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

Docking, synthesis, and anticancer assessment of novel quinoline-amidrazone hybrids

A group of new amidrazone compounds that include a quinoline component was produced through the reaction of hydrazonyl chloride, derived from 6-aminoquinoline, with appropriate secondary cyclic amines. The new compounds were confirmed through 1H-NMR, 13C-NMR, FTIR, and HRMS, and further verified by single-crystal X-ray diffraction. The antitumor potential of the synthesized compounds was tested against lung cancer (A549) and breast cancer (MCF-7) cell lines. Among the compounds, the ethyl carboxylate and o-hydroxy phenyl piperazine derivatives (10d and 10g) exhibited the strongest activity against both cell lines, with IC50 values of 43.1 and 59.1 μM for the lung and breast cancer cell lines, respectively. Moreover, the most potent compounds were subsequently docked into the c-Abl kinase binding site (PDB code: 1IEP) as a possible anticancer mechanism. In-silico ADMET study shows acceptable pharmacokinetic properties, and the toxicity profile for the most potent compounds is non-carcinogenic

trans-Dibromidobis(3-methylpyridine-κN)copper(II)

The asymmetric unit of the title compound, [CuBr2(C6H7N)2], contains one half-molecule, the whole molecule being generated by inversion through a center located at the CuII atom. The geometry around the CuII atom is square planar. Semicoordinate Cu...Br bonds [3.269 (1) Å] and nonclassical C—H...Br hydrogen bonds connect the molecules, forming chains running parallel to the a axis. These chains are further linked via additional C—H...Br hydrogen bonds into a three-dimensional network

4-(9H-Fluoren-9-yl)-4-methylmorpholin-4-ium bromide, C18H20BrNO

C18H20BrNO, orthorhombic, Pbca (No. 61), a = 8.4285(4) Å, b = 19.2055(9) Å, c = 19.7809(12) Å, Z = 8, V = 3202.0(3) Å3, Rgt(F) = 0.0427, wRref(F2) = 0.1025, T = 293(2) K

4-(4-Nitrobenzyl)pyridine

The title compound, C12H10N2O2, has a twisted conformation, with a dihedral angle between the planes of the pyridine and benzene rings of 78.4 (2)°. The nitro group is coplanar with the attached benzene ring within experimental error. The molecules form centrosymmetric dimers via Car—H...O interactions (H...O = 2.49 Å) and the dimers are π-stacked along the b axis [the separation between ring centroids is 3.788 (2) Å]

Halogen bond and polymorphism in trans-bis(2-iodo-5-halopyridine)dihalocopper(ii) complexes: crystallographic, theoretical and magnetic studies

The effect of halogen bonding interactions on polymorphism in Cu(2I5YP)2X2 has been investigated, where 2I5YP = 2-iodo-5-halopyridine, Y = Br or Cl and X = Cl or Br; these complexes are abbreviated as 2I5Y-X. Two conformers are possible for 2I5Y-X complexes: the syn-conformer where the two iodine atoms are located on the same side of the coordination sphere and the anti-conformer where the iodine atoms are located on the opposite side of the coordination sphere. The anti-conformers are more stable than the corresponding syn-conformer by 4.0 kJ mol−1 in 2I5Y-Br, whereas, in 2I5Y-Cl the syn- and anti- have almost the same stability (energy difference = 0.45 kJ mol−1). In 2I5Br-Cl, crystals of the syn- and anti-conformers were characterized using single crystal X-ray diffraction. However, only the anti-conformer of 2I5Br-Br was produced. The syn-conformer crystallizes in the monoclinic space group C2/c. Two packing polymorphs of anti-2I5Cl-Cl were characterized; they crystallized in the P1̄ and P21/n space groups. On the molecular level, the syn-conformer is stabilized by C6-H⋯X hydrogen bonding interactions and the anti-conformer is stabilized by I2⋯Cu interactions. On the supramolecular level, the C-I⋯Cl and C-Y⋯Cl interactions are stronger in the C2/c phase than the corresponding interactions in the P21/n phase as indicated by Y⋯Cl and I⋯Cl distances. The possibility of crystallizing the syn-conformer depends on the nature of the halogens atoms in the complex; the lighter the halogen on position two of the pyridine ring and the heavier the halogen on position five of the pyridine ring, the higher the possibility of crystallizing the syn-conformer. syn-Conformers are not observed in 2I5Y-Br complexes. These conclusions were supported by density functional theory calculations and analyzing the electron density using quantum theory of atoms in molecules (QTAIM). Both conformers of 2I5Br-Cl and 2I5I-Cl complexes show antiferromagnetic interactions; the data were fit to a 1D-uniform AFM chain model. The interactions are stronger in the syn-conformer than the corresponding anti-conformer as indicated by J/kB values, which are −3.77(8) K, −1.88(6) K, −1.75(6) K and −1.5(4) K for syn-2I5Br-Cl, anti-2I5Br-Cl, syn-2I5I-Cl and anti-2I5I-Cl, respectively. © 2023 The Royal Society of Chemistry

