Cs4 B4 O3 F10 : First Fluorooxoborate with [BF4 ] Involving Heteroanionic Units and Extremely Low Melting Point.

Herein, a new congruently melting mixed-anion compound Cs4 B4 O3 F10 has been characterized as the first fluorooxoborate with [BF4 ] involving heteroanionic units. Compound Cs4 B4 O3 F10 possesses two highly fluorinated anionic clusters and therefore its formula can be expressed as Cs3 (B3 O3 F6 ) ⋅ Cs(BF4 ). The influence of [BF4 ] units on micro-symmetry and structural evolution was discussed based on the parent compound. More importantly, Cs4 B4 O3 F10 shows the lowest melting point among all the available borates and thus sets a new record for such system. This work is of great significance to enrich and tailor the structure of borates using perfluorinated [BF4 ] units.