An Unusual Sodium-Ammonia Tetraborate Na1.33(NH4)0.67B4O5(OH)4·(H2O)2 Containing Tetranuclear Sodium ion cluster

A sodium-ammonia tetraborate Na1.33(NH4)0.67B4O5(OH)4·(H2O)2 (denoted 1) has been synthesized under mild solvothermal condition. The compound crystallizes in the chiral trigonal R32 (155) space group, with the following unit cell parameters: a = 11.172(3) A, b = 11.172(3) A, c = 21.282(10) A; V = 2300.4(14) A3; Z = 3. It has been characterized by single crystal X-ray analysis, element analysis, FTIR, PXRD, TG-DSC and Second-harmonic-generation response. Its structure contains [B4O5(OH)4]2− polyanions, which are further linked by a rare [Na4O18] cluster to form a 3-D framework.