Competition between Hydrogen and Halogen Bonding Interactions: Theoretical and Crystallographic Studies

Crystal structures of six iodopyridinium tetrahalocuprate­(II) salts are reported, (<i>n</i>IP)₂CuX₄, where X = Cl or Br, <i>n</i>IP is the <i>n</i>-iodopyridinium cation, and <i>n</i> = 2, 3, or 4. The supramolecular structure of these salts is developed based on N–H···X hydrogen bonding and C–I···X halogen bonding interactions. Comparing these structures with the previously published structures of the general formulas (<i>n</i>CP)₂CuX₄ and (<i>n</i>BP)₂CuX₄, where <i>n</i>CP⁺ and <i>n</i>BP⁺ are the <i>n</i>-chloropyridinium and <i>n</i>-bromopyridinium cations, respectively, allows us to investigate the competition between the halogen and hydrogen bonding interactions. Henceforth, the general formula (<i>n</i>YP)₂CuX₄ will be used to represent the 18 structures where <i>n</i>YP⁺ is the <i>n</i>-halopyridinium cation. Isomorphism has been observed in these structures. Isomorphic structures are divided into four sets. Analysis of the isomorphic structures allows us to apply the separation of variables principle; upon comparison of isomorphic structures, complications arise from geometrical factors due to the isomeric nature of the <i>n</i>YP⁺ cation and effects of intermolecular forces other than N–H···X hydrogen bonding, and C–I···X halogen bonding interactions are minimized and hence can be ignored. Comparing halogen and hydrogen bonding interaction parameters within each isomorphous set allows us to investigate the competition between these interactions. As the organic halogen becomes heavier and the halide ligand is unvaried, the N···X distance is either unvaried or becomes longer. In contrast, the Y···X distance becomes shorter even though heavier halogens have a larger radius. For example, for the isomorphous structures (2BP)₂CuCl₄ and (2IP)₂CuCl₄, the N···Cl distances are 2.926 Å and 3.070 Å, respectively, whereas the corresponding Y···Cl distances are 3.322 Å and 3.316 Å. Theoretical calculations have shown that bifurcated hydrogen bonding interactions are stronger than the corresponding linear ones. Also, calculations have shown that as the organic halogen becomes heavier, the halogen bonding interactions become stronger. This agrees with crystal structure data; as the organic halogen gets heavier and the halide ligand is unvaried, the difference between the two legs of the bifurcated hydrogen bond becomes larger (weaker hydrogen bonding interactions). For example, the three (4YP)₂CuBr₄ structures are isomorphous; the difference between the two legs of the hydrogen bond are 0.117 Å, 0.191 Å, and 0.246 Å for (4CP)₂CuBr₄, (4BP)₂CuBr₄, (4IP)₂CuBr₄, respectively. Surprisingly, the above two trends are valid in all isomorphous sets without exception, which is rare in solid state chemistry. Analysis of the Cu–X bond distances indicates that the Cu–X bond distance of the halogen acceptor is always shorter than that of the corresponding proton acceptor; which agrees with the theoretical calculations; hydrogen bonding interactions are stronger than the corresponding halogen bonding interactions

Synthesis, coordination modes, structures, and magnetic properties of halogen-substituted 2-hydroxypyridine

A family of 6-X-2-hydroxyprydine/pyridone (6-X-2-HOpy/pyridone) Cu(II) compounds, [Cu(6-X-2-HOpy)2Cl2] (1 X = F; 2 X = Cl) and [(6-X-2-pyridone)CuCl(μ-Cl)]2 (3 X = Cl; 4 X = Br), has been prepared. Solution-based infrared spectra displayed a correlation between tautomeric state, primarily driven by halogen identity, and coordination mode with neutral nitrogen coordination mode favored as Br ≪ Cl \u3c F. The tautomeric state of 6-Cl-2-HOpy is influenced by metal ion concentration (M) with lactam concentration increasing as M increases. Compound 1 has F–F contacts less than the sum of the van der Waals radii but falls outside of the typical halogen bonding angle parameters, R–X•••Y = R–Y•••X = 138.2°. Compounds 1 and 2 exhibit weak antiferromagnetic exchanges, fit with a one-dimensional quantum Heisenberg antiferromagnetic linear chain (1D-QHAF) model and J/kB = −1.99(1) K and −0.92(7) K, respectively. Compounds 3 and 4 exhibit a dominating ferromagnetic exchange and an antiferromagnetic exchange and were qualitatively fit to a ferromagnetic linear chain with an interchain interaction model. This model does not accurately represent the physical parameters of the system and was used to show that both exchanges exist and are nontrivial