Single crystals of the novel boroarsenate (K,Na)₂[As₂B₁₂O₂₄][B₃O₃(OH)₃] (I) were obtained using the borax flux method. The crystal structure of I was found to be triclinic, P-1, a = 8.414(5), b = 10.173(6), c = 15.90(1) Å, α = 79.56(1), β = 78.68(1), γ = 70.91(1), V = 1251(1) ų, Z = 2. The crystal structure of I is based upon the novel [AsB₆O₁₂]⁻ microporous boroarsenate framework formed by B and As coordination polyhedra. This framework can be subdivided into borate units that are interlinked by AsO₄ tetrahedra. In the case of I, the borate substructure is a chain consisting of triborate rings, □2∆, formed by two (BO₃) triangles and one (BO₄) tetrahedron connected through shared common oxygen atoms. The chains are extended along [011] and are interlinked by (AsO₄) tetrahedra in the [011] direction. As a result, the framework has large channels parallel to [100], having an effective diameter of 4.2 × 5.6 Ų. The channels contain occluded electroneutral ring triborate complexes, [B₃O₃(OH)₃]⁰, formed by three (BO₂(OH⁻))⁻ triangles sharing common O atoms, as well as K⁺ and Na⁺ cations. The triborate [B₃O₃(OH)₃]⁰ units correspond to similar clusters found in the crystal structure of the α-form of metaboric acid, HBO₂. According to information-based complexity calculations, the crystal structure of I should be described as complex, with I_G = 5.781 bits/atom and I_G,total = 625.950 bits/cell. Teruggite, Ca₄Mg[B₆As(OH)₆O₁₁]₂(H₂O)₁₄, the only known boroarsenate of natural origin, has almost twice as much information per unit cell, with I_G,total = 1201.992 bits/cell. The observed difference in structural complexity between I and teruggite is the consequence of their chemistry (hydration state) and different formation conditions.