After the reaction, dozens of single crystals in the form of thin sheets formed at the same location where the ingredients started. These crystals are mixed with some (NbSe 4 ) 3 I powder by-product, and the crystals can be easily picked out. The typical dimensions of these crystals can reach 2 × 2 × 0.1 mm. Additionally, a large amount of (Nb 4 Se 15 I 2 )I 2 single crystals also formed close to the opening of the smaller tube, in the temperature range of around 350 • C to 300 • C, matching the previously reported temperature range. The "empty" high-temperature portion of the larger tube contained some residual iodine after the reaction. A traditional single-tube CVT synthesis with starting materials at 430 • C and low temperature at 300 • C was also attempted, but NbSe 2 I 2 crystals did not form and only (NbSe 4 ) 3 I powder was left at the hightemperature side.