Square-Pyramidal/Triangular Framework Oxide:  Synthesis and Structure of PKU-6

PKU-6, a new aluminoborate (HAl<sub>2</sub>B<sub>3</sub>O<sub>8</sub>), has been synthesized in a closed system at 400 °C. The structure of PKU-6, characterized by using powder and single-crystal X-ray diffraction, consists of AlO<sub>5</sub> square-pyramidal chains and B<sub>3</sub>O<sub>7</sub> groups, which are interconnected and form a three-dimensional framework. The <sup>27</sup>Al NMR study indicates that the isotropic chemical shift of pyramidal Al is 34.6 ppm with a large quadrupolar coupling constant (<i>C</i><sub>Q</sub> = 4.2 MHz), mainly due to a nonspherical coordination environment.