Single crystals of Tl2[NbCl6] (1) and Tl2 [NbBr6] (2) are obtained as black needles on heating TlCl, Nb, S2Cl2 (1) and Tl, Nb, and Br2 at 400°C (2). Tl2NbBr6 also forms in the reaction of TlBr, Nb, Br2, and S at 500°C. Both compounds crystallize in the K2[PtCl6] structure type to form non-distorted octahedral [NbХ6]2– anions (Nb–Cl 2.397(4) Å and Nb–Br 2.516(2) Å). The magnetic properties of Tl2[NbBr6] in a range 5-300 K indicate an antiferromagnetic interaction between Nb4+ ion spins (d1, S = 1/2). On cooling, the compound becomes a noncollinear ferromagnet with Tc = 23 K.
- crystal structure