Synthesis and characterization of a new quaternary borate Na2Cs2Sr(B9O15)2 with the unprecedented [B9O19]11− group, notation of 3 × (3:2Δ + T)

Na2Cs2Sr(B9O15)2 represents a new structure type in which three [B3O7]5− triborate groups are bridged by two common oxygen atoms to form a [B9O19]11− group that is further condensed into a 3D [B9O15]3-∞3 network, with the intersecting open channels as well as pockets accommodating Cs+, Sr2+, and Na+ cations.277