Li6.58Na7.43Sr4(B9O18)(B12O24)Cl: unprecedented combination of the largest two highly polymerized isolated B–O clusters with novel isolated B9O18 FBB

A new borate, Li6.58Na7.43Sr4(B9O18)(B12O24)Cl (LNSBOC), was successfully obtained via a spontaneous crystallization method in an open system. LNSBOC crystallizes in a hexagonal crystal system with the centrosymmetric space group of P63/m, with a = 9.3046(2) Å, c = 24.3239(7) Å and Z = 2. According to the statistics, the structure of LNSBOC is extraordinary not only because of the discovery of the novel fan-like fundamental building block B9O18, but also for the unprecedented coexistence of the largest two highly polymerized (number of B atoms more than six) isolated B–O clusters in the structure. A discussion about the cause of the rareness of borates containing two polymerized isolated B–O clusters was carried out by investigating previous research and extant compounds. Even more significantly, a strategy to design compounds/crystal structures containing two polymerized isolated B–O clusters is put forward in this work from the viewpoint of structures and elements. In addition, thermal analysis and infrared and UV–Vis–NIR diffuse reflectance spectroscopy were performed for the title compound.