Photochemical reactions of Re(CO)(5)Br with tetraalkyldiphosphine disulfides (R=Me, Et, Pr-n, Bu-n, Ph) and the crystal structure of [ReBr(CO)(3)(Et2P(S)P(S)Et-2)]

WOS: 000184113200005The hitherto unknown series of complexes fac-[Re(CO)(3)Br{R2P(S)P(S)R-2}] 1a-5a (1a, R = Me; 2a, R = Et; 3a, R = Pr-n; 4a, R = Bu-n; 5a, R = Ph) and [Re-2(CO)(8)Br-2{cis-mu-R2P(S)P(S)R-2}] 1b-5b [1b, R = Me; 2b, R = Et; 3b, R = Pr-n; 4b, R = Bu-n; 5b, R = Ph] have been prepared by the photochemical reaction of Re(CO)(5)Br with R2P(S)P(S)R-2. The complexes have been characterized by elemental analysis, mass spectroscopy (EI), FT-IR and P-31{H-1} NMR spectrometry. The spectroscopic studies suggest cis-chelate bidentate coordination of the ligand in fac-[Re(CO)(3)Br{R2P(S)P(S)R-2}] and cis-bridging bidentate coordination of the ligand between two metals in [Re-2(CO)(8)Br-2{cis-mu-R2P(S)P(S)R-2}] (R = Me, Et, Pr-n, Bu-n, Ph). An X-ray diffraction study of [ReBr(CO)(3)(Et2P(S)P(S)Et-2)] confirms that the rhenium, adopts a distorted octahedral geometry with local C-5 symmetry. (C) 2003 Elsevier Science Ltd. All rights reserved

Photochemical reactions of metal carbonyls [M(CO)(6) (M=Cr, Mo, W), Re(CO)(5)Br, Mn(CO)(3)CP] with 3,5-dimethyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione (DTTT) and the crystal structure of [W(CO)(5)(DTTT)]

WOS: 000184113200009Five new complexes, [M(CO)(5)(DTTT)] [M = Cr; 1, Mo; 2, W; 3], [Re(CO)(4)Br(DTTT)] (4) and [Mn(CO)(2)Cp(DTTT)] (5) have been synthesized by the photochemical reaction of metal carbonyls [M(CO)(6)] (M = Cr, Mo and W), [Re(CO)(5)Br], and [Mn(CO)(3)Cp] with 3,5-dimethyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione (DTTT). The complexes have been characterized by elemental analysis, mass spectrometry, FTIR, H-1 and C-13{H-1} NMR spectroscopy. The spectroscopic studies show that DTTT behaves as a monodentate ligand coordinating via the sulfur (C=S) donor atom in 1-5. An X-ray diffraction study Of [W(CO)(5)(DTTT)] (3) confirms that the tungsten adopts a distorted octahedral geometry with local C-4nu symmetry. (C) 2003 Elsevier Science Ltd. All rights reserved

Stable methane hydrate above 2 GPa and the source of Titan's atmospheric methane

Methane hydrate is thought to have been the dominant methane-containing phase in the nebula from which Saturn, Uranus, Neptune and their major moons formed1. It accordingly plays an important role in formation models of Titan, Saturn's largest moon. Current understanding1, 2 assumes that methane hydrate dissociates into ice and free methane in the pressure range 1\ufffd2 GPa (10\ufffd20 kbar), consistent with some theoretical3 and experimental4, 5 studies. But such pressure-induced dissociation would have led to the early loss of methane from Titan's interior to its atmosphere, where it would rapidly have been destroyed by photochemical processes6, 7. This is difficult to reconcile with the observed presence of significant amounts of methane in Titan's present atmosphere. Here we report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behaviour of methane hydrate at pressures up to 10 GPa. We find structural transitions at about 1 and 2 GPa to new hydrate phases which remain stable to at least 10 GPa. This implies that the methane in the primordial core of Titan remained in stable hydrate phases throughout differentiation, eventually forming a layer of methane clathrate approximately 100 km thick within the ice mantle. This layer is a plausible source for the continuing replenishment of Titan's atmospheric methane.NRC publication: Ye