The structures of 1:1 and 1:2 adducts of phosphanetricarbonitrile with 1,4-diazabicyclo[2.2.2]octane

In the structures of 1:1 and 1:2 adducts of phosphanetricarbonitrile (C3N3P) with 1,4-diazabicyclo[2.2.2]octane (C6H12N2), the 1:1 adduct crystallizes in the orthorhombic space group, Pbcm, with four formula units in the unit cell (Z′ = 0.5). The P(CN)3 unit lies on a crystallographic mirror plane while the C6H12N2 unit lies on a crystallographic twofold axis passing through one of the C—C bonds. The P(CN)3 moiety has close to C 3v symmetry and is stabilized by forming adducts with two symmetry-related C6H12N2 units. The phosphorus atom is in a five-coordinate environment. As a result of the symmetry, the two trans angles are equal so τ5 = 0.00 and thus the geometrical description could be considered to be square pyramidal. However, the electronic geometry is distorted octahedral with the lone pair on the phosphorous occupying the sixth position. As would be expected from VSEPR considerations, the repulsion of the lone-pair electrons with the equatorial bonding electrons means that the trans angles for the latter are considerably reduced from 180° to 162.01 (4)°, so the best description of the overall geometry for phosphorus is distorted square pyramidal. The 1:2 adduct crystallizes in the monoclinic space group, P21/m with two formula units in the asymmetric unit (i.e. Z' = 1/2). The P(CN)3 moiety lies on a mirror plane and one of the two C6H12N2 (dabco) molecules also lies on a mirror plane. The symmetry of the P(CN)3 unit is close to C 3v. There are three P...N interactions and consequently the molecular geometry of the phosphorus atom is distorted octahedral. This must mean that the lone pair of electrons on the phosphorus atom is not sterically active. For the 1:1 adduct, there are weak associations between the phosphorus atom and one of the terminal nitrogen atoms from the C[triple-bond] N moiety, forming chains in the a-axis direction. In addition there are weak C—H...N interactions between a terminal nitrogen atoms from the C[triple-bond]N moiety and the C6H12N2 molecules, which form sheets perpendicular to the a axis.

Low-temperature crystal structure of 4-chloro-1H-pyrazole

The structure of 4-chloro-1H-pyrazole, C3H3ClN2, at 170 K has orthorhombic (Pnma) symmetry and is isostructural to its bromo analogue. Data were collected at low temperature since 4-chloro-1H-pyrazole sublimes when subjected to the localized heat produced by X-rays. The structure displays intermolecular N—H...N hydrogen bonding and the packing features a trimeric molecular assembly bisected by a mirror plane (m normal to b) running through one chlorine atom, one carbon atom and one N—N bond. The asymmetric unit therefore consists of one and one-half 4-chloro-1H-pyrazole molecules. Thus, the N—H proton is crystallographically disordered over two positions of 50% occupancy each.

Polarization Flipping of Even-Order Harmonics in Monolayer Transition-Metal Dichalcogenides

We present a systematic study of the crystal-orientation dependence of high-harmonic generation in monolayer transition-metal dichalcogenides, WS2 and MoSe2, subjected to intense linearly polarized midinfrared laser fields. The measured spectra consist of both odd- and even-order harmonics, with a high-energy cutoff extending beyond the 15th order for a laser-field strength around ~1 V/nm. In WS2, we find that the polarization direction of the odd-order harmonics smoothly follows that of the laser field irrespective of the crystal orientation, whereas the direction of the even-order harmonics is fixed by the crystal mirror planes. Furthermore, the polarization of the even-order harmonics shows a flip in the course of crystal rotation when the laser field lies between two of the crystal mirror planes. By numerically solving the semiconductor Bloch equations for a gapped-graphene model, we qualitatively reproduce these experimental features and find the polarization flipping to be associated with a significant contribution from interband polarization. In contrast, high-harmonic signals from MoSe2 exhibit deviations from the laser-field following of odd-order harmonics and crystal-mirror-plane following of even-order harmonics. We attribute these differences to the competing roles of the intraband and interband contributions, including the deflection of the electron-hole trajectories by nonparabolic crystal bands.

Skyrmion crystals in centrosymmetric itinerant magnets without horizontal mirror plane

We theoretically investigate a new stabilization mechanism of a skyrmion crystal (SkX) in centrosymmetric itinerant magnets with magnetic anisotropy. By considering a trigonal crystal system without the horizontal mirror plane, we derive an effective spin model with an anisotropic Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction for a multi-band periodic Anderson model. We find that the anisotropic RKKY interaction gives rise to two distinct SkXs with different skyrmion numbers of one and two depending on a magnetic field. We also clarify that a phase arising from the multiple-Q spin density waves becomes a control parameter for a field-induced topological phase transition between the SkXs. The mechanism will be useful not only for understanding the SkXs, such as that in Gd$$_2$$ 2 PdSi$$_3$$ 3 , but also for exploring further skyrmion-hosting materials in trigonal itinerant magnets.

