Cross-linking nanostructured spherical capsules as building units by crystal engineering: related chemistry

The compound [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₀{Mo₂O₇(H₂O)}{H₂Mo₂O₈(H₂O)}₃ (H₂O)₉₁]·ca. 140 H₂O 3≡3a·ca. 140 H₂O, an important educt for an unusual solid state reaction, can now be obtained easily by reacting (NH₄)₄₂[{Mo^V₂O₄(CH₃COO)}₃₀{(Mo)Mo₅O₂₁(H₂O)₆}₁₂]·10 CH₃COONH₄·ca. 300 H₂O 1 with FeCl₃·6 H₂O in water. Interestingly, the freshly precipitated crystals of 3 contain discrete spherical clusters of the type {Mo^VI₇₂Fe^III₃₀} with as yet unprecedented 30×5 unpaired electrons (S=150/2 at room temperature). Upon drying 3, its cluster units 3a get covalently linked to form layers in a step by step solid state reaction, according to the scheme described below, resulting finally in the crystalline reaction product [H₄Mo₇₂Fe₃₀O₂₅₄(CH₃COO)₁₀{Mo₂O₇(H₂O)}{H₂Mo₂O₈(H₂O)}₃(H₂O)₈₇]·ca. 80 H₂O 44a·ca. 80 H₂O. The linking process at the Fe sites follows the well known inorganic condensation process leading to Fe^III polycations in aqueous solution according to the scheme Fe(OH₂)+(H₂O)Fe Fe(OH)+(H₂O)Fe Fe–O–Fe and thus is based on a type of crystal engineering with nanostructured spherical building blocks. This process does not allow chaotic characteristics in contrast to the mentioned polycation formation. Careful investigation leads to the identification of an intermediate 5 containing clusters 5a — with the same cluster composition as 3a and 4a — in the closest possible non-covalent contact. The related materials are of tremendous interest for magnetochemistry (nano-magneto-technology).