A novel contribution to the M3B6O10X hexaborate family: The new silver compound Ag3B6O10Br and thermal behavior of Ag3B6O10(NO3) and Na3B6O10I.

In this work, we present a new borate, Ag 3 B 6 O 10 Br, as well as thermal properties of two recently reported members of M 3 B 6 O 10 X family, Ag 3 B 6 O 10 (NO 3) and Na 3 B 6 O 10 I. The structure of Ag 3 B 6 O 10 Br is non-centrosymmetric, Pnm 2 1 , and exhibits a new version of packing the ionic Ag–Br and covalent B–O frameworks. The non-centrosymmetry is induced by alternation of disordered and ordered borate "layers" normal to a. The Ag–Br sublattice is also strongly disordered and exhibits pronounced ahnarmonicity of thermal vibrations modeled using the Gram – Charlier series. Thermal behavior of Ag 3 B 6 O 10 Br, Ag 3 B 6 O 10 (NO 3) and Na 3 B 6 O 10 I was characterized using variable-temperature powder X-ray diffraction and thermal analysis. The thermal behavior of Ag 3 B 6 O 10 Br (α a = −0.5, α b = −7.4, α c = 41.5 at 200°С), Ag 3 B 6 O 10 (NO 3) (α a = 4.5, α b = 4.8, α c = 31.8 at 200°С), and Na 3 B 6 O 10 I (α a = 9.4, α b = −1.2, α c = 48.3 at 200°С) is strongly anisotropic due to the alignment of the hexaborate B 6 O 13 groups in the structure. [Display omitted] • A new non-centrosymmetric borate, Ag 3 B 6 O 10 Br was prepared. • Cationic [Ag 3 Br]3+sublattice shows strongly anharmonic displacement parameters. • Thermal expansion of Ag 3 B 6 O 10 X, X = Br, NO 3 , and Na 3 B 6 O 10 I is anisotropic. [ABSTRACT FROM AUTHOR]