Determination of Potassium Levels in Bananas Using an Optical Sensor with a Flat and Concave Mirror Plane

Potassium is a nutrient that plays a role in maintaining the function of the muscles and nerves that control the heart and is needed for body stability. The potassium content in the body can be obtained from foods such as bananas. The development of instruments and methods that are developed to obtain a more accurate measurement of potassium concentration requires an instrument that has high linearity and sensitivity. The instrument is in the form of an optical sensor system equipped with the use of optical fibers to guide the waveform to maintain its intensity stability. In this study, an experimental method was conducted with a sample of a standard solution with potassium as the solute and pure water as the solvent. Then continue to measurements on samples of banana milk and green banana fruit extracts. The results of the analysis of the measurement data using an optical sensor with a concave mirror reflection plane obtained a sensitivity of 0.36 mV/ppm and a linearity of 82.56%. In the plane of the flat mirror reflection, obtained an optical sensor with a plane mirror reflection plane shows a sensitivity of 0.12 mV/ppm and a linearity of 97.6%. The highest and most accurate linearity value is found in the plane mirror plane results. The next stage is the result of the maximum output voltage read on the optical detector through an optical sensor with a sample of extracts of milk banana and green banana. The results of data analysis on the linear equation with the highest linearity obtained the potassium content in milk bananas of 391.54 ppm and the green banana extract solution obtained 307.91 ppm, so it can be concluded that the potassium content in milk bananas is higher than green bananas with a linearity of more than 97%.

Synthesis and crystal structures of 3,6-dihydroxypicolinic acid and its labile intermediate dipotassium 3-hydroxy-6-(sulfonatooxy)pyridine-2-carboxylate monohydrate

A simplified two-step synthesis of 3,6-dihydroxypicolinic acid (3-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxylic acid), C6H5NO4 (II), an intermediate in the metabolism of picolinic acid, is described. The crystal structure of II, along with that of a labile intermediate, dipotassium 3-hydroxy-6-(sulfonatooxy)pyridine-2-carboxylate monohydrate, 2K+·C6H3NO7S2−·H2O (I), is also described. Compound I comprises a pyridine ring with carboxylate, hydroxyl (connected by an intramolecular O—H...O hydrogen bond), and sulfate groups at the 2-, 3-, and 6-positions, respectively, along with two potassium cations for charge balance and one water molecule of crystallization. These components are connected into a three-dimensional network by O—H...O hydrogen bonds arising from the water molecule, C—H...O interactions and π–π stacking of pyridine rings. In II, the ring nitrogen atom is protonated, with charge balance provided by the carboxylate group (i.e., a zwitterion). The intramolecular O—H...O hydrogen bond observed in I is preserved in II. Crystals of II have unusual space-group symmetry of type Abm2 in which extended planar networks of O—H...O and N—H...O hydrogen-bonded molecules form sheets lying parallel to the ac plane, constrained to b = 0.25 (and 0.75). The structure was refined as a 50:50 inversion twin. A minor disorder component was modeled by reflection of the major component across a mirror plane perpendicular to c.

Intrinsic in-plane nodal chain and generalized quaternion charge protected nodal link in photonics

Nodal lines are degeneracies formed by crossing bands in three-dimensional momentum space. Interestingly, these degenerate lines can chain together via touching points and manifest as nodal chains. These nodal chains are usually embedded in two orthogonal planes and protected by the corresponding mirror symmetries. Here, we propose and demonstrate an in-plane nodal chain in photonics, where all chained nodal lines coexist in a single mirror plane instead of two orthogonal ones. The chain point is stabilized by the intrinsic symmetry that is specific to electromagnetic waves at the Г point of zero frequency. By adding another mirror plane, we find a nodal ring that is constructed by two higher bands and links with the in-plane nodal chain. The nodal link in momentum space exhibits non-Abelian characteristics on a C2T - invariant plane, where admissible transitions of the nodal link structure are determined by generalized quaternion charges. Through near-field scanning measurements of bi-anisotropic metamaterials, we experimentally mapped out the in-plane nodal chain and nodal link in such systems.

Lithium dipotassium citrate monohydrate, LiK2C6H5O7(H2O)

The crystal structure of dilithium potassium citrate monohydrate, Li+·2K+·C6H5O7 3−·H2O or LiK2C6H5O7·H2O, has been solved by direct methods and refined against laboratory X-ray powder diffraction data, and optimized using density functional techniques. The complete citrate trianion is generated by a crystallographic mirror plane, with two C and three O atoms lying on the reflecting plane, and chelates to three different K cations. The KO8 and LiO4 coordination polyhedra share edges and corners to form layers lying parallel to the ac plane. An intramolecular O—H...O hydrogen bond occurs between the hydroxyl group and the central carboxylate group of the citrate anion as well as a charge-assisted intermolecular O—H...O link between the water molecule and the terminal carboxylate group. There is also a weak C—H...O hydrogen bond.

Polymorphism of dimethylaminoborane N(CH3)2-BH2

Dehydrocoupling of the adduct of dimethylamine and borane, NH(CH3)2-BH3 leads to dimethylaminoborane with formal composition N(CH3)2-BH2. The structure of this product depends on the conditions of the synthesis; it may crystallize either as a dimer in a triclinic space group forming a four-membered ring [N(CH3)2-BH2]2 or as a trimer forming a six-membered ring [N(CH3)2-BH2]3 in an orthorhombic space group. Due to the denser packing, the six-membered ring in the trimer structure should be energetically more stable than the four-membered ring. The triclinic structure is stable at low temperatures. Heating the triclinic phase above 290 K leads to a second-order phase transition to a new monoclinic polymorph. While the crystal structures of the triclinic and orthorhombic phases were already known in the literature, the monoclinic crystal structure was determined from powder diffraction data in this study. Monoclinic dimethylaminoborane crystallizes in space group C2/m with the boron and nitrogen atoms located on the mirror plane, Wyckoff position 4i, while the carbon and hydrogen atoms are on the general position 8j.