ABSTRACT
The impact of the surrounding ligand field is successfully exploited in the case of Eu2+ to tune the emission characteristics of inorganic photoactive materials with potential application in, e.g., phosphor-converted white light-emitting diodes (pc-wLEDs). However, the photoluminescence of Mn2+ related to intraconfigurational 3d5 -3d5 transitions is also strongly dependent on local ligand field effects and has been underestimated in this regard so far. In this work, we want to revive the idea how to electronically tune the emission color of a transition metal ion in inorganic hosts by unusual electronic effects in the metal-ligand bond. The concept is explicitly demonstrated for the weakly coordinating layer-like borosulfate ligand in the Mn2+ -containing solid solutions Zn1-x Mnx [B2 (SO4 )4 ] (x = 0, 0.03, 0.04, 0.05, 0.10). Zn[B2 (SO4 )4 ]:Mn2+ shows orange narrow-band luminescence at 590â nm, which is an unusually short wavelength for octahedrally coordinated Mn2+ and indicates an uncommonly weak ligand field. On the other hand, the analysis of the interelectronic Racah repulsion parameters reveals ionic Mn-O bonds with values close to the Racah parameters of the free Mn2+ ion. Overall, this strategy demonstrates that electronic control of the metal-ligand bond can be a tool to make Mn2+ a potent alternative emitter to Eu2+ for inorganic phosphors.
ABSTRACT
Borosulfates consist of heteropolyanionic networks of corner-shared (SO4)- and (BO4)-tetrahedra charge compensated by metal or non-metal cations. The anionic substructures differ significantly, depending on the different branching of the silicate-analogous borosulfate building blocks. However, only one acid has been characterized by single crystal X-ray diffraction so far. Herein, we present H2[B2(SO4)4] as the first phyllosilicate analogue representative, together with the homeotypic representative Cd[B2(SO4)4]. The latter can be considered the cadmium salt of the former. Their crystal structures and crystallographic relationship are elucidated. For H2[B2(SO4)4], the bonding situation is examined using Hirshfeld-surface analysis. Further, the optical and thermal properties of Cd[B2(SO4)4] are investigated by FTIR and UV-Vis spectroscopy, thermogravimetry, as well as temperature-programmed powder X-ray diffraction.
ABSTRACT
Borosulfates are classified as silicate analogue materials. The number of crystallographically characterized compounds is still limited, whereas the structural diversity is already impressive. The anionic substructures of borosulfates exhibit vertex-connected (BO4 )- and (SO4 )-tetrahedra, whereas bridging between two (SO4 )- or even between two (BO4 )-tetrahedra is scarce. The herein presented compound Sr[B3 O(SO4 )4 (SO4 H)] is the first borosulfate with a triple-vertex linkage of three (BO4 ) tetrahedra via one common oxygen atom. DFT calculations complement the experimental studies. Bader charges (calculated for all atoms) as well as charge-density calculations give hint to the electron distribution within the anionic substructure and density-of-states calculations support the interpretation of the bonding situation.
ABSTRACT
Borosulfates are compounds analogous to silicates, with heteropolyanionic subunits of vertex-linked (SO4 )- and (BO4 )-tetrahedra. In contrast to the immense structural diversity of silicates, the number of borosulfates is yet very limited and the extent of their properties is still unknown. This is particularly true for representatives with phyllosilicate and tectosilicate analogue anionic substructures. Herein, we present Ni[B2 (SO4 )4 ] and Co[B2 (SO4 )4 ], two new borosulfates with phyllosilicate analogue topology. While the anionic subunits of both structures are homeotypic, the positions of the charge compensating cations differ significantly: NiII is located between the borosulfate layers, while CoII -in contrast-is embedded within the layer. Detailed analysis of these two structures based on single-crystal X-ray diffraction, magnetochemical investigations, X-ray photoelectron spectroscopy, and quantum chemical calculations, unveiled the reasons for this finding. By in silico comparison with other divalent borosulfates, we uncovered systematic trends for phyllosilicate analogues leading to the prediction of new species.