Abstract Polycrystalline samples of Cu 3 TaIn 3 Se 7 and CuTa 2 InTe 4 were synthesized by the usual melt and anneal technique. X‐ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a = 5.794 ± 0.002 Å, c = 11.66 ± 0.01 Å, c / a = 2.01, V = 391 ± 1 Å 3 and a = 6.193 ± 0.001 Å, c = 12.400 ± 0.002 Å, c / a = 2.00, V = 475 ± 1 Å 3 , respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero‐field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T = 70 K (Cu 3 TaIn 3 Se 7 ) and 42 K (CuTa 2 InTe 4 ). A spin–glass transition was observed in Cu 3 TaIn 3 Se 7 with T f ≈ 50 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)