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 K 4 B 10 O 15 (OH) 4 ( 1 ) and KB 5 O 7 (OH) 2 ·H 2 O ( 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 C 2/ c, a = 18.077(6) Å, b = 6.857(2) Å, c = 13.266(4) Å, β = 95.271(4)°, V = 1637.4(9) Å 3, Z = 4, R = 0.0234; and compound 2 crystallized in the monoclinic space group P 2(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) Å 3, Z = 4, R = 0.0502. The stepped chains of 1 are built up from corner sharing of B 3 O 5 (OH) 2 3- and B 4 O 9 6- groups to form new fundamental building blocks (FBBs) of B 5 O 10 (OH) 2 7- constructed by corner sharing of one B 3 O 5 (OH) 2 3- cluster with a three-membered ring, one BO 3 3- unit, and BO 4 5- tetrahedron, while the double helical chain of 2 is built up by FBBs of B 5 O 7 (OH) 2 - . Adjacent chains in 1 and 2 are further connected into a 3-D structure by K + cations and H-bonding interactions.