The Renaissance of Black Phosphorus

One hundred years after its first successful synthesis in the bulk form in 1914, black phosphorus (black P) was recently rediscovered from the perspective of a two-dimensional (2D) layered material, attracting tremendous interest from condensed matter physicists, chemists, semiconductor device engineers and material scientists. Similar to graphite and transition metal dichalcogenides (TMDs), black P has a layered structure but with a unique puckered single layer geometry. Because the direct electronic band gap of thin film black P can be varied from 0.3 to around 2 eV, depending on its film thickness, and because of its high carrier mobility and anisotropic in-plane properties, black P is promising for novel applications in nanoelectronics and nanophotonics different from graphene and TMDs. Black P as a nanomaterial has already attracted much attention from researchers within the past year. Here, we offer our opinions on this emerging material with the goal of motivating and inspiring fellow researchers in the 2D materials community and the broad readership of PNAS to discuss and contribute to this exciting new field. We also give our perspectives on future 2D and thin film black P research directions, aiming to assist researchers coming from a variety of disciplines who are desirous of working in this exciting research field.Comment: 23 pages, 6 figures, perspective article, appeared online in PNA

Bis(2-amino­benzonitrile)tetra­aqua­cobalt(II) dichloride

In the crystal structure of the title compound, [Co(C7H6N2)2(H2O)4]Cl2, the CoII cation lies on an inversion center and is coordinated by two 2-amino­benzonitrile ligands and four water mol­ecules in a distorted octa­hedral geometry. The Cl− counter-anion links with the complex cations via O—H⋯Cl and N—H⋯Cl hydrogen bonding. Inter­molecular O—H⋯N hydrogen bonding links the complex cations, forming supra­molecular chains running along the b axis

Methyl 1-bromo-2-naphthoate

In the mol­ecular structure of the title compound, C12H9BrO2, the methoxy­carbonyl group is twisted by a dihedral angle of 29.8 (3)°with respect to the naphthalene ring system. An overlapped arrangement is observed between parallel naphthalene ring systems of adjacent mol­ecules, and the face-to-face distance of 3.590 (9) Å suggests there is π–π stacking in the crystal structure

3,5-Dichloro-N-(2-methyl­but-3-yn-2-yl)benzamide

In the title compound, C12H11Cl2NO, the amide group is twisted by a dihedral angle of 31.98 (2)° with respect to the benzene ring. In the crystal structure, mol­ecules are linked via N—H⋯O hydrogen bonds, forming one-dimensional supra­molecular chains

4-Benzhydryl-1-cinnamylpiperazin-1-ium nitrate

In the title compound, C26H29N2 +·NO3 −, the dihedral angle formed by the phenyl rings of the benzhydryl group is 66.18 (9)°. Crystal cohesion is enforced by cation–anion C—H⋯O and N—H⋯O hydrogen bonds