Anionic complex Cs+[EuL4]- (I) is synthesized by the reaction of Eu(NO3)3 · 6H 2O with 1-(1,5-dimethyl-1H-pyrazol-4-yl)-4,4,4-trifluorobutane-1,3- dione (HL) and CsOH in an aqueous-alcohol medium. Unstable adduct Cs +[EuL4]- · 2CH2Cl2 (Ia) is obtained from a solution in CH2Cl2. The structure of complex Ia is determined by X-ray diffraction analysis. The crystals of complex Ia at 100 K are monoclinic, a = 10.8435(5), b = 20.1353(9), c = 23.355(1) Å, β = 92.548(1)°, V = 5094.3(4) Å3, space group P21/n, Z = 4, and R = 0.0294. The coordination number of the Cs+ ion is 9. The Cs+ ion forms shortened (up to 3.3 Å) contacts with the O, N, and F atoms of four diketonate fragments joining the molecules into a three-dimensional structure. © 2013 Pleiades Publishing, Ltd.