Two new potassium borates, K₄B₁₀O₁₅(OH) ₄ with stepped chain and KB₅O₇(OH) ₂·H₂O with double helical chain

Two unusual chainlike potassium borates of K₄B ₁₀O₁₅(OH)₄ (1) and KB₅O ₇(OH 2·H₂O (2) have been synthesized under mild solvothermal conditions at 170°C. The structures were determined by single-crystal X-ray diffraction and further characterized by FTIR, powder X-ray diffraction, and thermogravimetric analysis. Compound 1 crystallized in the monoclinic space group C2/c, a = 18.077(6) Å, b = 6.857(2) Å, c = 13.266(4) Å, β = 95.271(4)°, V = 1637.4(9) ų, Z = 4, R = 0.0234; and compound 2 crystallized in the monoclinic space group P2(1)/c, a = 9.4824(8) Å, b = 7.5180(6) Å, c = 11.4154(6) Å, β = 97.277(3)°, V = 807.2(1) ų, Z = 4, R = 0.0502. The stepped chains of 1 are built up from corner sharing of B₃O ₅(OH)₂^3- and B₄O₉ ^6- groups to form new fundamental building blocks (FBBs) of B ₅O₁₀(OH)₂^7- constructed by corner sharing of one B₃O₅(OH)₂^3- cluster with a three-membered ring, one BO₃^3- unit, and BO ₄^5- tetrahedron, while the double helical chain of 2 is built up by BBBs of B₅O₇(OH)₂^-. Adjacent chains in 1 and 2 are further connected into a 3-D structure by K ⁺ cations and H-bonding interactions.