Shape-Selective Intercalation Reactions of Layered Zinc and Cobalt Phosphonates

Dehydration of layered metal phosphonates M(O₃PCH₃)· H₂O (M = Mg, Zn, Co) occurs topochemically to give anhydrous salts M(O₃PCH₃) with similar unit cell dimensions in the space group Pmn2₁ Mg(O₃PCH₃) absorbs water rapidly from air, forming Mg(O₃PCH₃)·H₂O; Co(O₃PCH₃) does so less readily, and Zn(O₃PCH₃) is unreactive even with liquid water. Anhydrous Co and Zn salts M(O₃PCH₃) react with ammonia and primary amines to form intercalation compounds M(O₃PCH₃)(RNH₂), R = H to n-C₈H₁₇. The intercalation reaction is shape-selective, as amines with branching at the α-carbon cannot access the metal coordination site. The packing of alkyl chains is different for primary amine intercalation compounds containing Co and Zn. In all Co(O₃PCH₃)(n-C_nH_2n+1NH₂) compounds, the chains pack as double layers. In the Zn(O₃PCH₃)(n-C.,H_2n+1NH₂) series, compounds with even n also adopt double-layer structures, while odd n compounds form more efficiently packed interdigitated monolayers in the interlamellar region.