Ba2(BO3)(1-x)(CO3)(x)Cl(1+x): a mixed borate and carbonate chloride crystallized from high-temperature solution

A mixed borate and carbonate chloride Ba(2)(BO(3))(1-x)(CO(3))(x)Cl(1+x) was obtained by spontaneous crystallization from a high-temperature melt in open air. It crystallizes in the trigonal crystal system with space group of P3m̅1 and lattice constants of a = 5.4708(8) Å and c = 10.640(2) Å. The structure can be viewed as an intergrowth of trigonal Ba(2)Mg(BO(3))(2) (001) slab and (111) slab of the cubic fluorite BaCl(2). During Fourier analysis of the single-crystal X-ray diffraction data, additional electron density was found locating at 1b (0, 0, 1/2) site and attributed to chlorine surplus, which was confirmed by chemical titration. Charge balance of the compound was found, unexpectedly in an acidic borate containing high-temperature melt, by partial CO(3)(2-) group substituting the BO(3)(3-) group. The existence of CO(3)(2-) anion in the crystal was detected by thermogravimetry-mass spectrum analysis and Raman spectrum. The transmittance spectrum shows that the crystal is transparent from ultraviolet to infrared with short-wavelength absorption edge at about 220 nm.