Single crystals of the novel boroarsenate (K,Na)
2[As
2B
12O
24][B
3O
3(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) Å
3,
Z = 2. The crystal structure of
I is based upon the novel [AsB
6O
12]
− microporous boroarsenate framework formed by B and As coordination polyhedra. This framework can be subdivided into borate units that are interlinked by AsO
4 tetrahedra. In the case of
I, the borate substructure is a chain consisting of triborate rings, ☐2Δ, formed by two (BO
3) triangles and one (BO
4) tetrahedron connected through shared common oxygen atoms. The chains are extended along [0
1] and are interlinked by (AsO
4) 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 Å
2. The channels contain occluded electroneutral ring triborate complexes, [B
3O
3(OH)
3]
0, formed by three (BO
2(OH
−))
− triangles sharing common O atoms, as well as K
+ and Na
+ cations. The triborate [B
3O
3(OH)
3]
0 units correspond to similar clusters found in the crystal structure of the α-form of metaboric acid, HBO
2. According to information-based complexity calculations, the crystal structure of
I should be described as complex, with
IG = 5.781 bits/atom and
IG,total = 625.950 bits/cell. Teruggite, Ca
4Mg[B
6As(OH)
6O
11]
2(H
2O)
14, the only known boroarsenate of natural origin, has almost twice as much information per unit cell, with
IG,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.
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