The Crystal Structure of Potassium Metaborate, K3(B3O6)

In order to find the configuration of the metaborate group the crystal structure of potassium metaborate was determined. The crystals are rhombohedral ar = 7.76A, α = 110° 36′ with six molecules KBO2. The density is 2.348. The space group is R3̄c(D3d6). All atoms are lying on twofold axes at positions: ±(u, ½—u, ¼) ↺ . The parameters were determined by means of two-dimensional Fourier analyses:Ku=0.689±0.003,Bu=0.361±0.006,OI0.465±0.006,OII0.146±0.006.The metaborate radical is (B3O6)—3, a ring of three BO3 triangles, rather than the endless chain of BO3 triangles found in CaB2O4. The BO3 groups are slightly distorted, the B–O distances being 1.33A, 1.38A and 1.38A, the O–O distances 2.30A, 2.38A and 2.38A. The nine particles of the radical lie in one plane. Potassium is surrounded by seven oxygen atoms at a distance 2.82A.