A novel cobalt(II) vanadophosphate with a quasi zeolithic intersecting tunnel structure: NH4Co2(H2O)(2)HVO2(PO4)(2)

A new cobalt(II) vanadophosphate NH4Co2(H2O)(2)HVO2(PO4)(2) has been synthe sized by hydrothermal method at 220 degreesC. Its original structure crysta llizes in the Pmc2(1) space group with a = 6.4394(4), b = 7.4299(5), and c = 9.854(1) Angstrom. It can be described by the assemblage of mixed "tetrah edral-octahedral" [VPO7OH](infinity) chains with either octahedral cobalt r utile type chains or chains of edge sharing CoO4OH pyramids. This framework delimits intersecting tunnels, where the NH4+ cations and the water molecu les sit. This structure exhibits a quasi zeolithic character, releasing two water molecules from the tunnels when heating at 350 degreesC under nitrog en and slowly readsorbing 0.5 molecule of water when exposed at 25 degreesC to air. The zeolithic character is nevertheless limited since the structur e collapses and becomes amorphous when it releases the ammonia at 460 degre esC.