Vanessa Machado

Bio: Vanessa Machado is an academic researcher. The author has contributed to research in topics: Monomer & Magnetic susceptibility. The author has an hindex of 1, co-authored 1 publications receiving 5 citations.

Structure and Magnetic Properties of a 1D Alternating Cu(II) Monomer―Paddlewheel Chain

Abstract: One-dimensional metal–organic coordination polymers make up a class of compounds with potential towards the development of practical, new magnetic materials. Herein, a rare example of an ABBABB coupled linear chain comprised of alternating dicopper(II) tetraacetate units bridged to copper(II) acetate monomer units via axial η2:η1:µ2 coordinated acetate is reported. Examination of the structure, determined by small molecule X-ray crystallography, shows that each Cu(II) ion is in a dx2–y2 magnetic ground state. Magnetic susceptibility and magnetization data were collected and, consistent with the structural interpretation, demonstrate that the Cu(II) dimer (paddlewheel) exhibits classic antiferromagnetic exchange, while the S = 1/2 Cu(II) monomer is uncompensated in the ground state (low temperature regime.) Data were therefore fitted to a modified Bleaney-Bowers model, and results were consistent with the only other reported chain in this class for which magnetic data are available.

Copper(II) halide complexes of aminopyridines: Syntheses, structures and magnetic properties of [(5CAP)2CuX2] and [(5BAP)nCuX2] (X = Cl, Br)

Abstract: Reaction of 2-amino-5-halopyridine molecules with Cu(II) halides in the solid state via mechanochemical techniques produced four coordination complexes, (5BAP)2CuBr2 (2a), (5BAP)2CuCl2 (3), (5CAP)2CuCl2 (4), (5CAP)2CuBr2 (5) [5BAP = 2-amino-5-bromopyridine; 5CAP = 2-amino-5-chloropyridine] In all compounds, the 5BAP or 5CAP ligands are coordinated to the Cu(II) ion through the pyridine N atom along with two halide ions Compounds 2 and 3 crystallized in the P-1 and P21/c space groups, respectively Temperature dependent magnetic susceptibility data for 2 were fit to the antiferromagnetic rectangle model (J = –45(2) K; α = 089(17)), while the data for 3 were fit to the uniform chain model (J = –420(6) K), indicating a significant difference in the interchain interactions Both 4 and 5 crystallize with the 5CAP ligands in the syn-conformation in the space groups I2/a and P21/n, respectively Compound 4 formed the expected dimeric structure via bridging chloride ions and the magnetic data were su

Modified strong-coupling treatment of a spin-1/2 Heisenberg trimerized chain developed from the exactly solved Ising-Heisenberg diamond chain

Abstract: A quantum spin-$\frac{1}{2}$ antiferromagnetic Heisenberg trimerized chain with strong intradimer and weak monomer-dimer coupling constants is studied using the many-body perturbation expansion, which is developed from the exactly solved spin-$\frac{1}{2}$ Ising-Heisenberg diamond chain preserving correlations between all interacting spins of the trimerized chain. It is evidenced that this perturbation approach is superior with respect to the standard perturbation scheme developed from a set of noninteracting spin monomers and dimers, and its accuracy even coincides, up to a moderate ratio of the coupling constants, with state-of-the-art numerical techniques. The Heisenberg trimerized chain shows the intermediate one-third plateau, which was also observed in the magnetization curve of the polymeric compound ${\mathrm{Cu}}_{3}{({\mathrm{P}}_{2}{\mathrm{O}}_{6}\mathrm{OH})}_{2}$ affording its experimental realization. Within the modified strong-coupling method we have obtained the effective Hamiltonians for the magnetic field range from zero to the one-third plateau, and from the one-third plateau to the saturation magnetization. The unconventional second-order perturbation theory provides extremely accurate results for both critical fields of the intermediate one-third plateau up to a moderate ratio of the coupling constants as convincingly evidenced through a comparison with numerical density-matrix renormalization group data. It is shown that the derived effective Hamiltonian also provides at low enough temperatures sufficiently accurate results for magnetization curves and thermodynamic properties as corroborated through a comparison with quantum Monte Carlo simulations. Using the results for the effective Hamiltonian, we additionally suggest a straightforward procedure for finding the microscopic parameters of one-dimensional trimerized magnetic compounds with strong intradimer and weak monomer-dimer couplings. We found the refined values for the coupling constants of ${\mathrm{Cu}}_{3}{({\mathrm{P}}_{2}{\mathrm{O}}_{6}\mathrm{OH})}_{2}$ by matching the theoretical results with the available experimental data for the magnetization and magnetic susceptibility in a wide range of temperatures and magnetic fields.