Structural, spectroscopic, and computational evaluations of cation-cation and halogen bonding interactions in heterometallic uranyl hybrid materials

Harnessing the nominally terminal oxo atoms of the linear uranyl (UO22+) cation represents a frontier within the field of f-element hybrid materials. Here we outline a route for systematically accessing uranyl oxo atoms via judicious pairing with Ag+ cations or iodobenzoates, and describe the syntheses and crystal structures of four new heterometallic compounds containing Ag+ cations, the UO22+ cation, and o- (1), m- (2), p-iodo- (3), and 2,5-diiodo- (4) carboxylate ligands. Vibrational and luminescence spectroscopic properties for all four compounds are reported, as are computational findings from quantum chemical calculations and density-based quantum theory of atoms in molecules (QTAIM) analyses. Single crystal X-ray diffraction analysis of compounds 1-4 shows that the nominally terminal uranyl oxo atoms are engaged in either covalent UO2-Ag cation-cation interactions (1 and 3) or non-covalent assembly via halogen bonding interactions (2 and 4). Raman, infrared (IR), and luminescence spectra of 1-4 are redshifted with respect to the free uranyl cation indicating that both halogen-oxo and cation-cation interactions weaken the UO bond, and in the case of 3 we note a rare example of activation of the uranyl asymmetric stretch (ν3) in the Raman spectra, likely due to the Ag-oxo cation-cation interaction lowering the symmetry of the uranyl cation. Quantum chemical calculations and QTAIM analysis highlight a quantitative difference between halogen bonds and cation-cation interactions, with the latter shown to significantly decrease uranyl bond orders and electron density at bond critical points

THE RATE OF BINARY BLACK HOLE MERGERS INFERRED FROM ADVANCED LIGO OBSERVATIONS SURROUNDING GW150914

A transient gravitational-wave signal, GW150914, was identi fi ed in the twin Advanced LIGO detectors on 2015 September 2015 at 09:50:45 UTC. To asse ss the implications of this discovery, the detectors remained in operation with unchanged con fi gurations over a period of 39 days around the time of t he signal. At the detection statistic threshold corresponding to that observed for GW150914, our search of the 16 days of simultaneous two-detector observational data is estimated to have a false-alarm rate ( FAR ) of < ́ -- 4.9 10 yr 61 , yielding a p -value for GW150914 of < ́ - 210 7 . Parameter estimation follo w-up on this trigger identi fi es its source as a binary black hole ( BBH ) merger with component masses ( )( ) = - + - + mm M ,36,29 12 4 5 4 4 at redshift = - + z 0.09 0.04 0.03 ( median and 90% credible range ) . Here, we report on the constraints these observations place on the rate of BBH coalescences. Considering only GW150914, assuming that all BBHs in the universe have the same masses and spins as this event, imposing a search FAR threshold of 1 per 100 years, and assuming that the BBH merger rate is constant in the comoving frame, we infer a 90% credible range of merger rates between – -- 2 53 Gpc yr 31 ( comoving frame ) . Incorporating all search triggers that pass a much lower threshold while accounting for the uncerta inty in the astrophysical origin of each trigger, we estimate a higher rate, ranging from – -- 13 600 Gpc yr 31 depending on assumptions about the BBH mass distribution. All together, our various rate estimat es fall in the conservative range – -- 2 600 Gpc yr 31