Highly porous nature of a primitive asteroid revealed by thermal imaging.

Carbonaceous (C-type) asteroids1 are relics of the early Solar System that have preserved primitive materials since their formation approximately 4.6 billion years ago. They are probably analogues of carbonaceous chondrites2,3 and are essential for understanding planetary formation processes. However, their physical properties remain poorly known because carbonaceous chondrite meteoroids tend not to survive entry to Earth's atmosphere. Here we report on global one-rotation thermographic images of the C-type asteroid 162173 Ryugu, taken by the thermal infrared imager (TIR)4 onboard the spacecraft Hayabusa25, indicating that the asteroid's boulders and their surroundings have similar temperatures, with a derived thermal inertia of about 300 J m-2 s-0.5 K-1 (300 tiu). Contrary to predictions that the surface consists of regolith and dense boulders, this low thermal inertia suggests that the boulders are more porous than typical carbonaceous chondrites6 and that their surroundings are covered with porous fragments more than 10 centimetres in diameter. Close-up thermal images confirm the presence of such porous fragments and the flat diurnal temperature profiles suggest a strong surface roughness effect7,8. We also observed in the close-up thermal images boulders that are colder during the day, with thermal inertia exceeding 600 tiu, corresponding to dense boulders similar to typical carbonaceous chondrites6. These results constrain the formation history of Ryugu: the asteroid must be a rubble pile formed from impact fragments of a parent body with microporosity9 of approximately 30 to 50 per cent that experienced a low degree of consolidation. The dense boulders might have originated from the consolidated innermost region or they may have an exogenic origin. This high-porosity asteroid may link cosmic fluffy dust to dense celestial bodies10.

A new route to metal azides.

Beside several other applications, metal azides can be used for the synthesis of nitridophosphates and binary nitrides. Herein we present a novel synthetic access to azides: Several metals, such as main-group, transition metals, and rare-earth metals, react with silver azide in liquid ammonia as a solvent giving the corresponding metal azides. In this work Mn(N3)2, Sn(N3)2, and Eu(N3)2, as well as their ammonia complexes were synthesized for the first time through low-temperature methods. Also a simpler access to Zn(N3)2 was possible. At room temperature and the respective vapor pressure of NH3, it became possible to grow single crystals of the dinuclear holmium azide [Ho2(µ-NH2)3(NH3)10](N3)3⋅1.25NH3. We are confident that this new route could lead to novel metal azides as well as nitrides of the main-group, the transition, and the rare-earth metals upon careful decomposition.

Crystal structure of Ag2(µ-SCN)2(NH3)4.

Di-µ-thio-cyanato-bis-[diamminesilver(I)], [Ag2(µ-SCN)2(NH3)4], was synthesized by the reaction of AgSCN with anhydrous liquid ammonia. In the binuclear mol-ecule, the Ag(I) atom is coordinated by two ammine ligands and the S atom of one thio-cyanate ligand. Two of these [Ag(SCN)(NH3)2] units are bridged by the S atoms of the thio-cyanate anions at longer distances, leading to a dimer with point group symmetry C 2. The distance between the Ag(I) atoms in the dimer is at 3.0927 (6) Šwithin the range of argentophilic inter-actions. The crystal structure displays N-H⋯N and N-H⋯S hydrogen-bonding inter-actions that build up a three-dimensional network.

Crystal structure of [Co(NH3)6][Co(CO)4]2.

Hexaamminecobalt(II) bis-[tetra-carbonyl-cobaltate(-I)], [Co(NH3)6][Co(CO)4]2, was synthesized by reaction of liquid ammonia with Co2(CO)8. The Co(II) atom is coordinated by six ammine ligands. The resulting polyhedron, the hexa-amminecobalt(II) cation, exhibits point group symmetry -3. The Co(-I) atom is coordinated by four carbonyl ligands, leading to a tetra-carbonyl-cobaltate(-I) anion in the shape of a slightly distorted tetra-hedron, with point group symmetry 3. The crystal structure is related to that of high-pressure BaC2 (space group R-3m), with the [Co(NH3)6](2+) cations replacing the Ba sites and the [Co(CO)4](-) anions replacing the C sites. N-H⋯O hydrogen bonds between cations and anions stabilize the structural set-up in the title compound.