Tris(acetonitrile)tris(trifluoromethanesulfonato)-europium(III), 1∞[Eu(OTf)3(CH3CN)3], is the first structurally characterized Ln(OTf)3-solvate where triflate is still in the coordination sphere of the Ln(III) cation and not substituted by solvate molecules. This fact is attributed to the unique crystallization conditions that an ionic liquid provides: 1∞[Eu(OTf)3(CH3CN)3] was obtained from a solution of europium(III) triflate, Eu(OTf)3, with acetonitrile in the ionic liquid [C4py][OTf] (1-butylpyridinium triflate). The crystal structure (triclinic, P1̅ (no. 2), a = 5.734(1) Å, b = 10.500(2) Å, c = 19.088(4) Å, α = 98.09(3)°, β = 93.79(3)°, γ = 91.46(3)°, V = 1134.5(4) Å3, Z = 2, R1 for 4388 reflections with Io > 2σ(Io): 0.0335) contains 9-fold coordinated Eu(III) atoms: Six trans coordinating triflate anions and three equatorial acetonitrile molecules form a tricapped trigonal prism around the central Eu(III) cation. These polyhedra are linked to 1D chains by bridging triflate ligands and are further connected into a 3D supramolecular structure via C–H···O and C–H···F bonds. Eu(OTf)3·3CH3CN loses acetonitrile already at room temperature. Thermogravimetry shows that upon heating to 165 °C all acetonitrile is lost and a complete decomposition occurs at 452 °C.