NaKB6O9F2: a new complex alkali metal fluorooxoborate with puckered layers

A new fluorooxoborate NaKB6O9F2 containing puckered layers has been synthesized using a high temperature solution method in a closed system. It is completely isostructural to NaRbB6O9F2. In their structure, the layers have two kinds of large empty holes composed of 16 element rings and super large rectangular rings. Through structural comparison, we found that the large empty holes in the layer and the introduction of the terminal F atoms may be the main reason for the formation of the structure containing puckered layers and the interlayer staggered arrangement tightly occluded together. Experimental and first-principles analyses were carried out to elucidate the optical properties.