2,972 research outputs found
Tetrel–Hydride Interaction between XH<sub>3</sub>F (X = C, Si, Ge, Sn) and HM (M = Li, Na, BeH, MgH)
No full textA tetrel–hydride
interaction was predicted and characterized
in the complexes of XH<sub>3</sub>F···HM (X = C, Si,
Ge, Sn; M = Li, Na, BeH, MgH) at the MP2/aug-cc-pVTZ level, where
XH<sub>3</sub>F and HM are treated as the Lewis acid and base, respectively.
This new interaction was analyzed in terms of geometrical parameters,
interaction energies, and spectroscopic characteristics of the complexes.
The strength of the interaction is essentially related to the nature
of X and M groups, with both the larger atomic number of X and the
increased reactivity of M giving rise to a stronger tetrel–hydride
interaction. The tetrel–hydride interaction exhibits similar
substituent effects to that of dihydrogen bonds, where the electron-donating
CH<sub>3</sub> and Li groups in the metal hydride strengthen the binding
interactions. NBO analyses demonstrate that both BD<sub>H–M</sub> → BD*<sub>X–F</sub> and BD<sub>H–M</sub> →
BD*<sub>X–H</sub> orbital interactions play the stabilizing
role in the formation of the complex XH<sub>3</sub>F···HM
(X = C, Si, Ge, and Sn; M = Li, Na, BeH, and MgH). The major contribution
to the total interaction energy is electrostatic energy for all of
the complexes, even though the dispersion/polarization parts are nonnegligible
for the weak/strong tetrel–hydride interaction, respectively
Ar-40-Ar-39 plateau ages of biotite and amphibole from tonalite of Huangling granitoids and their cooling curve.
No full textAb initio valence bond study on AB-type molecules. A description for XH (X = Li, Be, B, C, N, O, F) and XF (X = Li, Be, B)
No full textAb initio valence bond method is employed to quantitatively study the concepts of ionic resonance energy mid ionicity of a chemical bond in the cases of hydrides XH (X = Li, Be, B, C, N, O, F) and fluorides XF (X = Li, Be, B). By establishing the relationship between resonance and stability, and comparing the calculated ionicities with Pauling's earlier estimations in the above diatomic molecules, the merits of Pauling's classical resonance theory were demonstrated at the ab initio level
Synthesis and characterisation of some main-group compounds with bulky electron-withdrawring substituents
Full text linkSeveral new group 13, 14 and 15 derivatives with the ligands 2,4,6-(CF(_3))(_3)C(_6)H(_2) (Ar), 2,6- (CF(_3))(_2)C(_6)H(_3) (Ar') and / or 2,4-(CF(_3))(_2)C(_6)H(_3) (Ar") have been prepared. They have been characterised by multinuclear NMR spectroscopy and, for all isolated compounds, by elemental analysis and, where possible, single crystal X-ray diffraction. Reaction of ArLi or the mixture Ar'Li/Ar"Li with BCI3 has led to the characterisation of several mono- and disubstituted compounds, but attempted substitution in AICI3 was unsuccessful. Reaction of EC1(_4) (E = Si, Ge, Sn) with the Ar'Li/Ar"Li mixture yielded predominantly the less sterically hindered disubstituted product Ar"(_2)ECl(_2) for E = Si and Ge but to Ar'(_2)ECl(_2) for E = Sn. In the case of B or Si, chlorine exchange is observed and Ar(_2)BF, Ar(_2)SiF(_2) and Ar'(_2)SiF(_2) have been synthesised. Ar(_2)SiF(_2) is the only product identified in the reaction of ArLi with SiC1(_4). Reaction of ArLi or the Ar'Li/Ar"Li mixture, in an appropriate ratio, with group 15 derivatives gave rise to several mono-or disubstituted compounds of the type ArEX(_2), Ar(_2)EX, Ar'EX(_2), Ar"EX(_2), Ar"(_2)EX and Ar'Ar"EX (E = P or As; X = H, CI or Br). (^19)F NMR spectra of Ar'Ar"EX show that, for the two ortho-CF(_3) groups of the Ar' moiety, there is free rotation of the aryl group around the central atom. A series of variable temperature studies has been carried out, and allowed the determination of the rotational energy barrier of the molecule. For the first time, the molecular structures of derivatives containing three fluoroxyl ligands have been determined (Ar"(_3)B and Ar'Ar"(_2)Sb).The synthesis of some new platinum complexes has been facilitated by reaction of phosphanes with the platinum dimer [(PtCl(_2)(Pet(_3))](_2) or [(PtBr(_2)(Pet(_3))](_2). Reactions of the platinum dimer with arsane derivatives have not been successful. Halogen exchange was observed between bromophosphane ligands and CI groups on the platinum. Attempts have been made to synthesise new P=E derivatives containing the electron- withdrawing substituents Ar or Ar' via reaction with the chlorine abstractor W(PMe(_3))(_6)- ArP=PAr and Ar'P=PAr' have been prepared. Synthesis of the first phosphaalkyne containing Ar or Ar' has been attempted by reacting a phosphaalkene with a Pt(0) species
Self-assembly of hydrogen-bonded polymeric rods based on the cyanuric acid center dot melamine lattice
No full textThis paper describes the self-assembly of hydrogen-bonded polymeric rods based on the lattice of cyanuric acid and melamine (CA . M). Data from H-1 NMR spectroscopy, IR spectroscopy, gel permeation chromatography (GPC), and transmission electron microscopy (TEM) are interpreted as indicating that the self-assembly of a bisisocyanuric acid (bisCA) and a bismelamine (bisM) formed polymeric nanorods [(bisCA)(n)(bisM)(n)] composed of parallel CA . M rosettes. The TEM results suggest that these rods aggregate as bundles. The length of the bundles ranged from 100 to 1500 nm, and their diameter was in the range from 15 to 500 nm
