Expanding silver fluorooxoborate crystal chemistry: Ag2B5O8F with 3D double interpenetrating frameworks and Ag3B5O8F2 with 2D layers

Abstract

The rapid development of the chemistry of fluorooxoborates is associated with their important role as valuable optical materials. In this work, we reported the first two silver representatives of the family, Ag2B5O8F (1) and Ag3B5O8F2 (2). Both structures are based on pentaborate groups with a different degree of “fluorination”: 1 contains interpenetrating frameworks composed of [B5O10F] fundamental building units, while 2 consists of layers of [B5O10F2]. The thermal expansion of 2 is strongly anisotropic, minimal in-plane (α11 = 13, α22 = –1 × 10−6 °C−1), and maximal in the normal direction (α33 = 42 × 10−6 °C−1). We also discussed the stereoisomerism of the [B5O10F2] pentaborate groups.