Manganese Oxide Octahedral Molecular Sieves (OMS‐2) Multiple Framework Substitutions: A New Route to OMS‐2 Particle Size and Morphology Control

Self‐assembled multidoped cryptomelane hollow microspheres with ultrafine particles in the size range of 4–6 nm, and with a very high surface area of 380 m² g^?1 have been synthesized. The particle size, morphology, and the surface area of these materials are readily controlled via multiple framework substitutions. The X‐ray diffraction and transmission electron microscopy (TEM) results indicate that the as‐synthesized multidoped OMS‐2 materials are pristine and crystalline, with no segregated metal oxide impurities. These results are corroborated by infrared (IR) and Raman spectroscopy data, which show no segregated amorphous and/or crystalline metal impurities. The field‐emission scanning electron microscopy (FESEM) studies confirm the homogeneous morphology consisting of microspheres that are hollow and constructed by the self‐assembly of pseudo‐flakes, whereas energy‐dispersive X‐ray (EDX) analyses imply that all four metal cations are incorporated into the OMS‐2 structure. On the other hand, thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) demonstrate that the as‐synthesized multidoped OMS‐2 hollow microspheres are more thermally unstable than their single‐doped and undoped counterparts. However, the in‐situ XRD studies show that the cryptomelane phase of the multidoped OMS‐2 hollow microspheres is stable up to about 450°C in air. The catalytic activity of these microspheres towards the oxidation of diphenylmethanol is excellent compared to that of undoped OMS‐2 materials.     

Ligand influences on copper molybdate networks: the structures and magnetism of [Cu(3,4'-bpy)MoO(4)], [Cu(3,3'-bpy)(0.5)MoO(4)], and [Cu(4,4'-bpy)(0.5)MoO(4)].1.5H(2)O

The reactions of a Cu(II) salt, MoO(3), and the appropriate bipyridine ligand yield a series of bimetallic oxides, [Cu(3,4'-bpy)MoO(4)] (1), [Cu(3,3'-bpy)(0.5)MoO(4)] (2), and [Cu(4,4'-bpy)(0.5)MoO(4)].1.5H(2)O (3.1.5H(2)O). The structures of 1-3 exhibit three-dimensional covalent frameworks, constructed from bimetallic oxide layers tethered by the dipodal organoimine ligands. However, the [CuMoO(4)] networks are quite distinct. For structure 1, the layer consists of corner-sharing [MoO(4)] tetrehedra and [CuN(2)O(3)] square pyramids, while the layer of 2 is constructed from [MoO(4)] tetrehedra and binuclear [Cu(2)O(6)N(2)] units of edge-sharing copper square pyramids. The oxide substructure of 3 consists of [MoO(4)] tetrahedra corner-sharing with tetranuclear clusters of edge-sharing [CuO(5)N] octahedra. Crystal data: C(10)H(8)N(2)O(4)CuMo (1), orthorhombic Pbca, a = 12.4823(6) A, b = 9.1699(4) A, c = 19.5647(9) A, V = 2239.4(1) A(3), Z = 8; C(5)H(4)NO(4)CuMo (2), triclinic P, a = 5.439(1) A, b = 6.814(1) A, c = 10.727(2) A, alpha = 73.909(4)(o), beta = 78.839(4)(o); gamma = 70.389(4)(o); V = 357.6(1) A(3), Z = 2; C(10)H(8)N(2)O(8)Cu(2)Mo(2).3H(2)O 3.1.5H(2)O, triclinic P, a = 7.4273(7) A, b = 9.2314(8) A, c = 13.880(1) A, alpha = 71.411(2)(o), beta = 88.528(2)(o), gamma = 73.650(2)(o), V = 863.4(1) A(3), Z = 2. The magnetic properties of 1-3 arise solely from the presence of the Cu(II) sites, but reflect the structural differences within the bimetallic oxide layers. Compound 1 exhibits magnetic behavior consistent with ferromagnetic chains which couple antiferromagnetically at low temperature. Compound 2 exhibits strong antiferromagnetic dimeric interactions, with the magnetic susceptibility data consistent with the Bleaney-Bowers equation. Similarly, the magnetic susceptibility of 3 is dominated by antiferromagnetic interactions, which may be modeled as a linear S = 1/2 Heisenberg tetramer.