RESUMEN
Layered lead halide perovskites have attracted much attention as promising materials for a new generation of optoelectronic devices. To make progress in applications, a full understanding of the basic properties is essential. Here, we study 2D-layered (BA)2PbX4 by using different halide anions (X = I, Br, and Cl) along with quantum confinement. The obtained cell parameter evolution, supported by experimental measurements and theoretical calculations, indicates strong lattice distortions of the metal halide octahedra, breaking the local inversion symmetry in (BA)2PbCl4, which strongly correlates with a pronounced Rashba spin-splitting effect. Optical measurements reveal strong photoluminescence quenching and a drastic reduction in the PL quantum yield in this larger band gap compound. We suggest that these optical results are closely related to the appearance of the Rashba effect due to the existence of a local electric dipole. The results obtained in ab initio calculations showed that the (BA)2PbCl4 possesses electrical polarization of 0.13 µC/cm2 and spin-splitting energy of about 40 meV. Our work establishes that local octahedra distortions induce Rashba spin splitting, which explains why obtaining UV-emitting materials with high PLQY is a big challenge.
RESUMEN
A hexaazatrinaphtylene-based transition metal complex that exhibits single molecule magnet (SMM) behaviour is reported herein. Both monometallic (1) and bimetallic (2) CoII complexes with distorted octahedral geometries could be obtained through a straightforward change in synthetic conditions. Field induced SMM behaviour was exhibited by 1, with a D value of -60 cm-1 and Ueff = 17 K originating from the unquenched orbital angular momentum of the octahedral CoII (d7) centre. On the other hand, 2 exhibits weak antiferromagnetic interactions with a positive D value, thus preventing the observation of SMM behaviour. This investigation reveals the influence of both nuclearity and topology on the magnetic properties of HATN based complexes.
RESUMEN
Reducible 3,6-bis(3,5-dimethyl-pyrazolyl)1,2,4,5-tetrazine was employed to isolate supramolecular air-stable [Co4 ] and [Zn4 ] squares, which were achieved via careful selection of counterions rather than the use of reducing agents. Magnetic susceptibility studies revealed a strong radical-CoII exchange coupling (Jrad-Co /hc=-118â cm-1 , -2J formalism) with a spin ground state of ST =4, whereas the unreduced analogue revealed negligible coupling between the Co centers (JCo-Co /hc=-0.64â cm-1 ). Radical-radical coupling was also probed in the [Zn4 ] congener, which led to Jrad-rad /hc=-15.9(5)â cm-1 . These results highlight the versatile air-stable coordination chemistry of tetrazine and the importance of exploiting easily reducible delocalized radical to promote strong exchange coupling between spin carriers.
RESUMEN
Understanding the self-assembly of cluster aggregates remains an important challenge in coordination chemistry. A chelating tetrazine-based ligand was employed to isolate an unprecedented tetranuclear Hg4 complex exhibiting HgI/HgII mixed valence, which also contains metal-metal bonds. Single-crystal X-ray diffraction, X-ray photoelectron spectroscopy, solid-state nuclear magnetic resonance, and theoretical approaches (density functional theory) were employed to shed some light on the structure and self-assembly of this discrete molecule.
RESUMEN
A planar tetradentate 3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine (BpymTz) templating chelate affords the formation of an unprecedented BpymTzË- radical anion bridged {Ni} complex. Detailed magnetic measurements performed on the isolated air stable [Ni(BpymTzË-)Cl6(DMF)8]Cl·0.5(H2O) compound reveal strong ferromagnetic NiII-BpymTzË- interactions with a coupling constant of J = 98.84 cm-1.
RESUMEN
Powder X-ray diffraction patterns for 29 samples of magnetite, acquired using a conventional diffractometer, were used to build PLS calibration-based methods and variable selection to estimate mean crystallite size of magnetite directly from powder X-ray diffraction patterns. The best IPLS model corresponds to the Bragg reflections at 35.4° (h k l = 3 1 1), 43.0° (h k l = 4 0 0), 53.6° (h k l = 4 2 2), and 57.0° (h k l = 5 1 1) in 2θ. The best model was a GA-PLS which produced a model with RMSEP of 0.9 nm, and a correlation coefficient of 0.9976 between mean crystallite sizes calculated using Williamson-Hall approach and the ones predicted by GA-PLS method. These results indicate that magnetite mean crystallite sizes can be predicted directly from Powder X-Ray Diffraction and multivariate calibration using PLS variable selection approach.
