Diacetonitrile[N,N′-bis(2,6-diisopropyl-phenyl)ethane-1,2-diimine] dichloridochromium(II) acetonitrile solvate

The title compound, [CrCl2(CH3CN)2(C 26H36N2)]·CH3CN, was synthesized by the reaction of CrCl2(THF)2 with N,N′-bis-(2,6- diisopropyl-phen-yl)ethane-1,2-diimine in dichloro-methane/acetonitrile. The chromium center is coordinated by two N atoms of the chelating diimine ligand, two chloride ions in a trans configuration with respect to each other, and by two N atoms of two acetonitrile mol-ecules in a distorted octa-hedral geometry

Trans-Di-μ-acetato-[μ-N,N-bis-(diphenyl-phosphino)aniline] bis-[chlorido-molybdenum(II)](Mo - Mo)-dichloro-methane-tetra-hydro-furan (1/0.3/1.7)

The mol-ecular structure of the title compound, [Mo2(CH 3COO)2Cl2(C30H25NP 2)]·0.3CH2Cl2·1.7C 4H8O, features an Mo - Mo dumbbell bridged by two acetate groups which are trans to each other. Perpendicular to the plane spanned by the acetate groups, the Ph2PN(Ph)PPh2 ligand bridges both Mo atoms, having a P - N - P angle of 114.09 (19)°. In a trans position to the PNP ligand are two Cl atoms, one on each molybdenum centre. The Mo - Mo bond distance is 2.1161 (9) Å, within the range known for Mo - Mo quadruple bonds. The Mo complex is located on a crystallographic twofold rotation axis which runs through the N - C bond of the ligand. The site occupation factors of the disordered solvent molecules were fixed to 0.15 for dichloromethane and 0.85 for tetrahydrofuran. © 2009

[2,2-Bis(diphenylphosphanyl)propane κ2P,P0] tetracarbonylchromium(0)dichloromethane monosolvate

The title compound, [Cr(C27H26P2)(CO) 4]·CH2Cl2, was obtained by the reaction of Ph2PCMe2PPh2 with Cr(CO)6 in refluxing toluene by substitution of two carbonyl ligands. The CrC 4P2 coordination geometry at the Cr atom is distorted octa-hedral, with a P - Cr - P bite angle of 70.27 (2)°

Stability of accretion disk around rotating black holes: a pseudo-general-relativistic fluid dynamical study

We discuss the solution of accretion disk when the black hole is chosen to be rotating. We study, how the fluid properties get affected for different rotation parameters of the black hole. We know that no cosmic object is static in Universe. Here the effect of the rotation of the black hole to the space-time is considered following an earlier work of the author, where the pseudo-Newtonian potential was prescribed for the Kerr geometry. We show that, with the inclusion of rotation of the black hole, the valid disk parameter region dramatically changes and disk becomes unstable. Also we discuss about the possibility of shock in accretion disk around rotating black holes. When the black hole is chosen to be rotating, the sonic locations of the accretion disk get shifted or disappear, making the disk unstable. To bring it in the stable situation, the angular momentum of the accreting matter has to be reduced/enhanced (for co/counter-rotating disk) by means of some physical process.Comment: 24 Latex pages including 7 figures; Accepted for publication in Astrophysical Journa

[N,N-Bis(diphenyl­phosphino)isopropyl­amine]dibromidonickel(II)

The title compound, [NiBr2(C27H27NP2)], was synthesized by the reaction of NiBr2(dme) (dme is 1,2-dimethoxy-ethane) with N,N-bis-(diphenyl-phosphino)isopropyl-amine in methanol/tetra-hydro-furan. The nickel(II) center is coordinated by two P atoms of the chelating PNP ligand, PH2PN(iPr)PPH2, and two bromide ions in a distorted square-planar geometry

1,1,2,2-Tetra-phenyl-15-diphosphane 1-sulfide

In the title mol-ecule, C24H20P2S, the P - P bond length is 2.2263 (5) Å. The two phenyl rings attached to the three- and five-coordinated P atoms, respectively, form dihedral angles of 56.22 (5) and 71.74 (5)°

Global Dynamics of Advection-Dominated Accretion Revisited

We numerically solve the set of dynamical equations describing advection-dominated accretion flows (ADAF) around black holes, using a method similar to that of Chakrabarti (1996a). We choose the sonic radius of the flow $R_s$ and the integration constant in angular momentum equation $j$ as free parameters, and integrate the equations from the sonic point inwards to see if the solution can extend supersonically to the black hole horizon, and outwards to see if and where an acceptable outer boundary of the flow can be found. We recover the ADAF-thin disk solution constructed in Narayan, Kato, & Honma (1997, NKH97), an representative paper of the previous works on global ADAF solutions, although in that paper an apparently very different procedure was adopted. We obtain a complete picture in the form of $R_s-j$ parameter space which sums up the situation of ADAF solution at a glance. For comparison we also present the distribution of global solutions for inviscid flows in the $R_s-j$ space, which supports the view that there should be some similarities between the dynamical behavior of ADAF and that of adiabatic flows, and that there should be a continuous change from the properties of viscous flows to those of inviscid ones.Comment: 24 pages with 15 figures, to appear in ApJ Vol. 52

Secular instability in quasi-viscous disc accretion

A first-order correction in the $\alpha$-viscosity parameter of Shakura and Sunyaev has been introduced in the standard inviscid and thin accretion disc. A linearised time-dependent perturbative study of the stationary solutions of this "quasi-viscous" disc leads to the development of a secular instability on large spatial scales. This qualitative feature is equally manifest for two different types of perturbative treatment -- a standing wave on subsonic scales, as well as a radially propagating wave. Stability of the flow is restored when viscosity disappears.Comment: 15 pages, 2 figures, AASTeX. Added some new material and upgraded the reference lis