The crystal structures of α-Zr(OH) 2 (NO 3 ) 2 · 1.65H 2 O and β-Zr(OH) 2 (NO 3 ) 2 · H 2 O were determinedab initiofrom laboratory X-ray powder diffraction data. The two zirconium hydroxide nitrates crystallize with triclinic unit cells (P1) with the parameters:a=10.051(3) Å,b=10.357(3) Å,c=8.131(2) Å, α=108.30(2)°, β=112.02(2)°, γ=79.75(3)° for the α phase, anda=9.180(3) Å,b=10.465(4) Å,c=8.076(2) Å, α=109.58(3)°, β=98.96(3)°, γ=80.43(3)° for the β phase. An interpretation of the Patterson functions led to the location of two independent Zr atoms for the α and β forms. The light atom coordinates were determined from successive three-dimensional Fourier maps. The structure of α-Zr(OH) 2 (NO 3 ) 2 ·1.65H 2 O is built from edge sharing ZrO 8 trigonal dodecahedra, through double hydroxyl bridges, to form infinite neutral zigzag chains of chemical composition [Zr(OH) 4/2 (NO 3 ) 2 ] n , running along [011]. The 8-fold coordination of each Zr atom is completed by four oxygens from bidentate nitrate groups. They are involved in a complex hydrogen bonding network occurring between the chains via “free” water molecules. The loss of the weakly bonded water molecule leads to the β form without collapse of the 1D framework of the precursor. In the β variety, the 8-fold coordination is preserved for the two Zr atoms. However, the exact shapes of the polyhedra have not been precisely defined.