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.

Borosulfates are an ever‐expanding class of compounds and the extent of their properties is still elusive. Herein, the first two copper borosulfates Cu[B₂(SO₄)₄] and Cu[B(SO₄)₂(HSO₄)] are presented, which are structurally related but show different dimensionalities in their substructure: While Cu[B₂(SO₄)₄] reveals an anionic chain, [B(SO₄)_4/2]⁻, with both a twisted and a unique chair conformation of the B(SO₄)₂B subunits, Cu[B(SO₄)₂(HSO₄)] reveals isolated [B₂(SO₄)₄(HSO₄)₂]⁴⁻ anions showing exclusively a twisted conformation. The complex anion can figuratively be obtained as a cut‐out from the anionic chain by protons. Comparative DFT calculations based on magnetochemical measurements complement the experimental studies. Calculation of the pK_a values of the two conformers of the [B₂(SO₄)₄(HSO₄)₂]⁴⁻ anion revealed them to be more similar to silicic than to sulfuric acid, highlighting the close relationship to silicates.

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 Zn_1‐xMn_x[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.