Three series of intermetallic compounds Eu(T1,T2)5In (T = Cu, Ag, Au) have been investigated in full compositional ranges. Single crystals of all compounds have been obtained by self-flux and were analyzed by single X-ray diffraction revealing the representatives to fall into two structure types: CeCu6 (oP28, Pnma, a = 8.832(3)–9.121(2) Å, b = 5.306(2)–5.645(1) Å, c = 11.059(4)–11.437(3) Å, V = 518.3(3)–588.9(2) Å3) and YbMo2Al4 (tI14, I4/mmm, a = 5.417(3)–5.508(1) Å, c = 7.139(2)– 7.199(2) Å, V = 276.1(2)–285.8(1) Å3). The structural preference was found to depend on the cation/anion size ratio, while the positional preference within the CeCu6 type structure shows an apparent correlation with the anion size. Chemical compression, hence, a change in cell volume, which occurs upon anion substitution appears to be the main driving force for the change of magnetic ordering. While EuAg5In shows antiferromagnetic behavior at low temperatures, mixing Cu and Au within the same type of structure results in considerable changes in the magnetism. The Eu(Cu,Au)5In alloys with CeCu6 structure show complex magnetic behaviors and strong magnetic field-induced spin-reorientation transition with the critical field of the transition being dependent on Cu/Au ratio. The alloys adopting the YbMo2Al4 type structure are ferromagnets exhibiting unusually high magnetic moments. The heat capacity of EuAu2.66Cu2.34In reveals a double-peak structure evolving with the magnetic field. However, low-temperature X-ray powder diffraction does not show a structural transition
