Potassium pentaborate

Abstract

The title compound, K[B5O7(OH)2], was obtained from a hydrothermal reaction. The structure is composed of one K+ cation and a polyborate 1∞[B5O7(OH)2]− anion, which consists of two six-membered rings linked by a common BO4 tetrahedron. The [B5O7(OH)2]− units are linked together through two exocyclic O atoms to neighbouring units, forming a helical chain structure extending parallel to [010]. Adjacent chains are further connected into a three-dimensional structure by K—O bonds and weak O—H...O hydrogen-bond interactions.