Photoluminescence of Mn2+ in the Borosulfate Zn[B2 (SO4 )4 ] : Mn2+ -A Tool to Detect Weak Coordination Behavior of Ligands

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 590 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.

Rational Design of a Rare-Earth Oxychalcogenide Nd3 [Ga3 O3 S3 ][Ge2 O7 ] with Superior Infrared Nonlinear Optical Performance

Inorganic chalcogenides have been studied as the most promising infrared (IR) nonlinear optical (NLO) candidates for the past decades. However, it is proven difficult to discover high-performance materials that combine the often-incompatible properties of large energy gap (E_g ) and strong second harmonic generation (SHG) response (d_eff ), especially for rare-earth chalcogenides. Herein, centrosymmetric Cs₃ [Sb₃ O₆ ][Ge₂ O₇ ] is selected as a maternal structure and a new noncentrosymmetric rare-earth oxychalcogenide, namely, Nd₃ [Ga₃ O₃ S₃ ][Ge₂ O₇ ], is successfully designed and obtained by the module substitution strategy for the first time. Especially, Nd₃ [Ga₃ O₃ S₃ ][Ge₂ O₇ ] is the first case of breaking the trade-off relationship between wide E_g (>3.5 eV) and large d_eff (>0.5 × AgGaS₂ ) in rare-earth chalcogenide system, and thus displays an outstanding IR-NLO comprehensive performance. Detailed structure analyses and theoretical studies reveal that the NLO effect originates mainly from the cooperation of heteroanionic [GaO₂ S₂ ] and [NdO₂ S₆ ] asymmetric building blocks. This work not only presents an excellent rare-earth IR-NLO candidate, but also plays a crucial role in the rational structure design of other NLO materials in which both large E_g and strong d_eff are pursued.

Cd[B2(SO4)4] and H2[B2(SO4)4] - a phyllosilicate-analogous borosulfate and its homeotypic heteropolyacid

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.

Targeting Diverse Bridging Motifs within Actinide Borosulfates and Establishing an Unconventional Structural Hierarchy

The first actinide borosulfates, (UO₂)[B(SO₄)₂(SO₃OH)] (TSUBOS-1) and (UO₂)₂[B₂O(SO₄)₃(SO₃OH)₂] (TSUBOB-1), were synthesized solvothermally in oleum using UO₃. The classical borosulfate crystal structure of TSUBOS-1 is partially consistent with an established conventional hierarchy. Uranyl pentagonal bipyramids limit the anionic network linkages and isolate sulfate tetrahedra within the anionic network. Therefore, the classical one-dimensional chain established in the hierarchy does not fully describe the structure. The structure of TSUBOB-1 is the first actinide borosulfate that contains an unconventional borate-to-borate bridging mode (denoted B-O-B) and a zero-dimensional oxoanionic unit consisting of one sulfate tetrahedron that shares vertices with two B-O-B bridged borate tetrahedra that each share a vertex with two sulfate tetrahedra. As this structure departs from the existing structural hierarchy, a modified approach for understanding the unconventional borosulfate substructure and dimensionality is proposed, together with a new graphical notation. In the course of our synthesis experiments, a novel uranyl disulfate compound (UO₂)₂[(S₂O₇)(SO₃OH)₂] (TSUDS) was isolated and characterized. The structure of TSUDS is a framework consisting of uranyl pentagonal bipyramids and sulfate tetrahedra. Each uranyl pentagonal bipyramid is surrounded by five sulfate tetrahedra, two of which share a vertex creating a disulfate with a S-O-S bridging mode. The uranyl bipyramids are linked to one another via the singular sulfate or disulfate groups.

New alkaline-earth amidosulfates and their unexpected decomposition to S4N4

The amidosulphates Mg(NH₂SO₃)₂·4H₂O (P2₁/c), Mg(NH₂SO₃)₂·3H₂O (P1̄), Ca(NH₂SO₃)₂·4H₂O (C2/c), Ca(NH₂SO₃)₂·H₂O (P2₁2₁2₁), Sr(NH₂SO₃)₂·4H₂O (C2/c), Sr(NH₂SO₃)₂·H₂O (P2₁/c) and Ba(NH₂SO₃)₂ (Pna2₁) could be obtained as cm-sized crystals from aqueous solutions of the corresponding metal carbonates, hydroxides and amidosulphonic acid, respectively, by careful control of the crystallisation conditions. β-Sr(NH₂SO₃)₂ (Pc) and α-Sr(NH₂SO₃)₂ (P2₁) could be obtained by careful thermal dehydration of Sr(NH₂SO₃)₂·H₂O. Their crystal structures were determined by single-crystal XRD and revealed a rich structural diversity with a significant tendency to form non-centrosymmetric crystals. The compounds were characterised by powder XRD, FT-IR, Raman and UV/vis spectroscopy and thermogravimetry. Temperature programmed single-crystal XRD, powder XRD and Raman spectroscopy, as well as DFT calculations were employed to aid the interpretation of vibrational and thermal properties. For the first time, SHG measurements were performed on metal amidosulphates, revealing the SHG intensities of β-Sr(NH₂SO₃)₂ and Ba(NH₂SO₃)₂ that were comparable to quartz and KDP. Thermal decomposition was additionally studied by the preparation of reaction intermediates, serendipitously revealing the formation of S₄N₄ as the decomposition product. This unprecedented reaction represents the first sulphur nitride synthesis process that neither employs a sulphur halide nor elemental sulphur.

