Hendrik G. Visser

Synthesis of strong red emitting Y2O3:Eu3+ phosphor by potential chemical routes: comparative investigations on the structural evolutions, photometric properties and Judd–Ofelt analysis

In the present paper, a comparative investigation on the structural and photoluminescence properties of Y2O3:Eu3+ phosphor prepared by different wet chemical synthesis routes such as sol-lyophilisation (SL), combustion (CR), hydrothermal (HT) and microwave assisted hydrothermal combustion (MHWC), has been reported for the first time. The MHWC derived phosphor exhibited better photoluminescence than that of the samples obtained with other adopted methods. Such outcomes were due to the increased crystallinity, well defined morphology and improved compositional homogeneity in the MWHC technique. The growth of the prepared phosphors was explained in the light of chemical kinetics. Jorgensen formula and nephelauxetic ratio was used to understand the ligand behavior of Eu–O bond and to estimate the electron phonon coupling in Y2O3:Eu3+ phosphor. The spectroscopic behavior of Y2O3:Eu3+ phosphor, prepared by different routes, was determined using Judd–Ofelt theory. Thermal stability, purity and efficiency of the emitted colour were checked on the basis of different synthetic approach. An efficient synthesis method for Y2O3:Eu3+ phosphor, compatible for industrial appliances, was proposed.

Structure/reactivity relationships and mechanism from X-ray data and spectroscopic kinetic analysis

The development in crystallography is nothing short of phenomenal, showing an ever increasing trend towards applications, such as in molecular biology. ‘Traditional’ small molecule chemical crystallography tends to, in many aspects, be considered as trivial due to the exponential growth in computing power and the parallel expansion in software. However, many dynamic processes (still) occur at the molecular level. Thus, the fundamental understanding of subtle nuances in structural behaviour, and the associated influence on other (kinetic) properties, is often trivialized when conclusions are simply made based on thermodynamic observations alone. This review aims to emphasize the importance of crystallography in small molecule chemistry by presenting detailed evaluations of two extended ‘case studies’, i.e. the first on structure and dynamics of the middle transition metal cyanide-oxido complexes, and the second on rhodium model homogeneous catalyst precursors. Both underline the fact of understanding the overarching principles of dynamics, i.e. time-resolved behaviour of processes, but considered from a structural perspective. The reference point is to focus on an integrated and overarching mechanistic approach, utilizing structural data, but in particular reaction kinetics, to obtain a more complete picture of processes or systems being evaluated.

Identification of different Cr(III) nta complexes: crystallisation of Cs2[Cr2(nta)2(μ-OH)2]·4H2O in two space groups

Abstract Cs2[Cr2(nta)2(μ-OH)2]·4H2O (nta=nitrilotriacetate) crystallises in two different space groups due to a slight variation in pH of the reaction mixtures. The structures of Cs2[Cr2(nta)2(μ-OH)2]·4H2O have been determined from three-dimensional X-ray diffraction data. The complex crystallises in the tetragonal, I41/a (I) and monoclinic, P21/c (II), space groups. The two hydroxo groups bridge the two Cr centres with OH–Cr–OH angles of 81.5(3)° (I) and 82.08(10)° (II), respectively. The tetradentate nta ligand completes the octahedral geometry around the Cr centre. The Cr–OH bonds are 1.942(7) and 1.961(6) A for (I) and 1.987(2) and 1.991(1) A for (II). The Cr–N and Cr–O(av) are 2.048(9) and 1.967(8) A for (I) and 2.061(3) and 1.975(2) A for (II), respectively.

The syntheses and crystal structures of Cs2[Co2(nta)2(μ-OH)2] · 4H2O and (C10H10N3)2[CoCl4]

Abstract The crystal structure of Cs2[Co2(nta)2(μ-OH)2] · 4H2O (nta = nitrilotriacetate) has been determined from three-dimensional X-ray diffraction data. Two hydroxo groups act as bridging groups between the two Co metal centres. The CoOH bond distances are 1.899(5) and 1.897(5) A, respectively and the CoOHCo bond angles 98.2(2)°. The nta ligand acts as a tetradentate ligand and bonds with a nitrogen as well as three oxygen atoms to the Co metal centre. The CoN and CoO(av) bonds are 1.922(6) and 1.895(5) A, respectively. (C10H10H3)2[CoCl4] consists of discrete monoprotonated 2,2′-iminodipyridinium cations and CoCl42− anions. The anions assume a regular tetrahedral geometry, with the ClCoCl bond angles varying between 107.34(10) and 112.07(10)°. The CoCl bond distances are 2.270(2) and 2.282(2) A, respectively. The two pyridine rings in the cation assume an almost planar orientation with a derivation of 7.7(6)° for the dihedral angle between the two ring systems. The planar orientation can be attributed to weak hydrogen bonding between the unprotonated nitrogen atom of the one pyridine ring and the proton bonded to the other nitrogen atom on the adjacent ring.

