Syntheses, characterizations, and crystal structures of two new organically templated borates

Two new organically templated borates, [H₂DAB][B ₇O₉(OH)₅]·2H₂O (1) and [H₂DAB][B₇O₁₀(OH)₃] (2), have been synthesized under mild conditions in the presence of DAB acting as structure-directing agent (DAB = 1,4-diaminobutane). The structures were determined by single crystal X-ray diffraction and further characterized by FTIR, elemental analysis, and thermogravimetric analysis. Both 1 and 2 crystallize in the same triclinic system, space group P1 (No. 2); 1: a = 8.238(4) Å, b = 8.348 (5) Å, c = 14.574(8) Å, a = 101.050(3)°, β = 92.313(7)°, γ = 112.694(5)°, V = 900.3(8) ų, Z = 2; 2: a = 8.8769(3) Å, b = 9.3204(2) Å, c = 10.2204(5) Å, α = 74.474(2)°, β = 85.292(5)°, γ = 72.730(2)°, V = 778.01(5) ų, Z = 2. The structure of 1 consists of [B₇O₉(OH) ₅]^2- groups, which represents the first example of organically templated heptaborate. The structure exhibits interesting hydrogen-bonded network formed by borate polyanion [B₁₄O ₂₀(OH)₆]^4-, which can be regarded as being constructed from the dehydration of the FBBs in 1. The diprotonated organic amines are filled in the free space of the hydrogen-bonded network and interact with the inorganic framework by extensive hydrogen bonds.