(NH₄)₄[SO₄][CB₁₁H₁₂]₂: a new double salt with carbaborate anions crystallizing in a monoclinic variant of the anti-K₂NiF₄-type structure.

The new double salt with the empirical formula (NH4)4[SO4][CB11H12]2 can be obtained by the reaction between an aqueous solution of the free acid of the closo-carbaborate (H3O)[CB11H12] and aqueous ammonia (NH3), when the incorporated sulfate anions are introduced by a cation exchanger due to its regeneration with sulfuric acid (H2SO4). (NH4)4[SO4][CB11H12]2 is yielded as colorless, prismatically shaped crystals with a considerable size up to 1 mm. This ammonium sulfate carbaborate crystallizes in the monoclinic space group C2/c with the lattice parameters a = 2715.32(9), b = 713.91(2), c = 1391.24(5) pm and β = 109.203(2)° with four formula units per unit cell. Due to the formation of bridging hydrogen bonds, the [SO4]2− anions and the (NH4)+ cations form ∞ 2 {([(N1)H4]2/2[(N2)H4]2/2[(N3)H4]2/1[SO4])2+} layers parallel to the bc plane. Between these positively charged layers, the [CB11H12]− anions are placed in fashion of the anti-K2NiF4-type structure, where K+ is replaced with [CB11H12]− and [SO4]2−-centered [(NH4)+]6 octahedra, which share four coplanar corners, arrange to the above-mentioned layers. In the Raman spectra of (NH4)4[SO4][CB11H12]2, the dominating bands correspond to the well-known vibration modes of the closo-carbaborate cage. The bands resulting from the (NH4)+ and [SO4]2− ions are visible, but significantly less intense as compared to the vibrations of [CB11H12]−, which can be explained by the formation of hydrogen bonds. [ABSTRACT FROM AUTHOR]