Isolation of Elusive HAsAsH in a Crystalline Diuranium(IV) Complex

The HAsAsH molecule has hitherto only been proposed tentatively as a short‐lived species generated in electrochemical or microwave‐plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(Tren^TIPS)}₂(μ‐η²:η²‐As₂H₂)] ( 3 , Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃; Prⁱ=CH(CH₃)₂). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back‐bonding‐type interactions from uranium to the HAsAsH π*‐orbital. This experimentally confirms the theoretically predicted excellent π‐acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane‐1,2‐diide form.     

Large Zero‐Field Splittings of the Ground Spin State Arising from Antisymmetric Exchange Effects in Heterometallic Triangles

[Ru₂Mn(O)(O₂CtBu)₆(py)₃] has an S=⁵/₂ ground state with a very large zero‐field splitting (ZFS) of D=2.9 cm^?1, as characterized by EPR spectroscopy at 4–330 GHz. This is far too large to be due to the Mn^II ion (D <0.2 cm^?1), as shown from the {Fe₂Mn} analogue, but can be modeled by antisymmetric exchange effects.     

Fragile black holes

The AdS/CFT correspondence may give a new way of understanding field theories in extreme conditions, as in the quark–gluon plasma phase of quark matter. The correspondence normally involves asymptotically AdS black holes with dual field theories which are defined on locally flat boundary spacetimes; the implicit assumption is that the distortions of spacetime which occur under extreme conditions do not affect the field theory in any unexpected way. However, AdS black holes are [to varying degrees] fragile, in the sense that they become unstable to stringy effects when their event horizons are sufficiently distorted. This implies that field theories on curved backgrounds may likewise be unstable in a suitable sense. We investigate this phenomenon, focussing on the “fragility” of AdS₅ black holes with flat event horizons. We find that, when they are distorted, these black holes are always unstable in string theory. This may have consequences for the detailed structure of the quark matter phase diagram at extreme values of the spacetime curvature.     

[UIII{N(SiMe2tBu)2}3]: A Structurally Authenticated Trigonal Planar Actinide Complex

We report the synthesis and characterization of the uranium(III) triamide complex [U^III(N**)₃] [ 1 , N**=N(SiMe₂tBu)₂^?]. Surprisingly, complex 1 exhibits a trigonal planar geometry in the solid state, which is unprecedented for three‐coordinate actinide complexes that have exclusively adopted trigonal pyramidal geometries to date. The characterization data for [U^III(N**)₃] were compared with the prototypical trigonal pyramidal uranium(III) triamide complex [U^III(N“)₃] (N”=N(SiMe₃)₂^?), and taken together with theoretical calculations it was concluded that pyramidalization results in net stabilization for [U^III(N“)₃], but this can be overcome with very sterically demanding ligands, such as N**. The planarity of 1 leads to favorable magnetic dynamics, which may be considered in the future design of U^III single‐molecule magnets.     

Tripodal Thiols as Ligands for Molecular Magnets: Very Strong Antiferromagnetic Exchange Interactions in Vanadium(III) Clusters

The synthesis, structural and magnetic characterisation of [V^III₃O(tmme)₂(diimine)₂Cl] [diimine=2,2′‐bipyridine ( 1 ) or 1,10‐phenanthroline ( 2 )] and (HNEt₃)₂[V^III₄O(tmme)₄] ( 3 ) is reported, in which H₃tmme is tris(mercaptomethyl)ethane, MeC(CH₂SH)₃, the thiol analogue of the famous tripodal alcohol ligands typified by H₃thme [tris(hydroxymethyl)ethane, MeC(CH₂OH)₃]. Complexes 1 and 3 have “T‐shaped” and square topologies, respectively, and the latter is centred on a rare example of a square‐planar oxide. The tri‐thiolate ligands bind the periphery of the clusters and provide such strong antiferromagnetic exchange pathways that in both cases only a single total spin state is occupied up to room temperature, in the absence of metal–metal bonding. Magnetic data, electronic structure calculations and electrochemical data are reported.     

Morphology and statistical statics of simple microclusters

In this paper we discuss the statics of small assemblies of soft, rare-gas type atoms (N=4 to 13) interacting under simple two-body central forces such as the Lennard-Jones and Morse type. Our main concern is to characterize the problem of isomer multiplicity in small packed structures and to devise practical algorithms for the discovery of a representative majority, if not all, stable soft-packing structures for clusters of atoms in the above size-range.

We illustrate one such possible ‘Aufbau algorithm’ by demonstrating the existence of no less than 988 distinct, stable minimum configurations for 13 Lennard-Jones atoms and of correspondingly smaller numbers in the range N=7 to 12. The minimal structures obtained may be classified broadly into ‘crystallographic’ and ‘non-crystallographic’ types, the latter predominating among those of greatest binding energy.

A surprising result is that, when the softer (α=3) Morse potential is used, the great majority of the Lennard-Jones minima are not supported and only a much smaller class of distinct structures survive. Moreover, broadly speaking, crystallographic configurations are favoured by the softer potential, in confirmation of the intuitive view that relatively hard potentials dispose to amorphous structure.

These results, representing the probable structures of free condensation nuclei near 0 K, provide an interesting statistical morphology for small nuclei, as well as being a necessary first step in the construction of a statistical thermodynamics valid at finite temperatures.