title: Na5[MB24O34(OH)12].nH2O (M = Cr(3+), Al(3+)): unprecedented spherelike polyborate clusters from boric acid flux synthesis.
abstract: Two novel isotypic polyborate cluster compounds Na 5[MB 24O 34(OH) 12]. nH 2O (M = Cr (3+), Al (3+)) have been synthesized in a boric acid flux closed system at 220 degrees C by using gel as precursors. The structure of the Cr compound was determined by low-temperature single-crystal X-ray diffraction, and the Al compound was confirmed to be isostructural by powder X-ray diffraction and similar FT-IR spectra and thermal behavior. Na 5[CrB 24O 34(OH) 12]. nH 2O crystallizes in the monoclinic space group P2 1/ c with the cell parameters a = 17.4549(3) A, b = 11.1976(2) A, c = 21.2403(3) A, beta = 94.644(2) degrees , V = 4137.85(12) A (3), and Z = 4. The predominant feature of the structure are the spherelike polyborate clusters [MB 24O 34(OH) 12] (5-). The M (3+) cation is located at the center of the cluster, around which four hexaborate units ([B 6O 10(OH) 3] (5-)) are tetrahedrally assembled in almost a perfect T d symmetry. To the best of our knowledge, [MB 24O 34(OH) 12] (5-) is the first example of a polyborate cluster that contains 24 boron atoms. Upon heating, the compounds show two steps of weight loss, including the loss of the disengaged water and dehydration of the hydroxy groups. The first step is reversible, retaining the structure framework. The second weight loss is continuous and irreversible.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing, People's Republic of China.
authors.forename: Tao
authors.initials: T
authors.lastname: Yang
authors.forename: Junliang
authors.initials: J
authors.lastname: Sun
authors.forename: Lars
authors.initials: L
authors.lastname: Eriksson
authors.forename: Guobao
authors.initials: G
authors.lastname: Li
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zou
authors.forename: Fuhui
authors.initials: F
authors.lastname: Liao
authors.forename: Jianhua
authors.initials: J
authors.lastname: Lin