The Role of the Bi3+ Lone Pair Effect in Bi(H3O)(SO4)2, Bi(HSO4)3, and Bi2(SO4)3

Three new members in the Bi₂O₃-SO₃-H₂O system are identified by single crystal X-ray diffraction and Rietveld refinement after a fundamental examination of this phase space. Bi(H₃O)(SO₄)₂ crystallizes in space group P2₁/c (no. 14, a = 1203.5(4), b = 682.9(2), c = 821.2(2) pm, β = 102.99(1)°, 861 independent reflections, 88 refined parameters, wR₂ = 0.14) homeotypic with Nd(H₃O)(SO₄)₂ featuring edge-sharing BiO₉ polyhedra. Bi(HSO₄)₃ crystallizes in a new structure type in space group P1 (no. 2, a = 492.04(7), b = 910.8(1), c = 1040.8(2) pm, α = 85.443(5)°, β = 86.897(5)°, γ = 74.542(4)°, 3227 independent reflections, 154 refined parameters, wR₂ = 0.05) comprising dimers of edge-sharing BiO₈ polyhedra. For Bi₂(SO₄)₃, a new modification crystallizing in space group P2₁/n (no. 14, a = 1308.03(7), b = 473.25(3), c = 1452.61(8) pm, β = 100.886(2)°, 3189 independent reflections, 155 refined parameters, wR₂ = 0.03) isotypic to Sb₂(SO₄)₃ with noncondensed BiO₇ polyhedra is presented. The role of the Bi³⁺ lone pair effect as elucidated by density functional theory (DFT) calculations is discussed for all three compounds with respect to their structural and optical properties. Additionally, the Bi³⁺ lone pair activity is compared to the recently reported borosulfates Bi(H₃O)[B(SO₄)₂]₄ and Bi₂[B₂(SO₄)₆]. Geometrical calculations based on structural data are correlated with electron localization function (ELF) calculations to establish the origin of the direction and strength of the lone pair stereoactivity of Bi³⁺ in oxidic compounds. Finally, the thermal properties of the three compounds are reported.

Polymorphism and optical, magnetic and thermal properties of the either phyllo- or inosilicate-analogous borosulfate Cu[B2(SO4)4]

Two polymorphs of the borosulfate Cu[B₂(SO₄)₄] can be selectively prepared by solvothermal syntheses. The crystal structures of inosilicate-analogous α-Cu[B₂(SO₄)₄] (P1̄, no. 2, a = 5.2636(2), b = 7.1449(2), c = 7.9352(2) Å, α = 73.698(2)°, β = 70.737(2)°, γ = 86.677(2)°, 65 parameters, R_Bragg = 0.0052) and the new phyllosilicate-analogous polymorph β-Cu[B₂(SO₄)₄] (P2₁/n, no. 14, a = 7.712(3), b = 8.149(3), c = 9.092(3) Å, β = 111.22(1)°, 3829 independent reflections, 106 parameters, wR₂ = 0.054) are discussed. Further, the optical, magnetic and thermal properties of both polymorphs are investigated with focus on the role of the Cu²⁺ cation and its Jahn-Teller effect. The findings are confirmed by DFT calculations yielding insights in the stability of the synthesised polymorphs as well as a predicted γ-modification. Additionally, the crystal structures of two polymorphs of copper hydrogensulfate Cu(HSO₄)₂-I (P2₁/n, no. 14, a = 4.7530(2), b = 8.5325(4), c = 7.3719(3) Å, β = 100.063(1)°, 1063 independent reflections, 55 parameters, wR₂ = 0.052) and Cu(HSO₄)₂-II (P1̄, no. 2, a = 4.79.88(8), b = 7.857(1), c = 8.057(1) Å, α = 77.86(1)°, β = 87.02(1)°, γ = 89.82(1)°, 1044 independent reflections, 109 parameters, wR₂ = 0.132) as well as that of Cu[S₂O₇] (C2/c, no. 15, a = 6.6341(4), b = 8.7302(5), c = 9.0555(8) Å, β = 104.763(3)°, 1117 independent reflections, 48 parameters, wR₂ = 0.049) are presented and the cyclosilicate-analogous borosulfate Cu[B(SO₄)₂(HSO₄)] is fully characterised with respect to its optical and thermal properties.

