ABSTRACT
The thermal condensation of melamine into molecules melam, melem, and the one-dimensional polymer melon has already been reported. An interesting question arises about the impact of other compounds being present in this process of thermal conversion. The solid-state reaction of C3N6H6 with InCl3 leads to a novel compound featuring deprotonated melam units in a supramolecular assembly, based on the [C12N20H8]4- anion that is interconnected in the structure via N-In-N bonding. The reaction pathway of the formation of this compound is investigated by thermal analysis and the crystal structure of unique (NH4)[(InCl2)3(C12N20H8)]·â [InCl3(NH3)] is reported as well as its photoluminescence properties.
ABSTRACT
The development of new compounds in the domain of metal dinitridocarbonates is most efficiently performed via solid-state metathesis or simply by addition reactions. Our discovery of Pb7I6(CN2)4 is the result of a solid-state reaction of PbCN2 with PbI2 at 420 °C. Its crystal structure was solved and refined from X-ray diffraction data based on a single crystal with the space group P63/mmc. The crystal structure is based on a network of lead tetrahedra, lead trigonal bipyramids and lead octahedra interconnected by [NCN]2- and iodide. Properties of the material were investigated by diffuse reflection measurement, photoluminescence measurements, and electronic band structure calculations demonstrating that this material is a semiconductor.
ABSTRACT
Solvated tungsten iodide cluster compounds are presented with the homoleptic cluster cation [(W6I8)(CH3CN)6]4+ and the heteroleptic [(W6I8)I(CH3CN)5]3+, synthesized from W6I22 in acetonitrile. Crystal structures were solved and refined on deep red single-crystals of [(W6I8)(CH3CN)6](I3)(BF4)3·H2O, [(W6I8)I(CH3CN)5](I3)2(BF4), and on a yellow single-crystal of [W6I8(CH3CN)6](BF4)4·2(CH3CN) on the basis of X-ray diffraction data. The structure of the homoleptic [(W6I8)(CH3CN)6]4+ cluster is based on the octahedral [W6I8]4+ tungsten iodide cluster core, coordinated by six apical acetonitrile ligands. The electron localisation function of [(W6I8)(CH3CN)6]4+ is calculated and solid-state photoluminescence and its temperature depedence are reported. Additionally, photoluminescence and transient absorption measurements in acetonitrile are shown. Results of the obtained data are compared to compounds containing [(M6I8)I6]2- and [(M6I8)L6]2- (M = Mo or W; L = ligand) clusters.
ABSTRACT
This work deals with the determination of the external quantum yield of some selected inorganic up-conversion materials, which are able to convert blue light, as typically emitted using blue (In,Ga)N LEDs, into UV radiation. Recently, these materials have drawn tremendous attention due to their potential application in antimicrobial coatings of surfaces. To judge the viability of this approach to reduce the density of germs onto arbitrary surfaces upon indoor or outdoor illumination, the quantum efficiency for the conversion of blue light into UV is of large interest. We found that the quantum efficiency is between about 0.1% and 1%, which might be good enough if the illumination of the respective surface is performed for several hours. Then, a relevant reduction of the number of active microorganisms per area can be achieved.
Subject(s)
Light , Ultraviolet Rays , LightingABSTRACT
Microcrystalline powder of previously unknown thallium(I) chloride hydroborate Tl3Cl[B12H12] was obtained through the reaction of thallium(I) oxocarbonate Tl2[CO3] with an aqueous solution of (H3O)2[B12H12] in the presence of chloride anions. Tl3Cl[B12H12] crystallises in a primitive, orthorhombic lattice with the space group Pnma (a = 835.189(7) pm, b = 970.132(8) pm and c = 1597.912(12) pm for Z = 4) showing a distorted hexagonal anti-perovskite type arrangement of the ions. The structure features two thallium sites with mixed coordination spheres consisting of borate related hydrogen atoms and chloride anions with coordination numbers of eleven and thirteen. Tl3Cl[B12H12] shows strong excitation bands at 240 and 260 nm attributed to the 1S0 â 3P2 and 1S0 â 3P1 interconfigurational transitions of the Tl+ 6s2 cations, respectively. The emission spectrum at 300 K upon VUV excitation exhibits a broad band at 440 nm with a quantum efficiency of 41%. In addition, temperature-dependent emission spectra, colour points, reflectance, decay time, thermal quenching curve and radioluminescence spectra for Tl3Cl[B12H12] were determined.
