[en] The terbium meta-oxoborate Tb(BO₂)₃ (≡ TbB₃O₆) is obtained as single crystals by the reaction of terbium, Tb₄O₇ and TbCl₃ with an excess of B₂O₃ in gastight sealed platinum ampoules at 950 C after three weeks. The compound appears to be air- and water-resistant and crystallizes as long, thin, colourless needles which tend to growth-twinning due to their marked fibrous habit. The crystal structure of Tb(BO₂)₃ (orthorhombic, Pnma; a = 1598.97(9), b = 741.39(4), c = 1229.58(7) pm; Z = 16) contains strongly corrugated oxoborate layers _∞²{(BO₂)^-} built of vertex-linked [BO₄]^5- tetrahedra (d(B-O) = 143 - 154 pm, and angsph;(O-B-O) = 102-115 ) which spread out parallel (100). The four crystallographically different Tb³⁺ cations all exhibit coordination numbers of eight towards the oxygen atoms (d(Tb-O) = 228-287 pm). The corresponding metal cation polyhedra [TbO₈]¹³⁺ too convene to layers (composition: _∞²{(Tb₂O₁₁)^16-}) which are likewise oriented parallel to the (100) plane. (Abstract Copyright [2003], Wiley Periodicals, Inc.)