The crystal and molecular structure of [C~5H~4C(CH~3)(C~3H~7) CH~2CH=CH~2]Gd(OH)Cl.2MgCl~2.4THF are reported.The crystallographic data are as follows: triclinic, space group P1, a=1.2757(3), b=1.3571 (3), c=1.3725(3)nm, α=69.22(3), β=84.91(3), γ=63.48(3)ⅲ, V=1.929 (1)nm^3, Mr=862.75, Dx=1.423g/cm^3, μ=2.0832mm^-^1, F(000)=848, Z=2, R=0.096, ωR=0.113(I≥3σ(I)). In this molecule the coordination number of Gd(III) atom is 8 and the coordination geometry of Gd(III) is a seriously distorted octahedron. The coordinations of Mg(1) and Mg(2) are similar, their coordination numbers are both 6 and their coordination geometries are both distorted octahedra. The three octahedra are linked up by three coplanes.

Key words: BUTENYL GROUP, CYCLOPENTADIENYL GROUP, GADOLINIUM COMPLEX, CRYSTAL STRUCTURE, COMPLEX COMPOUNDS, RARE EARTH METAL COMPLEX