Synthesis, crystallographic, and theoretical investigation of fac-[ReI(salen)(CO)3(S)] complexes, salen = monocharged bidentate Schiff-base and S = pyridine, CH3OH

Two rhenium(I) complexes of the form fac-[Re(L–L′)(CO)3(S)] were synthesized (L–L′ = N–O salen-type bidentate ligand, S = coordinating methanol or pyridine) and the crystal structures of fac-[tricarbonylmethanol-(2-(3-methylbutyliminomethyl)phenolato)rhenium(I)] and fac-[tricarbonyl-(2-(3-methylbutyliminomethyl)phenolato)pyridinerhenium(I)] are reported. The influence of the coordinating neutral monodentate ligand in these fac-[tricarbonyl(N,O-salen)rhenium(I)] complexes was investigated both in solid state and at theoretical level using X-ray diffraction, IR, NMR, and DFT calculations.

A new reaction route for the synthesis of different cobalt(III)nitrilotriacetato complexes. The crystal structure of Cs2[Co(nta)(CO3)]·H2O

Abstract The crystal structure of Cs2[Co(nta)(CO3)]·H2O was determined from X-ray diffraction data. The carbonate ion in Cs2[Co(nta)(CO3)]·H2O acts as a bidentate ligand and the two CoO bond distances are 1.889(2) and 1.908(2) A, respectively. The nta3− ligand acts as a tetradentate ligand and completes the octahedral geometry around the Co centre with the CoN and CoO(av) bond distances being 1.920(2) and 1.900(2) A, respectively. Cs2[Co(nta)(CO3)]·H2O is used as starting reagent in the synthesis of other monomeric cobalt(III)nta complexes.

Aqua­tricarbon­yl(3,5,7-tribromo­tropolonato)rhenium(I) methanol solvate

The title complex, [Re(C7H2Br3O2)(CO)3(H2O)]·CH3OH, crystallized as a neutral ReI compound and one methanol solvent molecule in the asymmetric unit. The metal centre is coordinated facially by three carbonyl groups. The bidentate tribromotropolanate ligand and a water molecule complete the distorted octahedral coordination around the central metal. Intermolecular Br⋯O [3.226 (5) Å] and Br⋯Br [3.590 (2) Å] contacts are observed between adjacent molecules. These contacts, together with an array of O—H⋯O, O—H⋯Br and C—H⋯O hydrogen bonds, complete a three-dimensional polymeric network formed between the methanol solvent and the complex.

Di-μ-hydroxido-bis[tris(1,1,1,5,5,5-hexa­fluoro­acetyl­acetonato-κ2O,O′)hafnium(IV)] acetone solvate

The binuclear title compound, [Hf2(C5HF6O2)6(OH)2]·C3H6O, contains an HfIV atom which is eight coordinated and surrounded by three chelating β-diketonato 1,1,1,5,5,5-hexafluoroacetylacetonate (hfaa) ligands and two bridging OH groups situated on a twofold rotation axis. The HfO8 coordination polyhedron shows a slightly distorted Archimedean square anti-prismatic coordination with average Hf—O, C—O, C—CMe distances of 2.19 (2), 1.26 (2) and 1.49 (2) Å, respectively, and an O—Hf—O bite angle of 75.3 (5)°. Weak O—H⋯O hydrogen bonding interactions are observed between one of the bridging hydroxy groups and the disordered solvent molecule.

Tetra­ethyl­ammonium bromidotricarbon­yl(tropolonato)rhenate(I)

In the title salt, (C8H20N)[ReBr(C7H5O2)(CO)3], the ReI atom is octahedrally surrounded by three facially orientated carbonyl ligands, one bidendate tropolonate ligand and a bromide ligand. The small O—Re—O bite angle of 74.88 (12)° leads to a distortion of the octahedral coordination sphere. The bromide ligand and the axial carbonyl ligand are substitutionally disordered over two positions in a 0.922 (3):0.078 (3) ratio. An array of C—H⋯O and C—H⋯Br hydrogen-bonding interactions between the cations and neighbouring rhenate anions stabilizes the crystal packing.

Tetra­kis(8-quinolinolato-κ2 N,O)hafnium(IV) dimethyl­formamide solvate monohydrate

In the title compound, [Hf(C9H6NO)]·C3H7NO·H2O, the hafnium(IV) atom is coordinated by four 8-quinolinolate (Ox) ligands, forming a slightly distorted square-antiprismatic coordination polyhedron. The crystal packing is controlled by O—H⋯O and C—H⋯O hydrogen-bonding interactions and π–π interactions between quinoline ligands of neighbouring molecules. The interplanar distances vary between 3.150 (1) and 3.251 (2) Å, while centroid–centroid distances vary from 3.589 (1) to 4.1531 (1) Å.