Syntheses, structures and magnetic properties of Fe6 and Fe12 ferric wheels

Synthesis, Structure, and Magnetic Properties of an Fe36 Dimethylarsinate Cluster: The Largest "Ferric Wheel"

The synthesis and characterization of a high-nuclearity Fe^III/O/arsinate cluster is reported within the salt [Fe₃₆O₁₂(OH)₆(O₂AsMe₂)₆₃(O₂CH)₃(H₂O)₆](NO₃)₁₂ (1). The compound was prepared from the reaction of Fe(NO₃)₃·9H₂O, dimethylarsinic acid (Me₂AsO₂H), and triethylamine in a 1:2:4 molar ratio in acetonitrile. The Fe₃₆ cation of 1 is an unprecedented structural type consisting of nine Fe₄ butterfly units of two types, three {Fe^III₄(μ₃-O)₂} units A, and six {Fe^III₄(μ₃-O)(μ₃-OH)} units B, linked by multiple bridging Me₂AsO₂^- groups into an Fe₃₆ triangular wheel/loop with C₃ crystallographic and D₃ virtual symmetry that looks like a guitar plectrum. The unusual structure has been rationalized on the basis of the different curvatures of units A and B, the presence of intra-Fe₃₆ hydrogen bonding, and the tendency of Me₂AsO₂^- groups to favor μ₃-bridging modes. The cations stack into supramolecular nanotubes parallel to the crystallographic c axis and contain badly disordered solvent and NO₃^- anions. The cation of 1 is the highest-nuclearity "ferric wheel" to date and also the highest-nuclearity Fe/O cluster of any structural type with a single contiguous Fe/O core. Variable-temperature direct-current magnetic susceptibility data and alternating-current in-phase magnetic susceptibility data indicate that the cation of 1 possesses an S = 0 ground state and dominant antiferromagnetic interactions. The Fe₂ pairwise J_i,j couplings were estimated by the combined use of a magnetostructural correlation for high-nuclearity Fe^III/oxo clusters and density functional theory calculations using broken-symmetry methods and the Green's function approach. The three methods gave satisfyingly similar J_i,j values and allowed the identification of spin-frustration effects and the resulting relative spin-vector alignments and thus rationalization of the S = 0 ground state of the cation.

Alkali-regulated Fe6 and Fe18 molecular clusters and their structural transformation

A cyclic Fe6 like a “six-vane windmill” and a bricky Fe18 clusters as a “Chinese knot” were obtained. Moreover, the alkali-induced conversion from Fe6 to Fe18 has been achieved, realizing the nuclearity enlargement and structural regulation.

A new heterometallic pivalate {Fe8Cd} complex as an example of unusual "ferric wheel" molecular self-assembly

The interaction of the pivalate complexes of iron(iii), [Fe3O(Piv)6(H2O)3]·HPiv, and cadmium(ii), [Cd(Piv)2], in Et2O resulted in one more type of "ferric wheel" family complex, namely [Fe8(Piv)16{Cd(Piv)2}(μ-OH)8]·Et2O (1). The complex is an octanuclear iron(iii) wheel with a {Cd(Piv)2} moiety asymmetrically incorporated into the ring.