·CH 2Cl2
No full textThe first undeca-osmium cluster, [Os11 C(CO)27] 2- (1), has been isolated as a low-yield product of the vacuum pyrolysis of Os3(CO)12; the dianion (1) reacts with 1 equivalent of [Cu(NCMe)4][BF4] to give the monoanion [Os11C(CO)27Cu(NCMe)]- (2) which has been shown by X-ray analysis to have an unusual Os11 core geometry with the carbido atom occupying a trigonal prismatic cavity
Reaction of [Os5H2(CO)15] with pyridine: Crystal and molecular structures of [Os5H3(CO)14(C5H4N)] and [Os5H2(CO)14(C5H5N)]
No full textThe reaction of the hydrido cluster [Os5H2(CO)15] with pyridine, in n-octane under reflux, affords three neutral products [Os5H3(CO)14(C5H4N)] (1), [Os5H2(CO)14(C5H5N)] (2), and [Os5H2(CO)15(C5H5N)] which exists in two isomerisc forms (3a) and (3b), together with the monoanion [Os5H(CO)15]-. The complexes were characterized by spectroscopic, and in the case of (1) and (2) by single-crystal X-ray crystallographic techniques. Within the series of neutral compounds the pyridine ligand occupies a variety of co-ordination sites and displays different bonding modes. In the case of complexes (1), (3a), and (3b) the reaction with pyridine also results in a change in metal framework geometry from that present in the starting material. The structure of (1) consists of an edge-bridged tetrahedron of Os atoms with an orthometallated pyridyl ligand linking the apex Os atom of the tetrahedron to the Os atom which bridges the tetrahedron. In (2) the five Os atoms define a trigonal bipyramid. The pyridine ligand bonds to the cluster via nitrogen, and occupies a pseudo-'axial' site on one of the equatorial Os atoms. The spectroscopic data for (3a) and (3b) are consistent with the presence of an edged-bridged tetrahedral metal geometry, with the pyridine terminally bound to a co-ordination site on the edge-bridgine Os atom. In (3a) the pyridine occupies an equatorial site and in (3b) an axial site. A possible mechanism for the reaction is discussed
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