Quantum Monte Carlo and high-level ab initio molecular orbital investigation of dissociation channels of the positronic alkali-metal hydrides, [XH;e
No full textEnergy thresholds for dissociation channels of positronic alkali-metal hydrides, [XH;e+] (X = Li, Na, and K), to XH + e+(positron dissociation), XH+ + Ps (positronium dissociation), and X+ + [H−;e+] (positronic hydride ion dissociation) have been calculated using quantum Monte Carlo and high-level ab initio molecular orbital methods, and including quantum zero-point vibrational energy of all of the particles. As the atomic number of X increases from Li to K, the dissociation energy to XH + e+ increases because the dipole moment of XH increases with the atomic number of X, while the dissociation energy to XH+ + Ps decreases. The energy threshold for the ionic dissociation to X+ + [H−;e+] is also reduced, and we obtain 0.975 (3) eV, 0.573 (12) eV, and 0.472 (19) eV for [LiH;e+], [NaH;e+], and [KH;e+], respectively, for this channel. Our results strongly support the conclusion that, among these three channels, the lowest energy dissociation for [XH;e+] is the pathway to X+ + [H−;e+], where X = Li, Na, and K
Ca. 850 Ma intraplate magmatism in South China: implications for onset of the breakup of Rodinia
No full textDifferentially methylated genes shared by WRR<sub>h</sub> Vs. WRR<sub>l</sub>, XH<sub>h</sub> Vs. XH<sub>l</sub>, WRR<sub>h</sub> Vs. XH<sub>h</sub>, and WRR<sub>l</sub> Vs. XH<sub>l</sub>.
No full text<p>Differentially methylated genes shared by WRR<sub>h</sub> Vs. WRR<sub>l</sub>, XH<sub>h</sub> Vs. XH<sub>l</sub>, WRR<sub>h</sub> Vs. XH<sub>h</sub>, and WRR<sub>l</sub> Vs. XH<sub>l</sub>.</p
Neoproterozoic bimodal magmatism in the Cathaysia Block of South China and its tectonic significance
No full textSHRIMP U–Pb zircon age, geochemical and Sm–Nd isotopic results are reported for the Mamianshan volcanic rocks in the Cathaysia Block of southeastern South China. The Mamianshan volcanic rocks are bimodal in composition and are dominantly transitional to mildly alkaline basalts and subordinate alkaline rhyolite, with an eruption age of 818±9 Ma. The basaltic samples are characterized by LREE-enriched and “humped” trace element patterns, similar to many alkali basalts in continental rifts. Variable _Nd(T) values between +3.33 and-4.35 indicate that the primary magma of these basalts was derived from an OIB-like mantle source and underwent fractional crystallization plus crustal contamination. The rhyolitic rocks are highly enriched in Th, Ta, Nb, REE, Zr, Hf and Y and depleted in Sr, P, Eu and Ti, sharing affinity to A1-type granites. Combined with their slightly positive _Nd(T) values (+0.22 to +0.92), the Mamianshan felsic rocks were most likely generated by partial melting of the regional Paleoproterozoic Mayuan amphibolites. The Mamianshan bimodal volcanic rocks in the Cathaysia Block are coeval with the widespread intraplate magmatism around the Yangtze Block. Our results support the idea that a coherent South China Craton was formed during the ca. 1.0 Ga Sibao orogeny, and it subsequently underwent extensive continental rifting related to mantle plume or superplume activities beneath Rodinia since ca. 825 Ma
Middle Neoproterozoic syn-rifting volcanic rocks in Guangfeng, South China: petrogenesis and tectonic significance
Full text linkMiddle Neoproterozoic igneous rocks are widespread in South China, but their petrogenesis and tectonic implications are still highly controversial. The Guangfeng middle Neoproterozoic volcani-sedimentary succession was developed on a rare Sibaoan metamorphic basement (the Tianli Schists) inthe southeastern Yangtze Block, South China. This paper reports geochronological, geochemical and Nd isotopic data for the volcanic rocks in this succession. The volcanic rocks consist of alkaline basalts, andesites and peraluminous rhyolites. SHRIMP U-Pb zircon age determinations indicate that they were erupted at 827+- 14 Ma, coeval with a widespread episode of anorogenic magmatism in South China. Despite showing Nb-Ta depletion relative to La and Th, the alkaline basalts are characterized by highly positive eNd(T) values (+3.1 to +6.0), relatively high TiO2 and Nb contents and high Zr/Y and super-chondritic Nb/Ta ratios, suggesting their derivation from a slab melt-metasomatized subcontinental lithospheric mantle source in an intracontinental rifting setting. The andesites have significantly negative eNd(T) values (-9.3 to-11.1) and a wide range of SiO2 contents (57.6-65.6 %).They were likely generated by the mixing of fractionated basaltic melts with felsic melts derived from the Archaean metasedimentary rocks in the middle to lower crust. The rhyolites are highly siliceous and peraluminous. They are characterized by depletion in Nb, Ta, Sr, P and Ti and relatively high eNd(T)values (-3.0 to -4.8), broadly similar to those of the adjacent c. 820 Ma peraluminous granitoids derived from the Mesoproterozoic to earliest Neoproterozoic sedimentary source at relatively shallowlevels. We conclude that the Guangfeng volcanic suite is a magmatic response of variant levels of continental lithosphere (including lithospheric mantle and the lower-middle to upper crust) to the middle Neoproterozoic intracontinental rifting possibly caused by mantle plume activity
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