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

Abstract

Increaseds ynthetic control in borosulfate chemistry leads to the accesso fv arious new compounds. Herein, the polymorphism of phyllosilicate-analogous borosulfates is unraveled by adjustingt he oleum (65 %S O 3)c ontent.T he new polymorphs b-Mg[B 2 (SO 4) 4 ]a nd a-Co[B 2 (SO 4) 4 ]b oth consisto fs imilarl ayers of alternating borate and sulfate tetrahedra, but differ in the position of octahedrally coordinated cations. The a-modificationc omprises cations between the layers, whereas in the b-modification cations are embedded within the layers. With this new synthetica pproach, phase-pure compounds of the respective polymorphs a-Mg[B 2 (SO 4) 4 ]a nd b-Co[B 2 (SO 4) 4 ]w ere also achieved. Tanabe-Sugano analysiso ft he Co 2 + polymorphs reveal weak ligand field splitting and give insights into the coordinationb ehavior of the two-dimensional borosulfate anions fort he first time.D FT 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,t hermogravimetric analysis (TGA), and density functional theory (DFT) calculations.

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

“…Here, the O−S−O and O−B−O bending and the B−O−S bridging vibration modes occur. In accordance with earlier results on borosulfates, [3, 6, 8] the bands between 840 and 1040 cm −1 can be assigned to B−O stretching vibrations and the ones above 1100 cm −1 to S−O stretching vibrations. The UV/Vis spectrum shows an absorption edge in the UV region related to the fundamental absorption of the sample overlapping with allowed s–p transitions of Bi 3+ and is in line with the colourless powder.…”

Die ersten zwei Bismutborosulfate – eines davon enthält Oxonium und ein tektosilicatanaloges Anion

“…[8] Here, the O À S À O and O À B À O bending and the B À O À S bridging vibration modes occur. In accordance with earlier results on borosulfates, [3,6,8] the bands between 840 and 1040 cm À1 can be assigned to BÀO stretching vibrations and the ones above 1100 cm À1 to SÀO stretching vibrations. The UV/Vis spectrum shows an absorption edge in the UV region related to the fundamental absorption of the sample overlapping with allowed s-p transitions of Bi 3+ and is in line with the colourless powder.…”

“…Dort finden sich die O‐S‐O‐ und O‐B‐O‐Biegemoden und B‐O‐S‐Brückenschwingungen. In Übereinstimmung mit früheren Ergebnissen zu Borosulfaten [3, 6, 8] können die Banden zwischen 840 und 1040 cm −1 den B‐O‐Streckschwingungen und die oberhalb von 1100 cm −1 den S‐O‐Streckschwingungen zugeordnet werden. Das UV/Vis‐Spektrum zeigt eine Absorptionskante im UV‐Bereich aufgrund der fundamentalen Absorption der Probe, die von den erlaubten s‐p‐Übergängen des Bi 3+ überlagert wird, und ist im Einklang mit der Beobachtung eines farblosen Pulvers.…”

Ag[B(S2O7)2]: The First Transition Metal Borosulfate Featuring Disulfate Groups

“…Meanwhile we differentiate between classic and unconventional borosulfates. In classic borosulfates the anions consist solely of alternating borate and sulfate tetrahedra like in M [B 2 (SO 4 ) 4 ] ( M =Mn, Co, Ni, Cu, Zn), [5,13–15] and in the protonated borosulfate Cu[B(HSO 4 )(SO 4 ) 2 ] [13] . In unconventional borosulfates the anions may feature B−O−B bridges as reported for M 4 [B 2 O(SO 4 ) 6 ] ( M =Mn, Co, Ni, Zn) [3] .…”

“…Starting from the first borosulfate K 5 [B(SO 4 ) 4 ] eight years ago [2] ongoing research led to enormous progress in borosulfate chemistry. Besides the structural evolution, especially optical properties were investigated showing a weak coordination behavior of the borosulfate anions [3–5] or even second harmonic generation responses [6] . A striking prospect for borosulfate chemistry, however, could be as electrolytes for solid acid fuel cells, since a high proton conductivity for the ammonium borosulfates NH 4 [B(SO 4 ) 2 ] was reported, recently [7] .…”