Crystals of anionic Na[CuCl 2 (HOCH 2 CϵCCH 2 OH)] · 2H 2 O π-complex have been synthesized by interaction of 2-butyne-1,4-diol with CuCl in a concentrated aqueous NaCl solution and characterized by X-ray diffraction at 100 K. The crystals are triclinic: space group P1, a ϭ 7.142 (3), b ϭ 7.703(3), c ϭ 10.425(4) Å , α ϭ 105.60(3), β ϭ 99.49(3), γ ϭ 110.43(3)°, V ϭ 495.9(4) Å 3 , Z ϭ 2, R ϭ 0.0203 for 3496 reflections. The structure is built of discrete [CuCl 2 (HOCH 2 CϵCCH 2 OH)] Ϫ anionic stacks and polymeric [Na ϩ (H 2 O) 2 ] ϱ cations among the stacks. The Cu I atom adopts