2,5-Dibromo­pyridine

In the title compound, C5H3Br2N, C—H⋯N hydrogen-bonding inter­actions and Br⋯Br inter­actions [3.9418 (3) and 3.8986 (3) Å] connect the mol­ecules into planar sheets stacked perpendicular to the b axis. In addition, pyrid­yl–pyridyl inter­sheet π–π stacking inter­actions [centroid–centroid distance = 4.12 (1) Å] result in a three-dimensional network

(E)-1,3-Bis(2,3,4,5,6-penta­fluoro­phen­yl)prop-2-en-1-one

In the title compound, C15H2F10O, the two perfluorinated arene rings are tilted at an angle of 66.08 (5)° with respect to each other. The olefinic double bond adopts an E configuration and the single bond between the olefinic and carbonyl double bonds has an s-trans conformation. The carbonyl group is not in a coplanar alignment with respect to the neighbouring arene ring (0.963 Å from aryl plane) while being coplanar with regard to the olefinic double bond (0.0805 Å from olefinic bond). The crystal packing does not feature significant hydrogen-bond-type or stacking inter­actions

5,7-Dibromo-2-methyl­quinolin-8-ol

In the title compound, C10H7Br2NO, the mol­ecule possesses a planar geometry with an r.m.s deviation of 0.0383 Å for all non-H atoms. The crystal structure displays O—H⋯N and C—H⋯O hydrogen bonding, as well as Br⋯Br contacts [3.6284 (4) Å]

1-Bromo-2,3,5,6-tetra­fluoro-4-nitro­benzene

In the title compound, C6BrF4NO2, the nitro group is twisted by 41.7 (3)° with reference to the arene ring mean plane. The main inter­actions stabilizing the crystal structure include O⋯Br contacts [3.150 (2) and 3.201 (2) Å], while F⋯F inter­actions are minor [2.863 (3)–2.908 (3) Å]

Direct observation of the Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed matter physics. The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu$-$Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics, is prone to decay into a pair of low-energy Nambu$-$Goldstone modes in low dimensions. Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using the inelastic neutron scattering and applying the bond-operator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S=1/2 quantum antiferromagnet C$_9$H$_{18}$N$_2$CuBr$_4$ near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.Comment: 12 pages, 4 figures in the main text+3 figures in Supplementary Informatio

4′-(2,4-Dichloro­phen­yl)-1,1′-dimethyl­piperidine-3-spiro-3′-pyrrolidine-2′-spiro-3′′-indoline-4,2′′-dione

In the title compound, C23H23Cl2N3O2, the pyrroline ring adopts an envelope conformation and the piperidinone ring assumes a slightly twisted chair form. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds generate an R 2 8 graph-set motif and a short Cl⋯Cl contact of 3.478 (1) Å occurs

Bis(2,6-diamino-3,5-dibromo­pyridinium) hexa­bromidostannate(IV)

The asymmetric unit of the title compound, (C5H6Br2N3)2[SnBr6], contains one cation and one half-anion in which the Sn atom is located on a crystallographic centre of inversion and is in a quasi-octa­hedral geometry. The crystal structure is assembled via hydrogen-bonding inter­actions of two kinds, N(pyridine/amine)—H⋯Br—Sn, along with C—Br⋯Br—Sn interactions [3.4925 (19) Å]. The cations are involved in π–π stacking, which adds an extra supra­molecularity as it presents a strong case of offset-face-to-face motifs [centroid–centroid distance = 3.577 (3) Å]. The inter­molecular hydrogen bonds, short Br⋯Br inter­actions and π–π stacking result in the formation of a three-dimensional supra­molecular architecture

Bis(3-methyl­pyridinium) tetra­chlorido­cuprate(II)

The title compound, (C6H8N)2[CuCl4], is composed of two 3-methyl­pyridinium cation and one tetra­chloridocuprate(II) anion. The geometry around the copper(II) ion is that of a distorted tetra­hedron. In the crystal structure, the anions and cations are linked by three different N—H⋯Cl hydrogen bonds. In addition, the crystal structure exhibits aromatic π–π inter­actions between the pyridinium rings of two discrete units [centroid–centroid distance = 3.704 (2) Å]

Bis(2-bromo­pyridinium) hexa­chlorido­stannate(IV)

The asymmetric unit of the title compound, (C5H5BrN)2[SnCl6], contains one cation and one half-anion. The [SnCl6]2− anion is located on an inversion center and forms a quasi-regular octa­hedral arrangement. Hydrogen-bonding inter­actions of two kinds, viz. N—H⋯Cl—Sn and C—H⋯Cl—Sn, along with Cl⋯Br inter­actions [3.4393 (15) Å], connect the ions in the crystal structure into two-dimensional supra­molecular arrays. These supra­molecular arrays are arranged in layers approximately parallel to (110) built up from anions inter­acting with six symmetry-related surrounding cations