Crystal chemistry of alvanite, ZnAl ₄ (OH) ₁₂ (V ⁵⁺ O ₃ ) ₂ ·2H ₂ O, and ankinovichite, NiAl ₄ _(OH)12 (V ⁵⁺ O ₃ ) ₂ ·2H <sub>2</s

The crystal structures of two Al-rich layered double hydroxide (LDH) with vanadate anionic groups, alvanite ZnAl 4 (OH) 12 (V 5+ O 3 ) 2 •2H 2 O and ankinovichite NiAl 4 (OH) 12 (V 5+ O 3 ) 2 •2H 2 O, have been re-investigated.The single-crystal X-ray diffraction (XRD) data were processed in the space group P2 1 /n, a = 17.8100(8)/ 17.8073(13), b = 5.1272(2)/ 5.1212(4), c = 8.8860(4)/ 8.8637(7) Å, β = 92.175(4)/92.203(8) °, V = 810.84(6)/807.73(11)Å 3 , and Z = 2 for alvanite / ankinovichite.The structures have been refined to R 1 = 0.0447/ 0.0587 for 2353/ 2125 unique reflections with F o > 2σ(F).The crystal structures are built of alternating dioctahedral [or Al(OH) 3 -derived] layers with half of octahedral cavities occupied by M 2+ , i.e. {M 2+ Al 4 (OH) 12 } 2+ and interlayer of compositionThe topology of metal-hydroxide layer is identical for alvanite, ankinovichite and sulfate-members of chalcoalumite group (kyrgyzstanite, nickelalumite and chalcoalumite), but the layer stacking sequence differs.The arrangement of vanadate anions in the interlayer space is unique and unlike that of LDHs with other anions: vanadate groups form zweier-single chains of vertex-linked tetrahedra, extending along the b direction and