Strong Lewis and Brønsted Acidic Sites in the Borosulfate Mg3 [H2 O→B(SO4 )3 ]2

Borosulfates provide fascinating structures and properties that go beyond a pure analogy to silicates. Mg3 [H2 O→B(SO4 )3 ]2 is the first borosulfate featuring a boron atom solely coordinated by three tetrahedra. Thus, the free Lewis acidic site forms a Lewis acid-base adduct with a water molecule. This is unprecedented for borosulfate chemistry and even for borates. Quantum chemical calculations on water exchange reactions with BF3 and B(C6 F5 )3 revealed a higher Lewis acidity for the borosulfate anion. Moreover, proton exchange reactions showed a higher Brønsted acidity than comparable silicates or phosphates. Additionally, Mg3 [H2 O→B(SO4 )3 ]2 was characterised by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and density functional theory (DFT) calculations.

The First Bismuth Borosulfates Comprising Oxonium and a Tectosilicate-Analogous Anion

The first bismuth borosulfate (H3 O)Bi[B(SO4 )2 ]4 is only the second featuring a three-dimensional anion, the first tectosilicate-analogous borosulfate synthesised solvothermally without a precursor (from Bi(NO3 )3 ⋅5 H2 O and B(OH)3 in oleum); moreover, it is the first comprising two differently charged cations and crystallises in a new structure type in space group I 4 ‾ (no. 82) (a=11.857(1), c=8.149(1) Å, 1947 refl., 111 param., wR2=0.037), confirmed by a second harmonic generation (SHG) measurement. The B(SO4 )4 supertetrahedra are connected via all four sulfate tetrahedra resulting in a three-dimensional anion with both H3 O+ and Bi3+ cations in channels. Additionally, the crystal structure of a further bismuth borosulfate, Bi2 [B2 (SO4 )6 ], is elucidated crystallising isotypically to the rare-earth borosulfates R2 [B2 (SO4 )6 ] in space group C2/c (No. 15) (a=13.568(2), b=11.490(2), c=11.106(2) Å, 3127 refl., 155 param., wR2=0.035). Moreover, the optical and thermal properties of both compounds are discussed.

Ni[B2 (SO4 )4 ] and Co[B2 (SO4 )4 ]: Unveiling Systematic Trends in Phyllosilicate Analogue Borosulfates

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.

Synthesis-Controlled Polymorphism and Optical Properties of Phyllosilicate-Analogous Borosulfates M[B2 (SO4 )4 ] (M=Mg, Co)

Increased synthetic control in borosulfate chemistry leads to the access of various new compounds. Herein, the polymorphism of phyllosilicate-analogous borosulfates is unraveled by adjusting the oleum (65 % SO3 ) content. The new polymorphs β-Mg[B2 (SO4 )4 ] and α-Co[B2 (SO4 )4 ] both consist of similar layers of alternating borate and sulfate tetrahedra, but differ in the position of octahedrally coordinated cations. The α-modification comprises cations between the layers, whereas in the β-modification cations are embedded within the layers. With this new synthetic approach, phase-pure compounds of the respective polymorphs α-Mg[B2 (SO4 )4 ] and β-Co[B2 (SO4 )4 ] were also achieved. Tanabe-Sugano analysis of the Co2+ polymorphs reveal weak ligand field splitting and give insights into the coordination behavior of the two-dimensional borosulfate anions for the first time. DFT calculations confirmed previous in silico experiments and enabled an assignment of the polymorphs by comparing the total electronic energies. The compounds are characterized by single-crystal XRD, PXRD, FTIR, and UV/Vis/NIR spectroscopy, thermogravimetric analysis (TGA), and density functional theory (DFT) calculations.

