title: Hydrothermal synthesis and crystal structures of two novel acentric mixed alkaline earth metal berylloborates Sr3Be2B5O12(OH) and Ba3Be2B5O12(OH).
abstract: The synthesis and structure of the isostructural acentric compounds Sr(3)Be(2)B(5)O(12)(OH) (1) and Ba(3)Be(2)B(5)O(12)(OH) (2) are reported for the first time. These compounds crystallize in the space group R3m, and the unit cell parameters are a = 10.277(15) Å and c = 8.484(17) Å for 1 and a = 10.5615(15) Å and c = 8.8574(18) Å for 2. The structures consist of a network of [Be(2)B(4)O(12)(OH)] units interwoven with a network consisting of MO(9) polyhedra (M = Sr, Ba) and BO(3) triangles and exemplify how acentric building blocks such as [BO(3)](3-), [BO(4)](5-), and [BeO(4)](6-) can be especially suitable to build noncentrosymmetric long-range structures. Both networks are centered on the 3-fold rotation axis and present themselves in alternating fashion along [001]. Acentricity is imparted by the alignment of the polarities of BO(3) and BeO(4) environments. Infrared spectroscopy has been used to confirm the local geometries of B and Be, as well as the presence of hydroxide in the crystal structure. Another interesting feature of these compounds is the presence of disorder involving Be and B at the tetrahedral Be site. The degree of the disorder has been confirmed by observing a noticeable shortening of average Be-O bond distances.
authors.affiliation: Department of Chemistry and Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson University, Clemson, South Carolina 29634-0973, USA.
authors.forename: Colin D
authors.initials: CD
authors.lastname: McMillen
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Kolis