Exploring\na New Structure Family: Alkali Borosulfates\nNa₅[B(SO₄)₄], A₃[B(SO₄)₃] (A = K, Rb), Li[B(SO₄)₂], and Li[B(S₂O₇)₂]

Abstract

New\nalkali borosulfates were obtained by precipitation from oleum,\nsolid-state reactions, or thermal decomposition. The crystal structures\nwere characterized with single-crystal data. They are all based on\ncorner-linked BO₄ and SO₄ tetrahedra with varying\ncoordination of the alkali cations. According to the ratio of BO₄ and SO₄ tetrahedra, different frameworks are observed,\ni.e., noncondensed complex anions (1:4), one-dimensional chains (1:3),\nor three-dimensional (3D) networks (1:2). This is in analogy to silicates,\nwhere the ratio Si/O relates to the dimensionality also. For Na₅[B­(SO₄)₄], which exists in two different\npolymorphs, there are noncondensed pentameric units. Na₅[B­(SO₄)₄]-I: space group <i>Pca</i>2₁, <i>a</i> = 10.730(2) Å, <i>b</i> = 13.891(3) Å, <i>c</i> = 18.197(4) Å. Na₅[B­(SO₄)₄]-II: space group <i>P</i>2₁2₁2₁, <i>a</i> = 8.624(2)\nÅ, <i>b</i> = 9.275(2) Å, <i>c</i> =\n16.671(3) Å. A₃[B­(SO₄)₃] (A\n= K, Rb) are isotypic with Ba₃[B­(PO₄)₃] adopting space group <i>Ibca</i> [K₃[B­(SO₄)₃], <i>a</i> = 7.074(4) Å, <i>b</i> = 14.266(9) Å, <i>c</i> = 22.578(14) Å;\nRb₃[B­(SO₄)₃], <i>a</i> =\n7.2759(5) Å, <i>b</i> = 14.7936(11) Å, <i>c</i> = 22.637(2) Å] with vierer chains of BO₄ tetrahedra based on two bridging and two terminal SO₄ tetrahedra. Li­[B­(SO₄)₂] [space group <i>Pc</i>, <i>a</i> = 7.6353(15) Å, <i>b</i> = 9.342(2) Å, <i>c</i> = 8.432(2) Å, and β\n= 92.55(2)°] comprises a 3D network that is closely related to\nβ-tridymite. Li­[B­(S₂O₇)₂] [space\ngroup <i>P</i>2₁2₁2₁, <i>a</i> = 10.862(2) Å, <i>b</i> = 10.877(2) Å, <i>c</i> = 17.769(4) Å] represents the first example of a\ndisulfate complex with noncondensed [B­(S₂O₇)₂]⁻ units. Vibrational spectra were recorded\nfrom all compounds, and the thermal behavior was also investigated.