RESUMEN
Reacting RE2O3 and H3BO3 in an ultra-alkaline NaOH hydroflux at about 250 °C yielded pure, crystalline samples of Na2[RE(BO3)(OH)2] (RE = Y, Gd-Er). The compounds dehydrate to Na3RE(BO3)2 upon heating in air to about 500 °C. Na2[RE(BO3)(OH)2] (RE = Tb-Er) are photoluminescent under UV radiation. Their UV-Vis spectra show the typical absorptions associated with 4f-4f transitions and absorption edges in the UV (band gaps ≥ 5.7 eV). The RE3+ cation is coordinated by seven oxygen atoms, which define a distorted pentagonal bipyramid. The bipyramids share trans-edges of their base forming infinite chains. Triangular (BO3)3- groups connect the chains into layers. The crystal structure of Na2[Ho(BO3)(OH)2] was investigated at various temperatures in the range 100 K ≤ T ≤ 320 K. Above 310(2) K, the compound crystallizes in the orthorhombic space group Cmcm (ß-phase), below, it undergoes a displacive phase transition of second order resulting in a monoclinic structure in space group C2/c (α-phase). The critical exponents derived from different structural parameters indicate a cooperative distortion of the borate layers, but a rather uncorrelated adaptation of the sodium cations to their local environment. The other compounds of the series also adopt the structure of the α-phase at 296 K.
RESUMEN
In search of a suitable single-source precursor for the deposition of nanostructured PbS thin films at moderate temperatures under ambient conditions, we have synthesized the ligand N-(thiomorpholine-4-carbothioyl)benzamide and its corresponding lead(II) complex. The structures of both compounds were determined by single-crystal X-ray diffraction. In the complex, two ligands coordinate to a lead(II) atom in hemi-directed geometry through S and O atoms. Secondary intermolecular Pbâ â â S interactions group the complexes into pairs. As bulk powders, both the ligand and complex show nominal composition and purity as evidenced by elemental analysis, 1 Hâ NMR and IR spectroscopy. Thermal analysis of the lead(II) complex was carried out to understand its thermal decomposition behaviour for establishing a thin film fabrication protocol. Thin films of phase-pure PbS were fabricated using this new molecular precursor at the comparatively low annealing temperature of 250 °C. The film showed nanoparticles with cuboidal morphology and a blue-shifted optical absorption.