From S-O-S to B-O-S to B-O-B Bridges: Ba[B(S2O7)2]2 as a Model System for the Structural Diversity in Borosulfate Chemistry

Various different possible connection patterns of sulfate and borate tetrahedra enable a vast structural diversity in borosulfates, a rather new class of silicate-analogous compounds. Here we unravel a direct relationship from S-O-S to B-O-S to B-O-B bridges for the first time in borosulfate chemistry. Solvothermal synthesis in pure oleum (65% SO₃) yielded the first alkaline earth metal borosulfate comprising S-O-S bridges: Ba[B(S₂O₇)₂]₂ (I2/a, Z = 4, a = 1160.77(9) pm, b = 891.44(7) pm, c = 2130.26(19) pm, β = 104.0341(17)°) contains molecular [B(S₂O₇)₂]^- anions of a central boron atom and two chelating disulfate groups. By using equal amounts of sulfuric acid and oleum solely B-O-S bridges were obtained in Ba[B₂(SO₄)₄] (Pnna, Z = 4, a = 1279.08(18) pm, b = 1280.0(2) pm, c = 731.70(11) pm) featuring one-dimensional _∞¹[B(SO₄)_4/2]^- chains. The thermal analysis on Ba[B(S₂O₇)₂]₂ revealed the conversion from S-O-S bridges to B-O-S bridges in Ba[B₂(SO₄)₄] and to B-O-B bridges in Ba[B₂O(SO₄)₃] by a successive release of SO₃. Thus, BaO-B₂O₃-SO₃ is the first quaternary system for borosulfates uniting all three possible connection patterns enabling us to understand the fascinating but systematic chemistry in such systems. Both new compounds were also characterized by means of X-ray powder diffraction, electrostatic calculations, and infrared spectroscopy assisted by density functional theory (DFT).

Borosulfates-Synthesis and Structural Chemistry of Silicate Analogue Compounds

Borosulfates are oxoanionic compounds consisting of condensed sulfur- and boron-centered tetrahedra. Hitherto, they were mostly achieved from solvothermal syntheses in SO3 -enriched sulfuric acid, or from reactions with the superacid H[B(HSO4 )4 ]. The crystal structures are very similar to those of the corresponding class of silicates and their substitution variants, especially regarding the typical structural motif of corner-sharing tetrahedra. However, the borosulfates are supposed to be even more versatile, because (BO3 ) units might also be part of the anionic network. The following article deals with detailed reports on the different synthesis strategies, the crystal chemistry of borosulfates in comparison to silicates, and their hitherto identified properties.

On the phosphors Na5M(WO4)4 (M = Y, La–Nd, Sm–Lu, Bi) – crystal structures, thermal decomposition, and optical and magnetic properties

An exploration of the crystal chemistry of exciting luminescent title compounds – possible phosphors – is discussed also employing magnetic measurements.

M[B2(SO4)4] (M = Mn, Zn)—Syntheses and Crystal Structures of Two New Phyllosilicate Analogue Borosulfates

Borosulfates are a rapidly expanding class of silicate analogue materials, where the structural diversity is expected to be at least as large as known for silicates. However, borosulfates with cross-linking of the anionic network into two or even three dimensions are still very rare. Herein, we present two new representatives with phyllosilicate analogue topology. Through solvothermal reactions of ZnO and MnCl2∙4H2O with boric acid in oleum (65% SO3), we obtained single-crystals of Mn[B2(SO4)4] (monoclinic, P21/n, Z = 2, a = 8.0435(4), b = 7.9174(4), c = 9.3082(4) Å, β = 110.94(1)°, V = 553.63(5) Å3) and Zn[B2(SO4)4] (monoclinic, P21/n, Z = 2, a = 7.8338(4), b = 8.0967(4), c = 9.0399(4) Å, β = 111.26(1)°, V = 534.36(5) Å3). The crystal structures reveal layer-like anionic networks with alternating vierer- and zwölfer-rings formed exclusively by corner-linked (SO4)- and (BO4)-tetrahedra.

Tb(HSO4)(SO4) - a green emitting hydrogensulfate sulfate with second harmonic generation response

Recently, sulfates have attracted attention as materials for non-linear optical applications. This compound class is extended by Tb(HSO₄)(SO₄), which is solvothermally synthesised from Tb₄O₇ and sulfuric acid. The compound crystallises in the non-centrosymmetric space group P2₁ (Z = 2, a = 665.03(5) pm, b = 659.41(5) pm, c = 680.24(5) pm, and β = 104.640(2)°) and is homeotypic with Ni₂In. The terbium ions adopt the indium sites and the sulfate and hydrogen sulfate anions are situated on the nickel sites. The compound shows green luminescence based on f-f-transitions and the positions of the f-d-excitation bands reveal a weak coordination behaviour of the sulfate anions. Tb(HSO₄)(SO₄) exhibits a second harmonic generation response comparable to KH₂PO₄ (KDP). Furthermore, the material is characterised by electrostatic calculations, infrared spectroscopy and thermal analysis.