Single crystals of the neodymium(III) meta-borate Nd(BO2)3 and ortho-borate Nd[BO3]

Pale violet, transparent, air- and water-resistant single crystals of the neodymium oxoborates Nd[BO3] and Nd(BO2)(3) emerged from reactions of Nd2O3, NdF3 or NdCl3, and B2O3 in variable molar ratios during attempts to synthesize neodymium halide borates (e.g. Nd2F3 [BO3] or NdCl(BO2)(2)). The preparations were carried out at 700 degreesC in sealed tantalum capsules using CsCl as a flux, or at 850 degreesC in evacuated silica ampoules with an excess of NdCl3 as fluxing agent. Neodymium, ortho-borate lambda-Nd[BO3] (orthorhombic, Pnma; a = 573.51(5), b = 505.64(4), c = 809.16(7) pm; Z = 4) is isotypic with aragonite-type CaCO3 containing quasi-planar, discrete [BO3](3-) triangles (d(B-O) = 138 pm, 3x) and Nd3+ in ninefold oxygen coordination (d(Nd-O) = 239-269 pm, CN = 9). In the crystal structure of neodymium meta-borate Nd(BO2)(3) (NdB3O6; monoclinic, C2/c; a = 983.24(9), b = 809.32(7), c 637.71(6) pm, beta = 126.639(8)degrees; Z = 4) both [BO3](3-) triangles (d(B-O) = 133-142 pm, CN 3) and [BO4](5-) tetrahedra (d(B-O) = 145-149 pm, CN = 4) are present. They share common corners forming chains of the composition (1)(infinity){([(B1)(O1)(2/1)(e)(O2)(2/1)(e)][(B2)(O1)(1/1)(e)(O3)(1/1)(t)](2))(3-)} (equivalent to (1)(infinity){(BO2)(-)}) which run parallel to the [101] direction and are interconnected by Nd3+ cations in tenfold coordination of oxygen atoms (d(Nd-O) = 238-280 pm, CN = 10).