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

Abstract

The compound [Mo72Fe30O252 (CH3COO)10{Mo2O7(H2O)} {(H2Mo2O8(H2O8) }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 [{Mo2/VO4(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 {Mo72/VIFe30/III} 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)} {H2Mo2 O8(H2O)}3(H2O)87] ·ca. 80 H2O 4≡4a·ca. 80 H2O. The linking process at the Fe sites follows the well known inorganic condensation process leading to FeIII polycations in aqueous solution according to the scheme Fe(OH2) + (H2O)Fe →-H+ Fe(OH) + (H2O)Fe →-H2O 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). © 2000 Éditions scientifiques et médicales Elsevier SAS.