ABSTRACT
A series of new compounds MI(OCN) were prepared from the mixtures of MI2 and K(OCN) (M = Sr, Eu or Ba) by solid-state reactions that were controlled by differential scanning calorimetry (DSC) and differential thermal analysis (DTA) techniques. The presence of two phases is highlighted for BaI(OCN) which crystallizes in the Pnma (α-BaI(OCN)) and Cmcm (ß-BaI(OCN)) space groups. The SrI(OCN), EuI(OCN) and ß-BaI(OCN) compounds crystallize in the same orthorhombic Cmcm space group and the structure consists of a layered arrangement of [M2I2]2+ blocks separated by single layers of cyanate ions that are found to be related to the Sillén-type structure. The polymorphism of BaI(OCN) was also observed by analyzing the infrared (IR) spectra. This analysis showed for ß-BaI(OCN) splitting bands, which were ascribed to the presence of more than one resonant cyanate form that can be induced by the dynamical disorder of OCN units. In contrast, the α-BaI(OCN) vibration modes suppose the existence of one cyanate form that adopts a defined orientation. The SrI(OCN) and BaI(OCN) compounds were doped with Eu2+. The luminescence spectra recorded under excitation at 340 and 350 nm revealed a blue emission of Eu2+ at 431 nm for the ß-BaI(OCN) and SrI(OCN) phases and at 427 nm for the α-BaI(OCN) phase that was ascribed to the 4f65d1â8S7/2 (4f7) transition.
ABSTRACT
Photophysical properties of tungsten iodides with the [W6I14]2- cluster core have been described with respect to phosphorescence and phosphorescence quenching by molecular oxygen. This process involves energy transfer from excited triplet states of the cluster onto molecular oxygen. In the present study we investigate deactivation channels of exited triplet states of the [W6I14]2- cluster towards rare earth ions. For this purpose, we synthesized several supramolecular assemblies made of [W6I14]2- clusters and metal cryptates and investigated their crystal structures and photophysical properties. UV/Vis photoexcitation of solid [Crypt-A]-[W6I14] (A = alkaline metal) and [Crypt-RE]-[W6I14] revealed phosphorescence of the cluster, respectively of the photophysically active rare earth metal (RE) center. A cluster to cryptate energy transfer is proven with a photophysically active rare earth ion by the emission of Yb3+ at 977 nm (2F5/2-2F7/2) and Nd3+ 1072 nm (4F3/2-4I11/2). These results show that an effective excitation of near-infrared-emitting rare earth ions is possible under excitation up to 550 nm with [Crypt-RE]-[W6I14] assemblies.
ABSTRACT
The light-induced antibacterial and antifungal properties of A2[M6I8L6] with M = Mo and W, A = organic cation, L = ligand have been studied. The photoactive compounds (TBA)2[W6I8(C7H7SO3)6] and (TBA)2[W6I8(COOCF3)6] have been incorporated into a permeable silicone matrix and were measured for their application in the decomposition of multi-resistant bioactive species (hospital germs) such as S. aureus and P. aeruginosa as well as fungi. In addition, we present a new high volume synthesis route for these types of cluster compounds departing from the soluble compound W6I22.
ABSTRACT
The phase LixCa16-xSi17N32-xO2+x was synthesized by solid-state metathesis at 1050 °C in weld-sealed niobium ampoules. The crystal structure was solved from powder X-ray diffraction data in the space group F4[combining macron]3m (a = 14.7391(1) Å, Z = 4); it is closely related to the previously reported structure of Ca16Si17N34. The structure of LixCa16-xSi17N32-xO2+x is based on a complex network of [SiN4] tetrahedra with interstitial voids filled by Ca ions, partially substituted by Li. This Li substitution is charge-compensated by replacement of N by O in the structure. Theoretical calculations confirm that the unit cell volume decreases with increasing stoichiometric factor x. Europium doped samples of this compound show intense Eu2+ emission at 536 nm on excitation with near-UV or blue radiation at 350-480 nm. Ce3+ doping yields orange to red emission with two broad emission bands at 600 and 665 nm.
ABSTRACT
Octahedral tungsten iodide clusters equipped with apical ligands (L) are synthesized to implement substantial photophysical properties. The [W6I8(CF3COO)6]2- cluster reported herein is the first example of a family of ligand substituted [W6I8L6]2- clusters. Such compounds are expected to exhibit a rich photochemistry in which the apical ligands play a crucial role. The versatile solid state and solution phase photophysical properties of (TBA)2[W6I8(CF3COO)6] described herein parallel characteristics obtained in some photophysically active organic compounds, including a broad absorption in the UV/VIS region. Upon irradiation of this compound, a broad red emission is observed in the VIS/NIR region resulting from excited triplet states, and singlet oxygen (a1Δg) is generated in the presence of O2.
ABSTRACT
Tetracyanamidometallates with the general formula RbRE[T(CN2)4] (RE = La, Pr, Nd, Gd; T = Si, Ge) were prepared by solid state metathesis reactions starting from stoichiometric mixtures of RECl3, A2[TF6], and Li2(CN2). Reactions were studied by differential thermal analysis that showed ignition temperatures between 360 and 390 °C for the formation of RbGd[T(CN2)4] with T = Si and Ge. The powder diffraction patterns of RbRE[Ge(CN2)4] were indexed isotypically to the already known RbRE[Si(CN2)4] compound. IR spectra of RbLa[Ge(CN2)4] were measured and compared with those of RbLa[Si(CN2)4]. (73)Ge, (87)Rb, and (139)La solid state NMR measurements and density functional theory calculations were used to verify the novel homoleptic [Ge(CN2)4](4-) ion. Luminescence properties of Eu(3+), Ce(3+), and Tb(3+) doped samples are reported.
